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Torsion bar steel?
Benzine - 18/12/16 at 09:04 PM

I recently got a lathe and I've been playing with it. I turned some aluminium nicely, then I found a solid round bar about 40mm diameter by 15cm long. I thought I'd stick it in the lathe and see how my new bits cut it. I used cutting fluid but they were really struggling, and I'll need to re-grind one after only a short period of use.

The steel had been sitting in my garage for years, then I remembered it was a section that was cut out of a torsion bar from my old Daewoo Musso. Is that why it was so tough to cut? I was really getting disheartened after trying and failing to turn it nicely, so I'm hoping that torsion bars are made from some super high grade tough as flip steel.

bonzoronnie - 18/12/16 at 09:32 PM

Hardened Spring steel I suspect.

AJC - 18/12/16 at 10:09 PM

It may have been hardened. You could try using carbide tipped tooling.

mark chandler - 18/12/16 at 10:31 PM

Use carbide inserts, loads of stuff I have tried machining blunts machine tool steel, even good tool steel like Goliath.

It does not help that I probably cannot grind them up right, and use any old rubbish, that said when I have bought in en3 steel it has been a different experience.

Supporting the distant end with a revolving centre really helps as well.

[Edited on 18/12/16 by mark chandler]

907 - 19/12/16 at 08:49 AM

A torsion bar is just a straight spring that twists. Moggy Minors had torsion bars and were renowned for them braking the
bottom suspension joint and the arm on the end would did a grove in the tarmac.
They were only 16mm, maybe 20mm diameter though. I'm trying to visualise what a 40mm torsion bar would look like.
I know a Musso is a biggish 4x4 but surely not warranting 40mm. Happy to be wrong, but just doesn't seem right.


I've turned and threaded an allen key with index tips before now and apart from the screeching noise it did work.

Paul G

nick205 - 19/12/16 at 09:22 AM

If as you describe it a section of ARB then it will be spring steel and almost certainly hardened. Have you tried cutting it with a hacksaw to see how that goes? Might give you a similar indication of the toughness of it.

Theshed - 19/12/16 at 10:39 AM

As above carbide tipped tools are the way to go. If your lathe is home workshop size then the tips used for aluminium will produce a good finish in steel.


Cutting high carbon steel is a bit counter intuitive. If you go slow and take light cuts the tool rubs, blunts and dies. You have to be quite brave and go for it. The chips will come off blue with heat but you will get a lovely finish.

Benzine - 19/12/16 at 03:00 PM

Just tried the hacksaw and it's tougher to cut that some mild round bar I have

Also yeah it wasn't 40mm, more like 25! Whoops

nick205 - 19/12/16 at 04:57 PM

quote:
Originally posted by Benzine
Just tried the hacksaw and it's tougher to cut that some mild round bar I have

Also yeah it wasn't 40mm, more like 25! Whoops



Ø25mm sounds more like it for an ARB.

The hacksaw test seems to suggest it's a tough material too.

nick205 - 20/12/16 at 08:53 AM

A quick Google suggests EN24T material for torsion bars - selected for its "durability". Can't see anything about machine-ability of it though.

Theshed - 20/12/16 at 10:29 AM

EN24T machines beautifully when you get it right. It is not hardened when in "T" condition. That is not to say it is not hard......

Lots of good advice on the web about tooling/cutting speed in the home workshop - http://www.model-engineer.co.uk/forums/

Or more generally http://www.practicalmachinist.com/vb/