Chester 920 traverse issue

[flintandsteel]

Had this lathe about10 years now. Sorted, renewed and fixed most things and it does what it should.... till this morning.
As the table moves along the travers screw (not sure of technical name) it reaches a point where something must jam up as it gets closer to the chuck- sufficient to kick it out of gear.
Checked the under table box and all fine in there.
Only thing I did this morning was to change up on the gear box, try the speed then back to where it was.
Reset the drive gears so it can power the traverse screw again (table not engaged) and runs fine.
Fingers crossed engaged the table and it travelled the full length of the bed till about 6" off the chuck then it kicked out of gear again.
Thinking gear box issue. Just tried it in a different gear - same problem
Thoughts?

 

[flintandsteel]

Had a look in the gear/speeds box and all looks fine.
No bits of metal or teeth lying around
Worn transverse feed bar?

 

[ChaiLatte]

When you traverse the carriage along the bed manually, using the handwheel, does it feel any harder at the same point as the power-traverse struggles?

Have a look at the rack in which the manual handwheel pinion engages to make sure it is clean and sound at the problem point.

I think what you call the traverse screw would normally be called the leadscrew. Have you checked that is not burred or bunged up at the problem point? You can clean the leadscrew by setting it moving using the gearbox, making sure the carriage is not engaged to it and passing a piece of string round it in a U-shape. Holding both ends of the string, it will clean out the groove of the thread.

 

[Amplidyne]

As ChaiLatte says, it sounds more like either a problem with muck on the leadscrew itself, or with the saddle movement sticking somewhere rather than an actual gearbox problem. Sounds as if it's loading up the leadscrew / drive at some point, and kicking it out of gear somehow.

 

[flintandsteel]

Thank you all so much.
Last night had a quick look for on line (thesaleroom.com and Easylive etc) just in case. Some interesting old classic beasties on those sites and more modern "don't bother" types as well..
Anyways, it took a while but finally got it after several pieces of string and caressing it with a wire brush.
Noted some dark dust (just a little) in places in the groove on the leadscrew. Maybe a carriage strip down is in order if it reoccurs.

 

[ChaiLatte]

Noted some dark dust (just a little) in places in the groove on the leadscrew. Maybe a carriage strip down is in order if it reoccurs.

Any gunk on the leadscrew will not come from the carriage. It will be swarf falling onto the leadscrew from above where you are cutting.

Modern lathes have telescopic leadscrew covers, as much for safety so your long hair does not get dragged into it when machining in flip flops, baggy gloves and tight swimming trunks (tight gloves and baggy trunks are a lower risk), as for swarf protection.

A search for 'lathe leadscrew shield/guard/cover' would give you some ideas of what is possible and whether the hassle of making one is less than the string trick once a year.

 

[Amplidyne]

Those "flat spring" type shields are available as an aftermarket thing for most lathes I think.
Just brushing the leadscrew down after each use is a cheap substitute though. I keep an oily old paint brush by the machine.

 

[Fergie 307]

Old toothbrush is good especially if it has quite a fine pitch leadscrew.

 

[flintandsteel]

Thought I had it but no. Kicked out again.
The lead screw looks to be more worn at the chuck end which I guess is to be expected.
Kick out at roughly the same location, so wondered if it was a combination of screw and saddle gear failing meshing at that point.
Part stripped the carriage and freed the lead screw at the right hand side. However it all need so come out. To do that the left side needs to be freed. Now is that by removing the circlip in the drive compartment or is there a knock out pin in the linkage rhs of gear box? Don't want to go hitting it till I know.
Manually moving the carriage about, a large worn out washer dropped into the tray. Think this might be the issue. Washer about 2.7mm thick Worn thin and 1 edge missing) same internal dia a lead screw dia, and about 30mm o/d but with a flat on one side.
Think it's been floating and dropping into the threads while traversing.
So where / between what does it sit? Standard and replaceable or of special steel?