Have broken a cast bit of my lathe – any hope of a repair?

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Have broken a cast bit of my lathe – any hope of a repair?

This topic has 40 replies, 12 voices, and was last updated 14 February 2011 at 21:50 by John Coates.

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12 February 2011 at 10:41 #15503
John Coates
Participant
@johncoates48577
Tailstock lock broken
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12 February 2011 at 10:41 #63964
John Coates
Participant
@johncoates48577
I thought my hamfistedness was receding into the past but I was wrong

I have broken the locking mechanism on my tailstock. The lathe is a roundbed Barker from 1947 so finding a spare is probably not an option. Imagine two parallel iron bars with the tailstock base being two round sleeves over them with a flat jointing piece.

In one of the sleeves is a slit to allow a handle to close it to secure the tailstock against the bar. Well I have over tightened the handle and snapped the casting so the opposite side with the thread in has broken.

After nearly punching myself I began to think of possible solutions:

1. Have a new one cast but goodness knows what that will cost

2. “Glue” the two halves and then drill small holes to take carbon steel rods which will be glued or somehow welded in or the whole until somehow heated up to get them to bond

Can anybody suggest anything else or advise on the above?

I can get by with a temporary fix using timber stays of several lengths to brace the tailstock against the end of the lathe

Thanks for any help in this time of crisis

John
12 February 2011 at 10:54 #63965
Steve Garnett
Participant
@stevegarnett62550
I suspect that it might help if you could post a picture or two of the damage. I can’t imagine that a repair would be impossible, though – these things are usually manageable one way or another.
12 February 2011 at 10:55 #63966
Nobby
Participant
@nobby
Hi

Its a shame you did not post a photo of tailstock break in your album

Nobby
12 February 2011 at 11:02 #63967
Keith Long
Participant
@keithlong89920
Hi John

I don’t know the lathe apart from the pictures on Tony Griffiths’ site, but going from those I’m sure a repair can be effected. It looks to me as though the clamp that you are talking about is under the tail-stock at the rear, and the lugs that give the clamping action project downwards. If it’s one of those broken off your best bet will be to find a welder used to or capable of dealing with cast iron and get them to do the repair. You’ll probably have to clean the bore that goes on the bed afterwards but you’ve got a long contact with the bed so local filing should be ok and not affect the accuracy. if the worst comes to the worst it look as though the tail-stock is in two parts. The upper barrel assembly and the lower carriage. If so it looks as though a carriage shouldn’t be too difficult to fabricate from steel sections by welding, and you could make the parts and pin them together on the lathe for alignment before welding or brazing to make permanent.

Not a quick fix but both solutions do-able and shouldn’t be too costly.

As a temporary expedient can you make a clamp to fit around the split sleeve to squeeze it up or use a G clamp?

Keith
12 February 2011 at 17:01 #63978
Steve Garnett
Participant
@stevegarnett62550
I like Keith’s second idea, so I offer the following as something to at least think about…

I had a look at the pictures on T.G.’s lathe site (good idea, that!) and I think I can see how this works now. And it strikes me that if it’s possible for this to happen once, it could happen again. Also, unless I’m mistaken, the locking mechanism itself looks somewhat inaccessible. Which means that Keith’s idea of fabricating a new carriage could be a positively good idea – because you could then re-think the clamping mechanism so that it was more accessible, and probably end up with a more rigid tailstock carriage as well.

I would have thought that if you fabricated an assembly out of steel so that the split was effectively horizontal, then you could even fit the new assembly without dismantling the end of the lathe, if you extended the slit across the entire horizontal plane. In other words, you’d end up with a carriage that was sandwiched across and between the bars. So you’d bolt and shim the two halves at the front, and have a locking bolt facing upwards at the rear – in the middle of the carriage rather than at the end, where it is at present.

Okay, it’s not a quick fix, but it might be a better one.
12 February 2011 at 21:54 #63995
John Coates
Participant
@johncoates48577
Posted by Keith Long on 12/02/2011 11:02:20:

It looks to me as though the clamp that you are talking about is under the tail-stock at the rear, and the lugs that give the clamping action project downwards.

Yep that’s how it is. There is more metal in the lug than in the bit of the casting that broke hence the over tightening caused it to snap where it had the least strength. My brother in law is a coded welder so I shall ask him.

Thanks for all the suggestions. After a day with the kids away from the garage I feel more positive about things and can see a way out of this. When it happened this morning about 8am I could have happily punched myself for being so dumb at over tightening it.
12 February 2011 at 23:02 #63996
Terryd
Participant
@terryd72465
Hi John,

Any chance of posting a couple of photos in your album? There are some other methods of repair you could use but it depends on the casting.

Regards

Terry

Edited By Terryd on 12/02/2011 23:03:50
12 February 2011 at 23:49 #63998
ady
Participant
@ady
Hello sir.

The bottom line is:

“It’s up to you”

ahatammagonna dooo…lead you by the hand boy????

If you want to be like your forefathers.

Do not play games sir.
12 February 2011 at 23:51 #63999
ady
Participant
@ady
i cant do anymore than this because Im ratted out of my head.
12 February 2011 at 23:53 #64000
ady
Participant
@ady
This is really really annoying.

