Shaper Project: Cutting Internal Splines

After acquiring my Atlas 7B shaper, I had intended to disassemble, clean and rennovate it before starting to use it. However, in preparing to work on another project, I found that I needed to use it right away. I discovered that I was missing a 20 tooth change gear with internal splines for my lathe (Colchester Mk1, 13x24) that was necessary in order to cut some metric threads. The only source for the gear that I could locate wanted over $200 for it. I figured that if I could find a suitable gear, I could cut the internal splines with my shaper.

I found a 20 tooth, 16DP gear made by Boston Gear that had an I.D. slightly smaller than I needed and it cost only $15. Before I could cut the splines, however, I needed to do some preparatory work on the shaper. Firstly, I needed to figure out a way to mount my Ellis dividing head on the shaper's table. Since the dividing head is rather large for the shaper, I ended up making a table extension to hold the dividing head. A little cutting, drilling and welding resulted in a setup that I thought would do the job.

Secondly, I needed to make a toolholder for the shaper and an extension for it suitable for doing internal cutting. The toolholder and the extension are based on the drawings by Art Volz posted in the Files section of the Yahoo group "Metal_Shapers" (use this link to visit). More detailed information on the toolholder may be found here.

Thirdly, I needed to grind a cutting bit to match the profile of the splines. Although this may not be the best way to proceed, I figured that it would be easiest to cut the width of the spline at once using a very light downfeed.

Lastly, I needed to make a holder so the gear could be mounted on the dividing head. This was accomplished by boring a recess in a piece of 3/4 x 2" scrap stock into which the gear could be pressed. The boring operation was done on the lathe since I didn't have a mill at the time. The finished holder can be seen here.

Spline cutting setup.
The gear came with 2 keyways cut on opposite sides of the internal bore. These were slightly wider and slightly deeper than I needed but they were useful for getting the gear oriented properly for cutting the remaining six splines. I first bored out the I.D. of the gear to the dimension that I needed. After pressing the gear into the recess of the holder, the holder was mounted on a faceplate on the dividing head and the gear was aligned and oriented properly using a dial indicator. The picture to the left shows the tooling and fixture that I made and the setup used to cut the internal splines on the shaper.
Cutting the splines.
Here is a closer view of the cutter and gear. The cutter is mounted in 1/2" round stock which is pressed into a piece of 1" round stock that is turned to fit the holder.
The finished product.
Here is the finished product, still in the holder, after removal from the faceplate. The upper and lower splines are actually remnants of the original keyways - they're slightly larger than the splines that I cut.
The gear with its mating part.
And, finally, here is the finished gear together with its mating part. The fit seems just about right, it actually has slightly less play than the other change gears that I have.