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"Sharpening Files and Rasps

Don’t try this at home! Do it in the shop. This is a traditional method of sharpening files and rasps with acid. In the nineteenth century the time-honored technique was to soak the files and rasps in a bucket of urine. In the corner of the village Blacksmith’s shop was a bucket of urine to sharpen dull tools. I am sure the process was discovered after an old dull file was left out in the weather and rusted and someone discovered that it was sharp again.


The mechanics of rust, which is a slow oxidation process, is to remove more metal from flat areas that from pointy sharp areas. As the surface is reduced by acid etching in the form of rust from the acidic urine and the flatter surfaces etch quicker. As these flats are reduced the edge gets sharper. This works no matter how fine the file, riffler, float or rasp, nor how coarse the etching process is the same.


Today it may not be practical to keep a bucket of fresh urine in the corner of the shop, however if you are a traditionalist, go for it! Other acids can be used for the same process. Some of the acids are rather innocuous while others are down right dangerous! When handling any kind of acid always wear protective clothing, gloves, eye protection, etc., and Always Use Adequate Ventilation. The fumes can be dangerous. Use proper containers for acid, do not put in metal containers, some plastics might melt. Glass is usually a good choice, any material approved for acid.


First Thing


The first thing to do is clean the file, float, riffler or rasp with a wire brush to remove any swarf in the teeth. You can also use a file card. I use steel wire brushes as well as fine brass wire brushes on fine cut files. I have a fine piano wire pick I use to get difficult pieces. I also wash the tool in soapy water and scrub with an old toothbrush. This is to remove any surface grease that will resist the acid etching. I dry the tool and carefully inspect it for any clogged teeth or problem areas.


The whole idea behind this process is to get a uniform coat of rust on the rasp, float, riffler or file. The concentration is on the teeth and it doesn’t hurt to rust the handle unless you just don’t want to clean it. You can expose the tool to anything that will cause rust. You can put it outside in the weather, anywhere there is high humidity. You can expose it to a variety of chemicals to cause rust such as boggy soil or battery acid.


The Rust or Etch


The safest acid to use is household vinegar, this also takes longer but a few days soaking certainly is worth having a sharp tool. It may take longer or it may go quickly, keep an eye on the process, stirring the solution occasionally. When you put the metal tool into the acid you will see bubbles as the oxidation process begins to etch the metal. Gently stir the solution with the tool to dislodge the bubbles and refresh the concentration next to the metal.


The next safest acid is Muriatic acid which is used to clean brickwork. It is available at hardware stores and home centers and will work just fine as is or it can be diluted.


Always put the ACID into the WATER.


Have your distilled or filtered water ready in an appropriate container AND THEN add the acid. If you pour water into acid it will EXPLODE! This is real nasty when it happens, always use caution when diluting acid. Again stir the metal tool around to remove the bubbles from the surface to allow the acid to get to the metal to do its work. Watch the process and remove the files after they have a fairly uniform layer of rust on the surface.


The stronger the acid, the quicker the sharpening results. Some particularly dull tools may take a couple of treatments to get it back into usable condition. After the tool is rusted or etched, carefully remove it from the acid and rinse it with water. If you are using strong acid you will want to neutralize it with a mixture of clean water and backing soda (Sodium bicarbonate), then rinse with fresh clean water.


At this point you will need to remove the rust and using a metal brush such as a wire brush or file card can dull the newly sharpened teeth. I recommend a stiff old toothbrush to remove any loose surface rust and then I treat them with electrolysis to remove the rust. This is a method used by museums to remove rust and accumulations from metal artifacts. It works well on wrought iron and cast iron as well as steel. There are some precautions that need to be taken during this process because of hydrogen created during this procedure. Some files or rasps will sharpen without rusting as the acid will merely etch the surface, not producing rust but still sharpening the tool.


