View Full Version : How low of RPM do I NEED? Mill

12-29-2005, 12:00 AM
So you guys taught me to look at square column mills. Now, how low of RPM do I need in a mill? It would be nice to power-feed tap... Thanks in advance.

Your Old Dog
12-29-2005, 05:20 AM
I'm not qualified to answer your question but I know the guys who are will need to know what the most demanding use is likely to be. You plan on working mostly aluminum? Plan on running big planer type bits or smaller endmills and such? Give them a better idea of how you plan on using your mill.

I have a geared head but feel I don't have enough speed on the top end. But, now that I've parted with the cash I'll have to make do !!

12-29-2005, 06:40 AM
As I said in the other post, I have the top tech model from Penn tool. It goes down to 90 rpm and I find that I don't need any slower for my work or for tapping. Sometimes I use the next gear up while tapping. Also I have pulled 1in. bits in steel with no problem at that speed. I may consider a vfd later on just to make it more flexible in the speed ranges but I find it works great for my needs.

12-29-2005, 11:43 AM
I will surely work with mild steel, cast iron, aluminum. Boring 3" holes, etc, but not having a mill right now, I don't know what the most RPM demanding operation might be. Feel somewhat dumb. ;~)

12-29-2005, 08:11 PM
As supplied, my mill had a low speed of 192 rpm, which was not slow enough for 4" diameter slitting saws, or a boring head when doing a large-ish hole. Now that I've got a VFD, I can get down to about 35 rpm, which is pretty dern slow. Probably slower than one would ever need. So japcas's 90 rpm is probably reasonable, practical target to aim for. If you can get slower though, don't turn it down. It may be handy, someday.

What's the slowest speed a Bridgeport can go?

12-29-2005, 10:47 PM
I think a Bridgeport can go down to 80 RPM

12-29-2005, 11:16 PM
<font face="Verdana, Arial" size="2">Originally posted by Yucholian:
I think a Bridgeport can go down to 80 RPM</font>

Yes they do,at least the step pulley models do.
I have tapped thousands of holes with them,no tapping head,just spindle brake and reverse.Gun taps are a must,spiral flute are even better.
There also have been several people who reduced the 80 rpm figure down further through the use of a homebrew jackshaft on the side of the mill head.

12-30-2005, 09:16 AM
If your primary concern is power tapping, you should consider a tapping head. I have an old, used Procunier 1E which works a treat on smaller tap sizes (5/16" & under, I think). 0-80 tapped holes have been no problem at all.