Look ahead on a lathe???

[?Mark]

Hi all,

Is there a turning equivalent of a look ahead for lathes? I've never heard of such a thing so I searched the manuals for our moris here, but couldn't find anything.

tia

[Guest CNC Apps Guy 1]

It's really only necessary when milling.

[?Mark]

James, so adjusting/slowing feed is the only way of ensuring "true profile"?

We're really hauling when it comes to feedrates, but that causes some tolerance issues.

That's what I thought, but wanted to be certain.

Thanks.

[chris m]

Mark, there should be an exact stop command, G65 or something similar, that would tighten up your profile; we have the same issue on occasion and must invoke this to achieve our desired results. I am not sure about Moris, but Okumas for sure have this.

 

C

[Guest CNC Apps Guy 1]

James, so adjusting/slowing feed is the only way of ensuring "true profile"?

We're really hauling when it comes to feedrates, but that causes some tolerance issues.

That's what I thought, but wanted to be certain.

Thanks.

True Profile... There is no such beast. Just keep mving out the decimal place until you find error.

 

Where I normally see profile "issues" on lathes are radii. The smaller the radii, the slower you have to feed to meet profile the requirement. If you need a .005 edge break and your feed is .010, sorry, but you ain't makin' it. If thats feed's not around .001you're gonna have issues with that profile. I know that was an extreme example, but that is the thype of thing I see more often that not. A guy calls me yelling a screaming that "...Machine X is a piece of $#!+ !!!" That problem is not that machine, that problem is an issue with the process . The process of turning has it's issues and that's one of them.

[Guest CNC Apps Guy 1]

Mark, there should be an exact stop command, G65 or something similar, that would tighten up your profile; we have the same issue on occasion and must invoke this to achieve our desired results. I am not sure about Moris, but Okumas for sure have this.

 

C

Exact stop may or may not solve the issue. It depends on a lot of factors.

[chris m]

True Profile... There is no such beast

 

I am afraid that I must disagree with this comment, within reason; we turn parts to a gnat's xxxx with some very fussy contours that are verified with some pretty sophisticated equipment, BUT, we don't do it when "really hauling" with feedrates for sure. Exact Stop will help make an amorphous mess look more like the print by limiting the machine's desire to anticipate the next move, but it certainly won't create the perfect part at .016 per rev, as James correctly stated.

 

C

[Guest CNC Apps Guy 1]

You said "within reason". ... "True" makes no account for "reason.

 

I'm machined unreasonable parts before and when you have a profile tolerance of .0005 TOTAL (not ±.0005), and you're hitting it with 10 probe hits in the span of .125... you'll see error. At that point, the probe stylus "sees" the cusps of the process. I had a discussion with a QC guy (and I left him scratching his head ) I posed the question "...where is the profile derived from? The peak of the cusp, the valley of the cusp, the middle, or none of the above?" If "none of the above" was the answer then he was using the wrong probe stylus for measuring the feature. At that point n the conversation, he asked me to leave.

 

But you are correct, exact stop check can make a difference in some situations.

[88Matt]

James,

 

We hold .0002 all-around-profile on splines all day on our T-bed lathes. Of course they are polished before going to inspection so there aren't any cusps.