# Spline cutter for upcoming 302 transmission project



## gbritnell (Aug 25, 2010)

Gentlemen,
 While making the drawings for the transmission I had mentioned in another thread I came to the realization that to make it even close to the original I would need to cut some splines. I can truthfully say that with all the tooling I have made I have never had occasion to make a spline cutter. 
 I calculated a size that would fit my project, not wanting to do this more than I have to, and set about making the tools. First I would need a cutter to make the broach and also to cut the shafts. I layed out what I needed, .375 diameter, 12 splines, .032 deep and .04 wide at the root. To make the splines rectangular I would need to make the cutter with an angle of 14.48* on one side, 14.5* should suffice. 
 I indicated and turned a piece of .375 drill rod, cutting the required angles on the sides. I then ground up a tool with a .156 radius on the end and used that to just clean up the bottom of the teeth. At this point I hand filed the required clearances on the cutter leaving a minute line at the cutting edge so that I could hone it with a diamond after the tool was hardened. The tool was then hardened and finished.
George


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## gbritnell (Aug 25, 2010)

Next up would be to cut the broach to put the splines into the gears or synchronizers for the transmission. Not knowing what kind of force would be required to press this through the blank I settled on 3 steps of .02 (dia.) The gears would probably be around .130 thick so I made the steps .15 wide so that I wouldn't be trying to cut with 2 rows of teeth at the same time. I turned the steps and put back clearance on them, running the cutter almost to the cutting edge. As with the previous cutter I would hone the very edge after hardening. I then put the piece of .375 drill rod into my dividing head, indicated it true and set the new cutter on center. I then proceeded to cut 12 splines or better yet I removed the stock between the splines. After removing it from the dividing head a filed all the small burrs from the edges where the cutter had gone through. After the cutter was hardened and honed I made up a small circular blank to try out my tool. 
 I grabbed my broach, the blank and a spacer and went out to the garage to give it a go. 
 I only have a small arbor press and I wasn't having much luck pressing the broach through so I added a cheater bar to the handle. I got the first 2 rows of teeth through the blank but as the third row was about halfway through I heard a 'click' and the upper part of the broach hit the floor. Hmm, time for a re-engineering on the broach.


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## Jasonb (Aug 25, 2010)

I think I would only go about 0.005 per step on the broach, making each cut a lot less and not so much swarf to fill each gap.

The other option is a 12 slotted bush and just one standard broach, cut one slot then rotate the bush and use a key to hold it in the first slot while the next is cut and so on.

Jason


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## gbritnell (Aug 25, 2010)

I went back down to the shop (in my basement) and turned up another blank. This time I made the steps .012 per increment, still not knowing if they would work. Remember this is all new territory for me. I have used keyway broaches but would have no way of making mine 6 inches long and hardening it without warping the heck out of it. After turning, gashing, milling the slot, hardening and honing it was back out to the garage for the second installment. 
 I still needed the cheater bar but the broach went through much better than the first time. Now I discovered a new problem, well not so much a problem but something I didn't think of when I was 'engineering' this cutter. After the last row of teeth went through the blank I had a clearance diameter on the broach but left the shank at .375 diameter. This didn't allow the blank to slide off the cutter. I lined up the teeth with the slots and tapped it back through the blank. 
 The last two pictures show the second broach and the splined blank. 
 I sure would like to reduce the shank of the broach but when I hardened it the leading edge of the shank hardened also, so that means I would have to grind it. I think I'll leave well enough alone for now.
 I now know that I can make splines so the project will be a go this winter.

George


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## John S (Aug 25, 2010)

George,
Nice work, just a suggestion but if you can't make a long broach and I can understand this why not split the broaching into using two tools so reduce the load.
I see in the next to last pic that you have already lost a tooth on the final row.

In the last pic it looks like the internal spline has angled sides ? is it just a trick of how the pic was taken ?

John S.


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