Victor lathe fine X axis movement

[taiwanluthiers]

One problem I have with lathes is it's really hard to make fine X movement for facing cuts.

I was turning some brake discs, and one thing I can't do is move the X carriage by about 0.005" so I can control the depth of cuts for such a large facing cut.

Is there any trick for this without a DRO?

 

[darkzero]

To start, it sounds like you are not quite clear on the lathe axes. The cross slide is X & the carriage is Z.


Sounds like you are asking how to track the carriage movement (Z axis) for depth of cuts? If yes, one most common method without a DRO is to use a dial indicator with a magnetic back set on the way like this.

Another method is set your compound slide parallel with the bed ways (Z axis). Then instead of moving the carriage for depth of cut, use the compound slide & it's dial to advance for depth of cut.

 

[taiwanluthiers]

Thanks for the advise. Didn't think of that for some reason. Moving the compound slightly is a lot easier to do than moving the Z axis handwheel slightly.

For the record: I hate turning brake discs, dust flies everywhere. I only did it because someone was paying me to do it. I still messed up on it because he said the thickness was not consistent (as the biggest issue I had with the brake disc was not having a good way to clamp it, and no good reference points). He told me next time I do this I need to indicate it, and if it's too out of round then to toss it (brake discs do warp sometimes with use)

BTW is that a PM 1228 lathe by any chance? I used to have that lathe.

 

[darkzero]

I hear ya. When I worked at a shop I enjoyed turning rotors & drums on their brake lathe. At home I refuse to do it & will just pay the local auto parts store to turn em. I'll only turn cast iron if I absolutely need to like making chuck backplates. I've already made all that I need so hopefully no more big messes in the future. It's a PM1236.

 

[taiwanluthiers]

I hear ya. When I worked at a shop I enjoyed turning rotors & drums on their brake lathe. At home I refuse to do it & will just pay the local auto parts store to turn em. I'll only turn cast iron if I absolutely need to like making chuck backplates. I've already made all that I need so hopefully no more big messes in the future. It's a PM1236.

Yea, I turned cast iron basically to refurbish my chuck because it was coated in thick layers of rust. But I hated doing it. The cast iron dust flies off at a million mph and hurts when it hits you.

They have brake lathes for a reason, and they make it impossible to turn them out of round as they turn both sides at once. The guy told me "you don't need a brake lathe to turn discs".

But I still hate doing it on the victor lathe. This is considering that a car brake disc is basically at the limit of what the lathe is capable of turning so it was hell trying to do it.

Besides nobody turns brake discs today, they're made real thin and they are so cheap that you just toss them when they're done.

 

[darkzero]

Yup, chatter & harmonics can be an issue too. Brake lathes usually have dampeners for that.

Sucks in the throw away world we live in now. I'm still driving a 2001 Toyota, I always have an extra pair of rotors. When it's time for brakes, I get the spare set turned so I don't have to wait when I do the brakes.

 

[taiwanluthiers]

Yup, chatter & harmonics can be an issue too. Brake lathes usually have dampeners for that.

Sucks in the throw away world we live in now. I'm still driving a 2001 Toyota, I always have an extra pair of rotors. When it's time for brakes, I get the spare set turned so I don't have to wait when I do the brakes.

I was having a lot of chatter problems. I had to rig support under the brake disc to solve this. This likely contributed to poor tolerance.

If he was going to give me a bunch of brake discs to turn I'd go and buy a brake lathe.

 

[matthewsx]

Hard to imagine there’s enough work to justify buying the machine and giving over the shop space.

 

[homebrewed]

If you need even higher resolution for facing you can use an old machinist's trick. Rotate the compound over so the angle between it and your work is 30 degrees. Now when you advance the compound .001" the tool moves .0005" along Z. To get a 10X improvement you would need a 5.7 degree angle, but you may not be able to rotate the compound that far over. Probably achievable, 11.54 degrees will produce a 5X improvement but you'd have to do a little mental or calculator arithmetic to turn the compound position into the actual Z position.

In this approach, the compound moves along the hypotenuse of a triangle. The side opposite the angle I described is Z, so Z/C = sin(theta), where "C" is the distance the compound moves.

The angle may or may NOT be the same as what the dial on your compound indicates because different lathe manufacturers may use different conventions for the angle. For mine, I would have to set the compound over (90 - 30) degrees because "0" is parallel to the spindle axis.

One thing to keep in mind is that now when you move your compound you are moving the cutter on both axes. Not an issue for facing or (usually) when turning to a precise OD, or when thru-hole boring to a precise ID. But if you're going to do something like cutting pockets for press-fit bearings, you also will cut a little deeper into the bottom of the pocket. Maybe an issue, maybe not, depending on what your application is.

For very fine cuts you will need a very sharp tool, either an insert with ground edges or HSS.