# Switching over to D1-4  Chuck back plates



## COMachinist (Jul 1, 2018)

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


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## Bob Korves (Jul 1, 2018)

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...


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## mksj (Jul 2, 2018)

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.


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## Tozguy (Jul 2, 2018)

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.


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## Ray C (Jul 2, 2018)

Check this thread and look at post #14.   https://www.hobby-machinist.com/threads/ordered-a-6-jaw-lathe-chuck.65884/


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## Bob Korves (Jul 2, 2018)

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.


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.


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## Tozguy (Jul 2, 2018)

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.


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## Bob Korves (Jul 2, 2018)

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.


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.


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## COMachinist (Jul 2, 2018)

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.


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


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## COMachinist (Jul 2, 2018)

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.


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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## Tozguy (Jul 3, 2018)

CH, as mksj mentions in post no. 3, could you take a skim cut on the 'loose' backplate to improve the fit?


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## mksj (Jul 3, 2018)

If you are talking about the fit of the chuck to the back plate of the zero-set registration these will fit loosely with about 0.005" clearance to allow the zero-set screws to have enough adjustment to true up the chuck. In addition, some people leave 1-2 thousandth clearance between the registration step and the chuck body in non-zero-set (Set-Tru) chucks to allow one to tap the chuck into final alignment before tightening the mounting bolts. As mentioned, I mount the backplate to the lathe and check it for any runout. With inexpensive backplates I typically need to take both a skim and a registration cut, I would use either sharp HSS or ground edge insert to get a clean cut.

The Gator backplates run around $160 for their 8" (Ajax Industries), but are very well finished. Shar's and Grizzly Tools sell them for less but sometimes get you in the shipping rates.


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## COMachinist (Jul 3, 2018)

Tozguy said:


> CH, as mksj mentions in post no. 3, could you take a skim cut on the 'loose' backplate to improve the fit?


I guess i was not clear about fitting. The back plate seat all the way to the face with just a light pressure, like the tapper is oversize. The back plate the came with the lathe is tighter and needs help from the cam locks to fit with no gap at the spindle back plate matting surface. The back plate from Shars just about falls off when the cam locks are opened, and back plate just easily slides off the spindle.
Does that make sense?
Thanks for the sujestion.
CH


mksj said:


> If you are talking about the fit of the chuck to the back plate of the zero-set registration these will fit loosely with about 0.005" clearance to allow the zero-set screws to have enough adjustment to true up the chuck. In addition, some people leave 1-2 thousandth clearance between the registration step and the chuck body in non-zero-set (Set-Tru) chucks to allow one to tap the chuck into final alignment before tightening the mounting bolts. As mentioned, I mount the backplate to the lathe and check it for any runout. With inexpensive backplates I typically need to take both a skim and a registration cut, I would use either sharp HSS or ground edge insert to get a clean cut.
> 
> The Gator backplates run around $160 for their 8" (Ajax Industries), but are very well finished. Shar's and Grizzly Tools sell them for less but sometimes get you in the shipping rates.


Hi Mark 
I went to Ajax Ind. site didn’t see any D1-4 back plates for 8” chucks for under $300 +. I searched for a Gator D1-4 back plate but only Bison was listed. Do you have a direct link to the Gator back plate?
Thank CH


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## mksj (Jul 3, 2018)

I would recommend calling Ajax Industries, I can't find anything on their site and for that matter Google searches with part numbers are useless these days so I am back to calling around. You may need to get the semi-finished and cut the registration, I would check the dimensions against your chuck.
FLD-200D4: Machined for Plain Back Scroll
http://www.gts-tools.com/catalog/products.php?id=FLD-200D4&cid=d-gab-a-pbsc

FL-200D4: Semi-Finished for Plain Back Independent & Scroll Chucks
http://www.gts-tools.com/catalog/products.php?id=FL-200D4&cid=d-gab-a-pbisc

All my backplates easily come off the spindle nose, no tapping or gyrations. As long as it goes on/off and you can repeat the TIR to be ~same then I would be OK. Also, one always needs to carefully clean both mating surfaced before mounting. I lightly torques the three D pins and then go around again to tighten fully.


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## Tozguy (Jul 3, 2018)

COMachinist said:


> I guess i was not clear about fitting. The back plate seat all the way to the face with just a light pressure, like the tapper is oversize. The back plate from Shars just about falls off when the cam locks are opened, and back plate just easily slides off the spindle.



If the face of the backplate is cut slightly (faced) then the taper will go a bit deeper and fit tighter on the spindle.

Maybe that's what Mark is referring to when he writes ''With inexpensive backplates I typically need to take both a skim and a registration cut''


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## COMachinist (Jul 4, 2018)

ok I think I understand now I got the lathe on the stand today and this is what it looks like when just push the back plate  on.
Thanks for all the help.
CH


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## COMachinist (Jul 11, 2018)

Well I did a skim cut on the back plates and mounted the chucks the the spindle and back plates have less than a 10th TIR. When I mount the scroll chucks they are under the .002 which I guess is not bad for cheeper chucks  my Bison 3 jaw is around 1.5 thou that works for me, i have a new D1-4 independant 4 jaw, I’m going to do a check on head stock alignment using the Rollie’s Dad methood then I cant get serious.
Thanks all
CH


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