Switching over to D1-4 Chuck back plates

COMachinist

COMachinist

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Hi All
Just got my new lathe, the PM-1236T from QMT, very nice lathe it is built in Taiwan at the same factory the PM-1340 that Matt has on his site. Now I need to change over my chucks to D1-4 mounts. I will guess it the same as preping the back plate as a thread on. Once the back plate is mounted a skim pass has been taken, do you mark the bake plate so it goes back to index. I'll be mounting a plain back Bison 8" and the zero set 6" 3 jaw, and lastly 6" scroll 4 jaw. All the lathes I have owned had either L00 or threaded mounts. So this kind of new to me. I'll be getting it broke-in in a few days and getting it tuned for use.
Thanks
CH
 
Not quite related to your question, but watch out for D1 mounts. The cone shaped spindle pilot must contact the mount at the same time the flat back of the mount contacts the flat part of the spindle. Often, the spindle hangs up on the cone and the mount never seats properly to the spindle face. That leaves a chuck that tips on the cone, never giving a repeatable mounting. It is usually very easily fixed with just a little sandpaper cleaning up where it is hanging up. Dress the mount, not on the spindle. It usually takes far less metal removal than you might expect, and trying to do it with cutting tools often ends up with a disastrous loose fit from cone to spindle, which allows radial runout in the mounting. If that is not clear, I can try harder. Again, this is a common problem with D1 spindles and new mounting adapters, especially imports...
 
I use an index mark when mounting my D1-4 chucks, probably doesn't matter on an independent jaw chuck. If yo have Bison chucks, you can use Gator back plates and they are machined the same as the Bison and 1/2 the cost. Have used several Gator back plates and they did not need to be skimmed (measured 0.0001" on face), but probably need to slightly turn down the registration step. Depends on the back plate model. I only do a skim cut if the back plate doesn't measure true and if it comes with a registration step.
 
I am in the habit of indexing everything that goes on the spindle. It is good standard practice in my books.

One of my chucks is a tighter fit than the other and it happens to be the heavier one. I find that it helps to only lightly engage the 3 studs at first then turn them gradually tighter in steps, keeping the backplate as square to the spindle as possible. After a few rotations of the chuck the cams are snugged up tight.
I have more confidence in a tight fit than in an easy fit so the extra effort in fitting the tight chuck is not a problem for me.
 
Tozguy said:
I am in the habit of indexing everything that goes on the spindle. It is good standard practice in my books.

One of my chucks is a tighter fit than the other and it happens to be the heavier one. I find that it helps to only lightly engage the 3 studs at first then turn them gradually tighter in steps, keeping the backplate as square to the spindle as possible. After a few rotations of the chuck the cams are snugged up tight.
I have more confidence in a tight fit than in an easy fit so the extra effort in fitting the tight chuck is not a problem for me.
Click to expand...
The one that is tight could be made to fit better by marking it with high spot blue and then lightly dressing the high spots of the fit on the back plate. It usually takes very little to improve the fit. Make very sure that no gap is visible between the flat faces of spindle and back plate, Put a strong light behind the joint and look carefully. Only zero gap is acceptable.
 
Actually Bob the tight one does fit perfectly, the flat faces end up in full contact w/no gap. I would be suspicious of any fit where one can close the gap with only hand pressure and not need the cams to draw the final half thou in straight and even.
 
Tozguy said:
Actually Bob the tight one does fit perfectly, the flat faces end up in full contact w/no gap. I would be suspicious of any fit where one can close the gap with only hand pressure and not need the cams to draw the final half thou in straight and even.
Click to expand...
Agreed. And it should take a rap from a dead blow hammer to knock it loose. Still, a lot of us do not realize that the back plate needs to seat on the chuck face, and bad mouth their lathe and their chuck for the poor work they do, when the issue is fairly easily mitigated.
 
mksj said:
I use an index mark when mounting my D1-4 chucks, probably doesn't matter on an independent jaw chuck. If yo have Bison chucks, you can use Gator back plates and they are machined the same as the Bison and 1/2 the cost. Have used several Gator back plates and they did not need to be skimmed (measured 0.0001" on face), but probably need to slightly turn down the registration step. Depends on the back plate model. I only do a skim cut if the back plate doesn't measure true and if it comes with a registration step.
Click to expand...
Thanks that is nice to know Gator back plates work on Bison chucks. Bison back plates are nice, but they almost cost as much as the chuck.
Thanks
CH
 
Tozguy said:
Actually Bob the tight one does fit perfectly, the flat faces end up in full contact w/no gap. I would be suspicious of any fit where one can close the gap with only hand pressure and not need the cams to draw the final half thou in straight and even.
Click to expand...
The back plate I ordered from shars for the zero set chuck I bought in May fits by hand pressure which seamed realy lose compaired to the factory chuck which fits up tight with no gap. It has to be tapped with rubber dead blow to get it off. I may have send the zero set back plate back. I will try the 8” back plate for the Bison chuck tomorrow To see how it fits up.
Thanks
CH
 
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