# Chuck flange studs



## jdm23 (Jan 19, 2021)

Hello, I'm a new beginner member.

I have got an used Chinese 250mm x 550 lathe/milling machine and which I proceeded to completely refurbish and make any possible small improvement and refinishing.

One trivial question I have is about the studs on the chuck flange for the 3 jaws, which are M8 but the holes on the flange are 11mm. I was thinking of turning new studs with the smooth section matching the holes minus some clearance, probably that not something necessary but is there any reason why it should not be done? Perhaps a large clearance makes it easier to remove the flange/chuck?

I will also have to make M10 studs for the 4 jaws flange, as they did not come with it, so the same question about the optimal size applies.


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## DAT510 (Jan 19, 2021)

Welcome to H-M

Regarding the holes in the chuck flange, having the extra clearance sometimes can be an advantage.  Often when mounting a part in the chuck one will find runout slightly greater than desired.  Having the ability to slightly loosen the studs holding the chuck and bump the chuck ever so slightly in various directions allows one to index the part for better runout.  

On some more expensive chucks often referred as "Set-Tru" chucks, there are 4 screws that are used to adjust the centerline of the chuck separate from the Jaws.  Think of it as a Scroll Chuck combined with 4-jaw chuck.  The Scroll allow the jaws to open and close together while 4 "Set-Tru" screws allow you to dial in the runout of the part mounted in the jaws.

Stephan Gotteswinter has number of videos on his youtube channel, where he can be seen adjusting the runout on Stud type Chuck as you have.  








						Stefan Gotteswinter
					

Manual and cnc machining, a lot of miniature machining, some minor fabrication work and a lot of shopmade tools. Working as a machinist in a prototyping shop...




					www.youtube.com
				




Hope this helped.


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## markba633csi (Jan 19, 2021)

Usually, the flange (called a backplate here in the US) engages with the chuck by means of a step recess so that the bolts don't do the actual centering;  the oversize holes should be ok
-Mark


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## Mitch Alsup (Jan 19, 2021)

Instead of bigger bolts, think about making bushings to take up the slop.
Those bushings might even be threaded (ID) to convert the bolts to shoulder bolts.
Don't make them too tight.


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## jdm23 (Jan 19, 2021)

DAT510 said:


> Having the ability to slightly loosen the studs holding the chuck and bump the chuck ever so slightly in various directions allows one to index the part for better runout.


Yes, I did that today when refitting the chuck and got a test bar to 0.01mm or less TIR close to the chuck. Which is just a bit more than the runout at the spindle and flange registers. I think I'll leave the studs as they are and concentrate on more important things. Spent a lot of time smoothing and adjusting the gears today.
BTW I love Stephen's videos!


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## DAT510 (Jan 19, 2021)

Btw, On H-M we love pictures.  When you get a chance post some pictures of your lathe.


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## jdm23 (Jan 19, 2021)

DAT510 said:


> Btw, On H-M we love pictures.  When you get a chance post some pictures of your lathe.



Sure, there you go. It's just a common something to practice on. It has a basic DRO but I didn't installed it yet.  As I said I've completely cleaned it up and corrected all the small defects. For example I couldn't stand the painted and chipped carriage so I stripped the thick paint and filler, plus the primer underside, it was applied on rusted cast iron! Smoothed all surfaces and cold blued it. And a lot of other stuff which took a long time.


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