Categories
case

Corner Block Case Joints

Corner block joints are intermediaries. Instead of connecting two boards directly together, each board is connected to the corner block instead.

The corner block does not offer any structural improvements over other joints, however it does offer some design possibilities that might otherwise be unavailable, especially if the boards being joined together are manufactured woods such as plywood or veneered, where you might wish to hide the edges of the boards. The corner block can be molded or shaped, can be made of a different material or color than the main boards, or can even be a different thickness than the boards which are connected to it, possibly producing a proud corner.

The most common material for the corner block is solid wood. Though manufactured wood can be used, the shaping and stylistic benefits of corner blocks are lost since the surface of the block would still need to be covered in some way.

If a solid wood corner block is used, the proper orientation of the grain, relative to the case sides, is crucial. Misaligning the grain directions can cause joint separation and failure, and may even damage the wood of the case sides.

If the case side panels are made from manufactured material (such as plywood, MDF or particleboard), the block’s grain should be aligned parallel to the direction of the board’s edge (regardless of the direction of the grain on the surface veneer on plywood). This is because manufactured boards will not experience any significant movement due to seasonal moisture content fluctuations, but the hardwood corner block will. By aligning the corner block’s grain to run along the edge of the case panel, the expansion will not run along the length of the panel, and so it will have no effect. If the grain were to run in any other direction (out from the edge of the panel instead of along the length of the edge), the seasonal movement of the corner block would make it wider or narrower than the panel it is joined to, and the joint would fail.

If the case side panels are made from solid wood, the grain of the corner block must run in the same direction as the grain in the panels. Aligning the corner block in any other direction will cause the joint to fail due to seasonal wood movement. Note that this also means that the grain on the two panels being joined (through the corner block) must also have their grain running in the same direction.

Corner Block With Tongue-And-Groove

The tongue can be formed on either the side panel or the corner block, but it is often easiest to place the tongue on the corner block since forming details on the ends of long side panels can be difficult. If the corner block is used to join solid wood panels, it is recommended that the grain on the corner block run diagonally, from one tongue to the other. This is to provide maximal strength to each tongue so it can better resist the shearing force once it is mated with the panels. If the corner block is being used with manufactured boards, the block’s grain is running parallel to the edge of the panel and this is not a concern.

Corner Block With Splines

A full-length, stopped, or blind spline can be used to attach the corner block to the side panel. This eliminates the complexity of forming tongues on the narrow corner blocks, and it can also be accomplished with just one setup of the tablesaw or router table.

Corner Block With Biscuits

Instead of using long splines, biscuits can be easily substituted.

Categories
case

Butt Case Joints

Butt joints are one of the weakest forms of case joints, but they are the easiest and quickest to make. A butt joint is achieved whenever you join the straight and square end grain of one board to face grain of another board. End grain is notoriously difficult to glue or fasten, and butt-joints present the smallest amount of surface area to be used for gluing. In order to achieve any significant strength and sturdiness, you must reinforce the joint.

Glued Butt Joint

As its name implies, the glued butt joint is held together by the force of the glue adhering to the end grain of one board and the face grain of another. The face grain of most wood species providing a very good glue bonding surface. The end grain, however, is notoriously weak and is prone to failure.

Butt Joint with Glue Block

Glue blocks are square or triangular wedges of wood that are glued to the hidden side of the joint. These blocks can run the full length of the joint, or only be used in strategic locations. One problem with case joint glue blocks, though, is that their constructions usually has the glue block’s grain oriented perpendicular to the case boards’ grain, resulting in a cross-grain construction. This can cause problems when wood movement is involved.

Butt Joint with Fasteners

Nailed Butt Joint and Screwed Butt Joint

Nails or screws can be used to fasten a butt joint. Inserting the nails or screws at alternating angles strengthens the joint and prevents the boards from separating. In softer woods that have trouble holding screws or nails in the end grain, you can reinforce the end grain portion with a strategically placed dowel which provides enough cross-grain to increase the holding power of the screws.

Dowelled Butt Joint

Dowels are a decorative replacement for nails or screws. Again, they can be inserted in alternating angles, increasing their holding power. Blind dowels can be created by using stopped holes on the face grain board, however these holes are difficult to produce without the aid of specialized tools, since doing them by hand or even a drill-press is prone to uneven hole depths, or mis-aligned holes.

Using a contrasting wood type for the dowel can produce an attractive decorative element to the workpiece.

Biscuited Butt Joint

Biscuits serve two purposes in case joints: They provide positive registration between boards during assembly, and they provide a mechanical brace against shifting in the finished product. Biscuits are essentially thin oval wafers that are inserted and glued into a matching pair of slots that are cut into the two pieces to be joined.

When the biscuits are used at the top of an upright board, offset the location of the slots slightly by 1/4 to 1/8 of the upright’s thickness towards the hidden side of the vertical. This is because if the joint should fail, the damage done to the wood will be in a hidden location, and more easily repaired invisibly. If the biscuit were placed in the center, there is an equal risk that the damage would be exposed.

When the biscuits are used to secure a horizontal shelf to an upright member, the biscuits should be offset slightly by 1/4 to 1/8th of the shelf’s thickness towards the bottom of the shelf. When the shelf is loaded with weight, the biscuit will be applying force towards the top of the shelf. By shifting the biscuit’s location downwards, you thicken the amount of wood that is resisting that force.

