Steel Temper - Timber Bracketry

Hello again...

A couple months back I got some great advice from the group concerning a set of large steel brackets I'm fabricating for a timber frame house we're building. I have sixteen brackets to make, each with five pieces, weighing about 40lbs total per assembly when done. I designed the brackets so all the cutting could be done by my steel supplier. I now have (32) 1/4"x2"x34" bars that each need six 90 degree bends (insert loud groan). Since I'm doing this in my home shop, I plan to heat the bar at the bend spot to cherry red with a MAPP gas torch. I'll then quickly clamp the bar in my (large) bench vise and (hopefully) complete the bend using a sledge hammer. My question concerns temper. These parts are grossly over-designed for aesthetics, but I'd still like them as strong as possible. Will it do any good to quickly quench the bar in water after making each bend? I'd imagine that if I just let the bar cool on it's own, it will end up fairly soft. The steel is nothing special, just plain structural steel (probably A36) from the local yard. I don't want to get too fancy here, but if it won't hurt anything quenching in water seems easy enough to do. As I mentioned in my original post, I plan to finish these parts by planishing them with a ball peen hammer and then following up with some sort of rust resistant finish.


Richard Johnson Camano Island, WA

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Damn...I wish I had bought a house on Camano Island back in the days when it was "the sticks". That place is filling up quickly with lots of spendy houses!

Anyway, I wouldn't bother quenching them. If over-designed, there would be no real need for extra hardness anyway and you run the risk of over-hardening and possibly causing cracking. It's a small risk but not the kind of thing you want to find after installation.

As to finish, if these are way up where you have to really look hard, I'd have em powder coated. There are some powder colors that look like iron from a distance. On my in-laws place, some surface rust started showing up after about 10 years due to tiny amounts of condensation as well as some of the tannins from the wood. Not a big problem but it gets a little irritating to see your work with a rusty haze showing up.

Koz (who wishes he was out shore fishing off Camano island right now)

Rich->Hello again...

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You can't make that steel any softer no matter what you do. Nor can you harden it unless you case-harden it -- there simply isn't enough carbon in it.

I take it you are bending these the easy way?

This is simple forging work. Heat, bend, hammer flat, check for square, fix as necessary. Afterwards you will have some scale where it was heated. Bitty little 1/4" flat bar you can bend cold if you like. But you will get a cleaner bend and sharper inside radius if you bend it hot.

Also, you are confusing "hard" with "strong". Hardening something might make it more brittle and thus in a sense weaker.

I've heated bends with a torch while shipbuilding in Puget Sound many hundreds of times -- that's what shipfitters do. We just quenched with a plain water hose or let it air cool. It ain't a Swiss watch ..

This would be about an hour's work on an ironworker with a brake. Unless you mean to bend them the hard way, which is a horse of an entirely different color ..

Grant Erwin down in Kirkland

Rich-> Hello again...

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Grant Erwin

Hardening the steel probably would not be a good idea. With A36, it's especially not a good idea. A36 is graded for strength, not for alloy (it's typically made from re-melted mixed scrap), and you don't really know how it's going to behave after heat-treatment.

For starters, you don't have to get steel so hot for that kind of bending that it would quench-harden, anyway. A dull red should be enough to forge it over, and that's not hot enough to quench-harden.

It's true that you'll probably heat it enough to anneal it, more or less. But, if the design is overbuilt to begin with, take solace in the thought that by not quench-hardening it you've improved its ductility. In structural applications, that can be a benefit. It's less likely to fail catastrophically.

Good luck with your project. It sounds ambitious and interesting.

Ed Huntress

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Ed Huntress

Can't your steel supplier throw them in a pressbrake for you?

Reply to
Ernie Leimkuhler

OK, I won't worry about quenching. More trouble than it's worth and not likely to do me any good.

I experimented yesterday with bending the 1/4" x 2" bar stock. The reason I'm doing it myself is

__________ stirups (2) -->| | | timber | | | bolt ->MM | | MM bar-> [ ]| |[ ] ---- ---- || || base plate ----------------------

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Sorry about the half-baked posts - itchy trigger finger...

OK, I won't worry about quenching. More trouble than it's worth, not likely to do any good, possibly even some harm...

I experimented yesterday with bending the 1/4" x 2" bar stock for the stirups. The reason I'm doing this work myself is the top two bends on the stirups need to have 3/4" radiuses (to match the timbers they seat over), where the bottom 4 bends require a tighter radius (to match the 1"x1.5" bar that seats here). I though it easier to do this myself than to try to explain this to someone else and end up getting it half-right.

It was clear from my experiment that using a big lever to bend the bar would be better than whacking at them with a sledge hammer. I'm thinking of clamping the bar in my bench vise and then clamping on a large 2x4 as a lever. I'm planning to bend the 3/4" radius bends over a piece of pipe, also clamped in the vise. It took much longer than expected to heat the bend spot to glowing using a MAPP gas torch. Since I have 192 bends to make, I may just try to do them cold. The design I came up with is fairly tollerant if I don't get the four lower bends spot on. Slack can be taken up using two 3/4" x 6" bolts that thread down into nuts welded to the baseplates. For aesthetics though, they should be fairly symetric. I've included a crude text sketch showing the basic layout of these bracket assemblies.

__________ stirups (2) --> | | | timber | | | bolt -> MM | | MM bar-> [ ]| |[ ] \---- ----/ baseplate ------------------------ nut --> MM MM

Masonry Column

Thanks for the advice,

Rich Johnson Camano Island, WA

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if you want a quick and dirty forge to heat them up. dig a hole run a piece of pipe to it and connect the pipe to the blower end of your vacuum hose. Then fire it with charcoal or coal if you have it. Wear safety glasses. My brother is half blind in one eye due to a piece of scale getting on his cornea forging. Karl

Pork the MSG of the animal world.

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Karl Vorwerk

I think it will be a lot easier to get clean bends heating with a torch than with a forge. What Rich needs in my mind is an oxy-acetylene torch for heating.

With a forge, a larger area will get hot and bend along with the corner. The part in the vise will be ok, but the part on top will have an extended bend to it, which will need flattening out.

Rich, you're talking about doing it cold; how about getting a cheap hydraulic press and making some simple tooling for it (for instance, tooling that will give you the radius you want...).

Maybe you could have good luck using a lever made from square tubing and bending hot.

You almost certainly want to texture the bars *before* bending. Texturing after bending will cause your bends to need re-work.

Steve Smith

Karl Vorwerk wrote:

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Steve Smith

If you heat the material to cherry red you shouldn't need a sledge hammer to do the bend. If you're too rough while bending them hot in the vise you can leave a crease on the inside of the bend that will tend to crack. The crease is actually the impression of the top corner of the vise jaw. A radiused jaw cover helps if you have a lot to do.

A two pound hammer should do the job. I would just use a big Crescent wrench to make the bend or make up a bending bar.

It sounds like the planishing is more a hammer finish for decorative purposes. If you can do this hot and do it before you do the bends it will be a lot easier. What you have planned is a lot of hammer work, do some tests before you commit yourself. You might find that the flat stock looks fine the way it is or that hammer marks down the edge only looks pretty good.



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Kelley Mascher

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