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

Tailstock lock broken

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John Coates12/02/2011 10:41:50
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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
Steve Garnett12/02/2011 10:54:43
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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.
Nobby12/02/2011 10:55:00
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Hi
Its a shame you did not post a photo of tailstock break in your album
Nobby
Keith Long12/02/2011 11:02:20
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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

Steve Garnett12/02/2011 17:01:37
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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.
John Coates12/02/2011 21:54:17
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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.
Terryd12/02/2011 23:02:54
1926 forum posts
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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

ady12/02/2011 23:49:39
612 forum posts
50 photos
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.
ady12/02/2011 23:51:34
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i cant do anymore than this because Im ratted out of my head.
ady12/02/2011 23:53:39
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This is really really annoying.
 
10 years ago I could read everything, now I am a waste of space.
John Coates13/02/2011 07:54:41
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554 forum posts
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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
 
Dusty13/02/2011 10:31:13
467 forum posts
8 photos
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.
Keith Long13/02/2011 11:24:14
802 forum posts
10 photos

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

ady13/02/2011 12:06:22
612 forum posts
50 photos
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

_Paul_13/02/2011 12:33:49
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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
Steve Garnett13/02/2011 12:55:12
837 forum posts
27 photos
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.

John Coates13/02/2011 13:04:28
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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?

John Coates13/02/2011 13:11:11
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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
Keith Long13/02/2011 13:30:20
802 forum posts
10 photos

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

_Paul_13/02/2011 14:06:00
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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?

 
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

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