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วันจันทร์ที่ 7 กรกฎาคม พ.ศ. 2551

How to Set the Hoops on Japanese Chisels




How to Set the Hoops on Japanese Chisels


Bench and mortise chisels made in the Japanese tradition are hooped at the end of the handle. This is to keep the handle from splitting when it's hit with a hammer, and allows for a more slender wood handle that is very comfortable to hold. Paring chisels, which are not meant to be hammered, are not hooped. Wood moves with the weather, so it is traditional to ship the chisel with the hoops barely fitted to the handle so that the user can properly set the hoop on the handle. The actual time it takes to set a hoop on a handle is only a few minutes, although with an entire set of chisels the task may seem daunting. Fear not! One of the best things about setting the hoops on a new set of chisels is that you get a chance to really feel the fit of the handles in your hand and become acquainted with the tool. This is also a good time to remove any maker's labels on the handle, and if you wish, to refinish the wood. For those of you who may be a little hesitant about buying a set of Japanese chisels because you have to set the hoops, don't be put off by this! Like many tools - power tools in particular - Japanese chisels need to be set up before you use them for the first time. But it's well worth the effort. If the simple steps below don't convince you, see the note at the end of this page.



Warning: Hoops and handles are not interchangeable. The hoops and handle sizes may vary depending on the chisel size, so take care not to mix up which hoop goes with which handle. Some chisels arrive with their hoops tightly jammed onto the handle. This is really a temporary measure and the hoop will probably loosen up in use. Whether you decide to set the hoops correctly right away or wait until they loosen is a matter of personal preference, but here is the process.
Click on the images to enlarge

1. The tools you need to set the hoops are very simple: The chisel and its hoop, a rat-tail file, a Japanese steel hammer, and (optional) a cat's paw. I also used another chisel for trimming the handle and a spring clamp for holding the chisel in a glass of water (not shown).

Note: The best way of removing maker's labels is with a product called "Goo-Gone." It seems to be readily available in houseware and hardware stores and it is truly is a miracle product. It removes the sticky label gunk (labels, tape residue, mysterious sticky things) and doesn't damage the finish. One bottle will last a lifetime and we use it every time we buy something with a label on it.

2. Using a rat-tail file, file any roughness or ridges off the inside of the hoop. This step is very important.

3. Fit the hoop to the handle. It should easily seat about a 1 /32" - 1/16" below the top of the handle. Note that the bevel edge on the inside of the hoop should be facing downwards, towards the cutting edge. If it isn't, either file the hoop a little wider or slightly trim the handle all around with a knife. If, when the hoop was originally forced on the handle by the maker, a ridge in the wood was formed limiting how low the hoop will go, you may want to carefully trim down this ridge a little with a knife. Just slightly, to even it out a little.

4. Using a steel Japanese hammer, hammer the handle all around the area where the hoop will go. The purpose is to compress the fibers of the handle a small amount so the hoop slides down further. Use discretion - the handle will compress very slightly but not enough for you to see it easily.

5. With the hoop seating correctly, seat the hoop permanently by gently hammering the hoop down directly or using a cat's paw. Do not hold the handle in a vise, since hammering a clamped handle will loosen the blade. With wider chisels hammer the hoop with the blade resting cross-grain on a scrap of wood. For narrower chisels - such at the 1.5 and 3mm do NOT rest the blade on a scrap of wood as the hammering, if too strong, could crack the chisel. Either hold the chisel in your hand as described in step 7 or drill a hole in some scrap and support the chisel under the bolster.

5A: You can also seat the hoop using a cat's paw to hammer down the hoop evenly. It's a little faster then doing it just with a hammer and worth the investment for a large set of chisels.

6. Soak the top quarter inch of the handle in a partially filled glass of water (about 20 minutes seems right for oak, denser woods such as boxwood should soak longer around 30-40 minutes). This is to make the compressed wood of the handle swell back to its original size and to soften the wood for step 7. Be careful not to get the rest of the handle wet, since this will damage the finish on the handles. On this chisel I put some masking tape on the hoop and part of the handle to make sure I didn't get the handle wet. I used a spring clamp to keep the chisel supported vertically in the water.On my set of chisels, I ended up deciding to refinish the handles completely. I sanded off the entire handle finish before setting the hoops and applied a Danish oil finish after I was all done.

