Bent deck plate - can I bend it back?

[mlydon]

I have a 5” bronze deck plate which acts as the rudder post access, and additionally as the backing plate for a shaft-end bushing just under the cockpit sole. The 3/8” bolts clamping the two together got loose at some point, so the whole thing was moving around, and the original bronze bolts were totally deformed - the looked like esses when I discovered the issue and replaced them last year. I snugged everything up tight and sealed the plate watertight with a bunch of duct tape as it was mid-season. Now I’ve got the plate removed to do a proper repair and seal. I had a hell of a time getting the plate off the rim - it kept hanging up through each rotation, and I had to bea it open with a hammer on the plate-wrench - not something you’d want to do if you actually needed to us the emergency tiller.....

Anyway, it turn out that one of the bolts put a dent in the barrel from the outside. It’s very localized, and I’m hoping that I could bend it back and re-use the plate and fitting, as the mounting holes are already hogged out and countersunk for 3/8” flat head bolts, and a new one is $200, and would need to be modded for the bolts.

So, what’s the consensus? Beat it back out cold, heat it with a MAP torch, or what? Both using a wood drift, to hopefully preserve the threads.

Thanks,

Matt

[Oeanda]

I’d heat that section to dull red, let it cool, then try to hammer it back using a piece of hardwood shaped to the desired profile as a drift.

If that doesn’t work, I’d try doing the same thing, but while it’s still hot. (Or perhaps just cut to the chase and try option two first, though it may be a little bit trickier to handle.)

Propane should be hot enough. Even propane is technically hot enough to melt bronze, but a lot depends on how well you trap the heat (firebrick enclosure etc). So - try not to trap the heat too much.

Others may have wiser advice. It looks quite doable to me though.

[Oeanda]

Ran out of edit time. I meant to also say- I can’t see how mangled the threads are in the photo, or predict how much more they’ll be mangled later, but- that’s going to be the tricky bit. Still, reworking those should be quite doable as well, as long as you don’t mind careful fiddly jobs.

[tkeithlu]

A memory from my misspent young adulthood is of a firefighter tapping on a bronze hose coupling that had been run over until it was round again. Bronze can be tapped - little taps with a small hammer, over and over while it gradually changes shape. It is very plastic and not really elastic at all.

Yes, heat will help, but it may take more than a propane torch - I use oxy-acetylene and a rose bud tip - because the stuff conducts heatt away from your site very well. You'll pretty well heat the entire part to the temperature you want.

In sum, do not treat bronze as if it were steel. It's a very different material.

Good luck with it.

[Madehn]

I would be tempted to carefully grind the bulge away from the inside. Yes you lose some threads but I think it could be done

[Oeanda]

I have to say I’ve never worked bronze, (many others though) but have to believe that like all metals it will become more brittle with bending and hammering.

I’m assuming from the photo that the threaded lip is the only bent part. That re-bend shouldn’t take long, but if it does, reheat it to soften. Dull red is hot enough.

Bronze has a pretty low melting point so it’s easily possible to melt that thin lip if you overheat it. Regulate the heating process by how much you enclose the piece. As said, the heat rapidly conducts. Heating it in open air on the end of some vicegrips isn’t the same as heating it while nestled in a mass of hot coals or in a small enclosure.

[Geoff54]

I would only use heat or grind on it as a last resort – it would be so easy to completely mess up the threads. Here is what I would do; others may have an alternative. Get a piece of soft wood that will deform into the thread gaps and help keep them open. Round the end to approximate the curve that you are trying to achieve (no sharp corners) and tap the dent out a little at a time. Work back and forth along the dent a little at a time while trying to keep the wood as square to the threads as possible. Turn the piece over and back so that you are working from opposite sides. Be patient. Even then you may have to repair the thread with a thread file. You can also try to find a steel (harder than bronze) bolt with the correct pitch and roll it back and forth to reshape the threads. If the threads are closing up as you straighten the bend, use the bolt to force them back open, then continue tapping. Then grease the plate and work it into the rim going back and forth as you would if tapping a hole. The goal is to smooth any roughness in the thread. Applying some metal polish while doing this may be useful if the bronze on bronze isn’t working well.

[oleman]

Probably cost more than a new one in the long run but.
Chuck the base in a lathe and straighten out the circle. Re-run the threads in the now straight base.

Normally those plates are sealed by a thick O-ring so perfect fit does not have to be perfect.
The issue with lathe work today is the $150. US per hour for labor.
McMaster in the US has a good assortment of bronze hardware.

With cheap access to a machine and a learning curve, you could make a new one from your choice of materials.
Good luck with your project.

[Yojimbo]

An option you might consider: hammering by any means can reduce precision- overbending/unwanted deformity. A hydraulic pressure/ram would be my first choice but probably not doable in this case. Have you ever seen the tool used to spread the exhaust flanges/maintain their dimension for an exhaust manifold? They can be bought in most auto supply stores or you can cobble one together easily enough. It is essentially a threaded coupling with female threads at both ends into which bolts are threaded. Screw them in until they fit inside your piece and then reverse the bolt out to deform the flange back into shape. Localized heating of the area you want to effect should keep from throwing the other side out of round. Maybe a combination of screw force/localized heat and very controlled tapping with an appropriate drift. Can you keep a bolt threaded in the hole with some Neverseize while doing the repair to protect the threads? If you tried doing it with screw power, maybe bolting the other 3 holes to a plate to help maintain roundness would be advantageous.

[mlydon]

Update....

In the end, I clamped it in a vise, bent part down and towards me, heated it for a bit with a map gas torch, and gave the bent sections a couple of good wacks with a 5lb lump hammer with a bit of hardwood as a drift. It got a lot looser, so I did it again. It straightened out nicely, and the plate threads on freely now.

The hardwood end-grain conformed to the threads - no damage to them. I also tapped out the plate, after the success with the rim.

I was heating an area about 3” across, encompassing the bent inch and another to each side, both inside and out. While I put a good amount of heat on it, the assembly never got red-hot.



Matt

[Oeanda]

Good job. Happy ending