Categories
case

Box Case Joints

Box joints are the “poor man’s dovetail joint”. It has relatively good mechanical strength, but does not have the interlocking capabilities given by the sloping of the dovetail pins and tails. The box joint does still provide an incredible amount of gluing surface, making it a strong joint.

The basic box joint is formed by creating a regular series of slots and fingers, the length of which is the same as the stock’s thickness. It is recommended that the width of the fingers also be the same as the stock’s thickness since this gives the optimum strength for the least amount of cutting. Having thicker fingers actually reduces the gluing surface, weakening the joint. Having narrower fingers, however, can dramatically increase the gluing surface, at the cost of more labour to construct the joint.

In terms of aesthetic appeal, the box joint does suffer somewhat by its patterened appearance, but this can be overcome by some creative alternatives.

Decorative Box Joint

The standard box joint has all its fingers and slots the same width. The joint can be given some visual excitement by varying the width and spacing of the fingers that make up the joint. This does increase the difficulty in cutting the joint, and measurements must be carefuly made because the joining boards will no longer have identical setups.

Angled Box Joint

If the joint being formed does not conform to a 90º angle, an angled box joint can be created. This is accomplished by placing the board on the required angle while passing it over the tablesaw/router while creating the slots. Just remember to keep the same side “forward” as you pass it over the cutter in order to create a matching angle.

Half-Blind Box Joint

When you want the box joint to be visible from only one side, you can take advantage of the half-blind box joint. This is formed the same way as the half-blind dovetail, but is considerably easier to cut, and it can even be done on a tablesaw.

Categories
finishing

Wax as a Woodworking Finish

What it is

The wax that is used for finishing wood products is primarily carnauba wax, though virtually any kind of wax can be used (from bee’s wax to paraffin wax). Carnauba wax is extracted from the leaves of the carnauba palm (Copernica prunifera, native to northeastern Brazil) and then refining and bleaching the wax.

When to consider it

Because wax offers very little in the way of protection, wax has limited use in the modern woodworker’s arsenal of wood finishes. The wax is easily worn off, is easily damaged by high heat (such as a cup of tea), provides very little protection to water vapor, and requires re-application every year or so.

Because of these limitations, wax is almost never used as a primary finish, but is instead used to complement other finishes. Wax can be applied over oil finishes, such as tung oil, or over other finishes such as shellac. The benefit of wax on finishes such as these is that the wax can be buffed to provide a fine shine, and the wax is easy to re-buff as needed.

Advantages

There are many different waxes available. The following is a general list of advantages:

  • Mildly water resistant
  • Moderately resistant to acids and alkali
  • Does not color the finish of the wood
  • Easy and quick to apply (rub on, rub off)
  • Very forgiving during application
  • Easy to re-apply if the original finish becomes worn or damaged
  • Non-toxic and food-safe (Once solvent has evaporated! Be careful!)

Disadvantages

  • Damaged by alcohol
  • Must wait for underlying finish to cure completely, or solvent in wax may damage underlying finish

Variations

The only variations on wax that I am aware of are:

  • Paste waxes or waxes with solvents added (apply with rag, wait, buff to shine),
  • Solid waxes (usually applied to project spinning on lathe), and
  • Spray waxes (spray on, but toxicity unknown).

There are various types of waxes in use for finishing:

  • Carnauba wax is one of the hardest natural waxes, and takes a hard, glossy shine with a slick feel. By itself, it is brittle and very difficult to polish once it has dried.
  • Beeswax is a moderately soft, sticky wax with a wonderful smell, and it buffs out to a mellow glow. Although it becomes slippery when it melts, at room temperature it is too sticky to use for machine surfaces like table saw tops. This stickiness, however, makes it ideal for floors or for surfaces that should not slip too easily. Some people also find the beeswax smell objectionable.
  • Paraffin or canning wax is soft and very slippery (almost greasy), and tends to flake off if applied too thick. Can be used as an additive to make harder waxes buff more easily.

How to use it

As with any traditional product that has been used for many years, there will be many different opinions on how to use the product. What I will present here is the most simple and straightforward technique of applying paste wax, and I will identify optional steps as such.

Precautions

Be careful with the handling and disposal of the rags used to apply paste wax. The wax itself is not a problem, however the solvents used to make the wax soft enough to apply are highly flammable and combustible. Allow rags to thoroughly dry on a non-flammable surface (such as a concrete block), or washed, or soaked with water before placing in the garbage. Solvents can generate heat through an exothermic reaction with the air (oxidation), and this reaction accelerates as the rags get hotter, and this has been known to start unintended fires.

Preparation

As with any finish, your ability to fix woodworking mistakes is greatly diminished once you start to apply any finish. Ensure the wood surface is adequately prepared before you start to apply the product.

Sanding sealers are not usually beneficial under wax finishes. They may be used, however, under the primary finish that might have been applied to the project, such as under the oil or shellac finish that the wax is ultimately covering.

Sand the surface using progressively finer sandpaper until you reach 220 grit (or optionally 320-dry grit) sandpaper. This will leave the surface smooth and there should be no visible scratch marks that remain.

Since wax does nothing to accentuate your workpiece, you can optionally apply an oilshellac, or both oil then shellac finish before finally finishing it with wax.

Application

Use any clean, lint-free rag to apply wax. If you use a rag that has rough-cut edges, be sure to fold the rag so the rough edges are held in your hand and are not on the wood surface, since any loose wood fibres may catch the edge of your cloth and leave troublesome lint behind.

Use the rag to scrape a small amount of wax out of the can and proceed to apply the wax to the work surface. Work from the least accessible areas (interior or underside) first and work towards the easiest sides.

