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Metal spinning on a mini-lathe

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murrmac14/07/2015 20:10:41
73 forum posts

I intend spinning some 6" diameter cones out of .2mm thick aluminium and tinplate on my Amadeal mini-lathe.

To do this I will have to turn a hardwood mandrel against which to spin the blanks.

The problem with the Amadeal lathe is that unlike a wood lathe there is no threaded spindle on to which to screw a mandrel, so I am looking for suggestions as to how to go about it.

The lathe does have a MT3 taper in the headstock, so I thought maybe one way to go about it would be buy a MT3 taper arbour with a soft end and have the end turned down , and threaded, to the largest size of coarse metric thread possible.

I would tap a corresponding hole in the hardwood mandrel, screw the mandrel tight against the flange plate (which is an integral part of the headstock) and reinforce the whole caboodle with a couple of small coach screws through the holes in the perimeter of the flange plate.

What would be ideal of course would be a MT3 taper with a tapped hole in the narrow end so that I could tighten it up with a drawbar ... whether such is available I have no idea.

The tapped hole in the wooden mandrel would need to be a minimum of 20mm coarse pitch, to prevent the tapped threads from stripping, and even at that would need reinforcing with a couple of screws, as I mentioned above.

However, there may well be a better way of going about it totally different from what I am envisaging, and if there is, I know i will find it on here!

There will be several different mandrels of varying shapes btw, so I really don't want to make a separate metal faceplate for each mandrel ... threads in the wood should suffice.

Capstan Speaking14/07/2015 20:31:37
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177 forum posts
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How about a 100mm blank chuck back plate?

It will fit easily to the spindle flange and you could put holes in it in for wood screws to fasten the former on.

murrmac14/07/2015 20:42:09
73 forum posts
Posted by Capstan Speaking on 14/07/2015 20:31:37:

How about a 100mm blank chuck back plate?

It will fit easily to the spindle flange and you could put holes in it in for wood screws to fasten the former on.

I'm thinking there might be problems with registration if I took it off and put it back on again ... ?

JasonB14/07/2015 20:49:30
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M20 seems very large, I have screw chucks for my woodturning lathe and a 3/8" one will hold 6" work easily.

Get a blank end arbor from ARC which is threaded fror a drawbar, turn off the end then drill and tap M10. Buy a M10 dowel screw and screw that into the threaded hole. 7mm pilot hole in your timber and screw it onto the woodscrew end.

martin perman14/07/2015 20:58:46
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1636 forum posts
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murrmac,

I metal spin on my Clarke CL500m, I made my former out of Plywood and made a mount from steel which I hold in my lathe chuck and screwed the Ply disc to and then finished turning the ply to size.

Martin P

Capstan Speaking14/07/2015 21:00:38
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177 forum posts
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Posted by murrmac on 14/07/2015 20:42:09:
Posted by Capstan Speaking on 14/07/2015 20:31:37:

How about a 100mm blank chuck back plate?

It will fit easily to the spindle flange and you could put holes in it in for wood screws to fasten the former on.

I'm thinking there might be problems with registration if I took it off and put it back on again ... ?

A metal bush driven into the former and a spigot made from a dowel in the back plate?

Boiler Bri14/07/2015 21:13:46
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802 forum posts
285 photos

Sounds b@-;;y dangerous to me if you have never done it before. 100mm disk flying out of the lathe I hope you can 🐎 quick if it decides to fly.

But seriously, it's a very skilled art is metal spinning, we use a company in sowerby bridge and they do not let anyone have a go on there own until they have a least three years experience. Decapitation springs to mind.

I have to say that it is one of the things that I would like to have a go at but the dangers put me off. 👎

Bri

martin perman14/07/2015 21:26:27
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1636 forum posts
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I make the ends of round fuel tanks for my stationary engines out of copper and after spinning for a short while I remove the parts and heat treat to soften the copper and then place back on the former with no problem, I make my own form tools and use lard as a lubricant.

The copper is trapped between the former disc and a smaller disc using the tailstock to hold it all in place and on initial start up I do stand to one side, I never stand directly inline with the copper disc.

Martin P

murrmac14/07/2015 21:57:13
73 forum posts

@ Jason ... I will probably adopt and adapt your idea , thanks. What you suggest would be ideal for turning between centres, and would probably work even for normal faceplate turning, but metal spinning exerts way too much torque on the perimeter of the workpiece for a 3/8" screw chuck IMO. But I will in fact adapt your idea, and I will get a blank end arbor from ARC, as you suggest, thanks.

@Bri ... Hi Bri, actually it's a 150mm disk, even more lethal cheeky. fear not, I have had tuition from Terry Tynan who is the foremost metal spinner in the country, but his tuition was directed towards working on a Union Graduate lathe which has a 1.5" BSW 6TPI threaded spindle, which could hold a cartwheel. I have done plenty of woodturning, and I do know about , and observe rigorously, all safety precautions. I'm just trying to downsize my approach to suit my mini-lathe.

@ Martin... yes, that's the secret ... never stand directly in line with the spinning workpiece. And always wear full face protection.

It's as dangerous as you want it to be ... but operating safely isn't rocket surgery ...

Neil Wyatt14/07/2015 22:01:09
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> What would be ideal of course would be a MT3 taper with a tapped hole in the narrow end so that I could tighten it up with a drawbar ... whether such is available I have no idea.

They are easily obtained - two types of MT centre - tang and drawbar.

Neil

murrmac14/07/2015 22:18:35
73 forum posts
Posted by JasonB on 14/07/2015 20:49:30:

M20 seems very large, I have screw chucks for my woodturning lathe and a 3/8" one will hold 6" work easily.

Get a blank end arbor from ARC which is threaded fror a drawbar, turn off the end then drill and tap M10. Buy a M10 dowel screw and screw that into the threaded hole. 7mm pilot hole in your timber and screw it onto the woodscrew end.

Problem solved, thanks Jason. I see that ARC sell a MT3 arbor with a 40mm dia end , which will be ideal for threading to 1 1/2" BSW, same as is on the Union Graduate lathe (to which I have access but which I don't own) .

I have already bought a 1 1/2" tap from Tracy Tools for threading the mandrels for the larger cones which I shall be spinning on that lathe, so all I need to do now is find an engineer who can turn a BSW 6TPI thread on the 40mm end.

I don't know if it's good forum etiquette to invite anybody who wants to take the job on to message me privately?

If that is transgressing the rules, than I apologise.

murrmac15/07/2015 10:57:52
73 forum posts

Just to conclude, I have ordered a MT3 blank end arbor from ARC, 40mm diameter and my mechanic knows an engineer who will turn a 1 1/2" BSW 6TPI thread on the end.

Thanks to everybody for their suggestions and thanks to Jason for his heads-up regarding the MT3 arbors.

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