|Microbevels front and back.|
|Use a jig.|
|Copyright (c) 2002-14, Brent Beach|
A second page on slanted jigs shows an alternative. A slanted jig has the advantage of more space between the tool edge and the jig edge, allowing longer grinding/honing motion.
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:
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:
A visitor to this page asked me why I had not gone into more detail on this jig. I see that I took these pictures in February 28, 2006. Needless to say, I have no idea what distracted me then.
In any case, I put together a sketchup model of the second jig in May, 2013. You can see the dimensions.
Here are sketchup models, the first with shaded faces, the second with xray vision.
I wanted the view to show the various dimensions, so you cannot quite see that the screws go into the base. This prevents the jig from racking when you apply pressure when honing the edge.
If you can find 3" screws and the upright sides are 2 5/8" tall, the screws will go about 1/8" into the base.
You will have to use your ingenuity to get the holes lines up. There are some hints above. If you drill the holes through the top and bottom pieces before you glue it up, you will get those aligned.
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.
Still have questions? You can email me here.