7. Holding the chisel with one hand, "mushroom" the top of the chisel with a steel hammer by hitting the top of the handle all around the edge. You can't see it in the picture, but I'm holding the chisel in one hand and bracing my hand against my chest. In this case the edge of the chisel is unsupported (as opposed to when I was forcing down the hoop). I'm striking glancing blows all around the edge of the handle, and slowly the end grain of the handle mushrooms over. You can see in the next two pictures what the handle looks like when I'm all done.



Total elapsed time: about five minutes including the filing of the hoop (the most annoying part of the process) and 20 minutes or so for soaking.
8. Dry the chisel and oil the blade to prevent rust.
9. Let the handle dry completely.
10. If you plan to refinish the chisel, apply your favorite finish after the handle is completly dry.
Conclusion: While setting the hoops may seem like a lot of work, you only need to do it once per chisel per lifetime. Once you get in practice, you will set the hoops with very little effort. In time and with use and changes of weather the hoops may loosen up again. That's okay. The mushrooming is permanent and will prevent the hoops from coming off.Note: We have begun to import certain styles of chisels with their hoops already mushroomed by machine. This is a brand new product and we are one of the first companies to import these chisels to the United States. The look is different, and there is an added cost, but it may be right for you if you really want a Japanese style chisel but do not want to get involved with setting your own hoops.

Design Considerations



Design Considerations

Introduction
When we endeavour to introduce a new tool, the first consideration is what the optimum design for the tool should be. Though it might be tempting, we do not want to slavishly copy an old pattern. This is because one generally does not know enough about the context in which the design arose or exactly what the tool was originally used for. Sadly, too many designs have been "dumbed down" over the years, mostly because of cost. When we saw that there was a need for a really great turning saw, we wanted to make sure that we understood the classic saws’ engineering so as to reproduce only their best features.
First, a bit on terminology. Any saw with a blade tensioned in a frame is generally referred to as a frame saw. To this day, European woodworkers use frame saws of around two feet long, with wide blades to do all their main cutting of boards. In the English and American traditions (after 1700 or so) woodworkers used handsaws for those tasks, and a narrow-tensioned blade in a frame saw only for cutting curves. These smaller saws are typically called either bow saws or turning saws. Very small versions with blades of around 6 inches are known as coping saws, and are naturally used for coping joints and other intricate work. The frame consists of a pair of mortised cheeks held apart by a tennoned cross-member called the stretcher. The hardware, or pins, hold the blade in the cheeks and also provide a mount for the handles. Finally, the tension on the blade is kept by a twisted cord, a Spanish windlass type of traction device kept from unwinding by the all-important toggle. The typical full-sized bow saw has a distance between the cheeks of about 8 -16 inches - typically 12 inches. This is the type of saw we wanted to reintroduce.
We looked at every bow saw we could find, yet, there are very few bow saws with a known history that have remained unchanged from a documented era of production. Two saws in particular fit that bill: one in the Seaton Tool Chest in England and another in the Duncan Phyfe Tool Chest at the New York Historical Society. We also looked to the bow saws in our collection, including an interesting one from the late 19th century.
The task at hand was then to understand why each part of the saw was built the way it was. The Blade
The blade on all the saws we looked at was a ผ" wide band, held to the frame by a hole drilled into the blade and pinned with a loose pin or a short nail. All the modern bow saw makers we know use lengths of band-saw blades.
We hated the modern blades. What works for a powered band saw is usually too aggressive or too dull for a hand saw. They are almost always too wide as well, which means you can’t cut a really tight circle. That said, it’s not so easy to drill a centered, 1/16" hole on a blade that is much narrower. The antique saws had blades that were also ผ" wide, but only at the ends for drilling the pin holes, the part with the teeth was considerably narrower - making for a 3/16" or 1/8" wide blade, with the gullets of teeth moving to the centerline of the blade. These dimensions give a tighter turning radius.
We thought about re-grinding the backs of band saw blades to create narrower blades, but modern band saw blades are more brittle, and we don’t like having the line of teeth off-centered.
Also, changing a blade fastened with loose pins can be a pain the neck. You need to knock out the pins without dropping them, and that’s no fun. Then we had an idea; why not use coping saw blades? They’re narrow, inexpensive, and since the cross-pins are already installed, you can just hook them into the frame.
As far as we know, we are the first company to offer 12" coping saw blades. They work like a charm! They’re even narrower than most early turning saw blades, so you can saw very tight radii (just like a coping saw), but with a longer, faster, and smoother stroke and switching out blades is trivial. Problem solved!
There is, of course, the question; should the saw cut on the pull or push stroke? The advantage of saws that cut on the pull stroke is that the blade stays in tension, but in a frame saw the blade is in tension anyway and by pushing you get a lot more power. We tested both ways many times and with the right blade, pushing seems to work much better for most applications.
The Pins
The next problem was fitting the blade to the frame. Some more primitive bow saws used wooden fittings, but we felt that the cross-pins would eat at the wood over time. All the professionally made bow saws we examined used brass fittings. No problem! We machined a ผ" brass shaft with a slot and a hook in it. We also decided to include a regular hole so you could use old-style or wide blades. The pin has a shoulder machined in it eliminating worry about constant tension pulling the brass out of the handle.