Removing the Rust


The method of electrolysis from the 1840’s of rust removal works very well to remove just the rust leaving the sound metal intact. The positive pole (+) of Alessandro Volta pile is connected to a sacrificial anode in a bath of distilled water and sal soda (washing soda - hydrated sodium carbonate) and the negative pole (-) attached to the saw blade, which is soaking the bath. Use caution when dealing with electricity around water. When the connections are made the rust begins to fall off the rusty blade. (You can also use an automobile battery charger to provide the proper electrical current.)


The rust is actually attracted to the anode on the positive and operates best in ‘line of sight’ so the anode should be positioned along the length of the file or other object being cleaned in this manner. Bubbles of oxygen and hydrogen are released in this process and after sufficient time the rust will be completely removed from the metal. Use adequate ventilation and take normal precautions; the gases given off can be explosive. The connections are removed and the blade is removed from the bath and the file is then cleaned again with soap and water and a soft brush. The file, rasp, riffler or rasp is then completely dried and the teeth are checked once again. Once the blade is clean the next process can begin.


Harden steel tools such as files, rasps, rifflers, floats, saw blades, plane irons & chisels require special treatment after electrolysis. The tools need to be placed in the sun for the same number of hours it was in the cleaning bath to drive off excess trapped hydrogen in the steel. This process called hydrogen embrittlement can make the steel very hard and susceptible to breakage especially the teeth. Heating the tool up in an oven to a couple hundred degrees for 15 or 20 minutes will also drive off any trapped hydrogen. Not necessary on wrought iron and cast iron, just hardened steel.


Maintaining Files, Rasps, Floats and Rifflers


After you have gone to all of the trouble to sharpen your tools it is important to keep them in good condition. I have my files in a stand to keep them from touching each other, after all a file touching another file is the beginning of the dulling process. I also clean my files with a fiber brush after each use especially if I am using them on wood that is green, wet or if it is high humidity. The swarf in the teeth can attract moisture or contain moisture that will rust the blade. I know we just rusted the blade but that was controlled and uniform over the entire surface. This is localized rusting and can cause an uneven surface through pitting.


Use files, rifflers, floats and rasps only on the push stroke, lift the file and do not drag it backwards over the material being shaped as this will tend to dull the teeth. Place the file where it won’t bump into other tools to keep the teeth sharp.


To prevent teeth from being fouled with swarf, you can coat the teeth with chalk, (whiting or calcium carbonate) will prevent wood and most metals from clogging the teeth. Softer metals such as brass, copper, silver and gold will quickly obstruct the teeth preventing them from operating properly. The chalk applied as needed helps keep the teeth clean."

"Hand SawingPanel Saw


Hand sawing is a pleasure in itself. The sound of a well tuned saw cutting effortlessly through a board, right on the line, is truly an experience. Sawing by hand should not be regarded as something that must reluctantly be done when you can't make the cut with a power saw. I prefer hand saws and use power saws when they are the only way to make the cut or the amount of work makes hand sawing counter productive. In sawing by hand, and through using hand tools in general, we come closer to craftsmanship, not to mention the peace and quiet of being "unplugged".


There are basically two kinds of hand saws: A cross cut saw, which as the name implies cuts across the grain of the wood, has teeth that are sharpened into knife points that score and remove the cross grain wood. Rip saws cut with the grain of the wood. The teeth are sharpened like chisels and literally chisel the wood away as small shavings. The rip saw is used at a higher angle than the cross cut saw. The teeth on both types have alternating set and this set, whether on cross cut or rip, determines the width of the kerf. It also prevents the saw blade from becoming jammed in the kerf. The teeth are set slightly sideways so as to cut a channel or kerf wider than the thickness of the saw, preventing binding. Some blades are tapered from thicker at the tooth side to thinner at back side. This allows for less set on the teeth and a finer cut.


