Archive for ◊ September, 2008 ◊

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• Sunday, September 28th, 2008

Here’s a 6 mm Japanese chisel that I like for chopping tails. The diagrams show possible cross sections for Western style chisels with the sides at 78 degrees to the back.

 

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Author:
• Sunday, September 28th, 2008

 

The question of chisel geometry for chopping out dovetails has received a lot of attention. This is one of those woodworking matters that I think lends itself to analysis and I think a reasonable conclusion can be reached. The problem, as I see it, is that almost all chisel manufacturers are ignoring a sensible solution. Here’s my breakdown.

The concern has to do with the sides of the chisel. It is said that if the sides of the chisel meet the back in a relatively wide bevel (the height of the side), the tool will not properly fit into the recess between tails and thus will damage the walls of the tails. This is true if the sides meet the back at a 90 degree angle, as in almost all chisels, though only for the tail portion of the joint where the angle to be chopped and trimmed is less than 90 degrees, typically 80-83 degrees. This is not an issue for chopping and trimming pins since the wall of a pin meets the base of the socket at 90 degrees.

An influencing factor is the saw kerf for the tail ideally reaches exactly to the baseline, in which case is does provide sufficient clearance for some square-sided chisels. However, I certainly cannot consistently stop my saw kerfs so precisely; can anyone? There’s also a problem with damaging the walls of the tail socket when simply cleaning it up.

A recent review of chisels in Fine Woodworking magazine, issue #200, gives measurements of the height of the side flat (to the thousandth of an inch!) for each of 23 chisels, noting that a short side is an important desirable factor in choosing a chisel. The angle of the sides is not specified. I guess they are all 90 degrees. As the side height of the chisel gets very short, it is unfriendly to handle.

David Charlesworth provides an excellent discussion of this issue on page 116 of A Guide to Hand Tools and Methods. He discusses a sensible method to use a square-sided chisel to chop and clean up tails. However, the method of making a “release cut” may be difficult for narrow-pin dovetail layouts. He also mentions and diagrams a “custom” ground chisel with sides at 80 degrees.

There’s a simple solution to all this: chisel makers could just make the sides of the chisel at 78 degrees to the back. Why on earth don’t chisel manufacturers make this type of design available? There is no need to have sides that are .025″ high, or .010″ (ouch). Just make the sides a comfy 3/32″-1/8″ high and at 78 degrees to the back. This will work for dovetails as steep as 5:1. Since tail sockets are usually narrow, a set of 1/8, 1/4, 3/8, and maybe ½ inch, chisels with this configuration is all you need for the tails. Thickness of such a chisel would reasonably be about 1/8″-5/32″ for the smaller sizes, and perhaps 3/16 for the largest size.

Problem solved. Chop and trim the base of your tails with this type of chisel. I use a Japanese version. You would not need to custom grind them and these chisels would be just fine for general bench chisel work.

In the meantime, Hida Tool carries a chisel of this sort. Go to Woodworking>Chisels. Scroll down to the “arinomi” chisels. The sides are at 75 degrees to the back.

Category: Tools and Shop  | 2 Comments
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• Wednesday, September 17th, 2008

 

Here’s a seven-tenon version of the MWTM&T joint that is part of a casework project in progress in the shop. The wood hasn’t been varnished yet. I recently wrote an article for Popular Woodworking magazine detailing techniques for producing this joint. The article, using a small sample, explains step by step how to make the joint, with key differences from traditional teaching that make it easier to make, improve the appearance, and add to the long term stability of the construction.

The photo below shows the dry fit with the excess lengths of the tenons still projecting. The pinch rods were used to check the width of the case; going from front to back it widens just a hair to allow proper drawer fitting.

It is a moderately difficult joint to make but the work progresses predictably. Glue up for this piece was tricky but Bowclamp cauls were very helpful in getting a tight joint line along the full width of the boards. Sawing the tenons flush to reveal the finished joint is one of those great moments in woodworking!

Category: Techniques  | Comments off
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• Friday, September 12th, 2008

 

You’ve heard it in ads, seen it on magazine covers, and on TV.

Perfect dovetails, every time.

This square is dead accurate.

The plane comes with a dead flat sole.

Perfect edges in two minutes of sharpening.

Stop it. Nothing is perfect. Not my work, not yours. The joinery in the photo is not perfect, trust me.

Let’s eliminate sloppy, low quality work from this discussion. I’m referring to high quality work done by very skilled woodworkers, top quality tools, and so forth.

As an example, consider the sole of your expensive new plane. Is it really perfect? Flat to within what, 0.002″? .001 “? Everywhere? 0.0005”? Doubt it. But what’s really important? A skilled woodworker knows that there should be, for example, no hollow just in front of the mouth. If there is light blocking contact there, as well as at the toe, heel, and just behind the mouth, it won’t matter if there is a bit of hollow in the middle of the front or rear sections of the sole. The wooden soles of Japanese planes are intentionally nuanced in this way.

How about cutting the tails in making dovetails? Is the saw held perfectly square to the width of the board? Within what tolerance? A skilled sawyer attempts to directly split the layout line on the waste side, cutting at 90 degrees, but nevertheless knows on which side is the mountain and which the cliff. You are aware of a one-sided tolerance – if slight error is to occur, try to confine it to where it could be trimmed, or perhaps yield to the slight compressibility of wood, or at least won’t be noticeable in the finished work.

The point is that a good craftsman gets beyond naive notions of absolute perfection of process or outcome and instead understands how to manage tolerances. He knows what is – and is not – critical to produce superb quality and apportions his energy accordingly. Likewise, a new woodworker should not be intimidated by the illusory goal of perfection. Nor should the novice be seduced by the claims of machine manufacturers that promise perfect joints or perfect anything.

I hope for an educated, perceptive excellence in my work. Understanding is better than hype.

Category: Ideas  | One Comment
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• Wednesday, September 10th, 2008

For this first post, I’d like to relate how a couple of old, oily rags motivated me start this blog.

On his Woodworking Magazine blog, Chris Schwarz posted a discussion of the remarkably old rag that he uses to wipe down his tools to prevent corrosion. It has been exposed to all sorts of oils and, from the looks of it, to more than its share of sharp edges. I was struck at how it looks almost exactly like the similarly ancient rag that I use in my shop.

Now this is about as mundane as you can get in the world of woodworking. It is, however, of considerable practical significance. That rag is essential in my shop. Yet I’m reasonably sure you won’t find this topic covered in your favorite textbook that purportedly covers everything you need to know to work wood. You’ve got to stop by someone’s shop and look over his shoulder to get this kind of information.

Working alongside another woodworker would allow one to observe habits and acquire useful skills by absorption as much as by explicit instruction. Over time, one might discover the thinking of the craftsman, the logic and the wellspring of his work. A wide range of thoughts would likely be shared. Work with the hands is not far from the soul.

I believe we modern small shop woodworkers have much to gain from visiting each others’ shops, albeit in the virtual world. For so many of us woodworking is largely done in isolation while the abundance of formal learning materials still leaves us with a void.

So, in this blog, I invite you to stop by my shop, look over my shoulder, hear what’s on my mind, and, of course, offer your comments.

Category: Ideas  | 2 Comments