Another design issue: how to attach the handle to the brass? Some modern saws use an obvious solution – cross-pinning the handles to the brass. It’s not that hard to do, but we wanted to offer a kit that could allow everyone to make a saw. That meant adding cross-pins to the kit, and the need to locate and drill through metal and wood rounds together. This is a real problem if you don’t have the right tools. Gluing the hardware into the handle is simple enough, but brass doesn’t readily stick to glue. So, our ultimate solution was to cut some grooves in the shaft and then file a single flat. When the glue hardens in the handle, it catches in the grooves to prevent pulling out. Glue on the flat prevents the brass from turning in the wood. With the tension on the blade taken firmly by the brass shoulder, the glue doesn’t even have to be very strong.
Note: Holtzapffel’s, great 19th century English compendium of tools and craft, illustrates a turning saw with loose pinned blades, but a hooked pin is on only one side, "so that the saw may be removed sideways from the one handle, and allowed to move as on a joint upon the other, a provision that is often turned to a useful account." We have no evidence that this design was ever manufactured in the 19th century.

The Handles

How big should the handles be? Why are the handles the way they are? Is the bigger handle on the old saws really too short for a modern hand? There is a common thought that woodworkers today have bigger hands so the handles need to be a little bigger than what’s found on an antique. But how much bigger? A frame saw has two handles: a short and stubby one, called the toe, that is farther away from the user, and a closer one, which is bigger in all respects and used by the hand that pushes the saw.
Then it hit us---The toe is only really used to turn the blade in relationship to the cheeks. You wouldn’t normally hold on to it while sawing.
The handle is where all the action takes place and here is where understanding how traditional saws are used is helpful. All western saws (and planes) are used with the forefinger extended, like gripping a pistol. It gives control. What happens when you extend your forefinger so that it rests on the frame of the saw? First of all, you need a short enough handle to bring your hand close to the frame, but in use, we got all the control that we needed to cut fast, accurate curves. It was really something. On some early saws we noticed a slight concavity in the cheek, next to the handle--- a feature that disappeared in the mid-to-late 19th century saws. Originally, we thought was ornamental— some over-sculpting. Now we believe it to be the saw’s finger rest, an important feature that we chose to include on our saws.
Finally, the handle needs to be short enough to rest in the palm of your hand. This way, your entire arm aligns behind the saw blade and it will be easy to saw straight. Too long a handle tilts the hand off to the side and the saw becomes harder to control.
Note: In many 20th century woodwkring instructions books, including ones by noted authors Bernard Jones and Charles Hayward, a two handed grip is shown. We have also noted the two handed grip in some early 20th century shop photographs. We think that the reason for the two handed grip, where one hand is holding on much as we demonstrate and the other hand is held over the first hand and also grips the cheek, comes from heavier saw frames of the post 1850 era where the frame was too heavy to stay in place as the saw was turned to saw a curve. A second hand keeps some of the weight off of the saw so you can turn it easily and it prevents the frame from twisting unpredictablely. We find in tests that the two handed hold works but there is a loss in stroke, some speed, and it is more awkward and there is a loss of control. However if your saw frame turns under the weight of the cheeks it is the only grip that allows predictable results.

