Broaching without a broach or press?

[Chris D]

I need to cut some keyways in pulleys and don't have a broach and would prefer not to pay someone to do it. I know I have heard of people doing some such with a bridgeport or other vertical mill.

I have a Rong Fu mill that is pretty solid. I could lower the head down to keep the quill extension to a minimum.

I am guessing they do it with a short arbor and a square tool bit. Somehow lock the spindle from rotating, and just nibble away at the material.

Can anyone offer up some more information or details on this process?

TIA
CHris

[Kookaburra]

If you have a lathe you can use a square bit in the tool post and run it through, it is easier to stop a lathe spindle from turning, as for the bridgeport idea, it could work you would need to make a spacer that is counterbored to clear the rotating part of the spindle, and large enough in diameter to rest on the non rotating part of the spindle on the drawbar end and clamp it in place with the drawbar when you tighten your tool.

[rustyolddo]

You need to replicate the function of a Shaper. I've seen plans where someone made a broaching/shaper head for their mill & used the manual downfeed on the spindle to accomplish the job.

[DareBee]

Chris you can do exactly what you have mentioned (which ultimately is the same as Kooka's lathe setup) toolbit should be the width of the keyway with straight sides so it follows the walls without gouging. The front edge should have a positive rake on it. Depending on the material and key size you can take from .0005 to .005 cuts (unless you are Schwartzenegger). .25 keyway in CRS you will probably be cutting about .001 per pass and have to do some cleanup passes once in a while also use lots of cutting oil.
This will be a tedious process but works quite well.

[Kookaburra]

Originally Posted by DareBee (unless you are Schwartzenegger).

I don't think we need to bring politics in to this discussion!! lol

Good advice darebee, spot on, however, I think we still need to lock the spindle as I mentioned or something similar.

[Ken_Shea]

Chris,
The process can also be speeded up by pre-drilling or plunging with a end mill of appropriate size, then broach it.

Ken

[Chris D]

Wow, thanks for the really good information guys.

I had thought about it on the lathe, however, my lathe is one of those cheapo 9 x 20 lathes, if I tried this operation on there, I am afraid it would fall apart ;-)

I like the idea of straight sides on the tool bit - that makes a lot of sense as it would also guide the tool and keep it "on track". The front edge being positve makes a lot of sense too.

Pre-drilling may not be needed for these key ways as I am machining both aluminum and brass - no steel thankfully. I will need to make sure of the keyway size though, anyone have horsepower ratings for various key sizes?

Locking the spindle will probably be my biggest problem but I am sure with some clamps and such, I can lock it one way or another.

Thanks again guys - much appreciated!

Chris

[DareBee]

Machinery's handbook will list the industry standards.
.57 - 7/8 shaft is 3/16 key
7/8 - 1.25 shaft is 1/4 key
1.26 - 1.375 shaft is 5/16 key

sorry I amn't listing them all

[Chris D]

Thanks! That should do it for me.

Chris

[bennett71]

We have used the mill option on some blind keys. put it in low gear, lowest speed & hang a weight off the brake handle. This worked good in a pinch, but we also had a wide open tol.