Fairly long keyway in bore

Pattnmaker · Nov 18, 2021

I am currently currently cutting a replacement fan out of a 4" block of 6061. One of the last things I need to do is put a1/4" keyway in the 15/16 bore. The bore is about 3 inches long. I have been debating on whether to buy a broach and bushing or take it to an occasional customer who has a slotter. I have never used a broach. I just realized this morning a standard bushing may be too short? The other complication is the job is a rush and I had to commit to having it done for Tuesday next week. What's the safest way to put in this bushing as I will have about 40 hours into the part by the time the keyway has to be done?

Milland · Nov 18, 2021

We had a thread on this just last month:

Keyway broach 5 - 6 inch long help

If you have a CNC mill, make your own single-tooth slotting cutter and DIY. Take off a 1/2 thou (.01mm) or so each pass, should be a low stress op as long as everything is stable and you make sure your spindle is locked.

Do a practice bore if you're worried.

Micmac1 · Nov 18, 2021

We approach keyways 4 different ways depending on the part. Tight tol stuff goes to a contract broaching shop local to us, smaller nominal stuff we either make a broach bushing for the bore and broach with the arbor press. Bigger stuff we use a right angle milling head, and lastly we grind a hss bit and just use the mill or lathe and lock the spindle. For the sake of time i would either just machine a hss bit or MSC a broach & bushing overnight and do it by hand in a press. Honestly depending on the tolerence even if the standard broach bushing is short it probably would be ok for +/-.005 work as long as the bore fits the bushing well. you can always shim the bushing if the diameter is off.

Green Machine · Nov 18, 2021

What about sending for wire edm? Shouldn't cost too much for just one keyway.

Micmac1 · Nov 18, 2021

Might be tought to find a shop thats is going to turn it around in less than 40 hours per op.

DouglasJRizzo · Nov 18, 2021

If your customer has a slotter and can handle it, let him do it and save you the grief.

Pattnmaker · Nov 19, 2021

Started thinking about using mill as a slotter last night but then thought about the fact its a high speed spindle. And that I don't have time to hand code it. Called a local wire shop this morning dropped it off this morning and will pick it up later today.

Milland · Nov 19, 2021

Pattnmaker said:
Started thinking about using mill as a slotter last night but then thought about the fact its a high speed spindle. And that I don't have time to hand code it. Called a local wire shop this morning dropped it off this morning and will pick it up later today.

That works. Nice to get such a quick turnaround.

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