There are two basic types of handsaw: The open saw, such as a hand saw, dovetail saw, with a stiff blade that is strong enough to hold its shape when used. Some of these, such as a Japanese Dozuki or back saws, use a fairly thin blade but have a reinforcement section along the top. The other type is a web or frame saw. These are frameworks that with their tensioning device hold a thin blade taut between two points, i.e., coping saws, hack saws, sash saws, etc. The tension on the blade provides the strength to the thin blades, allowing turning of the blade while cutting. The blade in any saw must be straight and clean.


By striking a bent blade with well placed blows from a metal hammer, blades can and must periodically be straightened. To straighten a saw blade, place it on a flat metal plate or anvil with the convex side of the bent saw up. Strike the blade, if you use a ball peen hammer make sure you don't leave a lot of unsightly marks on the surface. Hammering or striking a metal blade moves the metal around, relieving and rearranging the bending stress. This movement slowly straightens the bent blade. Move the blows of the hammer around over the bend in the blade. Check by sighting down the blade and reverse and strike as necessary, and don't hit the teeth with the hammer. A crooked or dull saw cannot cut a straight line, so if you are going to be using your hand saw properly you must be able to maintain and sharpen your saw.


The blade should be straightened and cleaned before sharpening. There is an order to be followed here, and after taking the time and effort to do this tune up work you will treat your saws with a new respect, a respect that will be reflected in your work. Start by cleaning off all accumulations of dirt and rust from your blade. Scrape, wire brush, sand, and use alcohol or turpentine, anything you can to get your blade clean and shiny. You can successfully saw with a rusty, dirty blade but it tends to bind, discolor the kerf and doesn't look as good as a clean shiny blade. A highly polished blade is like a well sharpened and polished chisel, it glides effortlessly through the wood.


Next join or whet the top of the teeth so they are all level and the same height by running a flat file squarely along the teeth until the tip of each tooth is shiny. On badly damaged saw blades some teeth may need to be re-filed back into the blade. You then want to set the teeth, rejoin them and then sharpen the entire blade. A saw wrench, wrist or saw set is the tool used to set the teeth in their alternate set pattern. These range from the familiar pliers type saw sets to the traditional flat saw wrench with slots on the edge for different thickness of saw blades. It takes an eye for this tool, there is no stop so you can break teeth off by bending them too much. The final result should be that every tooth angles out from the blade equally, one left and the next to the right so that the kerf will be uniform. Any tooth not bent enough does not cut it, literally.. Any tooth bent too much will catch every time it goes into the wood producing an irregular cut.


Sharpening is done with a triangular or knife file, every other tooth is filed first down one side and then down the other. It sometimes helps to have the blade clamped solid and straight as you file, the important thing being that you use the same angle each time you file the tooth. Some teeth only need one stroke of the file, others may require several strokes to produce the same result, the object being to remove the flatness (& shininess) from the joining or whetting process that you did earlier. Whether sharpening a cross cut or rip saw, all strokes of the file are made parallel to the ground regardless of the direction of the stroke or the attitude of the file. Another way of saying this is that with the saw clamped with the teeth facing upwards, all file strokes will be made in a perfectly horizontal plane.


When sharpening a cross cut blade you sharpen every other tooth at an angle facing toward the tip of the saw blade at about 60°, to a knife point, the tooth angling back at about 80°. When sharpening a rip saw blade you sharpen every other tooth at 90° to the saw blade, the tooth angle at 90°. This angle produces a square chisel end to every other tooth. Again, just remove the flatness that resulted from the preliminary dressing and strive to make every tooth just like all the others of its set, all left set teeth the same and the alternating right set teeth also of uniform height, sharpness and angle of set.


When you are finished sharpening a cross cut saw, a test is to hold the blade teeth up by the handle with the other end resting on a bench and lift the handle up a bit. Place a needle on the teeth by the handle and gently raise the handle until the needle begins to slide. If everything is true the needle will ride the set and slide to the tip and go straight off the end. It really impresses your friends too. Another way to check is by looking down the teeth from the handle to the tip, everything must be uniform, every other tooth aligned with every other tooth.


