Lathe Cross Slide Problem

[dallen]

Just a thought, but while you have the slide off you may want to put some bluing on it and give it a rub on the old surface plate.

[EdK]

(04-21-2014, 06:58 AM)PixMan Wrote: Is that bushing pressed into a counterbore with a specific depth?

If so it seems to me that the best thing to do would be to get the bushing out, mill the opening square and parallel, them make a new bronze split nut to fit the screw at the correct centerline height which has a mating square on it.

What size thread is on the screw? Looks like 1/2"-10 Acme?

Ken,

No, the bushing is not pressed into a counterbore. It's just a straight bushing that's knurled and pressed into a hole.

I was thinking of pressing that bushing out and putting a counterbore on the top side of the cross slide and making a new bushing to press in. With the bushing pressed into the cross slide I would then mill the slot in the bushing on the underside thus assuring the slot is at a reasonably accurate right angle to the lead screw for mounting the nut.

I was also thinking of making a new nut since the existing one is not made very well and is made out of brass rather than bronze. What type of bronze would you suggest?
Any reason, design wise, not to make the new one the same as the old except machined better or is there a better design that you would recommend?

The lead screw has a major diameter of about .55" and the dimension between threads is about .12" so I'm assuming it's a 14mm x 3mm trapezoidal thread.

Thanks for the help.

Ed

[PixMan]

Ed,

You can determine the thread pitch easily by how many thousandths of an inch the dial moves the slide in one rotation, as long as it's direct to the screw and not geared.

As for the mounting, it might be a wise idea to re-engineer the whole thing and get the nut mounted securely with two socket head cap screws from the top side and a cone point set screw between them to adjust/spread the split in the nut to reduce backlash. That's how my lathe is designed and it works perfect (once I get that special lockwasher.)

I'd be willing to make you a new screw and nut, so all you'd have to do is mill, drill and counterbore the slide in preparation for the new configuration. I would just need a centerline height of the internal thread on the nut from it's mounting surface, and dimensions for the screw's lengths and diameters. I'd make the nut out of 660 bronze as I did Darren's elevation nut and the screw from 1117CRS, 1144SP or 1045TGP steel.

[EdK]

(04-21-2014, 09:47 AM)PixMan Wrote: Ed,

You can determine the thread pitch easily by how many thousandths of an inch the dial moves the slide in one rotation, as long as it's direct to the screw and not geared.

As for the mounting, it might be a wise idea to re-engineer the whole thing and get the nut mounted securely with two socket head cap screws from the top side and a cone point set screw between them to adjust/spread the split in the nut to reduce backlash. That's how my lathe is designed and it works perfect (once I get that special lockwasher.)

I'd be willing to make you a new screw and nut, so all you'd have to do is mill, drill and counterbore the slide in preparation for the new configuration. I would just need a centerline height of the internal thread on the nut from it's mounting surface, and dimensions for the screw's lengths and diameters. I'd make the nut out of 660 bronze as I did Darren's elevation nut and the screw from 1117CRS, 1144SP or 1045TGP steel.

Ken,

That's very generous of you and I think I'll take you up on your offer. I'll measure the thread pitch this evening. When I measured it I was in a hurry and was just looking for a rough idea of the thread dimensions. I had planned on doing exactly what you suggested using a dial indicator to get a more accurate measurement.

I want to machine the raw cast iron surface on the underside of the cross slide for the nut to mount on so I need to do that first since it'll affect the center-line height of the internal thread.

Thanks again!

Oh, and did you see this link I posted in another thread of a source for the bearing lock washers? http://www.jwwinco.com/products/section13/mb/

Ed

[EdK]

I put a dial indicator on the cross slide and consistently measured .099" for one revolution of the hand-wheel. Awfully close to 10TPI but also close to 2.5mm. Given that the diameter is .550 one would expect it to be a metric thread but that doesn't mean it is. I'm not sure where to go from here.

Any advise? Any reason I couldn't go with a 5/8-10 acme thread? That would be a bit stouter than the current lead screw.

Ed

[PixMan]

First, shall I assume the dial is graduated for .200" on diameter for one turn?

I'd go with the 5/8"-10 ACME. Is it a left hand or right hand thread? I have made a 1/2"-10 ACME for a friend's Atlas, and another's cross-slide screw of 5/8"-10 ACME, both left hand threads so I have the inserts for it and some nice 5/8" TGP (turned, ground & polished) 1045. I also have a threading tool for the 5/8"10 ACME internal thread, and a tap for the 1/2" version.

I believe you have a DRO for the machine, so the dial accuracy isn't critical, right?

P.S. - Yes I did see the link and ordered two of them, just in case I lose one in shipping. For $0.66 each, it won't break the bank and shipping will be quite a bit more.

[EdK]

(04-21-2014, 08:30 PM)PixMan Wrote: First, shall I assume the dial is graduated for .200" on diameter for one turn?

I'd go with the 5/8"-10 ACME. Is it a left hand or right hand thread? I have made a 1/2"-10 ACME for a friend's Atlas, and another's cross-slide screw of 5/8"-10 ACME, both left hand threads so I have the inserts for it and some nice 5/8" TGP (turned, ground & polished) 1045. I also have a threading tool for the 5/8"10 ACME internal thread, and a tap for the 1/2" version.

I believe you have a DRO for the machine, so the dial accuracy isn't critical, right?

P.S. - Yes I did see the link and ordered two of them, just in case I lose one in shipping. For $0.66 each, it won't break the bank and shipping will be quite a bit more.

Ken,

Turning the dial one revolution advances the cross slide in .100 so that would be .200 on diameter, right?

It's a left hand thread. I do have a DRO so dial accuracy is not critical. I'll get started on the drawings for the lead screw and get them sent off to you followed by milling the surface for mounting the nut so I can get you the center height dimension.

Let me know how much I owe you and I'll get it sent off immediately. You don't know how much I appreciate this Ken.

Ed

[EdK]

I'm working on the lead screw drawing now but thought I'd post some pictures of the existing lead screw to give you an idea of what's involved in making the new one.

Ed

   

   

   

   

   

   

   

[PixMan]

Cake. I've made similar ones before.

You should know well by now that I do NOT charge friends for work like that! If you need references on that, check with Neil (expat) and Darren (Mayhem.)

The second one would cost a small fortune though.

[Mayhem]

He speaks the truth Ed, it is hard enough to get him to let me pick up the cheque for lunch/dinner when I go visit.