Feed Rates

mickri

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The QCGB on my craftsman 12x36 lists feed rates ranging from .0042 to .0078. I have been wondering at what speed are these feed rates calculated at. Or asked another way how do the feed rates change, if at all, when you change the speed of the lathe. Do I need a chart for the feed rate at each speed?
 
I believe the correct answer for this is that the feed rates are per revolution of the chuck. So the RPM does not change feed rate. As an example .0042 carriage movement to one revolution of the chuck.
 
I believe the correct answer for this is that the feed rates are per revolution of the chuck. So the RPM does not change feed rate. As an example .0042 carriage movement to one revolution of the chuck.

I can confirm that this is the case for my South Bend.


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Those are in linear inches of carriage travel per spindle rotation. You do not need a chart for each spindle speed since inches/min isn't very useful.

You can do the math to determine the feed, or many tool manufacturers (carbide inserts mostly) will give you a range of acceptable depths of cut and feed per rev.
 
Thanks for the replies. Another mystery solved.

What about the feed rate on the cross slide? Does it run at the same rate?
 
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What about the feed rate on the cross slide? Does it run at the same rate?
On many (most?) lathes, the cross slide feed is a multiple of the carriage feed rate. This thread states 1.5x for a Craftsman 12x36.

YMMV
 
On my South Bend model A 9" lathe the cross feed is 3 times the carriage feed. On most industrial machines they are equal.
 
As stated above, the feed rate is how far per revolution the cutter moves. It is independent of speed.

The Atlas / Craftsman machines have a rather aggressive cut when the QC box is mounted. There is a video by Tubal Cain on the subject, but I copied it off to a local drive and don't have a link. He has a series of videos on the Atlas/Craftsman machine. The one I speak of is part of that series. Nr230 is related, although there is a video for an easy fix of just changing the gearing on the lead screw, going to exactly one half or one third. The one half is more practical for doing threading, although not decreasing the cutting depth as much.

Changing the feed rate nominally by one half would change the cross feed the same amount, half as fast. The cross feed is only fed off the lead screw and has no other bearing on the longitudinal feed. It is slightly faster, someone has given the value above. The two are interlocked, where only one or the other can operate. Removal of that interlock, while not advised, would allow cutting a 45* angle. But serves no other practical purpose.

*** EDIT *** It seems I misspoke about Tubal Cain, it was someone else. I include both links to replace what I posted earlier. I apologize for the incorrect information. Perhaps one of these will help you with your concerns. Of the two, my preference is for the first one using a 48/24 compound gear where the second is for a 32/16. The 48/24 can also be set up for 48/16, dividing the feeds by 3. That is more useful to me for my small model building, although I normally would run 48/24.
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