1. ## Tapered Holes

What is the best way to machine an ID hole that has a slight taper? It needs to be as smooth as possible as the tumbler media will probably not be able to finish it like I want.

Material is 7075 AL

Hole size is .485 tapered to .378

2. What is the distance from the large end to the small end or how thick is the
material or how deep is the hole?

Ernie

3. Forgot those Ernie...

Hole depth is .5 .. wall thickness will be .075 at the .485 dia.

4. The best way: Chuck it up on a lathe, bore it, then use a toolpost grinder to finish it.

The best way on a Tormach: You could grind the taper as above if you have a fourth axis. You will need to set the axis at the same angle as the taper.

Frederic

• Am I correct in assuming then, that we are talking about a cylinder that is .635
in diameter and .500 long with the tapered hole in it?

Ernie

• Originally Posted by ErnieD
Am I correct in assuming then, that we are talking about a cylinder that is .635
in diameter and .500 long with the tapered hole in it?

Ernie
Pretty much.....yes

• Originally Posted by TXFred
The best way: Chuck it up on a lathe, bore it, then use a toolpost grinder to finish it.

The best way on a Tormach: You could grind the taper as above if you have a fourth axis. You will need to set the axis at the same angle as the taper.

Frederic
The tapered hole is the ID, not the OD.

• Originally Posted by ErnieD
Am I correct in assuming then, that we are talking about a cylinder that is .635
in diameter and .500 long with the tapered hole in it?

Ernie
But let me add, it is a boss on the end of a 2.5IN OD Round. So the wall thickness will not be much of an issue as I can always remove that after the hole is tapered...

• Maybe a setup like this would work?

http://www.cnczone.com/forums/tormac...cal_lathe.html

• Originally Posted by btu44
Maybe a setup like this would work?

http://www.cnczone.com/forums/tormac...cal_lathe.html
I am contemplating doing that for other parts, but I do have a lathe. But I don't remember anything in that post on doing a tapped hole, just thru holes.

• Originally Posted by Magnum164
The tapered hole is the ID, not the OD.
That's what I was picturing. "Hole" generally implies that it's got an inner diameter.

You can grind an inner diameter, given a small enough stone. In this case, you could mount a Dremel tool in the toolpost to do the grinding.

Frederic

• I would use the forth axis or even a basic rotary table mounted at a 6.1 degree incline. Would a 3/8" (max. diameter) 4 flute end mill leave too rough of a finish?

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