JB Weld or what

[dusty]

I am putting together a second Mark V with used parts collected from here and there. Everything has been moving along well and I was about to begin reassembly. I was inspecting my paint job and that is when I noticed two cracks in the Headrest. They are located under the Headrest Lock Handle and I believe that is why I never noticed them before.

I have attached some pictures - to show where the cracks are located.

My question: Is this an appropriate application for JB Weld?

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Am I correct in saying that the Headrest Lock is the ONLY source of pressure that would exacerbate this crack?

[tsaguy]

Because it is cast, I would say yes. I have used JB Weld on cast pieces and parts. You cannot weld cast material, which JB Weld has turned to be a wonderful effective alternative.

If you are unfamiliar to JB Weld, be sure before application you can brace and hold your piece steady in order for the repair to remain effective. JB Weld is a fluid of sorts, and until that intial half hour passes, the bonding material will flow if given chance.

Roughing up the surface where you will be appling the weld is helpful, and to help 'dam' the weld, you can use simple modeling clay or glue a wood frame which can then be removed later.

I have never used JB Weld on a ShopSmith, so good luck.

[ddvann79]

A cracked piece that's still attached to the parent casting is indeed tricky, especially where yours is located. If it were completely broken off, that might be easier to fix! I would think you would need to make the crack BIGGER in some way, like drilling or grinding it out, in order to get the JB Weld in the crack... and that looks to be hairline in places.

I believe the cast aluminum can be welded without blowing it out - just not stick welded. Nick Engler mentioned it was possible in one of the SawDust Sessions (#21 - #24). If you have access to an oxy-acetylene rig, you can braze it back together. I also ran accross a "welding" compound called Alumaloythat is supposed to weld cast aluminium with just a propane torch and no flux. There are other similar products out there like HTS-2000.

[robinson46176]

Yes it can be welded. I don't even try, I have a very good neighbor who is a very expensive boat propeller repair specialist. I just mention that I need a weld and he is ready to do it. I try very hard to not take unfair advantage of him. We do each other favors quite a bit in this neighborhood. Many of the props he gets in to repair are $1500 to $2000 racing props. Some come in really mangled and go out looking new. I couldn't afford him if he charged me.
My point is that about any welding shop that does aluminum work much can due that job but it might be cheaper to pick up a used part.
Cast aluminum is not like cast iron at all in character.
I used to weld a good bit of cast iron mostly using nickel rod. They make some low temp solders for aluminum but I don't know just how strong it is. Probably stronger than J. B.
J.B. is a good product but it has fairly low level of strength compared to the original metal.

[beeg]

I'd think that you'd also have to drill a small hole at the end of the cracks. To keep em from spreading.

[robinson46176]

I'd think that you'd also have to drill a small hole at the end of the cracks. To keep em from spreading.

I think that might be a very good idea regardless of how it is repaired.

[holsgo]

Try PL construction grade polyurethane glue. I comes in a can like caulk. Force it into the crack so it pushes into the other side. It is thick and as it cures it expands. It is excellent, very strong and will glue almost anything together. It's also not brittle in cold. Let it foam out and then chisel of the foamed out material. You won't have to worry about the inside. You can also wet the area before hand is it cures in water (moisture). I've used this for just about anything, even stressed matrials.
I accidentaly got some on screw threads that I wanted to remove from a clamp up. I had to cut the screw.

[bhurley]

Have you thought about just getting a new headrest piece? There is very little market for these so they're pretty cheap. I'll take a look but I think I have 2 or 3 of them.

[ddvann79]

Try PL construction grade polyurethane glue. I comes in a can like caulk. Force it into the crack so it pushes into the other side. It is thick and as it cures it expands. It is excellent, very strong and will glue almost anything together. It's also not brittle in cold. Let it foam out and then chisel of the foamed out material. You won't have to worry about the inside. You can also wet the area before hand is it cures in water (moisture). I've used this for just about anything, even stressed matrials.
I accidentaly got some on screw threads that I wanted to remove from a clamp up. I had to cut the screw.

Sounds like good stuff and perfect for hairline cracks. How large a void will it fill? From Dusty's photos, it looks like there is a chunk missing.

It's not showing up in internet searches. All I'm getting is construction adhesive and Loctite products. Where can you get it?

[holsgo]

http://www.amazon.com/Henkel-P73948125- ... B001E3VQBE

This is it. It spans up to 1/8 I believe while maintaining structural strength. This is the same yet different than Gorilla glue. They are both polyurethane glues but this foams less and is far denser.