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remove stuck back plate from lathe chuck

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bbaley

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#1
Hi,
I am having a difficult time removing a back plate from a lathe chuck.
(NOT stuck on the lathe)

It has never been removed before, and is new, likely with all the "gunk" it was shipped with.

The back plate is cheap chinesium cast iron and the chuck a small cheap-o 5" three jaw.

I don't see any other bolts/screws...
I removed the three screws on back which typically hold the back plate to chuck, as is with my other chucks/plates.

I have tried 50/50 acetone+ATF soak overnight, some tapping with dead blow, twisting/rotating won't budge.
Also I tried holding it with the back plate up and the chuck down and rapping the sides also - hoping gravity might help during the sharp blows ( as opposed to hitting face or back with I thought might act like a hammer or axe head and handle and actually drive it inward instead)

I "gently" tried tapping the bolts while they were threaded most of the way into the chuck from behind - no go, but maybe I didn't whack them hard enough in fear of trashing threads.

My assumption is it is just stuck in their with gunk or rust where the "step" is that the back plate fits into the insert on back of the chuck (at least that is how my other chucks seem to be made and attached to their back plates)

I haven't yet figured out a good way to grip and hold the back plate with enough pressure to twist it - at least not without tearing it up being cast iron....
I also couldn't yet figure out how I might use heat on the chuck that a) wouldn't also heat the back plate at the same time, and b) burn all the grease/oil into a mess that would make everything worse)

I did try some all-around, gentle heating with a blow torch in case that would loosen or help release whatever gunk, rust, etc. in there.

The back plate is threaded for a spindle (on a BS-0 dividing head)

Any ideas ?
I am stuck, literally.
 

Cooter Brown

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#2
What type of spindle is it? I have a South Bend Heavy 9 headstock that had the backplate pinned on....
 

whitmore

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#3
Hi,
I am having a difficult time removing a back plate from a lathe chuck.

The back plate is threaded for a spindle (on a BS-0 dividing head)

Any ideas ?
Grab a hex nut with the chuck, to engage a slide hammer made from threaded rod and a heavy scrap?
In a pinch, you could drill the backplate in three places, tap the holes, and use a few bolts to jack
the assembly apart (beware drilling too deep, though). A thought: if the manufacturers thought of this,
the chuck mount holes might have internal threads for inserting plugs, to use tthe threaded backplate
holes for jacking.

If there isn't one already, you might want to make an index mark so as not to rotate the
parts if/when you reassemble.
 

benmychree

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#4
Drill holes between the bolt holes to just below the mating surface, bottom tap them, and use bolts to jack the backplate off; best to somewhat relieve the threads on the ends of the bolts.
 

JimDawson

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#5
If you are sure you have all the screws out then it should come loose. If brute force isn't working, then you are not using enough of it. :grin: If there are any tapped holes in the back plate then maybe you could use those for jack screws to pop the backplate off.
 

hman

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#6
If you can make a threaded plug (threads equal to the spindle nose), you can run it into the rear of the backplate. This will give you something to bang against with a drift.

Once the chuck and backplate are apart, save the plug for later use as a thread checker when threading new backplates, etc.
 

mikey

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#7
My assumption is it is just stuck in their with gunk or rust where the "step" is that the back plate fits into the insert on back of the chuck (at least that is how my other chucks seem to be made and attached to their back plates)
I suspect you are dead on here. They probably pulled the chuck onto the back plate step with the three chuck bolts and the only way it is going to come off is with force.

Would it be possible to grab a rod in the chuck jaws that projects back towards the spindle and then thread the chuck onto your spindle. You could then put another rod through the back of the spindle and tap the one held in the chuck, hopefully without stressing the spindle bearings.
 

BaronJ

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#8
Hi Guys,

One possible way to pull the backplate off is to have a long threaded plug that will thread into the backplate from the rear and can be screwed down onto the back of the closed jaws.

Though reading the OP, makes me wonder if the chuck he is trying to get the backplate off, is one that has a threaded body, so called "Narrow Body" chuck.
 

francist

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#9
As per usual, a picture or two would be really useful here....

-frank
 

bbaley

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#10
The holes in the back plate are NOT threaded. I did try screwing in bolts almost all the way into the chuck and tapping them to see if that would pop it free but was afraid to hit them too hard fearing ruining any threads.

The suggestions about drilling three new holes and using those to screw-jack it apart might be an option . good excuse to buy some bottom taps in an appropriate size I guess...

pics (links) here for reference
https://drive.google.com/open?id=1Ko8hPttmiIRcBtJ9BP2cA_Z1C387of38
https://drive.google.com/open?id=1_X8efNnTQmFfju7j1GAxsJwI2ZWxw2_W
https://drive.google.com/open?id=1X4l24XUqsObKyBWUNLyFseUta8gV59ph
 

kd4gij

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#11
Screw it to the spindle chuck the largest piece of bar stock you have in it and tap it up and down and side to side.
 