Once you have a straight, clean and sharp saw the fun begins. Take a scrap of wood, place a mark square to one edge and begin the cut. A starting nick on the waste side of the line is done with the nicking nub filed in the top end of traditional hand saws. While these may look like decoration, they actually have a function, that of nicking the board to provide a guide and starting place for the cut with the tooth side of the saw. Do not drag the saw backward to make the starting cut, it dulls the teeth and is inaccurate. The cut should be effortless, no binding or jumping, these are indicators that the set is not enough or unequal. The weight of the saw is what does the cutting. You will have problems if you try and force the blade through the wood.


Properly done, your hand holds the saw in alignment and gently guides the saw, letting the teeth do their work and the wood is easily cut. Make sure that the blade is at the proper angle you want it to cut, if you want a square cut, hold the blade square to the work. The beginning cut will determine how the rest of the cut will go. Start out slowly, this is the most important part of sawing, if you make a mistake you must correct it as soon as possible. Back up and use the side of the saw blade to cut back to the line, do not overcorrect or try and twist the blade. Keep the saw straight with no twist and re-correct the saw kerf by going back and straightening out the kerf with a straight saw. As the saw goes deeper into the wood cutting straight gets easier. Varying the angle of the cut depends on the wood and your preference. Use what is comfortable for you. When you approach the end of your cut make sure the waste wood is supported so as not to break off and ruin your piece of wood. Slow down and take it easy as the cut is completed. Back cutting on the scored cutting mark helps eliminate the final chip out, common in hand sawing.


The grip on the saw handle is important if you are going to do much sawing. If you try and squeeze the handle too hard you will soon tire. You just need to provide enough grip to have control of the saw. This provides a bit of a shock absorber between you and the saw. You really don't need to grip the saw handle too tight. Relax and feel how the saw handles as it cuts, don't force the saw, let gravity and the sharp teeth do the work, you are there to provide the reciprocating action necessary to cut the wood and to guide the saw as it cuts. Too firm a grip unnecessarily drags the teeth backward against the wood, a light grip helps in this process. If you have to force the saw there is something wrong with the saw or the sawyer. See Saw Sharpening."

"Saw Sharpening

Panel Saw


I have sent my handsaws out to be sharpened once and I learned my lesson. The saw was sharp, the teeth were properly joined and set, no attempt had been made to remove a slight bend in the blade and way too much metal had been removed by the modern grinding machines and there were still burrs on the teeth it had not been whetted. Since that time I have always sharpened my handsaws myself. The large rip saw with 5 ½ teeth per inch, being the easiest and the most difficult the small 24-point (24 teeth per inch) back saw. But what a pleasure to be able to take a rusted, bent and dull relic and transform it into a clean, straight, sharp and useful tool.


There are two types of handsaws; the very common crosscut saw and the much less common rip saw. One reason that crosscut saws outnumber ripsaws is the fact that wood can be easily and quickly split or rived with the grain while sawing with the grain takes much longer. As the names imply the crosscut saw cuts across the grain and the rip saw cuts with the grain of the wood. The crosscut saw has sharp knife pointed teeth that cut the fibers of the wood producing a fine dust, while the ripsaw has sharp flat teeth like a chisel or hand plane and remove small flat curls of wood. Look at the sawdust from each of these tools and you will notice the difference.


The process for tuning and sharpening saws are the same for both types up to the actual sharpening or filing of each tooth, at that point there are two different methods of making the particular type of teeth sharp. The first thing to do is remove the saw handle if possible and thoroughly clean the blade of surface accumulations and all rust. Even heavily rusted saw blades can be brought back to usable condition albeit a pitted blade. If the pitting is too deep then proper sharpening is nearly impossible. I wash the blade with soap and scrub the surface, carefully in the area of possible manufacturers signature stamping or etching. An abrasive such as pumice, rottenstone or whiting can be used to make the surface bright, which is the desired surface for a handsaw. If the surface is bright it goes through the wood with ease and the surface tends to resist rusting and decrease pitch accumulations. A bright surface also reflects the line of the edge of the work allowing you to visually determine you are cutting straight and square.


