I am slowly building up to being able to cut wheels on the Tormach PCNC440 with two possible methods.
The first is using Gearwheel Designer which is mentioned elsewhere on my blog.
The second route is more conventional using a PP Thornton or similar cycloidal tooth cutter and a dividing device on a rotary table. This later method is how wheels are traditionally cut in a lathe and there is a lot of information available on this.
In order to use the cycloidal cutters I need some form of arbor to mount the cutter in the Tormach spindle. I could simply turn a piece of steel bar to suit and mount this in a ER collet in the spindle. The downside of this simple approach is that every time the arbor was fitted into a collet the cutter would be at a different height from the table. I really wanted something a bit more repeatable as the centre line of the rotary table will always be the same so why not the cutter centering.
When I ordered the Tormach PCNC440 I also ordered the Tormach small rotary saw arbor (which to date I have never used). Pondering this last night I sketched up an adapter in Fusion 360 to allow an involute cutter to be fastened to the end of the saw arbor.
This is shown below. 
It is made from a piece of 19mm AF hexagonal steel bar with the hexagonal flats going to be used as a tightening it in place in the Tormach arbor. My Myford Super 7 when used with a 3 jaw self centering chuck is not bad on concentricity but for really accurate centering I swap the chuck for a collet face plate instead. This job was going to need both.
First operation was to turn the hex bar end that would screw into the arbor. This was done in the lathe chuck. It was a simple turn to a diameter and drill and tap the end with M6 to match the arbor mounting. The only pain was the arbor has a slightly protruding lip so I had to undercut the mounting face for this. Rather than trying to be clever I did it by hand using a graver.
While the hex stock was still in the lathe I roughly turned down the other end of the adapter to the primary diameter and slightly oversize for the cycloidal cutter bore diameter and then cut off the stock so far.
It would be important to get the cutter mounting running as square as possible so I swapped the lathe chuck for the collet plate and mounted the arbor end of the adapter in the collet. I carefully turned the shoulder for the cycloidal cutter diameter and then reduced the remaining length ready to cut a M6 thread.
Here are a couple of images of the finished adapter.
I am pleased to say the idea went almost to plan and it runs very true in the Tormach spindle.
I was a bit over enthusiastic with the graver but this is of no consequence.
With hindsight the shank between the cutter and the hex section ought to be longer as this will restrict the diameter of the wheel that can be cut before the blank catches the hex section peaks.
One step closer to trying this method. The next experiment is to work on a sub routine in GCode to move the cutter back and forth while cutting and with the ability to easily program the number of cuts.
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The outer holes are for the M8 clamping to the table and the four smaller holes are the tooling holes. Being tight with my materials I did not want to just mill out the centre of the plate and have a mountain of swarf (chips). Instead I designed it with two slots as shown, one for the clamping surface and one that almost cut through the stock. The partial cut was to ensure the central piece did not flip out once cut free and damage my cutter. First one half was drilled and cut and then the plate was rotated 180 degrees and the second half cut. This left the central island just held in place by less than 0.5mm of material. This was easy to hand cut through to liberate the central area. The plate was then turned over and the cut edge cleaned using the same tooling position and doing the same 180 degree rotation. To my surprise the rotation process on the tooling pins worked very well with only a minor step transition at the overlap point on all cuts. This was probably more down to my 3.7mm tooling pins being not quite concentrically turned from 4mm silver steel. With this finished I now had a much more robust clamp for the PCB material. I had made the clamping step 4mm deep so I could put sacrificial backing boards behind the PCB being run. This would allow drilling through as needed. Checking the flatness of a clamped PCB blank with my Haimer showed variation of a few thou in the top surface of the PCB Z position. The worst case variation in Z was at dead centre where the PCB’s natural bow was most dominant.
