Author Topic: Centre round bar in a 4 jaw chuck  (Read 10247 times)

Offline DaveH

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Centre round bar in a 4 jaw chuck
« on: December 21, 2011, 08:47:11 AM »
Hi,

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 small video.


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.

DaveH
« Last Edit: December 22, 2011, 08:28:26 AM by DaveH »
(Ex Leicester, Thurmaston, Ashby De La Zouch.)

Offline DMIOM

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Re: Centre round bar in a 4 jaw chuck
« Reply #1 on: December 21, 2011, 09:18:46 AM »
Nicely shown Dave, thanks for taking the trouble.

I do similar; one tiny trick I've found is that it can help to have two chuck keys so you can loosen one jaw and push with the opposite one.

The other thing I'd add is that if you're setting up something important which has any length to it, after clocking near the jaws, just move down and re-check near the tailstock end.....

cheers / Dave

Offline Pete.

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Re: Centre round bar in a 4 jaw chuck
« Reply #2 on: December 21, 2011, 09:31:33 AM »
Nice write-up!

For a short fat piece like that I eyeball it central on the face of the chuck and hold it there with the tailstock center. Then I wind all the jaws in until they are touching and use the dial.

If I'm dialling in a round piece, I do one direction like you have but instead of re-zeroing the dial I just use the same number, since if it's 11 one way it will be 11 the other.

Offline Fredbare

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Re: Centre round bar in a 4 jaw chuck
« Reply #3 on: December 21, 2011, 02:23:57 PM »
For a newbie like me, that is an excellent write up. Many thanks. http://madmodder.net/Smileys/default/happy0065.gif

John


Offline Brass_Machine

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Re: Centre round bar in a 4 jaw chuck
« Reply #4 on: December 21, 2011, 03:25:29 PM »
Nice write up Dave. That will be very helpful to everyone!

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline AdeV

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Re: Centre round bar in a 4 jaw chuck
« Reply #5 on: December 21, 2011, 03:28:30 PM »
Nicely shown Dave, that's exactly what I do too. I can't remember if I learned it from a video, or from reading a machining site...

One thing to watch out for, especially if you've got an old & possibly abused lathe, is that your chuck jaws are actually holding straight - I've got quite a taper on my 4-jaw, so you end up with one bit rotating perfectly true, the rest is wobbling about like a spinning top! Maybe I should just buy some new chucks....
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Or: Zhengzhou, China. An even longer way from anywhere...
Skype: adev73

Offline raynerd

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Re: Centre round bar in a 4 jaw chuck
« Reply #6 on: December 21, 2011, 08:15:37 PM »
Excellent write up and by the way, I think you have the same DTI stands as I do and they are FANTASTIC and make setting up the DTI a joy rather than the struggle I use to find it!! I have since binned all my old standard magnetic ones!! OK, well I`ve not really, they are in the cupboard but you  know what I mean!!

http://www.machine-dro.co.uk/mini-magnetic-base-for-dial-gauge-indicator-holder-with-fine-adjustment.html
 

Offline DaveH

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Re: Centre round bar in a 4 jaw chuck
« Reply #7 on: December 22, 2011, 07:04:06 AM »
Hi,

Thank you all for your nice comments, and thanks to Tim for cleaning up the first mess I made of it.

 :beer:
DaveH
(Ex Leicester, Thurmaston, Ashby De La Zouch.)

Offline spuddevans

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Re: Centre round bar in a 4 jaw chuck
« Reply #8 on: December 22, 2011, 08:04:56 AM »
Hi,

Thank you all for your nice comments, and thanks to Tim for cleaning up the first mess I made of it.

 :beer:
DaveH

Well, I'm not one to refuse praise, but it wasn't me who tidied up the old one, I think it was one of the other mods :thumbup:

If anything I helped to take the first one even further off-topic  :doh: :lol:

Anyway, before I do the same on this thread, I must say thank you Dave for showing so well how you centre "stuff" in the 4jaw :bow: :bow:


Tim
Measure with a micrometer, mark with chalk, cut with an axe  -  MI0TME

Offline DaveH

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Re: Centre round bar in a 4 jaw chuck
« Reply #9 on: December 22, 2011, 08:32:32 AM »

Well, I'm not one to refuse praise, but it wasn't me who tidied up the old one, I think it was one of the other mods :thumbup:

Tim


whoops - sorry, so thanks to the mod who did the cleaning up.

 :beer:
DaveH

(Ex Leicester, Thurmaston, Ashby De La Zouch.)

Offline Anzaniste

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Re: Centre round bar in a 4 jaw chuck
« Reply #10 on: December 23, 2011, 05:40:30 AM »

APOLOGIES FOR LACK OF PHOTOS BUT MY NEW LATHE DOES NOT HAVE A FOUR JAW CHUCK MOUNTED YET. :(


I used tO do it like that but some one told me a much quicker way.


Initially you  ignore the positions of the jaws until later .

1) Center closely by eyeball as described in the original method in this thread.

2) Mount the dial gauge on the cross slide  so the face is looking up. (I have mounted a dial gauge on a piece of square bar which I put into the tool holder)

3) Wind the cross slide in until the plunger touches the work piece.

4) Wind in until the needle is pointing to your right. Then the needle will move towards you if the work piece eccentricity causes it to move towards you and vice versa. I find this helpful even though not essential.

5) Revolve the chuck watching the needle  travel making a mental note of the maximum  and minimum readings and count the divisions between min and max, divide by two and set the bezel pointer at the mid point between the max and min readings  .  ( I  find it less confusing if I move the bezel pointer to either the max or the min point and work out the mid point from there)

Now is the time to look at the jaws.

6) Rotate the chuck til one pair of jaws is at 9 o'clock and three o'clock.

7) Adjust the jaws until the dial needle corresponds with the bezel pointer. It is a fantastic speeder up of this process if you have a  a chuck key for each jaw. Additionally if the dial gauge needle is pointing to the right the needle follows the work piece so to speak and is therefore more intuitive for the beginner.

8)  Repeat for the other pair of jaws.

9)  Bingo!you will find your work piece centalised perfectly. ( You might have to do a small amount of careful adjustment as you tighten up to working tightness on the chuck jaws.


I can centre in the 4 jaw in a tehth of the time it took me to write this.




Scrooby, 1 mile south of Gods own County.