Metal spinning a deep cup

[Oily RagParticipant @oilyrag]

Hello all!

I am looking for some advice on ‘metal spinning’ in the lathe – something that I have never had reason to do in some 60 years of engineering.

The Job:

Is to make a ‘dirt cover / grease retainer / component retainer’ for a 5 roller sprag clutch. The clutch body is 1.760″ (44.75mm) dia and the flange needs to be 0.711″ (18mm) deep. A Bendix gear will be retained by 2 ‘half moon’ plates positioned inside the cup and will be driven/released by the sprag, the whole assembly retained by peening over the rear of the clutch body.

I checked the forum for any earlier references to metal spinning and found Nigel Graham’s July 2024 contribution detailing his method for a boiler flangeplate which showed how he went about spinning his plate using a former and a copper bar in the tool post with lots of AFB lubricant! His flange was only 3/8″ deep and formed from a much larger diameter – which looked good but will I be able to form one as deep as 18mm? (on a 45ish mm diameter) What material is best to use? (note: the half moons will take up the end bearing surface form the bendix gear) I’m thinking along the lines of 16g mild steel or aluminium.

I would appreciate any suggestions or comments!

Martin

 

[bernard towersParticipant @bernardtowers37738]

Whilst I have only done it half a dozen times for items in brass and copper I was amazed at how easy it was as long as you continually anneal the blank.

[DC31kParticipant @dc31k]

Consider why an item might be produced by metal spinning as a conscious choice amongst the many alternative ways it might be produced.

Two immediate reasons are economy of material (starting weight vs finished weight) and economy of tooling (one former to make one part or one former used for 1000 parts).

For a one off, starting with a 1″ long piece of 45mm diameter aluminium and removing the excess by turning and boring could be faster and cheaper than trying to spin one. Remember you need to make the former over which the item is spun as well as make the tooling and toolrest to do the spinning.

Compare the high cost of a piece of large diameter solid copper bar from which to hew the flange plate against the minimal cost of the aluminium stock you would need and you can see why the flange plate is not a good comparison to your own situation.

You can look on the Internet Archive and find old textbooks about metal spinning.

https://archive.org/search?query=metal+spinning

[SillyOldDufferModerator @sillyoldduffer]

Ages ago I watched a short clip on telly showing a metal spinner who made it look extremely easy!  TalkingPictures show old ‘Look at Life’ and short industrial training films: it was in one of them.

What I remember:

• Big lathe
• A hefty woodworking style rest with a peg, not a toolpost
• The tools were about an inch in diameter and two or three feet long, allowing the operator to apply a lot pressure.
• Don’t recall any lube.
• Nor any mention of annealing, though that must be essential.   In the film, the blank was simply chucked up, and opened out with a few hefty sweeps.   The effort looked considerable, done by a sturdy man applying plenty of leverage.  Don’t remember what the item was, bowl shaped about a foot across, maybe for a brass band.

I suspect if I tried it, £500 quids worth of metal would be crumpled hopelessly in a few minutes!  Bernard’s comment is encouraging though – I should try it.

Dave

[Tony Pratt 1Participant @tonypratt1]

I’ve done it once in my 70 years, it was a flat steel blank which had to end up as a spherical end cap for a beer dispenser tower tube.

From distant memory a steel male former was held in a 4 jaw chuck, the blank was held against the former by a revolving centre.

I think we had some sort of ball race attached to a piece of bar fitted into the tool post and then the revolving blank was ‘spun’ into shape against the former by pressure from the ball race.

I actually think it went surprisingly well and the free edges were trued up in a second operation to achieve a clean surface for brazing.

Tony

[Grindstone CowboyParticipant @grindstonecowboy]

The only thing I know about metal-spinning (and why I’ve never tried it) was a graphic description of the personal damage that can result from a spinning disc coming off the machine related to me by a chap who was involved in making copper hot water cylinders. So be careful!

Although I have seen various videos that make it look ridiculously easy…

Rob

[Clive Brown 1Participant @clivebrown1]

If I were interested in experimenting, I’d perhaps try spinning, but if my main priority was to finish up with a good component in good time, then I’d surely machine from a piece of bar.

[JasonBModerator @jasonb]

Another one who has only had the need to do it once. Steel just over 2″ dia with a 3/8″ return. Think it was 22 or 24g

I turned a hardwood former and held a ring spanner in thetoolpost and used the hard chromed convex part of teh ring as my tool.

I have needed deeper cups a couple of times but took DC’s option of turning to about 1mm thickness from solid, then put it onto a wooden former to finish turn to 0.5mm thick wall and base, this one is stainless 303

A soft grade of aluminium or spinning brass may be easier than steel. This is a nice deep piston spun by a pro from spinning brass that came with the castings

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