The method of electrolysis from the 1840’s of rust removal works very well to remove just the rust leaving the sound metal intact. The positive pole (+) of Alessandro Volta pile is connected to a sacrificial anode in a bath of distilled water and sal soda (washing soda - hydrated sodium carbonate) and the negative pole (-) attached to the saw blade, which is soaking the bath. Use caution when dealing with electricity around water. When the connections are made the rust begins to fall off the rusty blade.


The rust is actually attracted to the anode on the positive and operates best in ‘line of sight’ so the anode should be positioned along the length of the saw blade or other object being cleaned in this manner. Bubbles of oxygen and hydrogen are released in this process and after sufficient time the rust will be completely removed from the blade. Use adequate ventilation and take normal precautions; the gases given off can be explosive. The connections are removed and the blade is removed from the bath and the blade is then cleaned again with soap and water and a mild abrasive as necessary. The blade is then completely dried and the surface brought to a bright condition. Once the blade is clean the next process can begin.


Harden steel blades such as saw blades, plane irons & chisels require special treatment after electrolysis. The blades need to be placed in the sun for the same number of hours it was in the cleaning bath to drive off excess trapped hydrogen in the steel. This process called hydrogen embrittlement can make the steel very hard and susceptible to breakage especially the teeth. Not necessary on wrought iron and cast iron.


Hammering or planishing is the first step in preparing a saw for sharpening. Hammering is only done on bent, bowed or kinked blades. If the blade is perfectly straight along its entire length then no hammering is required. If a blade has a kink or bend then these need to be removed, for if the blade is not straight, it will not cut straight. Even with just a slight bow in the blade will cause it to wander as the cut progresses, the blade must be straight. The method of straightening with a hammer can be done to hand saws with un-backed blades as well as backed blades, those with metal ribs along their back edge to stiffen and strengthen fine blades.


You first sight down the blade from end to end along the teeth and look for and visually mark the place where the blade is bent or kinked. Then sight down the back of the blade to see where the blade is bent. I use chalk to mark the problem areas on the convex side of the bend in the blade. With a hammer with a slightly convex face begin striking the blade against an anvil or piece of flat metal with the concave part of the bend down facing the anvil.


Begin striking with light blows and work in a circular pattern on the convex side of the bend, keep moving so you don’t strike in the same place. And start on the BACK edge of the saw blade not on the tooth side. While it is possible to get the kinks, bows or bends out by striking near the teeth, most problems on the tooth side of the blade go away after the backside of the saw is straightened first. So on backsaws always straighten out the reinforced back first before attempting to remove problems in other parts of the blade. A slight bow in the back is straightened by lightly hammering on the convex side moving back and forth along the saws back.


Periodically sight down the saw on both the backside and tooth side to monitor your progress. You want to gently and slowly remove the bow not cause the bow to go in the opposite direction. Straightening one area can cause other areas to bend, so work both sides as necessary until the back if perfectly straight. I then start work on the tooth side of the saw. I place the saw convex side up with the teeth overhanging the edge of the metal plate or anvil and always avoid hitting the teeth with the hammer. You may have to strike the blade close to the teeth so use caution when performing this delicate operation. Periodically check your progress and again check the back to see if problems have reappeared on the back. At that point go back to the back and straighten it out before continuing on the tooth side. If a dimple is within the field of the blade between the back and tooth edge this must be worked out flat to insure proper sawing operations. As dimples or bulges will bind up in the kerf.


