Grinding wheel collet

for the last several years I've been arduously grinding my tool and drill bits on a delta grinder and then hand honing them with small diamond grit paddles. I decided I wanted to speed up this process and make it far more accurate so I decided to make a grinding wheel setup to run on the lathe. I chose a 100MM diameter cup style diamond grinding wheel set and set about making the collet to hold them for use. As you can see below, the 100mm wheel just fits above the bed of the watchmakers lathe with about 50 thousands to spare. This maximizes rotation speed and surface size and has made for a very fast cutting and accurate grind on the tools.

grinding wheel and collet installed on watchmakers lathe

I started with a length of 1'' diameter 12L14 steel. This steel cuts so smoothly I love working with it. I roughed out the outer diameter of the collet taper first, then cut the shank, the thread diameter and the collet taper. I like to relieve a small groove at the top of the threads as it makes the threading die leave a cleaner end that doesn't bind up the draw bar prematurely. With the exterior chuck bearing in place the cut is smooth and steady with no chatter or movement even on this diameter of steel on this little lathe.

roughing out the collet

cutting to the collet outer taper diameter

reducing the shank to proper diameter

Finishing the thread major diameter and the collet taper

I installed the threading die holder, with its handles for rotating it, over the tailstock ram and quickly threaded the collet. So much easier using the die holder versus removing the part and going over to the vice to struggle with alignment and risky hand threading.

Using the die holder to thread the collet end

Threading the collet

The completed thread on the collet

I then set about cutting the keyway in the collet shank. I set up the milling head on the recently completed heavy duty cross slide. I then disconnected the drive belt to the headstock and installed the spindle lock I made last year and was ready to go. The cut was quiet, smooth and very stead.

Cutting the keyway on the collet with the grinding attachment

Cutting the keyway

The spindle lock in action

Then it was time to install the half completed collet into the spindle and finish the grinding wheel and washer seating surface. This required drilling the hole for the 1/4 - 20 bolt and threading it. This was a very pleasant task as I used the little hand crank I had made that installs into the draw bar tunnel and expands in place to allow hand turning of the spindle.

Turning the grinding wheel seat

Using the spindle hand crank to tap the collet 

I then set up some brass in the chuck and bored out the proper diameter hole in the center to fit over the 20MM mounting post on the collet. I made sure the depth of this retaining washer would exceed the shoulder height of the collet so that the nut would drive it home hard.

boring out the hole on the retaining washer

a bit more brass and the retaining knob was completed. I knurled the edge to give a good grip and you can see where I set the depth for the drill a little deep when drilling out the minor diameter for the threaded shaft. It pierced the top every so slightly. I'll probably remake this but for now its quite functional.

Finished retaining nut

retaining jut with all thread post locktited in place

Grinding collet assembly

All parts for the grinding collet

Now all that remained was to assemble and test it out. All parts fit quite close tolerance.

grinding collet inserted into the cup center hole

collet shoulder sits just below grinding cup inner surface

Installing retaining washer

Installing retaining nut

clamping down the retaining nut for a snug fit 

And Voila! I'm off to the races in grinding my tools!

grinding collet installed and in use on watchmakers lathe