10 years ago I could read everything, now I am a waste of space.
13 February 2011 at 07:54 #64007
John Coates
Participant
@johncoates48577
Posted by Terryd on 12/02/2011 23:02:54:

Any chance of posting a couple of photos in your album? There are some other methods of repair you could use but it depends on the casting.

Now added

Here is the underside (sorry for the out of focus)

And here’s the broken lug

Thanks again everyone

John
13 February 2011 at 10:31 #64011
Dusty
Participant
@dusty
I know it is slamming the stable door after the horse has bolted, but it may help others.

Any split clamp or bearing should have a shim fitted in the split to prevent this type of breakage.

First you should adjust the bearing or clamp to suit. Now measure the width of the split, make up a shim so that it is a good tight fit in the split. Put in the hole/s for the clamp bolt/stud insert the shim and Bob’s uncle. You should find that the bearing/clamp is adjusted perfectly. Do not be tempted to make the shim to slack if it is a clamp as just a few thou can cause the type of fracture we have seen.

I suppose I should go to the workshop and make my shims now as I have a couple of things with split clamps.
13 February 2011 at 11:24 #64014
Keith Long
Participant
@keithlong89920
John

You have my sympathies – that has to be one of the worst bits of design I’ve seen in a long time – I’m amazed that it hasn’t snapped before. Not only are you expected to try and close up the slit in the casting to lock the slide, at the same time the action of clamping is trying to force the whole end of the sleeve into a cone shape – hence the 45 deg or so line of fracture from the end of the slit to the “hinge line” for the lug. I suspect you’ve had a the beginnings of a crack on that hinge line for some time.

If you can get it welded I’d concentrate on getting the lug welded and not worry so much about the angled split (I’d even be tempted to file in a bit of clearance), clamping then would close down the intended slit with out trying to distort the rest of the sleeve which the original design is doing.

If the broken piece won’t go back in and weld satisfactorily then look a making a steel strap that can be brazed to the outside of the sleeve, braze the broken bit in as well so that it will clamp down on to the bar but eave enough give in the strap to allow it to close when clamping. Mild steel will put up with the stresses better than cast iron anyway. It probably wouldn’t look very pretty but I think it would be stronger, easier to get a good result and you’ll get the lathe back and working with it’s original parts.

Keith
13 February 2011 at 12:06 #64016
ady
Participant
@ady
Sober now, had the Wales Scotland game up here yesterday, apologies to all.

I would look seriously at a redesigned fix along the lines of a tailstock barrel locking mechanism.

The original design was always going to fail eventually, it has the same weakness as some headstock bearing adjustment systems on cheaper lathes.

So you would need to fit a collar, and make the mechanism running through it, but the fix would look good and be a permanent improvement for the old girl.

good luck

edit:

You could build the collar in two halves, and fit it around the ways, on either side, so it could also be used as a temporary stop if you need to use the tailstock for the repair job.

Disaster can often be the mother of invention.

I would also look at the unimat-sl tailstock locking mechanism, which has roundbars as ways.

So it’s a pain…but also an opportunity to show yourself what an amazing dood you are.

Edited By ady on 13/02/2011 12:16:38
13 February 2011 at 12:33 #64019
_Paul_
Participant
@_paul_
From the pictures it looks weldable, if you are handy at Arc welding you could try “Magna 770” rods after V-Ing the joint out then short welds & peen after every weld.

I’m no expert but have done some creditable repairs on “unknown” dirty cast iron with these rods.

Regards

Paul
13 February 2011 at 12:55 #64021
Steve Garnett
Participant
@stevegarnett62550
Posted by Keith Long on 13/02/2011 11:24:14:

You have my sympathies – that has to be one of the worst bits of design I’ve seen in a long time – I’m amazed that it hasn’t snapped before.

So am I – I’d seriously dispute whether repairing this was worth it at all, because without some extra precautions, it’s just going to snap again, isn’t it? Even just milling the whole of the bottom section flat, and having a flat plate with a couple of grooves and a clamping bolt from below up into the substantive upper part of the tailstock base would be better than rebuilding it, I think.
13 February 2011 at 13:04 #64022
John Coates
Participant
@johncoates48577
Posted by _Paul_ on 13/02/2011 12:33:49:

From the pictures it looks weldable, if you are handy at Arc welding you could try “Magna 770” rods after V-Ing the joint out then short welds & peen after every weld.

I’m no expert but have done some creditable repairs on “unknown” dirty cast iron with these rods.

I’ve got a 160 Amp MMA stick welder and my brother in law has the skills (it’s his day job!) so if I got some of these would they be the right ones?