Apply by rubbing along the grain. Do not apply too much wax since only the thinnest microscopic layer will remain after buffing. Your goal at this point is simply to “wet” the complete surface and to ensure you have not missed any spots. If there are any globs, remove them with your rag before continuing on to the next section of your project.

Approximately 1/2 hour after applying the wax, the layer that you just applied should be completely dry. The surface of your project should look like it has a hazy finish, like someone washed the surface with a soapy cloth. Rub the project with a clean rag to remove any excess surface wax. Follow this up with a more vigorous buffing. The surface friction that you generate with your buffing partially melts the wax and smoothens the surface. Some people feel that you can use an automotive car polisher to accomplish the buffing step, but this is highly dependant on the shape of your project, and how delicate it might be, and how much damage you might cause if the buffing pad catches on a corner of your project.

Your project is ready to deliver and use immediately.

Repairs

Repairs for projects finished with wax couldn’t be simpler. Simply use a clean rag dipped in the appropriate solvent to wipe off the existing wax finish, let thoroughly dry (1/2 hour at least), then re-apply wax as per the application instructions.

Removal

Wax is easy to remove by simply using a clean rag dipped in the appropriate solvent. The solvent-moistened rag can then be used to rub off the old wax. It is highly recommended that you wait for the solvent to thorough evaporate from the project before attempting to apply a new finish.

Where to get it

Lee Valley Tools

Cleanup

Please see the Precautions section above for appropriate disposal of rags used to apply paste wax.

Wax can be removed with a solvent such as turpentine or naptha.

Categories
finishing

Tung Oil as a Woodworking Finish

What it is

Tung oil, also known as China Wood Oil, Lumbang oil, Noix d’abrasin (fr.) or simply wood oil, is made from the seed kernels of the Tung tree (Aleurites fordii and Aleurites montana, family Euphorbiaceae). The A. fordii tree grows well in cooler climates, but can survive up to sub-tropical climates. A. montana is restricted to a more tropical climate. China, Argentina, Paraguay, Brazil and the USA are all major producers of tung oil.

Tung oil has been known about for hundreds of years in China, where it was used as a preservative for wood ships. The oil penetrates the wood, then hardens to form an impermeable hydrophobic layer (repels water) up to 5 mm into the wood. As a preservative it is effective for exterior work above and below ground, but the thin layer makes it less useful in practice.

When to consider it

Tung oil seeps into the grain of the wood, giving it a perpetual wet look that highly accentualizes the grain of the wood, commonly referred to as “making the grain pop”. Because of this, the color of the wood is slightly darkened, giving the wood a rich, warm color that is very pleasing.

Tung oil provides a relatively hard surface finish that, as long as the surface integrity is intact, provides a waterproof finish that is impervious to dust, alcohol, acetone (nail polish remover), and various acids such as fruit and vegetable acids (orange juice).

Tung oil has a proven history in exterior applications, both above and below the soil level. Though the dried oil is relatively hard, the finish it provides is not the most durable. Tung oil is usually chosen for its aesthetic appeal rather than its wearability.

In its pure form, tung oil is a non-toxic finish that is ideal for surfaces that are expected to come into contact with food. This includes wood cutting boards, salad bowls, salt and pepper mills and any other project imagineable.

Advantages

The following refers primarily to pure 100% tung oil. Please see the Variations section below for properties of those variations.

As long as the surface bearing the tung oil has not been damaged, tung oil provides the following benefits:

  • Waterproof (or at least highly water resistant on a well maintained surface)
  • Resistant to alcohol
  • Resistant to acetone (such as nail polish or remover)
  • Resistant to fruit acids and vegetable acids (such as orange juice)
  • Flexible. Oil finishes continue to protect as the wood expands and contract.
  • Accentuates the texture and grain of the wood
  • Easy to apply (rub on, rub off)
  • Very forgiving during application
  • Easy to re-apply if the original finish becomes worn or damaged
  • Non-toxic and food-safe (Pure form only! Be careful!)

Disadvantages

Tung oil produces a mildly disagreeable odor for a few days after it is applied. This odor lessens with time, however some find that it continues for quite some time afterwards. If the tung oil is to be coated with some other finish such as wax, shellac, lacquer or polyeurethane, this smell is no longer noticeable.

Tung oil takes time to dry. Today’s high-tech woodworker is often in a hurry, but true tung oil takes its time to cure.

Pure tung oil has relatively poor penetration, and scratches that penetrate the finish can expose the bare wood beneath. This can be compensated for by adding up to 50% turpentine as a thinning agent to improve penetration on the first coat only. Subsequent coats should be done with un-thinned tung oil.

Pure tung oil is difficult to store. Depending on temperature, and exposure to light, the surface of the oil in the container will start to form a film or there will be gummy deposits around the container’s edges. Once these symptoms appear, the entire container must be discarded, since the oil will no longer be able to cure properly if applied.

Variations

Please note that all these variations on tung oil go through processes that render the finish toxic. Only pure tung oil which has not been thinned can be considered non-toxic. Please be careful.

Tung Oil Finish (or Modified Tung Oil)

In an effort to give the consumer a product that produces a look of tung oil yet gives a harder and faster drying finish, many vendors are offering products with names such as “Tung Oil Finish”. These products usually include metallic drying agents, thinners, or less expensive oil additives. These additives improve the penetration, hasten the drying time, and keeps the product cost reasonably low.

