Play in Crossfeed Handwheel

[Ben17484]

I’ve a small amount of play in my cross slide which I tracked down to the hand wheel / cross feed screw assembly:

Hopefully you can see from the above pictures that the there is a gap in one picture and not in the other. This is where the play comes in. There appears to be a grub screw just beneath the red highlight, but this does not move. I’m not sure if it’s seized or stripped or maybe not even a grub screw. I also don’t see how this would help in stopping the play oin the parts. The lathe is a south bend 9 copy so I’m hoping there’s some expertise out there as to either how this adjusts or if I’m missing a circlip from somewhere. Is anyone able to help?


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[pontiac428]

I'd drill out the grub screw, drill and ream the hole with a tapered reamer, and drive a taper pin in there. It might take some light re-fitting or bushing the pilot to make a good fit. Or you could improve the fit of the parts and retain the grub screw. Either way, after you join those parts you should true them in v-blocks. You want any play or movement to be even all the way around, at least. Or you could braze the two, that's sort of temporary too.

 

[Ben17484]

I'd drill out the grub screw, drill and ream the hole with a tapered reamer, and drive a taper pin in there. It might take some light re-fitting or bushing the pilot to make a good fit. Or you could improve the fit of the parts and retain the grub screw. Either way, after you join those parts you should true them in v-blocks. You want any play or movement to be even all the way around, at least. Or you could braze the two, that's sort of temporary too.

Thanks Pontiac. So you think that the grub screw is the key to getting the whole assembly tighter? If I can get that free I can tighten it all up and remove the gap that gets generated by moving that part?


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[pontiac428]

If you have play and rocking between the lead screw and the extension, and that gap exists between the thrust surface and the acme nut, you will have backlash and inconsistent movement between divisions. A grub screw is a "single point" fixing arrangement, even though we would like to think that having a broad face on the screw somehow circumvents this. After at least 50 years of use, the wallowing has distorted the fit of the pilot and the mating face of the two parts. You can glue it if you're in a hurry (green loctite). Brazing is a sure fix. Taper pinning is appropriate for the machine's vintage but more involved to do. Just get that fit tight, true the shaft with v-blocks and a dial indicator, and put it back together. Set your backlash according to the manual, and see how you like it.

I had a 1937 Atlas lathe that was worn bad. I made new lead screws, replaced the acme nuts, and improved all the fits from the handwheel to the gibs on the cross and compounds, and kept that old machine going with .003 handwheel backlash. Huge improvement in use and finish.

 

[Ben17484]

I found some more info on this problem. It seems to be a problem for south bend 9s and therefore their clones.

From further inspection, I think there was a rubber seal between the dial ring and the handle which has perished. My guess is that’s where the gap has come from. The above suggests that adding a shim solves the problem. My issue now is that my lathe does t have a retaining nut to hold the handle on, it’s completely flat:

I’m now not sure how to get this handle off in order to fit a shim. That’s my next problem to solve…


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[jcp]

Is there not a cross pin driven thru the crank/shaft connection? If so it's probably a taper pin.

 

[Ben17484]

Is there not a cross pin driven thru the crank/shaft connection? If so it's probably a taper pin.

Do you mean this:

I couldn’t tell if this is a really small Allen bolt or a drift pin. I’m guessing drift pin and i guess this needs to be drifter out to get the assembly apart?


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[jcp]

Yes….

 

[jcp]

In your photo it appears to protrude on both sides.

 

[pontiac428]

Try the bronze washer. It will probably fix it for your lifetime, but will eventually wear out again because the parts are worn already from the wobble that's been there for presumably a long time. Depends on how far you want to chase it for your needs. I'd be interested in rebuilding ill-fitting parts if it were mine, but the washer will achieve similar ends for a reasonable amount of time put in. You'd be surprised how small .010 of a gap is, yet you will feel every thou in backlash, so optimize those fits if you can. Maybe even try precision shim washers.