4 Jaw Independant Issue

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slingshot

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I have finally got my lathe down to .002 taper in 7'' after leveling up the ways with a precision level. Now i need to move the headstock (which is adjustable) pm 12x36 to correct the taper.

Before I do that i really need to use my independent four jaw but i am having a issue with it.I used to stick a piece of known good stock in it 7'' out put a di on it toward the T/S end get it true run the di to the chuck end dead on. Now I have two independent 4 jaws with the same back plate for both.My old 4 jaw i can put a di on a known good piece and it has .120 run out.

Now I just got my new independent 4 jaw same as the old one boted it up put a 7'' piece of stock run the di to the t/s true it up run it to the chuck and have .030 run out/can someone tell me what is going on here.the back plate is running true
 
you might think twice about moving the headstock unless you are positive that it's going to give you the desired result.
your jaws may be ever so slightly out of square compounded by a shaft that might not be 100% straight at 7" too.
you may want to try an experiment,
center drill the rod and mount between centers, (a drive dog is not necessary , you are only checking alignment)
and give a run down the shaft with the indicator and see if there is an issue there.
if your alignment checks out between centers, you'll know for sure it's not Headstock to Tailstock alignment.
you'll have more info at that point to make further determinations.
 
Ulma Doctor said:
you might think twice about moving the headstock unless you are positive that it's going to give you the desired result.
your jaws may be ever so slightly out of square compounded by a shaft that might not be 100% straight at 7" too.
you may want to try an experiment,
center drill the rod and mount between centers, (a drive dog is not necessary , you are only checking alignment)
and give a run down the shaft with the indicator and see if there is an issue there.
if your alignment checks out between centers, you'll know for sure it's not Headstock to Tailstock alignment.
you'll have more info at that point to make further determinations.
Click to expand...


Just wanted to say it is a test bar that i am using and i am not interested in tailstock alignment at this point
 
You really have to check things on your lathe in a certain order.

Like UlmaDoctor said, your jaws may be ground funny and then holding the workpiece out skew.

Once you start moving the headstock around, you are getting into a realm of machine tool alignment that you need special tools or experience to be able to easily reverse if you are wrong. I am pretty sure, with patience, a home shop guy can do it, but it takes a lot of patience! Much more than aligning a tailstock!

I know you aren't interested in the tailstock right now, but I am quite sure it has to come first.

Many people grind out their lathe chuck jaws with a Dremel attached to the Toolpost, driven by the carriage. Anyone think this is a bad idea for his next step?

Bernie


Sent from my iPad using Tapatalk
 
itsme_Bernie said:
You really have to check things on your lathe in a certain order.

Like UlmaDoctor said, your jaws may be ground funny and then holding the workpiece out skew.

Once you start moving the headstock around, you are getting into a realm of machine tool alignment that you need special tools or experience to be able to easily reverse if you are wrong. I am pretty sure, with patience, a home shop guy can do it, but it takes a lot of patience! Much more than aligning a tailstock!

I know you aren't interested in the tailstock right now, but I am quite sure it has to come first.

Many people grind out their lathe chuck jaws with a Dremel attached to the Toolpost, driven by the carriage. Anyone think this is a bad idea for his next step?

Bernie


Sent from my iPad using Tapatalk
Click to expand...
I'd want to check the alignment with a test bar in a collet.
 
John Hasler said:
I'd want to check the alignment with a test bar in a collet.
Click to expand...
I have been around and worked in machine shops all my life just not with lathes .I have a precision level and have the ways perfect i have .002 taper I have tried twisting the ways to get the taper out but no change. so i am pretty sure the headstock needs moving.But right now i am more concerned with the 4 jaw chuck i can't fig out what is going on with this thing
 
It really sounds like the jaw centerline is not perpendicular to the chuck back. I had the same problem on a cheap 4-jaw and fixed it by chucking up on a shaft, and machining the back of the chuck to the jaws.
 
slingshot said:
Just wanted to say it is a test bar that i am using and i am not interested in tailstock alignment at this point
Click to expand...

Taking this extra step will save you a lot of headaches later on, but you are free to do as you wish.
good luck
 
John Hasler said:
I'd want to check the alignment with a test bar in a collet.
Click to expand...

That will be an easy way to check the alignment before the head comes off.

And handy if you do want to adjust the head as you would probably need a test bar in whilst you were adjusting.

Stuart
 
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