These products, while providing obvious benefit to the consumer, no longer behave or look like pure tung oil, and often these products contain only a small amount of tung oil and some do not contain any tung oil at all.

Polymerized Tung Oil

One of the main complaints of tung oil is the time it requires to properly cure once applied. Vendors have therefore produced a product called polymerized tung oil that has been through a cooking process to partially complete the molecular process that drying oils go through.

How to use it

As with any traditional product that has been used for many years, there will be many different opinions on how to use the product. What I will present here is the most simple and straightforward technique, and I will identify optional steps as such.

Precautions

Be careful with the handling and disposal of the rags used to apply tung oil. The oil itself is not a problem, however the solvents used to thin the tung oil are highly flammable and combustible. Allow rags to thoroughly dry on a non-flammable surface (such as a concrete block), or washed, or soaked with water before placing in the garbage. Solvents can generate heat through an exothermic reaction with the air (oxidation), and this reaction accelerates as the rags get hotter, and this has been known to start unintended fires.

Preparation

Since tung oil will highlight the grain and surface of the wood, it will also highlight any surface blemishes and scratches that are left behind. Therefore, take your time to prepare the wood surface before you start to apply the product.

Sanding sealers are usually used to fix problems with uneaven absorption of stains, however it is not required under penetrating oil finishes such as tung oil. If you do choose to use sanding sealers, it is recommended that you are sanding to 180/220 grit, and only move on to finer sanding once the sealer is applied.

Sand the surface using progressively finer sandpaper until you reach 220 grit (or optionally 320-dry grit) sandpaper. This will leave the surface smooth and there should be no visible scratch marks that remain.

Application

Use any clean, lint-free rag to apply tung oil. If you use a rag that has rough-cut edges, be sure to fold the rag so the rough edges are held in your hand and are not on the wood surface, since any loose wood fibres may catch the edge of your cloth and leave troublesome lint behind.

Apply a small amount of oil to your cloth (not the wood surface) and proceed to apply the oil to the work surface. Work from the least accessible areas (interior or underside) first and work towards the easiest sides. This will keep you from putting your elbow or forehead against a freshly oiled surface 😉

Apply by rubbing along the grain. Do not starve the wood, meaning you should not have to rub hard or often to get the surface wet, and if you are then re-oil your rag more often. Do not over saturate the surface either, meaning the surface should be wet but the surface should not have any standing puddles. If there are any puddles, remove them before continuing on to the next section of your project.

Approximately 1/2 hour after applying the oil, rub the project with a clean rag to remove any excess surface oil. Some people feel that a more vigorous buffing heats the oil and increases its penetration into the wood surface, however this          is an optional effort that may produce minimal returns at the expense of your elbow grease.

Let the project stand for at least 24 hours, or until dry. It may take weeks for a full curing/drying, but I am referring to the absorption of the oil by the wood surface. To obtain a super-smooth finished surface, rub the project surface with 0000 steel wool (or equivalent). The dust produced from this sanding should be a white powder, and if you get a gummy resin instead, wait another day before proceeding. Repeat the application of the oil, 1/2 rest period, and removal of the excess.

To get maximum protection, you should apply 3 coats of full-strength tung oil. You should also have sanded with 0000 steel wool the day after applying each coat.

As an optional step, you can use thin the first coat of tung oil by 50% or more using turpentine or naphtha. This will greatly increase its penetration into the wood surface, but you should still apply three coats of full-strength tung oil on          top. Please note that if you thin the first coat, the project will no longer be food-safe!

How do you know the surface is fully cured and has achieved its full hardness? If you push your fingers across the grain at various locations on your project, your fingers should slide smoothly and easily across the surface without any drag or grab. If there is any resistance, then the surface is not fully cured, and you should give it additional time before applying a different finish (such as shellac or paints).

Repairs

Repairs for projects finished with tung oil couldn’t be simpler. It follows the same model as the initial application. Just use a clean rag and apply a small amount of tung oil to it. Rub the damaged area with the tung oil, let stand for 1/2 hour, then wipe off any excess. After allowing to dry overnight, lightly sand with 0000 steel wool. Repeat the process two more times and the project is ready for use again!

Removal

Before full curing/drying

If you want to remove the tung oil within 24 hours of application, you can flood the area with a tung oil thinner (such as turpentine, naptha, xylene, or Sutherland Welles Ltd.® Di-citrusol) and use #0000 steel wool to rub the surface. The tung oil will soften and become gummy, and you will need numerous clean pads and fresh solvent to successfully remove it.

Note that completely removing any trace of the tung oil may be impossible without removing the outer surface of the wood…

After full curing/drying

Sandpaper and elbow grease is your only option. The tung oil chemically bonds to the surface, which is usually considered a benefit. If you absolutely must remove the tung oil, you must remove the surface of the wood that it was bonded to.

Where to get it

Lee Valley Tools
Sutherland Welles Ltd®

Cleanup

Please see the Precautions section above for appropriate disposal of rags used to apply tung oil.

Tung oil is essentially an oil product, and can be cleaned from hands using soap/detergent and warm water. Thinner (turpentine or naptha) can be used to remove tung oil from surfaces that can not be properly washed.

