# Centreing a 4 jaw chuck



## firebird (May 17, 2009)

Hi

I'm sure this topic has had a few visits already but I thought I would show you how I did it. I need to be able to hold some 1/2 inch square stock accurately in the 4 jaw chuck. I have used my 4 jaw on many occasions but never before needed to set up as accurately as this. A search on this forum soon gave me the info I needed, thanks Marv. (Unfortunately I can't find the link again, if your watching Marv could you oblige). This is one of those occasions where if you have the kit and its quick and easy to use the job is simple. If you don't have the kit then (like me) you try to get it right by eye disaster will follow including a waste of materials. So I spent a couple of hours this morning putting together a bit of kit that will make life easier. 

First job was to hold a piece of silver steel (drill rod) in a collet (not the 3 jaw chuck, they are not accurate enough) and turn a point on one end. I set the top slide over 30 degrees to do this. Then turn the rod over and centre drill the other end.







The rest of the bits came from the scrap box. A post is mounted onto the cross slide and held with a 'T' nut and stud. A bracket comes off of this onto which is fixed the DTI. The workpiece I held vertically in the mill vice and using an edge finder to locate the dead centre and centre drilled it. With the workpiece in the 4 jaw chuck the pointed bar is placed into the centre drilled hole and held there with a revolving centre in the tail stock. Wind the cross slide towards you while holding the DTI plunger clear. Whien it is dirictly above the rod release the plunger. Now by rotating the chuck by hand you can see the DTI move and adjust the chuck jaws accordingly. Simples. Heres a few pics of the set up.































A bit of video.





Now that I have spent the time making this kit, using the 4 jaw should be a pleasure not a chore.

Hope this helps.

Cheers

Rich


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## Metal Butcher (May 17, 2009)

Thank you! A very good demo of how to get the job done accurately. I don't have a four jaw but this is an important set up procedure that every one should now how to do including me.

I use a dial indicator mounted on a magnetic base to check run out on round bar stock mounted in a 3 jaw scroll chuck, and shim as required.

Question; How would accurate centering be accomplished by those that don't own a mill?

Thanks.-MB


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## mklotz (May 17, 2009)

Rich,

I'm not sure to which of my posts you refer, but this one addresses the subject

http://www.homemodelenginemachinist.com/index.php?topic=3859.msg39487#msg39487

and my use of what the old-timers call a "pump center". 

Rather than mounting the DI vertically, I prefer to have mine horizontal. I discovered long ago that centering is faster if one uses two chuck keys and adjusts the two horizontal jaws simultaneously. Having the DI mounted horizontally allows one to directly observe the result of said adjustment. (I've published a write-up of this procedure several times on this forum. If anyone wants a copy, contact me.)

Another hint is to make a flat, button tip for the DI, thus making it unnecessary to center the DI axis exactly on the lathe axis.


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## firebird (May 17, 2009)

Hi

MB, thats a question I can't answer but I'm sure someone will.

Thanks Marv

Cheers

Rich


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## tel (May 17, 2009)

Metal Butcher  said:
			
		

> Question; How would accurate centering be accomplished by those that don't own a mill?
> 
> Thanks.-MB



By indicating on the sides of the stock, rather than using the pump centre. I made up a dial indicator hold from *here* and it's been well worth every second spent building it.


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## mklotz (May 17, 2009)

> How would accurate centering be accomplished by those that don't own a mill?



...Or just attaching a sheet metal "flapper" to your DI

http://www.homemodelenginemachinist.com/index.php?topic=3820.msg39062#msg39062


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## tel (May 18, 2009)

Yeah, I do like your 'flapper' idea Marv - going to try it at the first opportunity.


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