Apron can be picked up off the ways by about 1/8 inch; is this OK?

[Bi11Hudson]

Seems to me that power up or down is not the primary concern here. If the cross slide is run on dovetails, as most of them are, lifting of the cross slide will affect the depth of cut. The Atlas (and Craftsman) machines notwithstanding, the dovetails keep the cross slide in position on its' longitudinal travel. When there is a gap, or potential for that gap, the cross slide can move in or out.

Since the work is the power in this scenario, and the dovetails (or diamond slides) have the mating surfaces at an angle, it seems to me that any movement would be attempting to move the tool outward, while at the same time the power is driving down. That, to me, generates "chatter" or inconsistant radius of cutting.

I base my theoretical thinking on a smaller machine, out of Taiwan. (a G-1550 Grizzly) The Atlas, with its' flat ways, uses the pressure from a vertical surface against the inside of the ways. The thoughts are theoretical because I am not willing to loosen the "shoes" that keep the machine tight.

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[Mitch Alsup]

When is this setup ever used?

9:30 into

SETUPS IN ORDER OF RIGIDITY:
1) TP front, tool up, CCW
2) TP back, tool up, CW (#1 and #2 are equal) I would argue that this is slightly (slightly) less rigid than #1
3) TP front, tool down, CW.
4) TP back, tool down, CCW.

#3 is more rigid than #4 because of the lever arm of the carriage, since the front of the carriage has little vertical play.

 

[SLK001]

Seems to me that power up or down is not the primary concern here...

Yeah, we have strayed off the thread starter's original concerns.

 

[SLK001]

2) TP back, tool up, CW (#1 and #2 are equal)

I would argue that this is slightly (slightly) less rigid than #1

I agree that it is probably less rigid than #1 (on most lathes), but I don't have any evidence to prove it. However, some lathes have mounting points for tools at the rear, so the rigidity differences are probably small.

 

[Superburban]

I think it all really depends on the lathe. I do not recall any with decent gibs to spread the forces on the underside of the front way. The ways and saddle spread out the forces pretty well, and are also easy to oil. How do you oil the underside? Granted, using a cutting tool is different then normal operations, and you generally are not moving the carriage, so wear on the underside is not as much a concern, but if all there is on the bottom, are a screw on one side, and the carriage lock on the other, that is not much. I think if I were to do much backwards cutting, I would make a second carriage lock for the left front of the carriage. Then you can lock down both sides of the front end when cutting.

My second concern would be the dovetails on the cross slide. How strong are they in the upwards direction?

 

[Mitch Alsup]

I agree that it is probably less rigid than #1 (on most lathes), but I don't have any evidence to prove it. However, some lathes have mounting points for tools at the rear, so the rigidity differences are probably small.

The front way have that vertical ^ along with the flat _ way so 3 surfaces locate the fron of the cariage.
The back only has the flat _ way so only 1 surface locates the back side of the carriage.

Thus the front is better "located" in X and Z than the back, but since the forces go into the flat _ way the ^ is only used for longitudinal support.

 

[Jim F]

The front way have that vertical ^ along with the flat _ way so 3 surfaces locate the fron of the cariage.
The back only has the flat _ way so only 1 surface locates the back side of the carriage.

Thus the front is better "located" in X and Z than the back, but since the forces go into the flat _ way the ^ is only used for longitudinal support.

Depends on the lathe.
My SB9 has a V front and back, with a flat in front and a V in back for the tailstock.

 

[SLK001]

Depends on the lathe.
My SB9 has a V front and back, with a flat in front and a V in back for the tailstock.

Ditto with my South Bend Heavy 10. Vees on both front and back of carriage. The tailstock has a vee up front and a flat at the back.