Subject: HELP: Seeking speeds/feed recommendations for small lathe

From: [email-masked] (Eric A. Beatty)
Date: 26 May 1995 03:14:26 GMT

Greetings!

Allow me to introduce myself.  My name is Eric Beatty and I am an
instructor of AutoCAD/drafting at a community college in Seattle. 
Recently, our dept acquired a Spectralight 040 CNC Turning Center made by
Light Machines Corp. in New hampshire.  I have been charged with the task
of learning to use the lathe and the accompanying CAM software.  I have
had some experience with CAM/CNC in the past but my machinist skills are a
little bit rusty (no pun intended :-) ).

If I may, i would like to pose a question or two to you all.  Since the
Spectralight machine is based upon Sherline lathe components, what would
your recommendations be as to the proper cutting/surface speeds for
turning aluminum and other light materials such as wax.  Allow me to list my 
current tooling setup.  The turret is an 8-station one with the following:

T1 -  carbide profiling tool

T2 - HSS boring bar

T3 - carbide 60 degree threading tool

T4 - 1/4" dia. center drill

T5 - HSS .045 thick cutoff/parting tool

I've looked in the Machinery's Handbook and other shop manuals that
recommend 600FPM surface speed for HSS turning tools and 1200FPM for
carbide turning tools for turning aluminum.  With my average workpiece
dia. being less than 1", that requires a spindle speed of upwards of 6000
rpm.  My machine is limited to 2500 rpm.  Hence my questions:

1) Can you recommend a decent cutting speed for aluminum & wax, bearing in mind
the 2500 rpm speed limit and the tool list above.

2) What about feed rates for roughing, finishing, drilling, boring and
especially parting (I'm embarassed to admit that I've broken both of my
parting tools with either execessive spindle speeds or feed rates ad my
dept. head isn't too keen on having to continually buy me new tools!)

3) Any other advice that you might have about using a micro-lathe?

Again, let me thank you in advance for any help you might be able to give
me.  I'm quite excited about the potential this machine has in my CAD
class as well as my own scale modeling endeavours.

Sincerely,
Eric A. Beatty
[email-masked]

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From: [email-masked] (Ron Metcalf)
Date: 26 May 1995 09:54:30 GMT

Eric...let's see if I can help here...with the caveat that I'm not familiar with 
your machine or with CNC's in general

In article <[email-masked]>, [email-masked] says...

>T5 - HSS .045 thick cutoff/parting tool

On the carbide tooling above, you might want to change to HSS.  Your machine may 
not have the HP or the speed to the use of carbide effectively ( carbide is 
designed to remove material in shearing action which requires more HP then a HSS 
tool would require).

>dept. head isn't too keen on having to continually buy me new tools!)

On your parting tool, 3 recommendations 1) lots of oil or coolant, 2) try 
backing the tool off periodically. In aluminum such as T6-6061, the material is 
not particurally free cutting and wants to gall. If you back it off 
occasionally, any chips lying  on top of the tool hopefully will release, and 
your coolant will flow onto the cutting area, and 3) grind a positive rake angle 
on the cutting tool- something like 3-5 degrees.
As far as speed goes for the parting tool... somewhere between 1500-2000RPMs to 
start with.
For feed rate, I have no idea...I do it manually.

Hope this helps
Ron Metcalf

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From: [email-masked]
Date: 28 May 1995 23:12:47 GMT

>  I would suggest you talk to Joe Martin of Martin Enterprises or Sherline Enterprises
in San Marcos.  He's the owner and designer of Sherline lathes and mills,
and a personal friend.  Very nice man, who until two weeks ago had no 
idea his product was being discussed in this newsgroup or any newsgroup.
I sent him down some postings so he could see, and he's quite fascinated
with all that we're discussing. Therefore, I'm sure he would be most helpful
on your technical questions.  Tell him you're calling at my suggestion.

Mark Rogo, Morton Machinery Company, Los Angeles, Ca.