Centring in a 4-Jaw Chuck

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John Antliff

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I have recently added a 4 jaw self centreing chuck to my arsenal and over the last few months I have not fitted my 3 jaw SC chuck once. I wonder now why I didn't buy the 4 jaw SC 20 years ago, it is so versatile. If I want precision I use ER colletts or the 4 jaw independent.
 

57mm_M18

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I'm surprised (or I missed it) no-one has mentioned the adjustable three jaw. I have one on a Myford, and very nice one on my big SouthWestern. Right now my big one typically holds anything from 1/4 to 6" or so within about 3 tenths of a thou. The four jaw takes a small crane to lift on, something I care to avoid unless I really need it
Steveastrouk, I have to admit I did not give an adjustable 3-jaw a tumble. I used one once a long time ago and found it to be less universal than the independent 4 jaw we had. I put it back on the shelf where I found it. I personally like the holding capabilities of the 4-jaw. For really odd shaped work I have found the face plate is an old tried and true method. I guess it all boils down to what a person grows old on.
 

Brian Lawson

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The only time I consider swapping out the 4 jaws for the 3 jaws is IF I have more than 10 parts to make in a row and are all non critical hack jobs that do need the micrometer and the vernier caliper is plenty accurate for the job at hand.
One has consider the time and aggravation to change the chuck and put the 4 jaws back against the dialing in of the part.

On second thought, if the job requirements are so loose, i may dial in the first part and then use jaws 1 and 2 leaving 3 and four untouched.
 

Brian Lawson

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I just use my 4-Jaw SCROLL chuck for more than one offs. Works a treat.
Brian Lawson
 

Noel Gordon

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Sorry Guys,
I meant to say that I had only used my 3 jaw chuck 3 or 4 times in 20 plus years.
As a pro machinist I would REALLY look down on the practice of using 2 chuck keys as very dangerous and if one of my apprentices did this I would have him sweeping the floor for a week so he had time to reflect on a bad practice..
I have almost finished my 5 cyl radial.. but I made many many changes to drawings.
 

tornitore45

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A self centering chuck has a scroll and all associated errors. It does not matter how many jaws. A 4 jaws self centering is no better at centering square or round stock than a 3 jaw self centering is at centering Hex or round stock.
 

goldstar31

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Both the 3 and the 4 jaw SC chucks are ideal for when little accuracy is needed. I have both or rather lots of both for different purposes - and in the case of the 4 jaw, the square material might not be that square either.

But =, but I have3 sizes of faceplate for my Myfords, and a faceplate for my Sieg together with 2 sizes of independent chucks for the Myfords and one for the Sieg but and but again, I have three sets of collets and the necessary conversion attachments to swop not only stuff from between both lathes- metric and imperial, but onto the mill drill and I can interchange all the chucks etc onto my several tool and cutter grinders as well as my miscellany of dividing heads and rotary tables.

I paid very little for this 'Pandora's Box' . A little independent and self centred thought worked wonders for me !
 

clockworkcheval

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The method Joe Pieczynski demonstrated with shims and a rubberband is new to me and really nice. The only thing different I would do is reading not top or bottom but far side or nearby side because if you use two keys you handle the far and close jaw, not the the top and bottom yaws.
 

Gordon

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I have have had the most problems with centering a square or even worse a rectangular piece. You have to back off the indicator in order to rotate the piece and unless the piece is perfectly horizontal the reading is off. The use of shims and rubber bands looks like a good solution to that. In the past I have put a piece in the mill and center drilled it so I can use an indicator against a wiggler or double pointed bar in the tail stock.
 