RJSakowski

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#12
The holes in the back plate are NOT threaded. I did try screwing in bolts almost all the way into the chuck and tapping them to see if that would pop it free but was afraid to hit them too hard fearing ruining any threads.

The suggestions about drilling three new holes and using those to screw-jack it apart might be an option . good excuse to buy some bottom taps in an appropriate size I guess...

pics (links) here for reference
https://drive.google.com/open?id=1Ko8hPttmiIRcBtJ9BP2cA_Z1C387of38
https://drive.google.com/open?id=1_X8efNnTQmFfju7j1GAxsJwI2ZWxw2_W
https://drive.google.com/open?id=1X4l24XUqsObKyBWUNLyFseUta8gV59ph
Screw the chuck/backplate on the dividing head spindle
Insert a disk on the spindle face
Thread a nut on an appropriately sized bolt (as large as practical and long enough to contact the disk)
Clamp the nut in the chuck jaws
Tighten the bolt to jack the chuck off the plate

If the nut pulls out, you can put a second nut with a washer between. Place the washer behind the chuck jaws and tighten the jaws on the outside nut. Jack the chuck off the back plate
 

Cooter Brown

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#13
Clamp the back plate in a vise stick an aluminum bar in the spindle hole and beat on the chuck with a hammer..... lol

or use a pipe clamp or bar clamp to clamp it to a table.....
 

bbaley

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#14
Screw the chuck/backplate on the dividing head spindle
Insert a disk on the spindle face
Thread a nut on an appropriately sized bolt (as large as practical and long enough to contact the disk)
Clamp the nut in the chuck jaws
Tighten the bolt to jack the chuck off the plate

If the nut pulls out, you can put a second nut with a washer between. Place the washer behind the chuck jaws and tighten the jaws on the outside nut. Jack the chuck off the back plate
trying to envision this....

I like this thread because it is taking on a very "6 guys standing around staring under the hood" feel.
Also, Rube Goldberg comes to mind :)

not sure I can get a washer/nut in a place to put contact on the spindle. the ID of the spindle is basically the same as the ID of the chuck (with exception of the threads). but I'll keep trying to visualize this...
 

bbaley

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#15
If brute force isn't working, then you are not using enough of it. :grin: I
I am not afraid of brute force, just looking to determine in which manner and direction to apply it :)
 

RJSakowski

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#16
If you have a 1.5-8 tpi thread on the spindle, the disk would be about 1.25 in diameter. Something smaller than the root diameter of the threads but larger than the through hole in the spindle. Place the disk on the end of the spindle before you screw the back plate on.
I would try a 1/2" bolt and nut. The bolt should be long enough to reach the disc and still have the head sticking out 1/2" or so. It should have enough threads so there is about 1/2" of extra thread when the bolt is contacting the disk and the nut is clamped in the vise jaws. Running the bolt in will put force on the disk which will push on the spindle and since the backplate is thread on the spindle, tend to push the back plate away from the chuck. Further thinking on the nut/washer/nut idea,it won't work as described. However, a flange nut would work. The nuts from your step clamp set will do.

I don't like to pound on things like chucks. Nor do I like to use heat. They are supposed to be precision holding devices after all.
 

KBeitz

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#17
Take a 4ft long smooth rod and weld a nut on one end. Stick the nut in the chuck and clamp the other end of the rod to up in the air to something. let the chuck drop and slide down the rod. the jaws will catch the nut and stop the chuck and the face plate will keep on going...
 

SamI

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#18
I'd re-mount it to the lathe spindle and clamp the largest length of sufficiently solid stock in it I could find then wiggle. With the mechanical advantage of the stock acting as a lever you won't need to hit it with anything and you won't risk the hammer blows shocking the spindle bearings. I've done this myself using a 1 meter length of 20mm bar to remove a chuck and it worked a treat. Just be sure to protect the ways in case it suddenly drops. I used a piece of an old shelf on top of the ways.

If that doesn't work and you wanted to use a twisting force you could try using the chuck to grab on to a solid piece (I've got a ground anchor that would work perfectly for this - look around I'm sure you can find something suitably solid) and making a real simple pin spanner to go in the holes in the back of the chuck. I'd drill and tap 2 holes in the end of a length of flat bar appropriately spaced. You could turn down the end of the threads if you're worried about damaging the holes int he back plate.
 
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markba633csi

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#19
I think I'd try tapping a knife blade in between, with heat
 

682bear

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#20
If and when you ever get it off, before you put it back on, drill and tap jack screw holes in it for 'next time'...

-Bear
 
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