Repairing a cracked casting

[Grindstone CowboyParticipant @grindstonecowboy]

Started trying to put together an old hand shaper I inherited some time ago – it's the proverbial "box of rusty bits with some bits missing" and I don't know when it may last have actually been in use. I think it's a Tom Senior as it's very similar to – but not exactly the same as – this example.

Anyway, to cut a long story shorter, I was happily cleaning things up when I discovered there is a crack in the dovetail of the cross-slide (saddle?) as shown in the photos. The crack is about two inches long in a piece that's five and a half inches long.

So my question is, what do you all think the best way of repairing this would be, given that I have no milling facilities, nor the skills, to re-cut a dovetail. I'm imagining the only feasible way would be to carefully drill and tap for some small diameter cap-head screws to try and hold it together, or some form of metal stitching, although that may be outside my budget, given it's only come from near scrap parts in the first place. It's more of a sentimental restoration, you might say.

More on the actual shaper – as I said, I think it's a Tom Senior, but seems to have been rather haphazardly assembled (bolt holes not in straight lines, some rather rough filing done to clean up the castings, etc.) so may have been made up from a casting kit.

Thanks for any suggestions that you can come up with, although I may just store it away for later if I don't think I'll be able to make a decent repair right now.

Rob

[Grindstone CowboyParticipant @grindstonecowboy]

Crack in dovetail on hand shaper

[PatJParticipant @patj87806]

We can cast you a new one in gray iron.

We have the technology.

[Grindstone CowboyParticipant @grindstonecowboy]

Thanks Pat, I'll bear that in mind although I think we are, unfortunately, separated by the Atlantic.

Rob

[Jeff DaymanParticipant @jeffdayman43397]

Find the true end of the crack, drill a hole there so it is less likely to keep opening up and getting bigger. Then vee it out with an angle grinder and bronze weld it with oxyacetylene torch. Slow preheat to near red heat is important before bronze welding CI. If you don't have the OA equipment and bronze rods, a good car garage, machine shop, or agricultural equipment repair place may be able to do it for you. If you are anywhere near southern Ontario Canada I could do it for you.

Edited By Jeff Dayman on 14/02/2021 01:00:33

[Grindstone CowboyParticipant @grindstonecowboy]

Thanks Jeff, all good points, particularly about stopping the crack. I'm in the UK, unfortunately, but many thanks for the offer. Thirty years ago I had access to oxy-acetylene (and lots of other good stuff), but now I'll have to ask around and pull in a few favours. In fact, whilst writing this, I've just thought of someone fairly local that may be able to do it – up until now, he'd totally slipped my mind. Memory playing tricks…

Keep well,

Rob

[PatJParticipant @patj87806]

Seems like I have seen people arc weld iron with a nickle rod.

As I recall, the part had to be preheated, and the cooling had to be very slow, ie: use an insulating blanket immediately after welding.

I have had things shipped across the pond, so it can be done.

All I would need are the dimensions of the piece in order to make the pattern.

So shipping would be one way only.

Local repair makes more sense though.

Edit:

Seems like from what I am finding, stick welding cast iron is not nearly as good at gas welding with bronze.

I saw my dad repair a number of large machines that had cracked frames, and he was very good with the bronze and gas torch.  I never saw one of his repairs fail or crack, and there were machines with cracks several feet long that he repaired.  I recall him preheating, and using insulating blankets after.

.

Edited By PatJ on 14/02/2021 02:00:10

[John OlsenParticipant @johnolsen79199]

A repair could be attempted by drilling though the material next to the dovetail in tapping size, open out the hole down to the crack with clearance size, and tap the end. Then a long screw can pull the crack together. In addition a strap could be screwed on the outside to cover the crack. This would not be all that pretty but would get the machine going. At that point you would have a machine that can cut dovetails, so if the cracked part is not too big for the machine you could make another.

One of my shapers had a piece broken away from a dovetail, on the side with the gib strips, so I was able to machine the broken part clean and screw on a piece with capscrews before cleaning it all up. Now you cannot tell that a repair has been done unless you look very closely.

John

[David Marks 2Participant @davidmarks2]

As previously stated Cast Iron is not the easiest material to weld. I have (during my working life) repaired CI with both high silicon rods and by bronze welding. With that particular item you then have the problem of restoring the dovetail to overcome any distortion caused by the welding. Personally, I would look at companies that repair cracked engine blocks for those people that restore vintage and veteran cars. There was a process called (I think) Cold Stitching used for this type of repair which as it is `cold' overcomes the distortion problem.

[Ady1Participant @ady1]

I'd just weld it and grind it down

I would be more concerned about how it happened in the first place, to me there's not enough meat there for tension work with cast iron, can a reinforcing plate be added to beef it up?

To me the unit has lifted under load, and the crack is angled like the slide failed

A new casting with more meat on that load point is the smart route IMO

Edited By Ady1 on 14/02/2021 08:43:16

[HopperParticipant @hopper]

Posted by John Olsen on 14/02/2021 03:28:05:

A repair could be attempted by drilling though the material next to the dovetail in tapping size, open out the hole down to the crack with clearance size, and tap the end. Then a long screw can pull the crack together. In addition a strap could be screwed on the outside to cover the crack. This would not be all that pretty but would get the machine going. At that point you would have a machine that can cut dovetails, so if the cracked part is not too big for the machine you could make another.

