Lathe crash!

[ChrisBParticipant @chrisb35596]

Hello gents, I got myself into a pickle and I need some help to get out

I'm in the process of cutting some threads on the lathe, being aware of the risk of crashing the tool post into the chuck I was being very careful. Half way through the thread cutting process on the first part it occured to me that if I had supported the part with a revolving center I would get a better finish – so, not wanting to disengage the half nuts I moved the carriage as far as I could towards the tailstock and started drilling. As the speed was set low for threading the center drill would not cut so I increased the speed – alas! I was not on time to stop the lathe The result was the carriage crashed into the headstock and got jammed. It will not bulge in either direction, and don't want to force it and make the already bad situation any worse…the half nuts remained engaged, moving the lever has no effect.

Noob mistake, no excuses all my fault so please don't rub it in! Just need to know if anyone ever had this problem and how it was tackled before I start dismantling it into pieces!

Ah, btw the lathe is a Warco WM280

Thank you

Chris

[ChrisBParticipant @chrisb35596]

Screw cutting disaster 🙁

[JasonBModerator @jasonb]

Think the first thing to try is gently rotating the chuck backwards by hand to see if you can wind off the tension that has built up in the drive train.

[ChrisBParticipant @chrisb35596]

I tried that Jason, chuck turns freely both ways but lead screw does not. It's steadfastly clamped in the half nuts.

[HopperParticipant @hopper]

Pull the cover off the end and have a look at the gear train driving the lead screw. Sounds like something has sheared. You might pull the gear off the leadscrew and try turning the leadscrew backwards until it takes the tension off.

[JasonBModerator @jasonb]

take the end cover off and check how far down the drive train is rotating, you should be able to see if the last gear is driving into the gearbox.

Move the lever to engage the feed shaft rather than the leadscrew which should dhow if something has gone in the gearbox, if the feed shaft turns move the lever back to screwcutting and see if the output is turning. There is a small brass shear pin that links the output to the screw which has hopefully gone. If it has then protect the screw and see if you can wind it back with grips.

[SillyOldDufferModerator @sillyoldduffer]

Posted by ChrisB on 20/12/2018 11:53:33:

…

Just need to know if anyone ever had this problem and how it was tackled before I start dismantling it into pieces!

…

Have I ever had that problem? Twice! And it was a WM280

First time was a gentle bump and I was able to unstick the half-nuts by reversing the lathe by hand as described by Jason,

Second time the impact was a good deal harder. I got out of that one by loosening the saddle. It wasn't necessary to dismantle it, a tad of slack was enough to unstick the mechanism.

I've an idea that releasing the end of the lead-screw would have provided enough movement to do the same job. The tail-stock end bearing block on a 280 is held by 4 bolts and two dowels and getting the dowels out is a little awkward. (Mine take an Allen key, they're not threaded, but I eased them out by turning the dowel while leaning the key gently to one side and pulling outwards. Not sure that's how it should be done!)

If the chuck turns and the leadscrew doesn't then the shear pin at the headstock end has probably broken. 

Jason introduced me to threading in reverse. Since then I've not had another crash…

Dave

 

Edited By SillyOldDuffer on 20/12/2018 12:25:41

[Neil WyattModerator @neilwyatt]

Is it possible to unfasten the apron from the cross-slide?

[JasonBModerator @jasonb]

Posted by Neil Wyatt on 20/12/2018 12:23:06:

Is it possible to unfasten the apron from the cross-slide?

It is but better to try some simple things first before pulling the machine to bits.

[ChrisBParticipant @chrisb35596]

Just had a look at the gear train, all seems fine there, all the gears turn and if I disengage the screw cutting lever, then the feed shaft turns when I turn the chuck. But still the carriage remains jammed when I turn the lever back to screw cutting – the lead screw does not turn it's truly stuck, I've gripped it with mole grips but it slipped. Will have a go at taking it apart hoping it will be the shear pin you mentioned Jason!

[JasonBModerator @jasonb]

So as Dave mentioned undo the block on the right that supports the screw and shaft then see if you can draw the screw to the right bringing the carrage with it

[Ian S CParticipant @iansc]

You have probably broken the lead screw sheer pin, it's not hard to do. In my early days with my 1326 belt head Taiwanese lathe I broke mine, I got muddled up, and in the process grabbed the carrage feed hand wheel just before the tool post hit the chuck. In the tool box that came with the lathe was two spare sheer pins.

Ian S C

[I.M. OUTAHEREParticipant @i-m-outahere]

You may have to back the half nut adjustment screws off a little to get them to release also .

