Bend Relief Lines

[Magic Rat]

Hi all I'm looking for advice on size of bend relief lines in 3/8" mild steel if anyone has any experience. I've got oxy but if I can get away without it I'd be interested to hear how you did it.

[jmersereau]

I don't bend 3/8" material in my projects so I can't give you any advise, but just to confirm... you are asking about a break relief cut (or several) that is in line with your bend?

David spoke about in this post from a few years ago https://www.plasmaspider.com/viewtopic. ... 17#p217217

[4130metalworks]

It sounds like with an oxy involved magic rat is trying to bend it by hand or in a vice. What sort of bending equipment do you have?

[tcaudle]

Bend metal is a more copmplex process tha it woudl at first seem. There are two main factors: the Bend Radius and the Bend allowance. When you bend metal it shrinsk and grows and it does not end up a sharp 90 deg turn. The thicker the material the bigger the bend radious . So the length of each leg "grows " by an amount of about 1/2 the bend radius length (the Lenght is section ot the circumference defined buy that 90 deg section .
As you get up in thickness there are more factors involved . The are charts by material thckness to give you the "average" bend radius form which you can determine how much the lengs of each leg change. On 3/8 material it woudl be a LOT more than say 11 ga (1/8")

so the position o f the bend line has to take into consideration growth in length it the outsides or inside dimension is important.
On thinner material I use the material thickness to approximate the bend limits and its usually pretty close but not super accurate for tight fits/.
Bending via heat and hammer is a lot less accurate than via a press brake but you need 80- 100 ton Press Brake to bend 3/8 mild steel without preheat/
Sometimes on thicker materials its easier to cut to exact dimension and weld than to try and bend a 90 deg or sharper angle if exact size is important

[Magic Rat]

Thanks for the replies folks sorry I'm on GMT here. Yes I'm familiar with bending allowance. I've never done this with anything heavier than 1/4" and find a min 1/8" line rather than a single kerf works better so was expecting I should go heavier on 3/8". I appreciate your input by the way.

[Magic Rat]

It sounds like with an oxy involved magic rat is trying to bend it by hand or in a vice. What sort of bending equipment do you have?

Yes hand bend in a vice probably bend is roughly 10" long.

[Magic Rat]

I don't bend 3/8" material in my projects so I can't give you any advise, but just to confirm... you are asking about a break relief cut (or several) that is in line with your bend?

David spoke about in this post from a few years ago https://www.plasmaspider.com/viewtopic. ... 17#p217217

Thats exactly what I was looking for thank you for the link.

[adbuch]

It sounds like with an oxy involved magic rat is trying to bend it by hand or in a vice. What sort of bending equipment do you have?

Yes hand bend in a vice probably bend is roughly 10" long.

For 3/8" thick x 10" long using manual bending (hold in vise, clamp to top of bench, etc.) and assuming you will be welding it up after bending, I would probably go with slots along the bend line - maybe 3/16" to 1/4" wide. Long slots with short tabs where the bend will occur. I would do a test piece first (as I showed at the post Jim referenced above) to make sure you can create the entire 90 degree bend without the slots "binding". Also, a bit of heat probably wouldn't hurt to make the material more malleable.

David

[Magic Rat]

Thank you Adbunch. A test piece is a good idea and yes I will be welding it up afterwards. Thanks.

[adbuch]

Thank you Adbunch. A test piece is a good idea and yes I will be welding it up afterwards. Thanks.

You are quite welcome! Let us know how it turns out.
David

[4130metalworks]

Magic rat, do you have a press at all? i made a very basic pressbrake attachment for mine, could possibly use the vice if it was heavy duty enough

[PlasmaDon]

At that thickness, and having to weld all along the edge anyway, why not just make 2 separate pieces ?

[adbuch]

Magic rat, do you have a press at all? i made a very basic pressbrake attachment for mine, could possibly use the vice if it was heavy duty enough

My little Harbor Freight press brake would work nicely for his part.
David

[cutnweld]

I have found that putting relief in thicker materials seems to result in the remaining material cracking when i applied the bend, so I used to end up making separate pieces and welding together. Now I use the brake with 8x die opening and it seems to work alright unless it is AR plate.