References

Chemistry of oils during the drying/curing process
Food and Agriculture Organization of the United Nations – Minor Oil Crops – individual monographs

Categories
finishing

Shellac as a Woodworking Finish

What it is

The form of shellac used by woodworkers as a finish is formed by dissolving flakes of shellac in an alcohol solvent. This shellac and alcohol mixture is then applied to the workpiece by the use of a rag. The origin of the flakes is actually the secretions of the female lac bug (Laccifer lacca, formerly the Coccus lacca), left on the banyan tree but sometimes on other types of tree, found in the forests of Assam and Thailand. Once these secretions are removed from the tree, it is called “seedlac”. The harvesting process leaves many impurities in the seedlac, and therefore it must be processed, resulting in a dry flaky substance.

These shellac flakes take on a range of colours orange to nearly transparent ‘white’ shellac (produced by bleaching orange shellac). Shellac is also available in waxed (natural) and dewaxed formulations.

When to consider it

Shellac is somewhat outdated or obsolete when compared to most other modern finishes, as it provides only minimal protection. It is, however, a very useful primer finish since many other finishes bond very well with it.

Shellac is used in the “french polish” technique of finishing, and therefore any project striving to create or restore a french polish finish would require its use.

Craftsmen desiring a food-safe finish should also consider shellac since it is entierly foodsafe if the correct solvent is used.

As far as appearance is concerned, shellac is suitable for virtually all wood types, from pine and cherry, all the way to imported exotics and tropical woods.

Advantages

As long as the surface bearing the shellac has not been damaged, shellac provides the following benefits:

  • Water resistant
  • Resistant to alcohol
  • Excellent as a primer coat, to seal and prevent the bleeding of resin or pigments, and to prevent wood stains from blotching
  • Can be applied under most other finishes. Note that polyurethanes have trouble adhering properly due to natural shellac’s wax content. Simply use de-waxed shellac to prevent these problems.
  • Easy to repair
  • Easy to apply (brush, rag, or spray on, thin cuts easiest)
  • Easy to re-apply if the original finish becomes worn or damaged
  • Non-toxic and food-safe (Use appropriate solvent)
  • User can control how quickly product is built-up by adjusting dissolved shellac concentration
  • Cold temperature application – Unlike other finishes, shellac can be applied in cold temperatures (5 °C/40° F and below) without concern over proper drying and curing
  • Non-yellowing and non-darkening as it ages

Disadvantages

  • Easily damaged by alcohol (it dissolves the finish)
  • Rare cases of allergic reaction (skin rash) during application
  • Once mixed with alcohol, shellac has a limited shelf-life of approximately 6 months. Use of mixed shellac that has begun to polymerize may suffer from never successfully drying!

Variations

Shellac Flakes

Shellac is primarily sold as flakes, and the woodworker must prepare the quantity required by dissolving the shellac flakes in alcohol. The color of a package of dry shellac indicates the degree of refinement the shellac flakes have undergone. Shellac, in its raw state, is a dark orange-brown color, which becomes lighter in the process of refinement.

Button shellac (button-lac), the least refined, is so named because it is in the form of dark brown buttons. It is suitable for use only when a very dark finish is desired.

Orange shellac, a more refined grade, is also recommended for darker finishes, but it allows more of the underlying wood to show through than does the button shellac.

Blonde shellac is a pale amber color. It imparts little change to the color of the finish.

White shellac has had all its natural pigment bleached out, and is quite clear. It is recommended for a very light-coloured finish.

These variations are not limited to the above, as the refinement process can be tailored by any manufacturer.

Each of these basic types are also available in de-waxed form, containing less than their natural 2% to 4% wax content.

Shellac Liquid (pre-prepared)

Sometimes called “French Polish” or prepared shellac, this is essentially shellac flakes pre-dissolved in alcohol (sometimes with an oil or other additive) to eliminate the mixing step. These products are beneficial, however they have a limited shelf life.

How to use it

As with any traditional product that has been used for many years, there will be many different opinions on how to use the product. What I will present here is the most simple and straightforward technique, and I will identify optional steps as such.

Precautions

Be careful with the handling and disposal of the rags used to apply shellac. The shellac itself is not a problem, however the alcohol used to dissolve the shellac is extremely flamable, and the even the vapors produced by the drying and evaporating shellac are flammable. and combustible. Allow rags to thoroughly dry on a non-flammable surface (such as a concrete block), or washed, or soaked with water before placing in the garbage.

Keep out of reach of children. The alcohol used is usually denatured alcohol, (making it somewhat umpleasant to drink), but some children are apt to investigate…

Wear a dust mask when sanding between coats. Fine dust is a woodworker’s hidden health hazard.

Preparation

Shellac has two primary uses in woodworking. First it can be applied as a sealer under some other type of finish, or it can be used as the final finish on the project. The only real difference is the number of coats that are applied, since the sealer coat does not need to be thick (other products will offer physical protection) while the finish coat needs to be thick enough to protect from physical abuse and the elements.

Ensure the surface is adequately prepared by sanding using progressively finer sandpaper until you reach 220 grit (or optionally 320-dry grit) sandpaper. This will leave the surface smooth and there should be no visible scratch marks that remain. If the final finish is to be some sort of paint, 120/150 grit is all that is required, since the paint will cover any imperfections that will remain, and you just waste money and your precious time sanding with no visible benefit.

Of course, if the shellac is being applied over some other finish, such as oil, perform the sanding steps before applying the oil.

Preparing The Cut

If you are using a pre-mixed shellac product, you can safely ignore this section.

Shellac flakes must first be dissolved with alcohol (cut with alcohol). The dissolved shellac is referred to by its concentration. Therefore, a 1-lb cut of shellac has 1 pound of shellac flakes dissolved in 1 gallon of alcohol. a 1-lb cut of shellac has 2 pounds of shellac flakes dissolved in 1 gallon of alcohol, and so on.