[ChrisBParticipant @chrisb35596]

This evening I had a go at it. Took the block which holds the shafts off and unbolted the apron from the carriage, and the whole thing came apart and free. As mentioned above, I found a small brass pin sheared at the lead screw – will a brazing rod of the appropriate diameter do as a replacement?

While at it, as I have the apron gearbox off I had a look at the oil – didn't look very nice so I poured it away, in the bottom there was a lot of dirt, like grit so I will clean the whole thing and put new oil in. What kind of oil should I put in it, gear oil or something lighter like engine oil?

Btw thanks a lot for the advice, much appreciated

[Thor 🇳🇴Participant @thor]

Posted by ChrisB on 20/12/2018 23:06:47:

While at it, as I have the apron gearbox off I had a look at the oil – didn't look very nice so I poured it away, in the bottom there was a lot of dirt, like grit so I will clean the whole thing and put new oil in. What kind of oil should I put in it, gear oil or something lighter like engine oil?

On my 290 lathe the manual says Mobilgear 627 or equivalent for the gearbox, I have used ATF on mine and use the same oil in the Apron.

Thor

[JasonBModerator @jasonb]

I just use the same 32 weight oil that I use in the head gearbox, they do both need topping up regularly as they tend to drip. Warco do "head oil" or ARC do this

Pin is 3mm so if you have rod that size it should be about the same strength or just turn down some brass to fit.

[LynneParticipant @lynne]

Amazon- Hydraulic oil- Triad 32- 5litres- £18.84- post- £6.34 DLJ.

[ChrisBParticipant @chrisb35596]

Thanks for the suggestions, I'll see if I can find something with similar specs locally (I'm not in the UK)

While going through the parts I removed I noticed that the worm gear on the feed shaft looked a bit odd, I would say it's got a fair amount of wear on it especially at the ends where it comes to knife edge, what do you recon, is it normal wear?

Edited By ChrisB on 21/12/2018 10:28:59

[I.M. OUTAHEREParticipant @i-m-outahere]

That gear is for the power long / cross feed , i have worse in my lathe and it still works i would have a real close look at the half nuts though .

[BazyleParticipant @bazyle]

I don't have this lathe but I suspect the 'knife edge' is as made. The leadscrew won't reach the bottom of the gear so wear will typically show up as a circular ridge near the bottom of the tooth. I don't see any on your picture. I t will mostly wear from one side as the motion is mostly towards the headstock. Worth cleaning off the swarf and grit regularly.

[ChrisBParticipant @chrisb35596]

You're right XD, it's the feed shaft gear. Good, nothing to worry about then…I'll get on with rebuilding the thing back and hopefully it will run again

[not done it yetParticipant @notdoneityet]

When the dial pinion wears out, some simply replace it with a plastic spur gear of the right size and tooth count – they do not usually do anything more than follow the lead screw and the plastic will soon conform to the shape of the thread.

[Anonymous]

Posted by ChrisB on 21/12/2018 10:10:26:

While going through the parts I removed I noticed that the worm gear on the feed shaft looked a bit odd, I would say it's got a fair amount of wear on it……..

No wear, it's what happens at the edges of a worm wheel. This is a detail of a home hobbed worm wheel for my traction engine steering:

If I hadn't truncated the ends of the teeth they'd be pointed, as per the photo posted by Chris.

Andrew

[Howard LewisParticipant @howardlewis46836]

Having done the same thing, on power traverse, rather than screwcutting, a 5mm dia Rollpin is MUCH too strong!

"Shearpin" (Rollpin) did not fail, but it took some work to unjam everything, ready for repair. (Needed new pinion / shaft, and dressing of the rack)

After repairs, repaced the Rollpin with a 5mm brass shearpin, but came to the conclusion that that was still too strong, so removed it and drilled a 2.5mm down the centre before replacing it.

So far, no failures, (Has withstood 0.100" cuts in steel with feeds of upto 0.016"/rev) but if I do make another boo boo, the damage should be less.

Howard

[ChrisBParticipant @chrisb35596]

Finished put everything together yesterday – looks like it's working fine. For a shear pin I'm using an aluminium pin for now as I don't have any brass available at the moment.

I know the frustration now Howard, luckily for me the WM280 comes with a clutch on the power feed shaft which saved me lots of times!

While at it I examined the change gears on the banjo to see if anything suffered as a result from the jam-up – and sure enough I found one of the keyed bushes cracked. Not sure if it's the result of what happened or it it was there before, but the material for the bushes is quite brittle. The question is can these be purchased? Machining one seems out of question. Really hate the change gears system on this lathe, if I could find a cheap source of gears I would do another banjo with a gear train set for regular machining.

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