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Bending stainless rod

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Paul Ainsworth19/10/2019 10:34:47
97 forum posts
15 photos

I have to put a 45deg bend in this part where it meets the pin. The 10mm shaft that's in the collet has to remain true as it will run in a bush, the 25mm collar stops me using a normal 2 pin approach (I think).

Heat or not?

Would you build a differnt jig?

How would you do it?




Edited By Paul Ainsworth on 19/10/2019 10:37:26

KWIL19/10/2019 17:02:22
3401 forum posts
66 photos

Assuming that the large pin in the vice is where you want the 45 degere bend and that in fact its a radiused bend (large pin ) then a second pin snugly against the radius of your 25mm collar should hold it all.

Needs to be firmly mounted in your new jig. Lots of heat away from jig, quickly inserted and pulled around with some form of lever pivoting on your large dia pin? (Just like a copper plumbing pipe bender with shaped pressure plate to protect the part being bent)

Tim Stevens19/10/2019 17:11:47
1433 forum posts

Let me guess - the part to be bent is shown held in a collet-holder, and the bend needs to start as close as possible to the radius where the long smaller-diameter section starts to increase in diameter? And the part is solid and made of mild steel?

If so, I suggest that you abandon the collet idea (it is likely to get too hot), and find two steel tubes, one large, one small, to fit over each end of the part. The fit needs to be loose enough to fit easily over the small end even when it has expanded with heat (say 1-2mm clearance); the tube for the larger end can be a light push fit, or if looser than that, make a slot along it so the vice will close it onto the part to hold it firmly in the vice. The larger diameter tube will be held in the vice horizontally (so the full length of the tube is held firmly with the part inside it). Then heat the length to be bent with a fairly large flame (a big propane job or oxy-acetylene), and when the relevant length is nicely red-hot, slip the short tube over the end of the part which is sticking out, and pull it towards you keeping the newly-bent section horizontal (or it might slip round in the vice).

Depending on how accurate your 45 degrees needs to be, it would help, before you start heating, to mark a template (eg cardboard) with the required angle as a guide to the pulling operation. To get the angle exact, if your first go is not good enough, it would be best to wait until the whole set-up has cooled (eg overnight) before you heat the bent section again, otherwise the whole thing is going to get much too hot - vice as well. It might be possible to tweak the angle a degree or two when cold, using the same tooling, if you handle-tube is long enough, the vice is firmly bolted to the bench, and the bench to the wall. The more you can concentrate the heat on a short length, the tighter the radius will be, and the harder you will need to pull.

The heat will of course cause the heated surfaces to blacken in the really hot bits, with various colours working outwards. These surface effects can be removed back to bright steel with time and emery cloth, or using a soft abrasive wheel in a polishing rig.

If the steel is not a mild steel, it is likely to be harder to bend, and the heat treatment is likely to modify its properties - especially hardness. How much this matters depends on the use of the finished article. In this case do not risk cooling any part of the job more quickly by spraying with water (etc) as this is likely to cause odd heat-treatment effects. With a mild-steel part, cooling in water should not have any effect - that's why it is called 'mild'.

I hope this helps ...

PS just read the title again - the olny place it says 'stainless' but which spec of stainless, I wonder?


Edited By Tim Stevens on 19/10/2019 17:18:00

Edited By Tim Stevens on 19/10/2019 17:19:21

Tony Pratt 119/10/2019 17:24:13
1587 forum posts
8 photos

Use heat & don't use the collet.


Paul Ainsworth19/10/2019 17:30:44
97 forum posts
15 photos

Better photo without collet, bend needs to be on blue mark in line with one of the end flats.  303 stainless



Edited By Paul Ainsworth on 19/10/2019 17:31:24

Edited By Paul Ainsworth on 19/10/2019 17:45:20

Edited By Paul Ainsworth on 19/10/2019 17:47:24

Tim Stevens19/10/2019 17:52:27
1433 forum posts

If the first attempt ends in disaster, somehow, I suggest that your second should delay machining the flats until the bending is done. That way you line the flats up with the bend (easy) rather than bending a red hot bar in line with flats you can't see.

303 should bend OK with my method, but don't cool with water or anything else. Just allow to cool. And the blackened surface will respond to fine abrasive just like mild steel.


Edited By Tim Stevens on 19/10/2019 17:54:35

Vidar19/10/2019 18:05:07
57 forum posts

Tim has got good point there.

As for the bending I think I would have roughly encased everything that is to stay the same in some sturdy structure. Then cast in a lump of low melting point metal for a perfect supportive fit. Possibly complete with a bend radius and direction guide - maybe an external flat on the casing parallel to the flat on the part for direction reference.

Then I'd go with brute force sliding pipe extender or press for the bend. The 3xx series is quite ductile, and 10mm should be within manual range even cold.

Edited By Vidar on 19/10/2019 18:07:48

vintage engineer20/10/2019 11:50:33
254 forum posts
1 photos

Make a dummy split collet, clamp it solid in a vice and use a oxy propane pepper pot burner to heat it up and the bend to suit. Afterwards pack in dry sand to allow it to cool slowly.

Never cool any steel in water as this could cause chemical changes or hardening. Even mild steel will change it's structure. Unless the steel is "new" you don't know what else is in the steel!

Modern cars now contain all sorts of exotic steels and when the cars are scrapped most of them go through a frag machine which grinds up the steel ready for recycling. This material contains boron, vanadium, chrome, nickel and high carbon steels. This all goes into the pot for mild steel.

Unless you can find a supplier who supplies new steel you really don't know what your buying.

If I need a specific grade of steel I ask for a Certificate of Conformity and the steel is normally more expensive.

Paul Ainsworth20/10/2019 12:38:30
97 forum posts
15 photos

Revised jig, I'll see how this goes.


Paul Ainsworth20/10/2019 14:30:51
97 forum posts
15 photos

New jig worked a treat, thanks for advice fellas. Steep learning curve this stuff as I only started messing with metal recently.

vintage engineer20/10/2019 14:51:21
254 forum posts
1 photos

Just the sort of jig used for production work in a forge!

Posted by Paul Ainsworth on 20/10/2019 12:38:30:

Revised jig, I'll see how this goes.


Paul Ainsworth27/10/2019 19:47:18
97 forum posts
15 photos

The end result


Nigel Graham 230/10/2019 18:56:23
1618 forum posts
20 photos

Lovely work!

Going back to what Tim Stevens suggests, not using the collet as it will become overheated...

Indeed - but I am not certain what the collet was doing there in the first place. Neither I nor presumably Tim would dream of putting any sort of precision machining collet anywhere near a bar-bending operation anyway, hot or cold!

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