Magnetic chucks on lathes

[David ColwillParticipant @davidcolwill19261]

Hi. I have a number of thin washers to face off. I’m thinking of using a magnetic chuck to hold them. Obviously I’m aware that magnets don’t have great holding power when resisting a turning motion but I was only going to take very light cuts with a sharp tool. Is this a good idea (bearing in mind I have to mount the chuck on a backplate first)? What are the pitfalls apart from having your throat cut by a rapidly spinning shuriken?

Many thanks in advance.

Dave.

[David ColwillParticipant @davidcolwill19261]

[Steve GarnettParticipant @stevegarnett62550]

I have no idea what the answer might be, but I would also like to know whether anybody’s tried it and found it to be practical. I ‘inherited’ a couple of magnetic chucks a while back and wondered about machining washers myself (and I have exactly the same issue with a backplate).

 

The only conclusion that I came to was that the degree of grip would be directly proportional to the surface area of the washer, all other things being equal. So if it’s a large washer, it stands a better chance of staying put. But even with a light skim, I’m seriously dubious about its ability to remain in one place, especially at the start of a cut.

 

Holding washers with a magnetic chuck seems to work if you are surface-grinding them – but I would have thought the forces involved were less than for any sort of cut. Has anybody tried it?

[David ColwillParticipant @davidcolwill19261]

My chuck as a 1/2 1nck hole about 1/4 inch deep in the centre which I intend to use as a register to centre the washer and to stop a certain amount of slip.

[John McNamaraParticipant @johnmcnamara74883]

Hi David

 

Ditto. I was given an 8inch magnetic chuck by a retired engineer recently. It has a small pin in the centre. He told me that when they used the chuck in production a center piece was made and placed over the pin Sized for the ID of the work. the work was located by that. naturally light cuts for this setup.

 

Cheers

John

Edited By John McNamara on 18/01/2012 14:52:08

[Steve GarnettParticipant @stevegarnett62550]

Not sure what’s in the centre of mine – I’ll have a look later.

[Tony MartyrParticipant @tonymartyr14488]

I used to use Loctite to ‘glue’ thin (brass) plates to a faceplate in order to machine the knife edges of windage baffles. We then used to heat the whole assembly to break the bond. This was a standard way of working when I was at work but I can’t remember what grade of Loctite was used!

Someone on the forum will be able to quote grade numbers

Tony

[jason udallParticipant @jasonudall57142]

with magnetic chucks ,you also need to consider pole spacing…you need to stradel a number of poles in the chuck… Work very well in grinders ,we add blocks to cover extra poles to act as extra lateral resistance

[JohnFParticipant @johnf59703]

Hi David,

I don’t think a magnetic chuck is the way to go, why not make yourself an expanding mandrel.

Simple to make, I used to make them in industry for this type of job. Use a piece of whatever from the scrap box about the same O/D of your washer, turn a register for the I/D [close fit] then drill and tap for a suitable countersunk allen screw. Remove from the lathe and put say 6 or 8 saw cuts about 3/4 to 1 inch long down the bar. The allen screw when tightened will expand and grip your washer so you can face it up. these work well on many projects and can be modified for another use if not going to be used again.

 

Best to use in a collet or 4 jaw to ensure concentricity or modify the production of the mandrel by leaving the I/D register oversize and finishing after making the saw cuts.

 

If you need a sketch please message me.

 

John

[John Stevenson 1Participant @johnstevenson1]

Squirt of PVA glue onto a faceplate and work round with fingers.

Then a piece of cartridge drawing paper onto the glued face and then PVA glue onto the part and position and hold tight with the tailstock and a block of some description.

 

When dry this will hold very well indeed, hot water to remove.

 

John S.

[BERTOParticipant @berto]

Not sure how thin you mean but have you seen Harold Halls thin piece collets ?

They were in his book Lathework a complete course WPS # 34 or you may find them in MEW or His website .

 

Ian.

[Sub MandrelParticipant @submandrel]

Loctite. In the old days they used shellac.

 

Both release with heat.

 

Neil

[Steve GarnettParticipant @stevegarnett62550]

Posted by jason udall on 18/01/2012 21:24:09:
with magnetic chucks ,you also need to consider pole spacing…you need to stradel a number of poles in the chuck… Work very well in grinders ,we add blocks to cover extra poles to act as extra lateral resistance

 

Good point – I had a look at the one I’ve got – an Eclipse 5″ one, and the poles are rather more widely spaced than I had realised.

 

Also, it’s dead flat right across – no centre indent of any description. It’s going to be quite interesting to work out what actual use it is for anything!

[Harold Hall 1Participant @haroldhall1]

Not sure about magnetic chucks

 

Place a piece of steel in the chuck and face the end but with a short spiggot in the middle to fit the hole in the washer. Cover the rest of the end with double adhesive tape but do not overlap it causing double thickness in places.

 

Place the washer over the spiggot and use the tailstock drill chuck to hold the washer against the adhesive for a couple of minutes. This should hold the washer sufficient for the task.

 

See– http://www.homews.co.uk/page274.html           and the link to the  next page.        

 

If you have a lot to do, or require to do it often, then the collets mentioned above by Ian are excellent for the job.

 

An even more adaptable method would be to use soft jaws in the three jaw,

 

See– http://www.homews.co.uk/page100.html

 

Harold

Edited By Harold Hall 1 on 19/01/2012 23:27:21

[David ColwillParticipant @davidcolwill19261]

Further to my earlier post I have now fitted the chuck to a spare back plate ( it would have been pretty useless otherwise ) and have had a play. It works surprisingly well. As an experiment I faced an M12 washer ( 13mm od 23mm id ) with few problems. I don't envisage doing anything this small but it's nice to know that I can. The only problems I had were slipping due to taking too heavy a cut but the centre piece held the washer central and there didn't seem to be any danger of it flying off.

So if you have one it could be a useful addition to your lathes armoury.

[colin hawesParticipant @colinhawes85982]

I have used double sided tape to hold shims for skimming to a thinner size. Can only take max 2 thou cut though using a sharp tool.With a magnetic chuck I would have thought magnetic swarf could be a problem.You could ,of course, hold brass etc. using double sided sticky tape.

Colin

[David ColwillParticipant @davidcolwill19261]

The swarf is not a problem as it is is attracted to the face of the chuck and is easily wiped off when the chuck is de-energised.

[Author]

Posts