chucks

[crabsign69]

how do i true up a chuck. my lathe chuck i just checked is not true i put a known straight bar in there and check it and its 20 thoyu out so i asume i need to bore it true (the jaws) so how do i go about doing this. im thinking a piece of pipe the out side diamiter of the chuck larger in size so i could put presure on it so i could then procede to bore the jaws out a littlee..  is this right or wrong.  pics would be great if u got them . if not then ill just put the four jaw on and learn to love it. (probably better anyway)    

[Rob.Wilson]

Hi crabsign69

Any chance we could see some photos of how you are checking the chuck ,,, the run out could be due to the chuck mounting and not the jaws ,, if it is the jaws ,, and they are the standard jaws (not soft jaws ) , then you will have a hard job boring them ,,, you will need to grind them with a tool post grinder ( DREMEL  ). also you will have to make a small fixture so that the jaws are loaded in the correct way .


Rob

[crabsign69]

im using a spindle from a micrometer for the test bar so that should be perfect. i tried a diferent bar and it was the same results heres the pics they may be large

[Bogstandard]

Crabsign,

1. It is a waste of time measuring the outside of the chuck, they can be almost any shape.

2. It is a waste of time measuring the outside jaws as you have them, they can be in almost any position without being clamped to something. Put a large bar in there and clock off the bar near to the chuck.

3. I would suggest you put your inside jaws into the chuck. Make sure you have the right jaw in the right slot, they should be numbered, and insert them one after another starting with #1. THEN put a piece of ground stock, or a milling cutter into the jaws, and clock off that. Only then should you mention the results.

Anything up to 0.003" (3 thou) runout is perfectly acceptable on a standard sort of 3 jaw.


Bogs

[Rob.Wilson]

Try the other set of jaws ,, if the reading it the same ,,, looks like the chuck register is at fault .



Rob

[crabsign69]

the others jaws are perfect they are out by 001 002.   so these are not good and those jaws are clamped tight and just for shits and giggles i put the test bar i was using in the mill its perfect  stays on 000 so those other jaws are whats bad now i need to know how to fix it with what i have on hand. 

[Rob.Wilson]

What do you have at hand ? 


Looks like you will have to grind them true ,,,,, Grind the outer two steps first with the chuck gripping your bar ,,, then when done remove the bar and fit a ring to one of the two outer steps ,, some thing like a bearing outer ,, so your grinding spindle can pass through the centre and grind the inner step .

Cover your lathe ways

Then you will have to strip the chuck and give it a good clean

Rob

[Bogstandard]

One word of warning about grinding chuck jaws.

It will only be perfectly accurate in exactly the same position and loading forces it was ground in. Somewhere else on the scroll and under a different loading, it can be just as bad as before.

If you are desperate for accurate outside jaws, buy yourself a set of soft jaws to fit your chuck and turn them to fit the job using the correct procedures.


Bogs

[crabsign69]

One word of warning about grinding chuck jaws.

It will only be perfectly accurate in exactly the same position and loading forces it was ground in. Somewhere else on the scroll and under a different loading, it can be just as bad as before.

If you are desperate for accurate outside jaws, buy yourself a set of soft jaws to fit your chuck and turn them to fit the job using the correct procedures.


Bogs

hummm ill try and set the chuck at different loads and see if its the same. funny the other set of jaws is damed neer perfect .
ill play with it some more i got a drimel tool just have to make a holder for it. i hardly use these jaws but i did not want to change them out  cause i was goting to use them again for a round thingy im working on but needed to  turn a .250 inch  bar down a little thats when i found the runout
thanks guys