Here are the fruits of my latest labors in the shop... This is a straddle knurl. For those who don't know what the advatages are, they create a knurl without putting stress on the cross slide and headstock bearings. In addition, it is autiomatically self centering. It also allows small or long pieces to be knurled without deflection.
All the pieces were handmade by me except for the button head screws, spring, circlips and the knurling wheels.
The goal was to produce a rigid tool with no perceptible slop in the hinges. This allows one to simply stop a knurl cleanly, although the convex wheels installed into the tool are designed for axial feed to a groove or off the end of the workpiece.
The whole thing, except for the thumbscrew, is made from W1 tool steel... It all came out of either a 5/8 or 1.25 inch round stock scrap bin piece. The hinge and wheel pins were hardened and left untempered. They ended up so hard, a Carbide lathe tool did little more than polish it. In any event, I tried to break them to test brittleness and they held up.
As a test of the assembled tool and to create the thumbscrew, I installed a simple hex nut onto the threaded piece and knurled the thumbscrew. Obviously, it works. More important though it that its performance exceeded my expectations! Why was I using a bump tool for all this time?
The wheels installed are 64 DP (diametral pitch), M42 cobalt, TiN coated units from Accu-Trak. They are expensive, but worth it IMHO. They'll last a lifetime for an HSM and create supurb knurls. In any case, these beat the living heck of of the import jobs. The advantage to the diametral pitch knurls (as opposed to the traditional circular pitch knurls) is that they will simply track on any diameter which is a multiple of 1/64" (other DPs will track in 1/32" increments but are a bit fine for my tastes). This means no calculations of circular pitch vs workpiece circumference afre required to guarantee tracking. For those that choose to mash the knurls into tracking, I accept that... I've done it too...
The knurl pins are held in by a retaining clip design which engages a groove in the pin. This is in lieu of a circlip. This idea came from Guy Lautard's Machinist's Bedside Reader book.
Here are the pictures...