Cutlb/galoz1/qtg/L
(metric)
Use
1-lb.14120Pre-stain sealing, French Polish finishing
2-lb.28240Pre-finish sealing; general wood finishing
3-lb.312360Floor finishing; sealing knots & sap streaks
4-lb.416480Sealing tough knots & sap streaks, stains2
1 The oz listed is ounces of weight. Use your scale, not the measuring cup for this!
2 The 4-lb. cut is generally used by professionals, and is considered difficult to work with by most hobbyists.                  

Beginners and those unsure of the outcome are strongly advised to use a 2-lb or smaller cut. Even I prefer to apply two coats of a 1 1/2-lb cut, since I find the 2-lb cut asks for less hesitation, and is not as easy to apply on highly figured workpieces. But if your workpiece has large clear surfaces, the 2-lb or 2 1/2-lb cut may save you alot of time since you won’t need to mess with many corners.

To produce a cut, you need a scale to weigh your shellac, a measuring cup (of whatever size you find appropriate), and a glass jar with a tight fitting lid that large enough to hold the quantity of shellac you intend to make. Since the measuring cup will only be used for denatured alcohol, it is safe to use a kitchen measuring cup and simply wash it afterwards.

Metal cans should not be used as the shellac will react with the metal, darkening the shellac.

You will often require less than a galon to finish a project. One liter/quart of a 1 1/2 cut is enough to apply three or more coats to a pair of bedside tables and drawers. Remember to only make as much as you think you will use. It is quick and easy to make more shellac, but is expensive and wasteful to make too much and throw it away.

If you have an accurate kitchen digital scale ($20 at most department stores), the easiest method to proceed is to measure your alcohol and place it in your glass container. Place this container on the digital scale and reset/zero the scale. Now you can add shellac flakes directly to the container until the scale reading reads your desired cut weight. Note that if you take too long adding the shellac flakes, some scales go to sleep/turn off and you will not be able to tell how much shellac you have already added!

Another method is to weigh the shellac flakes separately, measure out the alcohol, then add the flakes. Both methods work fine, but this method requires you to clean the container that you measured the shellac flakes in.

After mixing the shellac flakes, it takes up to 24 hours to dissolve. Seal the container and let it sit overnight, occasionally mixing/shaking the jar.

Do not be concerned about being overly accurate. The difference between a 1-lb cut and a 1 1/2-lb cut is not overly significant, and it is easy to correct by just adding some more alcohol if desired. Once you start applying the shellac and seeing how it dries, you can always adjust your shellac for the next coats.

After the shellac is fully dissolved, it should be strained through a fine-mesh cheesecloth before use to remove any impurities. Shellac is made from the secretions of the lac insect and a few bits of insect carcass are often left in the shellac flakes.

Shelf Life

Shellac that has been cut with alcohol undergoes a chemical change making it take longer and longer to dry. If the shellac is applied once it has started to undergo this process, the finish that it produces will be softer and will be more prone to water damage and scratches. Also, exposing the pre-mixed shellac to heat will accelerate this process, so keep the prepared shellac in a cool (less than 24 °C/75 °F), dark location, in a tightly sealed container (mason jars work great). Since shellac is dissolved in alcohol, there is no worry about cold weather unless you think it will be exposed to temperatures near −114 °C (-173 °F)…

Application

Tools

Shellac can be successfully applied using a rag, brush, or sprayer. If you plan on using a brush, I suggest you keep to a 2-lb or less cut of shellac, or keep a close eye out for brush marks drying into your project that you will have to sand out if you want a smooth finish.

Techniques

Before shellac in the liquid state is used, it should be shaken or stirred thoroughly and allowed to stand for a few hours.

If using a brush, shellac should be applied using long strokes in the direction of the grain. A good-quality brush with a chisel tip should be used. Its bristles should be dipped about 3/4 of the way into the shellac and gently cleared of excess shellac against the rim of the container. This gives a reasonably full brush for full strokes without incorporating any air in the shellac. Place lid on the jar to reduce the evaporation in the jar.

If using a rag, fold the lint-free cloth in such a way that you have multiple layers of cloth (allowing the cloth to hold more shellac), but make sure the bottom layer that you run across the workpiece is smooth and not creased or wrinkled, as it may leave marks on your project.

If using a conventional, HVLP or airless spray system, use a 2-lb or thinner cut. For convntional and HVLP sprayers use the same pressure and tip size as used for lacquer or consult manufacturer’s operation guide. For airless sprayers, use a .011 to .013 tip and 800 to 1000 psi. For all sprayers, apply shellac evenly to the surface in thin, overlapping passes.

Shellac should be sanded between coats and each coat should be allowed to dry thoroughly. If the shellac is dry, sanding will produce a fine powder on the surface. If the shellac is not dry, it will be somewhat tacky to sand and the paper will clog. If your project has complex shapes, you may find that 000 or 0000 steel wool gives you adequate sanding without fall the fussing with delicately folding sandpaper. After sanding, the piece should be wiped thoroughly with a tack cloth and recoated. Depending upon temperature and humidity conditions, you should allow between two          and four hours for each coat to dry. Some craftsmen prefer to do their finish sanding of the raw wood after first giving it a coat of shellac, since this stiffens the wood fibers and allows any rough portions to be fully sanded off.

Projects should receive at least two coats, and thinner cuts of shellac will require more coats to build up the same level of protection.

