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G1K
05-09-2009, 09:49 PM
I just acquired a bison 3 jaw (not set tru) plain back chuck. I'll need to purchase a d1-3 back plate so the chuck will work with the monarch. Based on some searches I see that CDCO and Shars both sell backs (Shars is $58 on ebay), and they're decent quality. Also, the bison back plate will be $107.XX + shipping during one of the MSC 40% sales.

My question is how to machine the back plate to ensure the chuck is true to the spindle? Seems like it would be very easy to mess this up and have the chuck run off center.

Ryan

Jeffw5555
05-09-2009, 10:07 PM
It's really quite easy. The plain back chucks are made to run true against the recessed lip on the back of the chuck. You mount the backing plate, & first run a face cut to true the plane of the backing plate. Should only need just a few thousandths cut just to clean it up true. Measure the diameter and depth of the recessed section of the back of the chuck. You now just take successive facing cuts to rough out the lip that the chuck will fit against, but leave 20 thousandths or so oversize. You don't want this lip to bottom out in the chuck; maybe 25 to 50 thousandths clearance. On your final facing cut, just skim it.

Now you can finish out the lip. Take light cuts, and creep up on the final diameter. It is critical that this lip fits tightly in the back of the chuck; a slight interference is best.

After this is accomplished, you can mark out the attaching bolt holes, drill and tap. Remember that these bolts are not intended for any truing, they are simply there to hold the chuck tight on the lip.

Since your lip on the backing plate is cut true to your spindle, and the recessed bore of the chuck is made true to the centerline of the chuck, if you fit this tightly together, then you have done all you can possibly do to have the chuck run true.

Spin Doctor
05-09-2009, 10:30 PM
As an aside. Last week at work I had to rebore a carrier for a gearbox that mounts on a piece of equipment that runs about 6000 rpm*. And the primary IDs that have to run true, one was welded up and the other was not accesible to indicate. Fortunately we had a spare back plate handy so I turned and faced the back plate to a light press fit for the part to be machined transfered the mounting holes and faster then you can say Jack Robinson an instant fixture that runs dead nuts.

* We work on decanters/centrifuges for a variety of industries

G1K
05-10-2009, 09:18 PM
It's really quite easy. The plain back chucks are made to run true against the recessed lip on the back of the chuck. You mount the backing plate, & first run a face cut to true the plane of the backing plate. Should only need just a few thousandths cut just to clean it up true. Measure the diameter and depth of the recessed section of the back of the chuck. You now just take successive facing cuts to rough out the lip that the chuck will fit against, but leave 20 thousandths or so oversize. You don't want this lip to bottom out in the chuck; maybe 25 to 50 thousandths clearance. On your final facing cut, just skim it.

Now you can finish out the lip. Take light cuts, and creep up on the final diameter. It is critical that this lip fits tightly in the back of the chuck; a slight interference is best.

After this is accomplished, you can mark out the attaching bolt holes, drill and tap. Remember that these bolts are not intended for any truing, they are simply there to hold the chuck tight on the lip.

Since your lip on the backing plate is cut true to your spindle, and the recessed bore of the chuck is made true to the centerline of the chuck, if you fit this tightly together, then you have done all you can possibly do to have the chuck run true.

Thanks for the explanation. If I understand, the diagram below is how I cut the face plate and how it interfaces with the chuck, the contact area in red?

http://i531.photobucket.com/albums/dd358/gonekayatgmailcom/mount01.jpg

Ryan

lakeside53
05-10-2009, 09:25 PM
Yes...but the LIP fit (not shown in red) is the most important contact area....

G1K
05-10-2009, 09:36 PM
Yes...but the LIP fit (not shown in red) is the most important contact area....


Shown in blue? This should be a very tight fit right? Any "looseness" here could result in runout ...

http://i531.photobucket.com/albums/dd358/gonekayatgmailcom/mount2.jpg

R

Frank Ford
05-10-2009, 09:42 PM
I just fitted up a new Bison chuck exactly that way, and I think I got pretty good results:

http://www.frets.com/HomeShopTech/Projects/Bison/BisonAnime/bisoncloses.gif

That's a "tenths" indicator showing .001 runout on a 1" ground steel bar. Riding on the freshly machined surface of the back plate the indicator needle was nearly motionless.

lakeside53
05-10-2009, 09:48 PM
Shown in blue? This should be a very tight fit right? Any "looseness" here could result in runout ...

http://i531.photobucket.com/albums/dd358/gonekayatgmailcom/mount2.jpg

R

Yes, just a light press fit. Keep testing with trial fits and make sure the plate isn't hot from cutting. You might need undercut the shoulder if your chuck lip radius is less than your tool.

Dunc
05-11-2009, 08:31 AM
Not saying this is better... I have read - maybe in one of the British hsm books - that a bit of relief on the 'blue' areas is useful for zeroing work in the chuck. A few light taps should be sufficient. Once done, work will run true in that chuck until age overtakes it.

That said, all my chucks (from LMS for my mini-lathe) have the 'tight blue' setup.

lakeside53
05-11-2009, 11:28 AM
Then you are just relying on the three bolts and chuck-back to backplate face friction to keep the chuck aligned...

I think I'll stay with a tight shoulder;)