The Frame

The early turning saws we looked at all had very thin, almost spidery frames. The reason for this, of course, is that the weight of the frame will influence the cut. When you turn the saw in the cut, you want the entire saw frame to move, so that the blade stays straight in the frame. A beefy frame will cause the saw to feel top-heavy in use. The handle will move with respect to the frame, twist the blade, and the cut will meander. We wanted a thin nimble frame.
This brings us to the question of the wood. A turning saw can be made from almost any wood that can take a little tension. The bigger the saw, the more tension it can take. A lighter-weight wood is preferable because of the nimbleness factor outlined above. The traditional wood that English companies used for these saws is beech, which works fine. However, good quality, straight-grained beech is hard to find in quantity. In the United States, we have oodles of great wood that is flexible, tough, and can tolerate a lot of tension: Hickory. Our saw is made of American Hickory. It is only slightly more than 11/16" thick at its thickest with the cheeks thinning toward the top. The stretcher is held in place with a shallow mortise that is intentionally over-long. The mortise exists to register the stretcher. A little slop allows the saw frame to adjust slightly as it goes under tension. We have seen saws where the stretcher is mortised in to the cheeks with a curved joint.This is handy when dealing with many different lengths of saw blade but with hickory, which is flexible, and of course with our factory made blades, consistent length isn’t a problem. So, initially we elected to use straight mortise joints. However, upon further thought we realized with the extra hole our pins offer it would allow the use of a fairly wide range of blades and we decided to go with a curved mortise face.
Note: Bow saws in Vietnam (and perhaps other places) are used for everything, and the saw-makers there don’t bother with mortising. The stretch is butted to the stiles and held in place by tension. This system works fine and greatly simplifies construction.
Another issue was where to put the stretcher in relationship to the cheeks. We found the positioning on the old saws, with the stretcher slightly above the midline of the frame, to function the best. This provides a little more depth of cut without throwing the weight of the saw too far back.

Tension

The next thing to consider: how to tension the frame. We found several methods to choose from: (1) A twisted rope held in place with some sort of a toggle that rests against the stretcher which is the most popular method in the English and American tradition. (2) Catalogues from the later 19th century show a sort of steel turnbuckle in the middle. This appealed to our mechanical sensibilities, but otherwise isn’t stylistically pleasing and wasn’t very popular. (3) In Europe, modern big frame saws usually have a threaded rod with a wing nut at one end. Again, not a very elegant solution. (4) In Vietnam, the frame is held in tension by a wood or metal hook, and a nut at the end of the blade holder tensions the blade. We liked the Vietnamese solution, but it complicates the handle geometry considerably, and requires a new part for the top of the saw.
The best solution is the twisted rope. It’s also the lightest option, which means it’s the method that causes the smallest momentum effect on the sawing, especially with the rope all the way at the end of the frame. This is the method we chose, using heavy, braided fishing line, which is pretty darn strong. Most saws we looked at had a lot of twine of varing thickness and as you turned the toggle the toggle got harder to turn. However on examination we found this is because the toggle was spending most of it's time twisting the rope, not bending the frame. We found that only a few loops, about 4 or so, allowed us to tension the saw very easily without increased difficulty in turning.
The Toggle

Almost all the post-1850 catalogs show a flat paddle intertwined between ropes that is twisted until it hits the stretcher, and has to slide between the ropes for clearance to be twisted further. The problem there is that it becomes harder and harder to slide the toggle between the twisted ropes as the ropes gain tension. We have seen a couple of recent solutions to this problem in which the toggle slides in a nut, which keeps the rope away from the toggle and gives the toggle a protected place in which to slide. We liked this solution, but even with the nut in place, the toggle gets harder and harder to slide up and down as the saw tensions. It wasn’t until we looked more closely at some 18th century saws that we found an elegant solution. These saws use a swinging toggle - a turned piece with a groove at the top to locate the twine. The groove prevents the toggle from sliding, but its cross section where the ropes cross is thin enough so that the toggle can swing easily to clear the stretcher. It’s an ingenious solution, provided the toggle is strong enough to withstand the compression and twisting. For this, hickory is particularly well suited, so it was the perfect solution for us.
That all being said the swinging toggle style is almost too easy to turn. With the sliding toggles as we said tensioning each turn gets harder. With the swinging toggle, coupled with only a few loops of rope, rotating doesn't get harder and even with the saw overtightend it's not hard to underestimate the amount of tension and easily add in another twist or two. The downside here is that you can be deceptively lulled unto overtightening the saw until it fails. We still love this method, but as people used to sliding toggles it took getting used to.
Summary

So, that’s how we arrived at the numerous features of our saw. If you want a solid bow saw that captures the best of the early 19th century tradition, we urge you to consider getting one of our original Gramercy Tools bow saws. We are pretty proud of our engineering, and we think it’s great value.
We are also happy to give you our drawings that reflect all our research and design if you’d like to make your own saw. We stock kits of blades, brass and turned parts so all you need to do is the woodworking. Even within the constraints of good engineering design there is an opportunity to make a customized saw that has nice aesthetics. Just be careful the wood you chose is clear, straight-grained and strong enough to take the tension you need to make the saw work. Remember, the bigger the blade, the more tension you will need.