After the desired number of coats have been applied, the finish can be rubbed with 0000 steel wool or FFF pumice with paraffin oil. Rubbing should always be done with the grain. If it is desired, a coat of paste wax can be applied 24 hours after the final rubbing and the surface buffed to a finish.

Repairs

Repairs for shellac couldn’t be simpler. Shellac has the wonderful benefit that each layer of shellac that you apply softens the previous layer, and the two layers essentially bond together.

If a wax has been used on top of the shellac, make sure to remove the wax first.

Simply prepare some shellac (don’t forget that shellac has a limited shelf life), then brush or wipe on one or more coats using the techniques described above. If you are simply filling in a scratch, refinishing the entire surface is not necessary, and you can use a fine brush to target your application of the shellac. Just be careful that your sanding step does not cut through the surrounding shellac. In these cases, a lighter cut usually produces a smoother finish without the need for sanding since the shellac has a better chance to self-level before drying. The only downside to this is that you must use more coats to develop the same level of protection, but for some that is a reasonable tradeoff.

Important tip from the Experts– If you know your piece of furniture is truly an antique and still has its original shellac finish think carefully before refinishing. The value of an antique increases tremendously if it still has its original finish. If the finish is badly worn or damaged bring it to a professional furniture refinisher.

Removal

You can remove the majority of shellac by using ethyl alcohol (or any other appropriate solvent) and rubbing the surface. The solvent will soften the shellac, and you need to wipe away the softened shellac. If the shellac was applied on top of an oiled wood (such as linseed or tung), the shellac should be possible to remove completely. If the shellac was applied directly on fresh wood, the shellac would have been absorbed into the fibre of the wood, and may not be removed completely without sanding. This is usually considered a benefit of shellac, but in this case it makes removal difficult.

Where to get it

Pre-mixed shellac is available at most big-box construction stores, and the flakes are slightly harder to track down because of their limited popularity.Lee Valley Tools – Shellac
Lee Valley Tools – Solvent / Thinner

Cleanup

Please see the Precautions section above for appropriate disposal of rags used to apply shellac.

Shellac is dissolved in alcohol, and alcohol such as ethanol and isobutyl alcohol are ideal for cleanup, or as a solvent for the preparation of shellac.

Wikipedia – Shellac
Zinsser – Shellac brushing instructions (also a vendor)
FDA application (and approval) of orange shellac as “made with organic” food coating
Excerpt from US FSIS USDA report suggesting shellac is generally regarded as safe (GRAS): “Drying agents and diluents that are generally recognized as safe (GRAS) – Title 21 Section 73.1. Specifically, may use water, dextrose (corn sugar), isopropyl alcohol, ethyl alcohol, shellac, and acetone.”

Categories
finishing

Oil as a Woodworking Finish

Oil finishes have been used for centuries to treat and preserve wood. Oil finishes seep into the wood and penetrate the wood’s fibers. Because of this, oil finishes cannot be built up to a thick coat like polyurethane or varnish can. They are probably the easiest finish to apply, however they offer less protection since they are succeptable to wear. Another advantage is that minor repairs can be accomplished by simply wiping on more oil.

When referring to wood finishing, oils are commonly divided into two major types: drying and non-drying oils. The term drying is somewhat of a misnomer, but refers to the hardening or curing aspect of the oil. Non-drying oils should be avoided since they have numerous disadvantages for wood finishing: the finish may remain sticky for a long time, the finish will stain objects in contact with the finish, the finish continues to penetrate the wood (reducing its effectiveness over time), and often bacteria can penetrate the oil and make it emit a rancid smell.

In general, oil finishes create a film that is typically hard, non melting and usually insoluble in organic solvents (varies with the particular oil).

Linseed oil and Tung oil are both oils that cure and work well as finishes

Categories
finishing

Linseed Oil as a Woodworking Finish

What it is

Linseed oil is made from the pressing of the dried ripe seeds of the flax plant (Linum usitatissimum, Linaceae) which gives flaxseed oil. This oil is then exposed to a solvent extraction process to produce linseed oil.

Pure linseed oil is a non-drying oil, and therefore is not a practical finish for wood. This type of oil may be available in health-food stores, but is not intended for wood.

Boiled linseed oil is not actually boiled, but has been processed (by oxidation, or adding metallic thinners) to speed its drying time. The remainder of this page refers to “boiled” linseed oil.

When to consider it

Linseed oil seeps into the grain of the wood, giving it a perpetual wet look that highly accentualizes the grain of the wood, commonly referred to as “making the grain pop”. Because of this, the color of the wood is slightly yellowed which darkens slightly with age.

Linseed oil has long been used as a preservative for wood, hemp (natural) rope, masonry, and as an additive in oil paints.

Advantages

As long as the surface bearing the linseed oil has not been damaged, linseed oil provides the following benefits:

  • Water resistant. Water left on the surface may penetrate given enough time
  • Flexible. Oil finishes continue to protect as the wood expands and contract.
  • Accentuates the texture and grain of the wood
  • Easy to apply (rub on, rub off)
  • Very forgiving during application
  • Easy to re-apply if the original finish becomes worn or damaged

Disadvantages

  • Linseed oil takes time to dry. Boiled linseed oil dries much faster.
  • Lack of any UV inhibitors
  • Linseed oil can support the growth of mildew
  • On surfaces where abrasion will be frequently encountered, linseed oil may not harden sufficiently, requiring frequent repair

Variations

Pure Linseed Oil

Pure linseed oil can take up to a week for each coat to dry, and is not considered a practical product for woodworker use. The only practical use for pure linseed oil is on products that are to come into contact with food products, and even then you should be properly warned that product labelling is somewhat deceptive, and may not be truly pure (or safe to eat).

