Lathe Cross Slide Problem

[EdK]

I got the lead screw drawing done, at least I think all of the important information is there.

Ed


  leadscrew_01.pdf (Size: 35.32 KB / Downloads: 10)

[PixMan]

Looks great Ed. I'd want a little more info on the fit of the feed gear to the screw. Is it a slip fit or RFT? (Really F'n Tight)

Can you measure the 12mm diameter with a really good micrometer that reads out in "tenths" or microns?

We need to design the nut, as I would make that FIRST (because it's tapped) and then make the screw fit into it snug.

[EdK]

(04-23-2014, 09:14 PM)PixMan Wrote: Looks great Ed. I'd want a little more info on the fit of the feed gear to the screw. Is it a slip fit or RFT? (Really F'n Tight)

Can you measure the 12mm diameter with a really good micrometer that reads out in "tenths" or microns?

We need to design the nut, as I would make that FIRST (because it's tapped) and then make the screw fit into it snug.

Ken,

The feed gear is a slip fit onto the lead screw. It's pinned on using a 4M x 20mm roll pin. The only critical length dimensions of the whole lead screw are the ones starting at the shoulder to the left of the hole for the spring pin and going right to the end of the lead screw. That total distance sets the location of the feed gear. I actually added an inch to the length of the acme threads because I wanted the cross slide to be able to move further towards the rear of the lathe. There were a number of times I could have used the extra travel distance.

I used the Mitutoyo digital micrometer to measure the diameters but I didn't note them to the "tenths" so I'll remeasure them again and update the drawing.

I'm hoping to get to machining the underside of the cross slide for the nut this evening. You suggested using two screws to mount the nut but I'm wondering about the location of the screws. Do they get put down the center-line of the nut or one on each side?

Thanks Ken!

Ed

[stevec]

I can't remember if you guys have discussed drilling the pin hole for the gear but, I'd recommend drilling it with the gear as a guide, about half way from each side.
Another thing I've wondered is, what about cutting the screw longer than needed and part it off so as to provide enough to make a "tap" to" finish size" the nut for a nice fit?

[Mayhem]

Would you have to harden the section you turn into a tap Steve, or would it be good for the once off fit?

I believe Ken already has the correct size tap, so not an issue here and I'm pretty sure the minor diameter is too small for an internal threading bar using the size 16 inserts that Ken loves. He had to single point mine with a HSS bit!

[PixMan]

I feel there will plenty of room between the base of the nut and it's big internal thread to put the two mounting screws in line/on center with the big Acme screw.

No need to go re-measure every dimension Ed. You know which ones should have tighter tolerance. That's really what I'm looking for, a tolerance. Just let me know which dimensions should have a "plus nothing, minus .0005" tolerance and which can be plus or minus a football field.



No need for that Steve. I've made a couple similar screws in the past and just as easy to cut the external thread to a good fit. The tapped hole tends to be a bit big, so the screw is compensated. If I can find the old internal boring bar I'd made for the tiny internal HSS Acme threading bits I had made years ago, I'll single-point thread the nut.

[stevec]

OK thanks, the next acme pair I make I'll cut the external thread to fit the nut which I'll single point first. I'm pretty sure my Asian 12x36 will be needing a new pair soon.

[EdK]

(04-24-2014, 06:35 AM)PixMan Wrote: I feel there will plenty of room between the base of the nut and it's big internal thread to put the two mounting screws in line/on center with the big Acme screw.

No need to go re-measure every dimension Ed. You know which ones should have tighter tolerance. That's really what I'm looking for, a tolerance. Just let me know which dimensions should have a "plus nothing, minus .0005" tolerance and which can be plus or minus a football field.



...

OK, I'll update the drawing this evening with the tolerances.

Ed

[EdK]

(04-24-2014, 06:14 AM)stevec Wrote: I can't remember if you guys have discussed drilling the pin hole for the gear but, I'd recommend drilling it with the gear as a guide, about half way from each side.
...

Steve,

As is usual with these import lathes, the hole in the gear is not through the center. It's drilled at an angle so I'm probably going to rotate it 90 degrees and drill a new hole with it attached to the new lead screw to assure alignment. Hmmm, that means I should add a note to the drawing so Ken doesn't drill it when he makes the part.

Ed

[EdK]

New drawing with the tolerances called out. Let me know if they're unrealistic. I just took somewhat of a WAG at it.

Ed


  leadscrew_03.pdf (Size: 33.1 KB / Downloads: 9)