Re: what is your max feed rate on your hobby CNC conversion ? was lathe threading BS

>For example - Spindle speed ~1100 RPM, 24 TPI thread = 46 ipm feed approx.
> Within the capabilities of most lathes I would have thought.

Paul many things come into play when threading. A poor finish at 200 rpm will not get much better
at 800. A good tool will cut well in steel at a very wide range of RPM's.

The critical thing about threading on a CNC lathe is NOT whether or not the machine can keep up
at the specified pitch. It is whether or not it can change direction and pull out before it bangs into a
shoulder, or whether or not it can withdraw from the thread in a controlled manner so that the final
thread on a rod is the same pitch as the rest of them, even though there is no undercut at the shoulder.
It is also important to be able to accelerate up to speed in a timely manner for those nasty threads
that you can't start too far in front of.

In order to get good results when threading on a lathe you need a sturdy grip on the material, a strong
tool holder, and a hefty frame in your machine. If any of these are compromised, poor finish, chatter,
and damaged tools will result. If the tool is not close to perfect in the first place, even with the other three,
a poor thread results. Since it seems that the majority of people that have commented about lathes in
this forum in the past have been using Sherlines or Taigs in hobby applications, it seems that it is not
practical to recommend high feed requirements, especially, as I mentioned, that it is NOT necessary to do
that, and also that it does not actually save you much time as the total cycle is still largely dependent on
the rapid motions, not the feed motions.

If you were cutting a 1/2-13 thread at 1100 RPM your feed rate would have to be nearly 85 ipm. Both 46
and 85 ipm are at the very top of what I would expect a hobby machine to be capable of.

Just out of curiosity, what are the top feed rates on the Sherline-MaxNC-Taig, 3 in 1, etc., cnc conversions, either mill or lathe?

Please everybody DON'T post your answers with my entire text re-quoted!!!


Best Regards, Fred Smith- IMService
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