PM 12x36

Hello everyone,

Well I finally Had a chance to do some more work,I got my taper cut out on my face plate trued and ready to go,I also have got my 4 jaw back plate trued up man it's heavy. :phew:

I am have a problem with my three jaw chuck I have trued the back plate,when I put a DI on the spindle I have 0 run out both ways same with my three jaw back plate 0 TRI.The problem comes when I bolt the 3 jaw to the back plate the body has 5 thousands run out.I put a 12 inch test bar in the chuck leave .500 out and put my di on it and I have 12 thousands run out.

I put my three jaw in the 4 jaw chuck to check the run out on the back of the chuck where it bolts to the back plate and it's only 1 thousand off .So I'm not sure where the problem is.:thinking: while the lathe is running you can clearly see the wobble in the body but the back plate has no wobble. any info would be appreciated.

Thanks JB
 
With a 3 jaw, you can mount a good rod in it, loosen the backplate just enough to hold it in place then adjust the body until the rod is zeroed -then tighten the backplate. Just another option. Of course, you could zero the body but then, you'll need to grind the jaws. Most of the time, the scrolls are not even and the jaws only center in a small range of the overall travel. Pick your poison... :)


Ray
 
Okay so basically, If I am reading this right I could loosing the back plate from the chuck and maybe put a shim between them and tighten it? Them I am guessing that this would make my jaws off or maybe not.
 
Woah, wait a minute... Are you saying the face of the chuck has runout or the body? If the face is off, something else is wrong.

... I'll be able to reply more tomorrow.


Ray


slingshot said:
Okay so basically, If I am reading this right I could loosing the back plate from the chuck and maybe put a shim between them and tighten it? Them I am guessing that this would make my jaws off or maybe not.
Click to expand...
 
No it is the body that is out. The body shows 5 thousands out of round, but my test bar is showing 12 thousands out you can clearly see the wobble. so it maybe that the jaws are off to?

I may be in the market for a new chuck very soon,not to say that this one can't be helped lol.


Thanks.
 
OK, we're on the same page...

You can, if you want, try the procedure I mentioned. It should not be that far off. Give this a try...

Put a decent shaft in the jaws, loosen the plate holding bolts just snug, put a DI on the shaft 1" from the jaws and tap the body into position such that the dial zeroes. Snug-up the plate bolts. Now put a DI on the body. Let me know the results. We'll go from there.


Ray

slingshot said:
No it is the body that is out. The body shows 5 thousands out of round, but my test bar is showing 12 thousands out you can clearly see the wobble. so it maybe that the jaws are off to?

I may be in the market for a new chuck very soon,not to say that this one can't be helped lol.


Thanks.
Click to expand...
 
BTW: Most jaws on "economy" chucks do not hold square. If you follow the procedure below, after you measure the RO on the body, the next thing I'm going to ask you is to measure the RO on the shaft about 3" further down from where you first took a measurement. You will most certainly see a difference of a 3-5 thou. If it's off way more than that, then it's time to true-up the jaws. Under the best of circumstances 3-5 thou off is normal because there's no way in heck the jaws will settle into place repeatably.

BTW: when you're tightening a shaft in the jaws, it's a good practice to wiggle the piece with your fingers to help it settle into a normal and flat position in the jaws. That's common practice and good habit as it can help the piece not get chewed-up by the jaws.


Ray
 
Okay,I did not know there was that much adjustment in the screws on the back of the face plate.Okay so here it goes,I adjusted until I got with in 4 thousands on the test bar at the jaws ( man I sure was hoping to ge it down to at least 2 thousands )I moved the di out ummm 3 three inches and I have 11 thousands run out, so the jaws must be out. I need my sponge filled with info. :whistle:


Thanks


Ray C said:
BTW: Most jaws on "economy" chucks do not hold square. If you follow the procedure below, after you measure the RO on the body, the next thing I'm going to ask you is to measure the RO on the shaft about 3" further down from where you first took a measurement. You will most certainly see a difference of a 3-5 thou. If it's off way more than that, then it's time to true-up the jaws. Under the best of circumstances 3-5 thou off is normal because there's no way in heck the jaws will settle into place repeatably.

BTW: when you're tightening a shaft in the jaws, it's a good practice to wiggle the piece with your fingers to help it settle into a normal and flat position in the jaws. That's common practice and good habit as it can help the piece not get chewed-up by the jaws.


Ray
Click to expand...
 
Tanks Ray for your help. so where is all the others on this forum? Anyway @three inches out I can get it to 0 ro with the screws lightly snugged but when I start to tightening it don't matter which one or how much pressure it draws it back to where I started,

Looks like the 4 jaw is going to go back on.
 
I am really starting to think that the chuck back that mates to the plate really,IS not true to the body & jaws.
 
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