Unimat 3 Carriage Lead-screw problem

[lwilton651]

Hi all,

I have finally acquired my first lathe, an Emco Unimat 3, which, though I understand is very very small, is exciting to me!

It arrived in a big polystyrene box, not particularly well secured with the hand wheels removed. After a quick clean up the cross slide lead screw works great, very smooth. However, after hours spent looking over the Carriage lead-screw I can't get it to operate properly.

Inital issue:
After screwing in the hand wheel (23) and Acorn Nut (24) it seems to pull the lead-screw into its bearing surface (22) causing enough drag to make it very very hard to turn clockwise (same direction as tightening the hand wheel to the lead-screw), and counter clockwise both the hand wheel and acorn nut un-thread themselves before the carriage moves.



I have since sorted that issue out, repeated applications of sewing machine oil and elbow grease seem to have smoothed it out alot. However, turning the hand-wheel clockwise is still very rough, and the carriage is 'jumping' along when moving towards the head-stock, moving 1mm for every turn of the hand-wheels, but all at once, as the lead-screw moves back and forth along it's axis. Are these issues linked?



I appreciate any help, I hope I am not being too dumb. :wall: :hDe:

 

[MRA]

Looks to me like you might be doing the plastic handle up hard against the hanger for the leadscrew. I'd try putting a washer between the handle and the shoulder on the lead screw it does up against, small enough to not hit the bracket.

Also, sounds like there should be a thread inside the plastic handle - you do it up (onto the lead screw shoulder, or perhaps as I am suggesting, the new washer in there) just to take the play out but not tight, then tighten the acorn nut against it without tightening the handle any further.

Any use?

 

[Jasonb]

The handwheel should not be screwed up tight against the block, it should have a slight gap which sets the tightness of the screw. The dome nut should be tightened against the handwheel to lock it in place.

Easiest way to set would be to slip a feeler gauge between handle and block to stop it getting too tight then while holding the handwheel so it does not turn tighten the nut up against the handwheel. remove feeler gauge and things should turn smoothly.

The gap will determine howmuch backlash there is in the screw so you may need to play about with that to get a free turning screw with minimal backlash.

The other thing I notice from your photo is that the steel sleeve the end of the screw runs in looks to be below the level of the cast block which would mean the handwheel is bearing against the casting. Your drawing is not for the U3 but there is a grub screw under the block, loosen that and slide the sleeve out until it is just proud of the cast surface and retighten, then fix handwheel as I describe above

 

[lwilton651]

It would be great if I had a functional lathe to whip up a quick washer with!
I will pick up one from the hardware store when I have a chance.
The hand-wheel is threaded, do you mean to use the hand-wheel as a 'jam-nut' and tighten the acorn nut against it to lock them in place?

I found an actual diagram of the unimat rather than the Chinese copy and this might help.



It would appear the lead-screw is longitudinally located between the bushing (3) and the hand-wheel (4). I read disassembly instructions on the Unimat3 Yahoo group (for which my membership is pending) which say the bushing is Bronze, whereas the one I have is very clearly steel, which may be part of the issue.

Thanks for your input! :thumbup:

 

[Jasonb]

You don't need a washer and a steel bush is OK so not part of the problem

 

[lwilton651]

Hi Jason,

For whatever reason your first message hadn't appeared when I replied to MRA.
Thank you very very much, I'm not sure why the bushing was sunk so deep in the bed, but marks in the paint show it has definitely been used like this previously.
The Grizzly manual said to set in .002 - .003 backlash and using a .003" feeler gauge it feels great, very slightly tighter than the cross-slide hand-wheel.

The action is now nice and smooth, very happy with how it feels I can finally do some turning.

Thanks guys!