Boiled Linseed Oil

One of the main complaints of linseed oil is the time it requires to properly cure once applied. Vendors have therefore produced a product called boiled linseed oil that has been through an oxidation process, or been given metallic additives, to partially complete the molecular process to speed the drying process.

Polymerized Linseed Oil

Polymerized linseed oil has been heat-treated, and does not contain any additives. HOWEVER, vendors of polymerized linseed usually use additives to improve the performance of the product, so careful reading of lables and monographs must be done if you are looking for a food-safe product.

Polymerized linseed oils dry faster, harder and are more durable than “pure” linseed oils

How to use it

As with any traditional product that has been used for many years, there will be many different opinions on how to use the product. What I will present here is the most simple and straightforward technique, and I will identify optional steps as such.

For full instructions on how to apply linseed oil, please refer to the technique for tung oil, as the application of these two products are virtually identical.

Precautions

Be careful with the handling and disposal of the rags used to apply linseed oil. The oil itself is not a problem, however the solvents used to thin the linseed oil are highly flammable and combustible. Allow rags to thoroughly dry on a non-flammable surface (such as a concrete block), or washed, or soaked with water before placing in the garbage. Solvents can generate heat through an exothermic reaction with the air (oxidation), and this reaction accelerates as the rags get hotter, and this has been known to start unintended fires.

Repairs

Repair instructions for linseed oil projects are identical to the technique for tung oil.

Removal

Sandpaper and elbow grease is your only option. The linseed oil penetrates the surface, which is usually considered a benefit. If you absolutely must remove the linseed oil, you must remove the surface of the wood that it was penetrated into.

Where to get it

Lee Valley Tools
Sutherland Welles Ltd®

Cleanup

Please see the Precautions section above for appropriate disposal of rags used to apply linseed oil.

Linseed oil is essentially an oil product, and can be cleaned from hands using soap/detergent and warm water. Thinner (such as turpentine) can be used to remove linseed oil from surfaces that can not be properly washed.

References

Chemistry of oils during the drying/curing process

Categories
imported-softwood

Pine, Radiata (Pinus radiata)

Pine, Radiata is an imported softwood

Location

Radiata pine (Pinus radiata), also known as Monterey pine, is planted extensively in the southern hemisphere, mainly in Chile, New Zealand, Australia, and South Africa. Plantationgrown trees may reach a height of 26 to 30 m (80 to 90 ft) in 20 years.

Characteristics

The heartwood from plantation-grown trees is light brown to pinkish brown and is distinct from the paler cream-colored sapwood. Growth rings are primarily wide and distinct. False rings may be common. The texture is moderately even and fine, and the grain is not interlocked. Plantation-grown radiata pine averages about 480 kg/m3 (30 lb/ft3) at 12% moisture content. Its strength is comparable with that of red pine (P. resinosa), although location and growth rate may cause considerable variation in strength properties. The wood air or kiln dries rapidly with little degrade. The wood machines easily although the grain tends to tear around large knots. Radiata pine nails and glues easily, and it takes paint and finishes well. The sapwood is prone to attack by stain fungi and vulnerable to boring insects. However, plantationgrown stock is mostly sapwood, which treats readily with preservatives. The heartwood is rated as durable above ground and is moderately resistant to preservative treatment.

Primary Uses

Radiata pine can be used for the same purposes as are the other pines grown in the United States. These uses include veneer, plywood, pulp, fiberboard, construction, boxes, and millwork.

*Much of the base wood information presented here is made available by the USDA FPL FS. If you are interested in a much more technical description of wood properties, I encourage you to visit the source.

Categories
tools

How to Choose a Scroll Saw For Woodworking

Whether you’re working on detailed crafts or simply need to make freehand cuts, the flexibility of a scroll saw is just what you need. Scroll saws are bench-mounted tools for cutting precise shapes and details in wood, metal or plastic. They’re often used in intricate crafts and are very handy for making homemade puzzles. Though usually associated with small projects, most scroll saws are capable of cutting stock up to 2″ thick.

Scroll saws are available in 15″ to 18″ models. A scroll saw is sized according to the distance between its blade and body. The size indicates how much of a work piece can be cut between the body and the blade. For example: a 15″ saw will accommodate 15″ of stock between the saw blade and the body. With this information you can determine that a 15″ saw can cut to the middle of a 30″ diameter work piece. Select your scroll saw based on the size of the work pieces you intend to use.

Miscellaneous Features

A worklight mounted on the saw’s arm illuminates the work piece and reduces eye strain.

A blower mounted near the blade keeps sawdust clear of the blade. The blower makes it easier to see cut lines.

Variable speed controls allow you to set the blade’s speed to match the material you’re cutting.

A tilting table gives you the ability to make bevel or compound cuts in one pass.

A quick or tool-free blade change feature speeds work and reduces downtime.

A work hold-down makes the saw easier to use and also serves as a blade guard.

Choosing Scroll Saw Blades

One of the most important parts of the saw is the blade. Blades are rated by the number of teeth they have per inch (tpi). The higher the tpi, the smoother the finished cut. Different blades are available for cutting wood, plastic or metal. Always follow the manufacturer’s instructions when choosing blades for your saw.