[ELM3060]

Hi all, I am wondering if it is possible to make a round spline broach. The broach is to form an inner spline on a brass gear approximately 20mm thick (still working on the finer points).
Gears will need 3 splines (equal spacing) with a max diameter of around 14mm with a tooth depth around 3 to 5mm.

I am planning to attempt to build my own prototypes (2), each unit will have approximately 8 gears to suit this spline size, so I am just trying to find the cheapest way to produce the gears I need, and though I am not sure what a professionally made broach would cost, I am sure it would not be cheap.

If it is possible to turn or cnc one, Just how would you do it?
What would be the best steel?
How would you harden it?

I have no experience with machining on a lathe or CNC mill, but am in the processes of buying both so I can attempt to build the prototypes.

I am also in the process of either building a furnace for alloy casting or buying a kiln. Since learning more about the processes that I will need to undertake, I am leaning towards a kiln for a more controlled heat, any thoughts.
Regards
Eddie

[rowbare]

It looks like you will putting together a pretty capable workshop.

Since you are making a limited number of gears in a soft-ish material, you might be able to get away with taking one of the shafts, cutting it square at the splines and and undercutting the splines with a dremel or something of the sort. You would want to have inner diameter of the gears cut to size as well as removing as much of the material from inside the splines as possible. This will reduce the stress on the cutter.

See what Frank Ford did here to make a bit for his rotary broach. HomeShopTech

You might also want to look into rotary broaching: Broaching (metalworking) - Wikipedia, the free encyclopedia

Little Machine Shop sells a cheap rotary broach holder but they aren't that hard to make. Someone shows how to do it online but I couldn't find the link: LittleMachineShop.com - Rotary Broach Tool Holder 2MT

oh and if you are making gears, you might want to look into Gearotic...

bob

[ELM3060]

Gee, thanks Rowbare. I tried doing some searches, but could not find much, I will check out those links.

I was thinking I could also cast my own brass rod, but with the spline already cast into it. If I could cast the spline, then I could use a spline as a pin to machine them on, but then if it is not a perfect fit, then machining the teeth will not work so well I assume. If I have some shrinkage when molded, then I could use a breach to ream it and being pretty close to size/shape already, should not be to hard to push through.

Ow and yes, at this stage it appears as though I am going to have to get some gear (also learn how to use it (gulp)).

First stage is learn alloy casting while I look for a cnc mill with 4th axis & lathe. I have been thinking if it is possible to build a CNC mill over the top of a lathe, so I can use the lathe spindle as my 4th axis (kill 2 birds with one stone).

Just tossing coins over electric kiln for my furnace, or to make a gas one with a reil burner. I started to think about the parts I will need to harden (possibly including a broach) and for that, the ability to control temp with an electric is making sense, just a bit worried about the cost compared to making a gas unit.

[polygon]

Just for reference, rotary broaching 3-5mm tooth height at 20mm depth is over the normal recommended stock removal of .010-.030". You also might consider some type of shaping or single spline broaching operation.

[rowbare]

Depending what you are making, you might not need a kiln right off the bat. Smaller things like broaches and cutters can be made from oil hardening tool steel and heat treated using a torch, a magnet, a bucket of oil and a toaster oven.

A process I have seen recommended for oil hardening tool steel uses the magnet hanging from a string to determine the appropriate temperature. You heat the tool until it doesn't attract the magnet then quench it in oil. The steel at that point will be quite hard and brittle, so you temper it in an oven.

Here is a link to a pretty good article: A Woodworker's Guide to Tool Steel and Heat Treating

If you can put off needing a kiln it might free up more $$$ for the mill and lathe.

bob