I want to bend some stainless sheet, I have a piece which is 340 mm square, from an old case, and I need to bend two sides 90 degrees , I dont have a brake. So I will hammer it over the edge of my workbench.
my question is,
is it better to heat it us first, or just to bend it cold, its 1mm thick. I am making a cover for the drain in the bottom of my swimming pool.
Stainless is much harder to bend than mild steel. I don't think the edge of the bench will be any good to support it for bending. I would suggest a piece of bright steel flat to provide a hard, sharp bending edge, something like 1/2" thick x 1.1/2" to 2" wide, by the length of your sheet, or longer. You will need another piece of the same, on edge, so that the max width is vertical, to clamp down on the sheet. Then you might manage to bend the edge with a heavy hammer. I'm afraid you are unlikely to get a very neat bend though because of the nature of stainless sheet. The pieces of 1/2" steel strip as clamps, will help. Heating before hand might help but generally it doesn't help much. Bending while red hot definitely helps though, if you can. Problem there would be the edge of the wooden bench isn't going to like the heat! Hope that helps.
Post by ettingtonliam on Apr 11, 2019 21:02:36 GMT
Workhardening does depend on the grade, but yes, stainless is prone to that. Many years ago when I was driving a rustbucket car, I decided to do a really good patch repair to the floor using some stainless sheet which I had, but had to give up, because i could never form the right angle bends. If you really want to try, I recommend a couple of pieces of heavy steel angle, clamp it between that, then belt the corner over if you can. Heating it is a waste of time because by the time you've clamped it up, 1mm sheet will have cooled down.
Hi Jem, One was is to use a couple of pieces of angle as vice extensions, and file at least a 1mm radius on the one receiving the fold. You could use a piece of flat bar that's big enough to cover the entire piece you're wanting to bend and hit that with a heavy mallet with it held against the sheet. The problem with forming anything with a hammer is that you get lots of localised bruising and bending rather than getting an even fold. Using an interposing piece between the mallet and the sheet helps to spread the load and hence get a more even bend without it getting too damaged. Some heavy gloves would be handy to hold the flat bar so it's not so hard on your hands.
As pault suggests - go to the local tin basher. It's many years ago since I had anything to do with stainless steel sheet forming and had forgotten about the grades of stainless. All the commonly available stainless steels, like 304 and 316, are Austenitic. All Austenitic stainless will work harden quickly. Martensitic stainless doesn't work harden but it can be heat treated to harden it and can be annealed with heat. Unfortunately Martensitic stainless sheet is not so easy to get hold of in sheet form so you are going to have difficulties trying to do your bending at home. If you can find a supplier of 420 grade stainless sheet, that is Martensitic but will a lot more expensive. The tin basher is the way to go. He will use a press-brake so the bend will be formed quickly and work hardening, of either 304 or 316 stainless, won't be a problem, but bending it over with a hammer will work harden it very quickly and you will almost certainly get the metal cracking in places, along the fold.
I've just looked on the 'net. West Yorkshire Steel Ltd sell 420 stainless sheet, if you do want to do it yourself.
This thread reminds of the time in the late 60's when the cills on my BMC Mini went rotten - as they all did- and the MOT was due! Our Base Workshop had a lovely big bender, and I made up some cills in 18g stainless. I fixed them on with araldite and pop rivets. The MOT tester refused to accept them, and I replied that as my method was good enough for Concorde then it should be good enough for him! He relented and said that if I covered the cills with underseal he would pass it. John
Last Edit: Apr 12, 2019 10:12:48 GMT by simplyloco
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thank you very much for so many replies, I should have said that my bench has a piece of angle steel on its edge, so can be bashed over that. but from what you all say, it would seem to me to be better to cut the steel, and then mig weld a piece of angle onto the edges. I would certainly like to go to a tin basher, but the only one that I know has a hugew machine, and I fear that it would take ages to set it up for my "little job" My main question was to heat or not to heat, which has been well answered so thank you all for your help.
success, It was very much easier to do than I had expected, I put a steel bar in the vice behind my stainless plate, and bent it by hand part way then belted it with a big hammer, and the bend came out really well. My vice is a huge one, which I got off a shipwreck 50 years ago, so plenty of meat to play with. So thank you once again, for your help.
In 1969 a ship sank 1 km from Cala Mesquida Beach. in 1970 I got the concession to run the water sports for Pontinental from this beach. so the ship wreck in 4 meters of water was a perfect diving training spot. there were a group of salvage workers who would blow the wreck up and then take scrap from it. We would come along later and collect spanners, and all manner of other bits and pieces. and one day a huge vice, so bit that we couldn't lift it onto the inflatable, we tied it under the boat and bought it back to the beach, and my workshop. it had been down underwater for a year when we found it, slightly damaged, but otherwise in good condition. Still in use today nearly 50 years later. There is very little left of the wreck now, however a friend of mine found a porthole a couple of years ago, a nice piece of brass.