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I Forge Iron

cold steel spring back

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To cut a long story short I've got a job on to make 6 curved benches, so far I've made the first one as a prototype. I've been hot forging/bending all the parts around jigs I made to bolt to my bench. The arms/legs are made from 40 x 8mm and the seat slats are 40 x 6mm.

I need to speed up the process to stay on budget. 40 x 6mm will bend cold, but if I want it to bend to the right shape I need to make a new jig that's "over curved" to allow for the spring back.

Avoiding trial and error, is there are any way of calculating how much extra curves I need to put into the jigs that'll allow for the cold steel spring back?





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A starting point would be a 10% tighter radius, although this is just an approximate starting point. The spring back varies on cross section sizes, material batches, hot/cold rolled....etc.

Trial and error is the path. I've made benches similar to that and cold bent everything - yes its time consuming but with an original pattern to compare to they can be done, but still does take some time.


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Bend using the length of the stock as a lever. Then cut to separate the product from the stock after the bend has been made.

It would appear that you have close to 200 of the back and seat pieces for the project. Once the proper size jigs are figured out, manually bending against the jig would work, building a bending tool (with lever arm) could make things easier. Make one bending tool jig to make only one bend. Then retool and make the next bend, etc. You may find this makes the pieces uniform in shape, and speeds up the process.


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Thanks for the thoughts. Annoying thing is this isn't the most time consuming part of the job, but is probably the only part of the job where I may be able to scrape some time off.

My girlfriend gave me a hand bending these the other day & after I figured out the best method of stretching the heat out on the bar so the heat ran the full length we were smashing these out in 1 heat, in under a minute each.

That was doing it in the coke forge so the only way I can currently see the times all making sense is to either buy/make a big gas forge, or put additions onto my existing jigs to increase their angles. I had a go at packing additions infront of my jigs and bending against them, then taking them out to see if the slat sprung back correctly, but without more forethought I don't think that'll work in a hurry because that attempt came out rubbish.

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13 hours ago, ThomasPowers said:

Yes this is one place that the gas forge excels---long heats!

Needless to say I'm not going to make a HUGE gas forge that'll heat the full length of each bar just by throwing them in there & closing the doors, so how long a gas forge do you think I'd need to be able to heat the full length of the 48" long bars by pushing/pulling them through the forge a few times to stretch out the heat?

Allowing for clinker clear out time as well, in the coke forge we were doing 6 an hour, so it was about 8 mins heat time + 1 min bend time per slat. One at a time.

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