770 rods on ebay
13 February 2011 at 13:11 #64023
John Coates
Participant
@johncoates48577
Keith, ady and Steve

Point taken. I think a bit of redesign should go along with the work to restore it (cosmetically at least) to original

If my brother in law says it’s weldable with the rods suggested by Paul then I think I might get him to do it so it looks original, but then design something else to actually lock the tailstock

First thoughts are a kind of handcuffs arrangement that clamp over the two bars but then each cuff has a horizontal lug facing outwards that is slit with a locking screw or bolt. At least that way the forces are distributed evenly rather the locking being done on only one of the bars, as with the original design

Thanks everyone. I really am feeling an awful lot better now about my cock up and have stopped beating myself up about it

John
13 February 2011 at 13:30 #64024
Keith Long
Participant
@keithlong89920
Hi John

If you’re looking at a new clamp design then have a think about using a split cotter for the clamping as an alternative to closing down on a slit. The split cotter design places relatively little stress on the material through which it passes and I understand REALLY gets a grip on the bar, as it works by taper wedging. I’ve seen quite a bit on Quorn forums about people there changing the design from slit castings to split cotters and I believe that you need much less torque on the actuating lever to get as good a clamping action or better. The other beauty of them is that if anything breaks it should be just a small piece of threaded rod that is easily replaceable.

Good luck

Keith
13 February 2011 at 14:06 #64025
_Paul_
Participant
@_paul_
Posted by John Coates on 13/02/2011 13:04:28:

I’ve got a 160 Amp MMA stick welder and my brother in law has the skills (it’s his day job!) so if I got some of these would they be the right ones?

770 rods on ebay

Thats the exact same one’s I use, and at £8.50 I think i will buy some off this chap myself.

Just bought an old Boxford which has damaged backgear teeth i’m welding enough metal into it to re-cut 2 missing teeth this afternoon using these rods.

I have an Aldi 145 amp buzz box nothing special.

My welding is ok it’s the gearcutting I have to get better at

Good luck

Paul
13 February 2011 at 14:18 #64026
Steve Garnett
Participant
@stevegarnett62550
FWIW, I Iike Keith’s split cotter idea, and I should have thought of that before… as it’s generally the way (well on decent lathes, anyway) that the tailstock quill is secured anyway. And by the looks of it, it is on the Barker as well. So one wonders what on earth they were thinking of when they ‘designed’ the rest of the tailstock, doesn’t one?

But if you are going to weld bits onto it, couldn’t you incorporate one? If you fill up the original slit, and weld something large enough underneath, then you could incorporate one anyway. Personally at this stage I wouldn’t be too worried about keeping the lathe in its original state – I’d be more concerned with keeping it long-term usable – by whatever means.

Edited By Steve Garnett on 13/02/2011 14:23:58
13 February 2011 at 14:34 #64027
Keith Long
Participant
@keithlong89920
Hi Paul

Do those rods give a hard or soft deposit, I’ve often wondered what you could use for repairing cast iron, but some of the possibilities I’ve heard of over the years sound as though they leave a hard metal in the weld that’s difficult to do anything with.

If it’s two teeth on the gear I think you’ve got an ideal opportunity to practice your filing (or use a Dremel type drill with the small grinding wheels). Seroiusly I’ll think you’ll find you’ll get just as good as job with a file as trying to use a cutter with all the lining up you’ll have to do, as well as it being a lot quicker. You’re not really after precision and good looks so long as it works well and is STRONG.

Keith
13 February 2011 at 14:54 #64029
_Paul_
Participant
@_paul_
Posted by Keith Long on 13/02/2011 14:34:06:

Hi Paul

Do those rods give a hard or soft deposit, I’ve often wondered what you could use for repairing cast iron, but some of the possibilities I’ve heard of over the years sound as though they leave a hard metal in the weld that’s difficult to do anything with.

If it’s two teeth on the gear I think you’ve got an ideal opportunity to practice your filing (or use a Dremel type drill with the small grinding wheels). Seroiusly I’ll think you’ll find you’ll get just as good as job with a file as trying to use a cutter with all the lining up you’ll have to do, as well as it being a lot quicker. You’re not really after precision and good looks so long as it works well and is STRONG.

Keith

Hi Keith,

The weld metal is easy to file by hand feels just like filing native cast iron here is the rod spec.

Lining up accurately is a problem I have so far tried two different methods one was to use a single point HSS cutter in the mill and the other was to cut using the shaper.

Shaper was easiest to setup by using adjacent good teeth to align the cutter square to the gear then cutting to scribed lines measured from teeth either side.

Sad thing was it didnt produce that good a finish despite “tweaking” the HSS formtool several times in an effort to improve the profile a bit of hand filing tidied it up enough though.

Getting it right on the mill was harder I found the easiest way was to offer a good tooth up to the cutter, clamp gear in the vice take measurements scribe and cut, produced a much better finish but only light cuts as the cutter was held in a home made BMS holder.

Again a tidy up with the file and Dremel produced an acceptable finish.

Off to have a go at another gear this afternoon

Regards

Paul

(apologies to the OP for the OT post)
13 February 2011 at 16:07 #64032
Nicholas Farr
Participant
@nicholasfarr14254
Hi, the Magna rods mentioned should be suitable for the job if they do what they claim, however a true data/spec sheet seems to be elusive.

BOC do an electrode that is sutable and a data/spec sheet is avalable on the link below, page 123

http://www.boconline.co.uk/industrial_catalogue/

Regards Nick.

Edited By Nicholas Farr on 13/02/2011 16:09:05
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