Try using some threaded rod or some stove bolt of about the right length.
Capture the chisel between two fender washers and hold those between two
nuts (maybe wing nuts would be easier). Adjust the position of the nuts so
that the chisel is whatever angle you need. In use, the chisel would ride on
the sharpening stone while the bolt end would ride on the workbench. If you
want a microbevel, slip a couple of business cards under the end of the bolt
and hone the micro bevel.
I use this technique routinely. Before I start sharpening, I color the bevel
of the chisel or plane blade with a permanent marker - this allows me to
quickly see where the stone is taking off metal and I can adjust (shimming
under the stone or bolt end) for a perfect sharpening. Consider this
contraption to be a guide which helps hold the blade at the right angle -
the sharpening pressure goes on the blade.
Have a look at the following sites for an idea for a homemade version.
Made myself one which cost me nothing. I used the bearings from an old
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