Violin Forum/Message Board

[John Cadd]

There is a simple trick for sharpening plane irons. Lay a tin steel ruler on the side of a diamond plate and hone the back edge to make a tiny reverse bevel . That`s well known already .
For some reason the same trick is disapproved of for chisels. But there is a difference . If you lay the ruler across the end of the plate with the chisel blade laid along the plate --full length You can sharpen the end of the back without spending hours trying to get the back flat . One snag arises with older chisels that were hammered to death when they were produced . The surface near the handle may not be exactly parallel with the blade edge.You can see a shiny spot on the left side near the handle with a shiny spot diagonally opposite on the edge. If you have a Dremel you can work that high spot down to match the edge .Once the handle end and edge are matching the chisel can be sharpened with a consistent flat back section near the tip. That applies if the older chisel has rounded edges all along the back .
The length of a chisel blade can be the radius of a circle.Work out the circumference of that circle and compare that to a 1/2mm thin ruler .You can work out how small the angle on the reverse bevel is .But the chisel can maintain that shape for many years without getting a steady increase in curvature that will happen with many sharpening methods seen on youtube .

[John Cadd]

In case you want the exact reverse bevel angle .Assume the chisel blade is 20 cms long.The circumference of that radius is about 125cms.The ruler is 0.5 mm so the full circle of 360 degrees is divided by 250 (125x2). That gives just under 1.5 degrees angle at the tip of the blade . That is controlled ,for several years ,between the tip and handle end so there is no chance of wobbling .To be pernickety change the upper bevel angle to 28 .5 degrees for a working 30 degree cut .