Chisel jig
	Finest abrasives.
	Microbevels front and back.
	Use a jig.
	Copyright (c) 2002-13, Brent Beach

Overview

• They vary in length. I have butt chisels that are only a couple of inches long, and paring chisels with blades over 8 inches long.
• They vary in thickness. A paring chisel may be only 5/32" thick, while a heavy mortise chisel ("pigsticker") is 7/8" thick.

There is the jig set for a 30 degree angle and a standard sized chisel - perhaps a little longer than some.

This is the jig, from the front. The jig was made entirely from a scrap of Douglas-fir. I do not recommend Douglas-fir for jig making - it produces more slivers than you really want from a jig, and it is not durable enough. I made another jig in beech.

All the thin strips are almost exactly 1/4" thick. It is not important exactly what thickness you chose. It is important that the strips are of uniform thickness. I ripped 2 16" pieces of beech, planed then to about 1/4", then sawed them up into short pieces.

There are 8 short strips - 2 3/4" long allowing for a chisel almost 1 3/4" wide. You may need a wider jig. That should be no problem. The two long strips are 4 3/4" long, or 2" longer than the short strips. The two tall pieces are 2 5/8" tall.

Hardware - 2 machine screws 3" long, two washers, two T-nuts. To avoid splitting the wood, I folded two of the pins on each T-nut flat, and turned the nut so that the remaining pin was on the inside, the two pins in different lines of the wood.

For each slot in turn, put a chisel in each slot and measure the height of the chisel back. Then using the extension calculator and this height (blade thickness 0!), you can calculate the blade extension for each position. I wrote the extensions on the front of the jig (inches, thirty-seconds) for both 25 and 30 degree honing angles.

To setup the jig:

1. measure the blade length and pick a slot for the angle you want, tightening the screws so the blade does not slip, but can be moved [because chisels are tapered, they do tend to slip out of the jig much more easily than most plane irons -- be careful here]
2. set the extension on a combination square
3. set the extension of the chisel from the front of the jig, using the combination square [see the Plane Jig pages for how to set the extension.]
4. square the chisel to the front of the jig using the combination square.
5. tighten the screws -- because this jig has much thicker pieces, you can put lots of tension on the screws, but don't strip the T-nuts.
6. when using the jig, apply pressure on the chisel near the end, with only light guiding pressure on the jig itself. That is, don't try to hold just the jig and use twisting pressure on the jig to hold the chisel against the abrasive.

Improvements:

• The screws are a bit of a problem - machine screws long enough are just not common. These are 3" #8 in stainless steel, the only type I could find this long. It might make the jig a little stronger if the screws actually reached into the bottom of the jig. Look for screws before you size the other parts of the jig.
• The T-nuts are a little hard to find as well. So, get the metal hardware before starting the jig and dimension the jig based on the hardware.
• I wrapped the short pieces in two small bundles with bits of masking tape so they would not twist while I was drilling the holes. Drill one bundle through (with a backing board), then use that bundle to start the holes in the second bundle. Use one of the bundles to start the holes in the upper arm of the jig. I should have marked the pieces in each bundle so it would have been easier to keep them in order in the jig. Because the holes are not identically placed, some orientations are very uneven.

To show the versatility of the jig, I took pictures of two pretty extreme cases.

The first is a heavy mortise chisel, of the variety affectionately called a "pigsticker". The blade portion is over 7" long. The blade, where it is being held by the jig is over 3/4" thick.

Because these big chisels are driven across the grain into hardwoods, the final microbevel angle must be quite high - often 30 degrees or more. No problem with this jig.

I don't know of any commercially available jig that works with these really big chisels.

In order to handle a blade this thick I had to remove two of the strips.

This paring chisel is over 8" long, 0.15" thick at the jig.

Paring chisels often have very shallow angles - often as low of 15 degrees. Again, no problem with this jig.

Because you can put the jig near the handle, the chisel has good balance during sharpening.

Because the jig holds the chisel between wooden strips that are compressed from both sides, and because the strips in this case are quite thick, the chisel is well held during honing.

I made a second jig using a few scraps of beech and mahogany.

Again, I used the extension calculator to determine correct blade extensions for various angles, then wrote those extensions on the strips. In the picture, the second strip from the bottom has extensions 2 26/32 in the 20 degree column, 2 7/32 in the 25 degree column, 1 25/32 in the 30 degree column.

Using the jig with a particular chisel (for example, a bench chisel with a 5 inch blade, or extension about 4 inches) involves:

• Deciding roughly where the jig will grip the chisel (about 4 inches from the tip)
• Deciding on the angle (25 degrees)
• Selecting the slip with the approximate values. There are three choices of extension: 3 27/32", 4 13/32" and 4 30/32" (look at the middle column, the entries for strips 5, 6 and 7 from the bottom.
• Assume you decide that an extension of 4 13/32 will work. Put a mark on the back of the blade this distance from the edge.
• Slide the chisel under the strip with 4 13/32 in the 25 degree column, positioning it to the mark, then tighten the screws enough so the the chisel is held, but can still be moved.
• Set the extension (using a combination square) to 4 13/32 and tighten the screws.

Cautions

Marking the approximate extension of the back of the blade with a magic marker lets you get near the required extension without trying to hold the chisel, the jig, and the combination square.

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