10f Cross Slide Feed Rate

[cdhknives]

On a standard 10F like my QC54, the QCGB lever E is to set carriage feed rates in lieu of TPI. There is even a nice list of feeds in inch per revolution.

What are the corresponding feed rates for the cross slide? In other words, if I set my QCGB on slowest feed of .0042 in/rev but engage the cross slide drive to feed the milling attachment across a mill, what is the working feedrate?

 

[kd4gij]

I have never checked. But you could put your lathe in gear with the cross slide engaged set up a DTI remove all back lash zero the DTI then turn the chuck by hand 1 rev. And let us know what you come up with.

 

[cdhknives]

I was thinking about doing just that, but hoped someone knew the ratio of leadscrew rev to cross slide advance off the top of their head. It's too late at night to go get greasy, but it's bugging me.

 

[pdentrem]

I was under the impression that it is over 2:1. The drive gear 24th is twice the driven gear at 12th, but the two leadscrews are 8 tpi and 10 tpi, so it is not an even numbered ratio.

 

[Rob]

The feed rate is the same in both directions. Even through the 2 leads crews are different the bevel gear ratio is such that it compensates for the different pitches.

 

[cdhknives]

It sure seems like the cross slide feeds much faster...but that is based on simple observation. Experiment time...

 

[Mondo]

Yes, the feed rate is the same in thousandths of an inch per spindle revolution for any given change gear set up or QCGB setting. A couple other Atlas/Craftsman lathe owners and I beat the crap out of this on another forum some time back. Casual observation would suggest a difference, but both measurement and calculation show the feed rates to be the same.

Yes, the lead screw is 8 tpi while the cross slide screw is 10 tpi, but as RO noted because of the bevel gear ratio the two feeds come out to be exactly the same.


Spiral_Chips

 

[wa5cab]

I did the cross-feed rate experiment (on a 3996). I keep a dial indicator mounted in a QC holder for quick run-out checks. So I mounted it to the TP, put a hardened surplus part that I keep around for this sort of thing in my 3-jaw, and checked that the runout was still less than 0.001". Then I engaged the tumbler and cross-feed, slacked the motor belt (so I wouldn't have to spin the motor), and turned the chuck by hand several times to take up all of the slack, stopping the chuck with the tightening socket at TDC. Next I zeroed both the cross-feed dial and the dial indicator, checked that the QCGB was set to 0.0042, and rotated the chuck in the proper direction 10 times. Both the cross-feed dial and the dial indicator read 0.042". So the cross-feed rate is in fact confirmed as being the same as the longitudinal feed rate. Not twice it as numerous people have said or written.

I have to admit that I definitely expected the answer to be different. It just looks faster. But in this case, appearances were definitely deceiving. I think I'll call Myth Busters and see whether they want to do a segment.