One of my shapers had a piece broken away from a dovetail, on the side with the gib strips, so I was able to machine the broken part clean and screw on a piece with capscrews before cleaning it all up. Now you cannot tell that a repair has been done unless you look very closely.

John

^^^^^^^ +1 on this good advice. I might even take it a bit further and drill and tap several long screw holes along the length of the crack for added strrength. Also drill a hole at the end of the crack if you can to minimize it continuing. And add the plate on the side with screws for sure.

I would avoid any kind of welding or brazing in this situation, ie a precision machined dovetail. The heat will distort the dovetail and even as little as one or two thou distortion will mean it needs remachining before it is useable. Which creates a whole new set of problems.

Screw it first. If eventually it breaks, then you can mess around with welding and machining..

[Martin DowingParticipant @martindowing58466]

About 10 years ago one guy have repaired a vice with dovetail cracked very much like your..

He just painted it very well and sold it to me. I have never seen him again (car boot sale).

[HopperParticipant @hopper]

Posted by Martin Dowing on 14/02/2021 08:42:42:

About 10 years ago one guy have repaired a vice with dovetail cracked very much like your..

He just painted it very well and sold it to me. I have never seen him again (car boot sale).

LOL. I bought (cheap cheap) a big old solid 6" Record brand UK-made bench vice at a garage sale. Guy said to me when I bought it "You won't break that one in half like one of those Chinese vices.". Few months later when I got around to wire brushing it down and painting it, it had a big strip of bronze welding/brazing across the base and up both sides where someone had broken the base right in half and repaired it. But it had done a lot of work since then, judging by the paint and crud covering it. And has worked for me for years since. But the jaws never have lined up exactly so it's not my precision vice, rather my heavy duty flogging vice. So far so good.

[Ady1Participant @ady1]

I have found that cast iron in tooling welds really reliably

Probably because it is already a reasonable quality cast iron to start with

[Ramon WilsonParticipant @ramonwilson3]

Given that you say in you OP that you have no milling facilities and that budget is limited I would be inclined to do what you consider – drill and tap it.

I would echo Jeff Daymans suggestion of drilling a hole at the end of the crack to prevent further running then drill through the entire thickness as central to the material between dovetail apex and side as possible. Drill right through with the tapping drill first and tap from one side as deep as possible before turning over to drill the clearance hole until the thread is reached. C'Bore for the cap head if desired. Two or three strategicaly placed capheads will certainly hold that good enough but a plate on the side as Hopper suggests would reinforce it even more

Welding cast iron without knowledge or facilities is not a road I would take here – you could end up doing more damage than what you have at the moment and as you say all you require is a sypathetic recovery.

Regards – Tug

Edited By Ramon Wilson on 14/02/2021 11:10:05

[Howard LewisParticipant @howardlewis46836]

Metal stitching is often used to seal cracked castings such as water jackets on engine cylinder blocks.

Would be wary of metal stitching in this context. Metal stitching effectively forces a series of plugs into the crack. Unless there is a large mass of metal on each side of the crack, to provide compressive force, it might make matters worse.

If veeing out, preheating and welding or brazing is impossible, drilling and tapping for a series if small screws to compress the two sides of the crack may be the way to go. Countersunk screws may be the best way to disguise the repair.

Howard

[Dave HalfordParticipant @davehalford22513]

Posted by Ady1 on 14/02/2021 08:40:41:

I'd just weld it and grind it down

I would be more concerned about how it happened in the first place, to me there's not enough meat there for tension work with cast iron, can a reinforcing plate be added to beef it up?

To me the unit has lifted under load, and the crack is angled like the slide failed

A new casting with more meat on that load point is the smart route IMO

Edited By Ady1 on 14/02/2021 08:43:16

I'm betting the chamfer on the end started the crack .

If welding worries you drill the end of the crack, bolt and JB weld a strap over the crack to reinforce the dovetail Personally I would at least weld the end where the crack started.

The trick with welding distortion sensitive metal is in keeping the heat LOW . You can butt weld car bodywork without the buckling if you tack every inch, then infill every half inch and so on till you have joined all the tacks up.

Same with cast iron use a cold weld 100% nickel rod, tack, listen, if you hear a tinkling sound from the weld, the weld won't work because that the sound of the weld breaking off the iron. Otherwise continue short tacks then run a full weld over the top.

[Grindstone CowboyParticipant @grindstonecowboy]

Thanks very much to all who have replied and offered help. It seems the way to go would be as described in detail by John, Hopper, Tug and Howard – a series of screws through the apex of the dovetail to hold it all together, not forgetting a hole to prevent the crack spreading further.

Thanks again,

Rob

Edit – I agree with Ady1 that they could have made the casting a bit beefier

Edited By Grindstone Cowboy on 14/02/2021 15:04:10

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