Wobbly chuck, how to diagnose?

[homebrewed]

The fact that your 4-jaw installs properly indicates that your spindle threads are OK, and the registration surface on your spindle is OK. But maybe the threaded portion on your 3-jaw has a problem. Maybe some embedded swarf or debris.

If you don't find a problem with the threads try bluing the back of your problem chuck, install it, take it off, and look for where the bluing has been rubbed off. Maybe there's a high point, or some embedded swarf. Or you could do the reverse, blue up the registration surface on the spindle and look to see where it's been transferred to the chuck. I also have used old-fashioned carbon paper for that (less messy if the situation permits its use). Look for scratches on the registration surfaces that might be due to debris.

Some good eyeballing is advised.

 

[AlexPeel159]

took the chuck apart. Back plate has had 4 holes drilled and tapped in it 3 of which went almost all the way through and dimpled the back side. The dimple seems to be about 26 thou and the mating face on the chuck has a recess which is about 27-28 thou. Makes sense because it looks like the holes were made with the chuck still mounted as one broke though fully and I see a drill mark on the back.

All that being said that does not directly impact the faceplate not registering fully. The registration face lies completely flat on a surface plate. Not sure what else to measure or check though because it seems like the issue would be between the orthagonality of the thread seating to the registration face. I checked the threads with a pointed hook and there were no chips in the grooves. There is some chipping at the thread peaks but it seems to be clean breaks as I can’t feel anything grabbing with the hook. Here are some pics showing the plate on the spindle (note thin gap at bottom) and some of the plate itself.

 

[woodchucker]

Take some facing cuts on the backplate. Clean it up. That will for sure give you a flat plate, no run out . You didn't measure the run out while just the back plate was managed did you?
That's important. You want to know what your starting with. Also cleanup the register the chuck mounts onto the backplate. You don't want it too tight that you can't bump the chuck into it's best position.



So far it looks like it can be fixed up.
What is pic 5614? I am confused by that pic. I can't tell what it is? Is that another plate that mounts on the backplate to the chuck? Having trouble with it.

 

[Jim F]

Put the backplate on backwards and lightly face the registration surface and then see what you have.

 

[AlexPeel159]

Take some facing cuts on the backplate. Clean it up. That will for sure give you a flat plate, no run out . You didn't measure the run out while just the back plate was managed did you?
That's important. You want to know what your starting with. Also cleanup the register the chuck mounts onto the backplate. You don't want it too tight that you can't bump the chuck into it's best position.



So far it looks like it can be fixed up.
What is pic 5614? I am confused by that pic. I can't tell what it is? Is that another plate that mounts on the backplate to the chuck? Having trouble with it.

Pic 5614 is the back half of the chuck, which splits in two around the scroll. That's the face that mounts to the backplate.

With the faceplate fully threaded on I am getting a +13.5 thou high spot almost the direct opposite side to the low spot. Seems like a smooth transition between the two so no additional warping or anything.

What order should I do the facing in, the spindle registration first and then the other side? I am a complete novice and have not used the lathe at all to this point so any advice would be worth while.

Do I reverse thread the faceplate on the spindle and do a facing cut for the spindle registration and then flip it and assuming I have full seating with the newly faced registration surface reface the chuck mating side?

 

[AlexPeel159]

Put the backplate on backwards and lightly face the registration surface and then see what you have.

Ok I can do that. Think I will give do some practice facing first with my 4 jaw and some scrap steel.

 

[Jim F]

Also, pic 5613 seems to show a chip embedded in the plate.
that could have cause the plate to bend,

 

[woodchucker]

Put the backplate on backwards and lightly face the registration surface and then see what you have.

Why backwards? I face my backplate by putting it on as it would normally be used.

First face the face, use light cuts. Use power crossfeed to do most of the facing, at the end go manual .
You should be less than 1/2 a thou ideally 0 run out on the face. Then do the registration boss for the chuck.

 

[woodchucker]

that's the spindle where the gap is.
that's a problem
is that where the swarf is stuck in there? mark the plate remove and see.
there should not be a gap there.

 

[yota]

that looks like a huge gap.