Centre round bar in a 4 jaw chuck

[DaveH]

This is how I do it, I’m not saying it is the right way or only way just how I do it.

Sit back and enjoy.

A piece of ordinary round stock ( dia) chucked in the 4 jaw. I did clean it up first with a bit of emery cloth to get rid of any “dings”
You will notice I have numbered the jaws 1, 2, 3 & 4. Just to make it easier to see.


Chucking the bar in the 4 jaw is important, try to get it centred, it really does make life easier the better it is centred to start with. Use the rings or some other reference to get the bar centred.

This initial centring is particular important when using round stock, if it is too skew it makes it difficult to move the work piece, so try to get it within about .040” / .050” before you start. Not tight just pinched some movement is required.

I started with jaw # 4. The dial gauge is adjusted to zero by moving the cross slide, the magnetic base for the dial gauge is on the cross slide. All zeroing from now on is done by the cross slide, there is no reason to touch the dial gauge bezel.


Turn the chuck 180 deg to jaw # 2. Ignore what the dial needle does, until Jaw # 2
Here the needle has moved 22 divisions. So jaw # 4 was zero, jaw #2 ( which is exactly opposite) is 22 divisions more.


Using only jaws # 2 & 4 (the two opposite ones) move the work piece so the dial needle is on 11 divisions. ie half of the total movement. It is here a delft touch comes in handy keep it light and gentle, just pinch up the work piece.
Now wouldn’t you just know it that bluudy stupid thing on the bezel gets in the way Huh. Anyway I think it is on 11 divisions. Best not to touch the bezel.
This is where we are.


Now turn the chuck to back to jaw # 4 Don’t worry where the needle ends up we are using jaw #4 as the reference so zero it using the cross slide – not using the bezel
There it is zeroed. This is where we started a few photo’s ago all we are trying to here is centre the work piece between Jaw # 4 and jaw# 2.


Lets see how far we are out now – turn the chuck to Jaw # 2
Well that’s not too bad. I division = 0.01mm = 4thenths of a thou – so we are about 1.5 div or 6 tenths of a thou. That will do for the time being.


Now we are going to centre the work piece between jaw # 1 and jaw # 3 in exactly the same way we did it for jaws 2 & 4.
Turn the chuck to jaw # 1 and set the gauge to zero using the cross slide.


Turn the chuck to jaw # 3 see what we get. Seems like last time 20 divisions, but it is not 20 divisions it is 80 divisions, notice the small needle and where it is. The needle has moved 80 divisions.


We need to move the work piece 40 divisions using only the jaws # 3 & 1 – like so.


Now back to jaw # 1 and zero.


Let us see how far out we are, move the chuck to jaw # 3 That’s not to bad ¾ of a div about 3 tenths of a thou.


Now up to this point we have not been tightening the jaws too tight just a hard pinch. Lets see what we have. Check the dial gauge for each position of the jaws.
Jaw # 4


Jaw # 2


Jaw # 1


Jaw # 3


A little bit out here and there – just remember we have no fully tightened up all the jaws yet
Here is a some videos.




There is a movement of 1 div may be 11/2 div = 6 tenths of a thou

Now remember we did not fully tighten the jaws, so now we can tighten the jaws up fully but by paying close attention the dial gauge and tightening the opposite jaws very carefully so that the difference in the dial reading is zero. Exactly how we did it above.
After fully tightening of the jaws this is what we have.




This shows a close up of the dial.




Just to recap a little

This is for round bar.
Get the bar centred quite well before you start better than 0.050” total run out.
Try not to tighten the jaws too tight just enough to hold the bar, use a gentle touch.
Only adjust opposite jaws ie # 1&3 or # 2&4

If you think you are just going round in circles getting no where, especially the last thou or two, just stop.
Carefully, carefully loosen all the jaws just a touch, gentle, then go and have a cup of tea or coffee.

Now you feel refreshed start again from the beginning – you are nearly there, you’ve done all the hard bit, just a little adjustment of jaws # 1&3 and # 2&4 and you are there – done.

It is quite a difficult process to learn and remember, practice will help,

Well that’s how I do it, go on have a try. No skill required just some patience.

DaveH

[doubleboost]

Hi
Dave
Very well shown & explained
I think your dial guage is broken on the last video clip as it has stopped moving
John

[aametalmaster]

Thats how i was taught moons ago. But now that i am lazy i use a sharpie marker or the edge of the tool bit against the part until it runs true. Unless the part has to be perfect then the indicator comes out...Bob

[DaveH]

(03-28-2012, 05:00 PM)doubleboost Wrote: Hi
Dave
I think your dial guage is broken on the last video clip as it has stopped moving
John

Nah, not broke I super glued it, easy to un-glue it, get it red hot and hit it with a 2lb hammer - all fixed again


DaveH

PS. Just in case, I'm kidding

[krv3000]

HI good post dave

[starlight_tools]

http://www.metalworkingfun.com/showthrea...08#pid2408

Here is the QCTP Dial Indicator Holder I made up to hold the dial indicator when setting up the four jaw chuck.

Drop onto QCTP, lock down and go, already set for proper height each time. and no flimsy Magnet base to fight with, or clear away chips to mount.

Walter

[lemelman]

Quite apart from the measuring needed to centre the 4-jaw, a good time-saving tip is to use two chuck keys in opposing jaws. It's quite amazing how much faster it is - so much so that if you don't have a second key it's actually worth while making one.

[DaveH]

(07-16-2012, 06:13 AM)lemelman Wrote: Quite apart from the measuring needed to centre the 4-jaw, a good time-saving tip is to use two chuck keys in opposing jaws. It's quite amazing how much faster it is - so much so that if you don't have a second key it's actually worth while making one.

That's true, makes it easier as well, once you have get the hang of it

DaveH

[sasquatch]

Good post Dave, thanks for posting this.

[DaveH]

Thanks Sasquatch

DaveH