When you are hammering you are causing the metal to expand thereby making it move on the side being hammered. Try hammering around the edge of the bulge or dimple and see how the metal behaves. Some will go from convex to concave as you hit them with one blow. You need to get familiar with how the metal will react as you hammer or planish the surface. As you hammer the metal you are working the molecules and this does generate some heat and work hardens the metal. This is usually not a problem but excessive hammering can harden the metal to the point where it may be brittle. If the blade needs to be annealed the teeth should be protected from the heat to allow them to maintain their necessary hardness.


If the entire blade is annealed then the teeth should be harden by quenching as part of the process. It is best to harden the teeth after they are properly joined, set, sharpened and whet the saw. Some blades straighten out after a few well-placed blows with the hammer, others with bulges, kinks, bows and twists can keep you beating on them for an hour. And there is no alternative, the blade must be perfectly straight and flat to work properly and hammering is the only way to make them true.


I have sharpened saw blades in a bench vise but I have to keep repositioning the blade so the part I am working on is held steady. A handy tool for holding the blade during most process of saw sharpening is the saw chops. Made of stiff wood or more modern iron ones, these tools are wide jaw clamps made to hold a large portion of the blade rigid and at the proper height for easy access to the blade while joining, setting and sharpening. Some wooden models have concave hollows along the top edges that collect the iron filings for use in making stains. The hollow trough helps keep the filings in one place for easy cleanup.

(** Waste not want not **)

(...)

Whetting is done after all of the teeth are sharpened. Whetting is usually done on a fine whetstone. I use a small stone and gently pass it over the side of the teeth starting at the handle end and passing the stone over the teeth to remove the burrs and making the set or kerf of the saw uniform and consistent. One tooth that is too high or set too much will snag with every stroke of the saw through wood. First one side is whet then the other. I place the stone on the blade so that one of the long sides of the stone rests on the blade and the other side is on the teeth hanging over just slightly. This keeps a constant angle that will produce the best results. Use an equal number of strokes or passes on each side of the blade to insure uniformity. You can also use your favorite sharpening method, i.e. sandpaper or a fine file held flat on the side of the blade.


After the blade is whet, the handle is reattached and the saw blade is tested for a tight uniform kerf by sawing into a piece of wood a couple of inches. The blade should be slightly loose but not able to rock from side to side. If there is a lot of side-to-side movement, then the kerf is too large and the blade needs to be whet again to reduce the size of the kerf. If the saw tracks to one side that side is not whet enough or the other side is whet too much. Uniform whetting will insure a straight cut. Whetting is an extremely important process in order to make the saw cut smoothly. I can't emphasis this point enough, always whet your blades.


There is nothing more satisfying that taking a dull, bent and rusty saw blade and produce a tool that will easily and accurately cut a fine straight line. There is a lot of work in bringing back an old saw to usable condition, you have to clean the blade thoroughly, hammer the blade flat, join the teeth and maybe even file new teeth back into the blade. It must be set, sharpened and whet before it can be used. But after that point the saws are much easier to maintain, sometimes only joining, sharpening and whetting are all that is necessary to tune the saw back to working condition.


After you have spent this much time tuning your saw you will want to protect the teeth. I have most of my saws hanging from the beams in the ceiling but a couple doesn’t hang and I have made tooth guards for the blades. I also have a blade guard for saws I take to job sites. The guard is a thin piece of wood the length of the blade with a small groove made down the length of the wood about half way through the piece of wood. This is slipped over the teeth to protect them during transport or while they are on the shelve so the teeth don’t hit any metal object and become dull or broken.


I live in an area with low relative humidity so I don’t put anything on the blades to prevent rust. If rust is a problem the blade should be very clean and then warmed slightly and coated with linseed oil. After any has soaked in I wipe off the excess and allow to dry for 24 hours. Absolutely all-excess oil must be wiped off or the blade will be sticky. Once dry it will be protected from rust. This coating will mechanically wear off, so it needs to be refreshed occasionally. Don’t use non drying oil such as machine oil or wax as they will leave a residue on the wood you are cutting and can effect gluing during the assembly process.

Handmade Woodworking Tools

My Dovetail Saw