Brian Lawson

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A self centering chuck has a scroll and all associated errors. It does not matter how many jaws. A 4 jaws self centering is no better at centering square or round stock than a 3 jaw self centering is at centering Hex or round stock.
Hey again,
If this was directed to my submission, I think I may have misled you. My 4 jaw chuck with scroll has INDEPENDENT ADJUSTMENT OF THE FOUR JAWS, and the scroll feature merely allows release and re-place new stock super quick. Where zero "runout" is required I usually do a DTI check to assure it is either offset as required or centered each time, but so far it has never been "out".
Brian Lawson
 

57mm_M18

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Sorry Guys,
I meant to say that I had only used my 3 jaw chuck 3 or 4 times in 20 plus years.
As a pro machinist I would REALLY look down on the practice of using 2 chuck keys as very dangerous and if one of my apprentices did this I would have him sweeping the floor for a week so he had time to reflect on a bad practice..
I have almost finished my 5 cyl radial.. but I made many many changes to drawings.
I agree with Mr. Gordon on the issue of using more than one chuck key. I can speak from personal experience that his take on safety is valid. I was an apprentice when I learned that leaving the key in the chuck was a cardinal sin. If your hand was removed from the key it had better be setting the key down on the bench or place it was kept on the lathe. It was not tolerated even for a moment to leave it alone in the chuck. That said, I have never found it necessary to use more than one key at a time to dial in a piece of work. I personally feel there is marginal return on using more than one key. Sorta goes along with my feeling of multitasking. Thank you Noel G for your take on using two chuck keys.
 

ALEX1952

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If your 3 jaw is good and not worn or abused the use of a 4 jaw is in my view unnecessary on round bar. if you are turning several diameters on one end and not taking it out of the chuck then the finished work will be bang on concentric, if not you have a serious problem with your tooling. Even when swapping ends providing your tolerances allow you will be okay using a 3 jaw, the problem in this hobby is an awful lot of drawing are un-toleranced therefore people try for perfection, which although desirable is for the most part not required. Four jaw chucks are for irregular shaped work or of you do not have a 3 jaw.
Self centering chucks are not just for production, walk in any tool room and if its round it will be a 3 jaw being used even on cylindrical grinders if the tolerances on the drawing allow it. As for using 2 chuck keys whoever thought that up wants hanging it is so dangerous, it is easy to forget one key let alone exacerbating the problem by adding another. And my question is why would you want to lean over a machine to do this especially if its of any size.
 

mcostello

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Gordon, You don't have to wind the indicator back each time, just put the indicator on the tool post and move it. It's easier to move the carriage. Then rock the chuck to find the low spot, or rock the chuck to indicate off the corners.
 

kuhncw

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Sorry Guys,
I meant to say that I had only used my 3 jaw chuck 3 or 4 times in 20 plus years.
As a pro machinist I would REALLY look down on the practice of using 2 chuck keys as very dangerous and if one of my apprentices did this I would have him sweeping the floor for a week so he had time to reflect on a bad practice..
I have almost finished my 5 cyl radial.. but I made many many changes to drawings.

Noel, why do you consider using two chuck keys dangerous?

Chuck
 

Cogsy

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I'm wondering why exactly using two chuck keys is dangerous as well?

My procedure is to indicate the part and note how much the piece needs to move. So if it's 20 thou higher on one side it needs to move down half that. With the indicator still in place I insert a chuck key into each side and loosen one as I tighten the other until I've moved my indicated 10 thou. As I nip up each side i can keep it 'centered' on the zero. At no point does my hand ever leave either chuck key while they are engaged with the chuck. Now this wouldn't work for a huge lathe that needs two hands on a single chuck key, but a hobby lathe in the home shop is a different beast.

Alex1952 - you said "As for using 2 chuck keys whoever thought that up wants hanging it is so dangerous, it is easy to forget one key let alone exacerbating the problem by adding another". To me this suggests you let go of the chuck key while it's engaged with the chuck - this is extremely dangerous and I while I wouldn't suggest hanging as a punishment for your behaviour I do think you should change this practice. As I said earlier, I never take my hand off the chuck key while it's in the chuck so I have NEVER had a forgotten chuck key incident.
 

goldstar31

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I'm wondering why exactly using two chuck keys is dangerous as well?


Again, O would question the logic of what seems to be a form of bullying young apprentices in being forced to a menial floor sweeping task and consequently actually not learning anything.

My view, naturally

Norm
 

Gordon

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