Thread: Help with method of holding disk for turning down outside

Hi Rod,

Is a center punch at the center of one face acceptable?
If so center punch it, Face piece of 25mm bar in the chuck.
hold the disk against the bar with a live center in the center punch.
Go easy

Stuart

Hi Stuart,
Unfortunately I need to face the disk as well so it will have to be held from one side.
Sorry I should have said that.

I have been pondering on this for a while and keep putting it on the back burner.

Best I have come up with is super glueing it to the end of a shaft held in a chuck but that won't be easy to centre it before the glue dries.

Hi Rod,

Whats the disk made out of?
I've soft soldered workpieces to mandrels before.

I'm told super glue works, but havent used it myself. There are many recipes for glues for this sort of thing.

Is the work piece currently round?

You could make a jig that is bored the size of the mandrel you are going to use with a shallow counter bore to center the disk while the glue sets(but unless you only have a tiny amount to remove and you are turning the outside to size why does it need to be centered so well? )

Stuart

How centered is centered? Could you machine a bar 27mm on the lathe, face it and superglue onto the face using the bar as a guide for center? Otherwise I guess you could make a small bush to slip over the bar to hold the disk central for gluing, then remove the bush.
The other thing to try maybe what Stuart said only don't center punch the disk, put a say 10mm thick disk, center drilled on one face between the disk and the live center. With reasonable force on the ts the disk shouldn't move......but I have not tried it.

Originally Posted by Ueee

With reasonable force on the ts the disk shouldn't move......but I have not tried it.

I have, it doesn't(move that is), but its a less preffered option(for me anyway). The center punch makes me feel better.... though how much difference it would make if things went pear shaped I have no idea......

Stuart

Not saying I am doing this but if you wanted to make a doubled sided coin you would make a socket out to the rim of one coin and then make a corresponding insert to neatly fit in the socket.

The insert would require the diameter reduced and one face turned down to match the insert diameter and depth of the socket.

A bush to centre the insert on a shaft might be the go.

How many of these do you need to do.

If its only one there is a lot of work in making all those jigs.

Have you considered using one of those earth magnets attached to a piece of faced bar in the 4 jaw chuck,mount the magnet to the bar and the disc to the magnet and then set up to the od of the disc,from what I have seen they should be strong enough to hold the disc whilst it is turned and faced.

Unfortunately they are not magnetic - shame becasue I have some rare earth magnets that would have done the job.

Originally Posted by Ueee

How centered is centered? Could you machine a bar 27mm on the lathe, face it and superglue onto the face using the bar as a guide for center?

That's what I would do. Then use a heat gun to remove it and acetone to remove the leftover superglue.

Originally Posted by jack620

That's what I would do. Then use a heat gun to remove it and acetone to remove the leftover superglue.

+1 on this method.

I've used superglue like this a few times and it works well. Handy if you want to reduce valve shim thickness.

Rob

If i was to try this, my approach would be to mount a piece of easily machined bar in a chuck with modest overhang, (say 10mm), face end of bar and then machine a recess in the end to the diameter of your workpiece and depth equal to the finished thickness you require. Glue (Locktite or superglue) the blank into the recess and allow glue to set while the 'mandrel' is still in the chuck.

Once cured, blank is centred by rim of recess and you can face to required thickness by machining till you are just touching the rim of the recess (can't access rear face of blank to measure from). Then turn off the rim to obtain access to edge of blank and machine to finished diameter. Release the blank with heat/solvent etc appropriate to adhesive used and clean up blank.

Repeat process for second part.

If you are doing what I suspect with an adhesive centre in the sandwich, face and recess the 'mandrel' to almost full depth of the composite and mark the rim at one point for reference, push blank 1 into the recess after aligning a significant feature with the mark on the rim, apply drop of adhesive to faced part of blank 2, and insert it into the recess, with the same feature aligned to the same rim mark. Maybe use a pad of some sort mounted in the tailstock to press the two blanks together. Allow to cure, then turn the rim down to recover the assembled component.

If you feel that you need to glue blank 1 into the assembly tool to finish machine the assembled edge, use a different adhesive sytem to that used to assemble the blanks, so that the the solvents used to clean the face don't upset the bond between blanks.

Thanks for all the input.
I'll give it a go and report back on how it went.

What is it you're making Young Rod?

Hi Bob,
See post #7.
It's for a nephew that asked some time ago if i could do it for him.