Subject: Re: Question on Lathe tolerances

From: [email-masked] (James D. Szura)
Date: Sat, 08 Jun 1996 07:18:05 GMT

[email-masked] (Jonathan M. Elson) wrote:

>Jens ([email-masked]) wrote:
><snip>
>: As is, I chucked up a piece of pipe to turn it down as a test cut and
>: I was quite horrified as to the finish. It is basically one continuous
>: strip of tiny gouge marks - the cut was a very light cut only.
>: Any thoughts anybody ?  I don't want to change the tool post just to
>: find out the flex is normal or is generated in the compound slide.

My experience with pipe is that  it is a difficult material to produce
a good finish on. Before you panic, check your tool angles and
clearances. Use a good cutting oil. Increasing the RPM will sometimes
produce a better finish.

Orca

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From: [email-masked](Dale A. Keltie )
Date: 8 Jun 1996 11:26:43 GMT

>clearances. Use a good cutting oil. Increasing the RPM will sometimes

I'll second the comment on pipe machining finishes.  If the suggestions
given above don't help, and nothing else seems to work either, that's
normal.  My limited (and frustrating) experience with machining pipe
suggests that the problem is that the material of which pipe is made
tends to rub on the cutting tool which sets up a vibration in the pipe.
I would think that there should be some optimum set of tool angles that
would minimize this but I've never been able to determine what those
might be.

Regards,
Dale

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From: PPIERCE <[email-masked]>
Date: Sat, 08 Jun 1996 06:36:18 -0700

Dale A. Keltie wrote:
> >a good finish on. Before you panic, check your tool angles and.....

> given above don't help, and nothing else seems to work either,....
> which sets up a vibration in the pipe.

How about using your follower rest?  Or at least a large center... 

Paul in AJ AZ

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From: [email-masked] (Jens)
Date: Sat, 08 Jun 1996 14:03:02 -0700

Thanks to all the people making suggestions on my lathe finish
problems. I have pretty much solved my problems and thought the group
might be interested in the outcome.
My problem has three causes:

1) I was trying to cut way too deep for the kind of lathe that this is
(1/2 hp) . Thanks to Steve Rayner for pointing this out. He also
pointed out that finishing cuts should be in the 0.001 or so range. I
was trying to cut too deep in both roughing and finishing cuts.

2)This being the first time for me running a lathe, I really didn't
know what I was doing with the tool shape. I was so far out that I
consider myself lucky to just have had chatter. Thanks to John
Dammeyer for giving me lessons on tool design and for all his help in
getting things going.

3) The motor produces a vibration that can be seen on the work piece
as a harmonic pattern. This will eventually be eliminated once I
isolate the motor mounting a bit better. Again, thanks to John
Dammeyer for helping to sort that out.

Thanks to all the other suggestions from people out there in net land.

Jens

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From: [email-masked] (Nigel Cliffe)
Date: Mon, 17 Jun 1996 15:41:19 +0100

> clearances. Use a good cutting oil. Increasing the RPM will sometimes
 
I'd also worry about the material. I don't know what your pipe is made
from, but I have a piece of 20mm steel bar which is impossible to turn to
a good finish, instead I get ridges as you describe. 
I think it is because the composition is wrong for turning. Where possible
I make sure I get stock materials to good free-cutting standards. With the
right material, and a good tool edge superb results are easy.

- Nigel.

-- 
Nigel Cliffe,   mailto:[email-masked]   BT Labs, Ipswich, UK
   Opinions my own, they may or may not be shared by my employers