On Sun, 15 Dec 2013 19:39:18 -0500, Bob Engelhardt
wrote:

I put an motor-driven feed on my lathe
(http://www.MWDropbox.com/dropbox/ServoPowerFeed.pdf) which I built to
give a minimum feed of .003. I don't know why I chose that value - it's
probably the smallest that the change box will do.

I was just watching a Tubal Cain video on YouTube about the power feed
he put on an Atlas lathe. The Atlas gears only went down to .0046
(IIRC) and he wanted much finer. (His other lathes went to .0016 & .00076.)

My first thought was to modify my feed to go much finer/slower. But I
got to thinking that there must be some limit. It seems that if the
feed was too fine the bit would just rub until enough feed had
accumulated and then the bit would bite and jump. And the bit's edge
would be critical - razor sharp or better.

How fine do you feed? What are the considerations in doing a very fine
feed?

Thanks,
Bob

It largely depends on what your tool nose radius is.

This may be of some assistance


http://www.custompartnet.com/calcula...face-roughness

Google "tool nose radius surface finish"

75,000 hits

Many/most of my clients use .007-.009 feed rates at speeds up to 4000
rpm. In fact..its largely the "standard" feed rate for roughing and
even finishing. And it really..really depends on the tool nose radius.

Use a sharp, pointed tool..and finish is gonna suck..really suck.
Increase the "roundness" of the tip of the tool..and it gets better
and better. Many of my clients standardize on .016 tool nose radius
for most operations from roughing to finish. Some go to .030 for
finish.

If your lathe is worn badly and is loose..then doing all your cutting
with a very round tool nose is indicated.

Gunner

--
"Owning a sailboat is like marrying a nymphomaniac. You don’t want to do that
but it is great if your best friend does. That way you get all the benefits without any of the upkeep"

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