Threaded Chucks and Rotary Tables

[JasonBModerator @jasonb]

[JasonBModerator @jasonb]

I got an e-mail today asking "how do I stop a threaded chuck comming undone when using on a rotary table?"

Not having used lathes with threaded chucks I could not give an answer except do it up tight. I know some people have screws to stop the chuck comming off the lathe spindle but do they just act as a safety measure or lock the thread solid which would be needed if say dividing on the rotary table.

So the question is for those of you that have one of the MT adaptors that fit into a rotary table to screw your Myford chuck onto is how do you stop the cutting forces from the milling cutter unscrewing the chuck?

Thanks, J

[David Clark 13Participant @davidclark13]

A better way would be to fit the chuck on a larger backplate and bolt it to the table.

[Ian PParticipant @ianp]

Posted by David Clark 1 on 14/10/2015 20:50:53:

A better way would be to fit the chuck on a larger backplate and bolt it to the table.

But that does not answer Jason's question.

Do it up tight is the only way if its a threaded chuck. Same if its a dividing head with an integral spindle threaded for a lathe chuck.

Ian P

[John Stevenson 1Participant @johnstevenson1]

2 opposing locking pads or 3 depending on the table, fitted to the tee slots and pressing on the chuck body ??

[Michael ToppingParticipant @michaeltopping17870]

I was using a threaded chuck on my dividing head today to hold a loco chimney whilst I fly cut the radius on the base. Taking about 25 thou cuts, on a 6.187 diameter,no problem. I have never had the chuck come unthreaded whilst milling or drilling. I use a bar across the chuck jaws to tighten it up. For the rotary table where you can be taking heavier cuts I made a backplate to bolt to the table top.

Michael

[Bruce EdneyParticipant @bruceedney59949]

I have a threaded chuck on my lathe. It has a grub screw which supposedly locks it to the spindle. When I go to remove the chuck it always seem well locked even without the grub screw. It also has a second grub screw hole at about 90 deg which would provide further locking. I suppose you could make slight locating dimples on the spindle which would provide more positive locking.

Bruce

[JasonBModerator @jasonb]

When using on a lateh the cutting forces tend to tighten the chuck, its only if you stop the spindle suddenly or run in reverse that there is a risk of it comming undone. Also to some extent the same with flycutting although part of teh cut will be acting against the thread direction. >>

The backplate is what I use but kind of defeats the idea of being able to leave work in the chuck after turning so you keep it concentric, and a chuck with integral Myford thread may not be the easiest to centre and bolt to a table/backplate>>

Take a cut like this, the work is rotating clockwise yet the cutting force from the endmill is trying to push the work clockwise which could unscrew the chuck.>>

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