Newsgroups: rec.crafts.metalworking
Subject: Re: 4 jaw ind. chuck
From: jmorton@euler.Berkeley.EDU (John Morton)
Date: Fri, 19 Feb 1993 19:59:06 GMT

In article <ENDERS.93Feb19113200@warp6.cs.misu.NoDak.edu> enders@warp6.cs.misu.NoDak.edu (Todd Enders A262 857-3018) writes:
>
>In article <1993Feb18.183024.3669@pasteur.Berkeley.EDU> jmorton@euler.Berkeley.EDU (John Morton) writes:
>
>>On the other hand, with a dial indicator and some patience, you
>>can make a 4-jaw do almost anything, slowly.
>
>     Anybody have any helpful hints for setting up with a 4-jaw?  Seems I
>spend an inordinate amount of time fiddling with it sometimes, while other
>times I get set up and going relatively quickly.  Or am I just lucky
>sometimes? :-)
 
You don't say what it is you're doing.  For the general case of chucking
a cylindrical part so that it is true to a pre-existing face and outer
diameter:
 
	- use a tape or scale to set the jaws to their approximate
	locations
 
	- pad the jaws, if the O.D. is a finished surface; I prefer
	.05" copper strips, long enough to wrap around the sides
	of the jaw
 
	- insert the part and wrench the jaws loosely into contact
 
	- here it depends on circumstances:
 
		- if you're working on all the surfaces, just
		put it where it looks right; tighten and you're done.
 
		- if you want to face parallel to the back surface,
		you can speed things up by tapping the part down
		to the jaw flats with a lead hammer.  Or against
		the chuck face, if the jaws are reversed.  Or
		against some parallels or toolbits, if you want
		to build the part away from the jaws to have
		access to more of it; these are removed before
		you spin up the machine :-).
 
		- I also keep a selection of sets of 4 aluminum
		bits, 1/8, 1/4, 1/2" thick, etc. which I attach
		with double-sided sticky tape to the jaw flats,
		to put the part just where I want it.
 
	- attach the indicator base to the compound, bring the
	stylus near the face and see how it runs.  Tap with the
	soft hammer to correct obvious runout.  If you are already
	against the jaws or shims when indicating any face,
	you will have to begin by tapping or prying the part
	out slightly.
 
	- bring the stylus to contact and repeat until you are
	within .001 or .002".
 
	- move the indicator to the O.D., eyeball the runout,
	then use the stylus to get within .001"
 
	- move the indicator and check the face again
 
	- usually 2 or 3 interations of this procedure will
	true the part
 
	- if it is important that the back be parallel to
	your facing cuts, you can indicate that instead; you
	will have to withdraw the cross slide each time you
	check a spot on the back face, to clear the jaws
	as they turn
 
 
John Morton					University of California
jmorton@euler.berkeley.edu			Mechanical Engineering
{decvax,cbosgd}!ucbvax!euler!jmorton		Machine Shop

Newsgroups: rec.crafts.metalworking
Subject: Re: Centering material in a 4 jaw chuck
From: jmorton@euler.Berkeley.EDU (John Morton)
Date: Thu, 4 Mar 1993 15:16:07 GMT

In article <1n2mg7INN6tj@news.cerf.net> jonesm@nic.cerf.net (Matthew Jones) writes:
>When I am centering a a rod in my 4 jaw chuck (My 3 jaw never centers
>anything and is basically useless.) I am finding that I should not tighten
>the jaws down but keep the jaws as "loose" as possible at first and gradually
>tighten the jaws more on the material as I get close to the proper center and
>only tighten the jaws fully when it is fully centered.
>
>Is this a good strategy?
 
Pretty much.  When you're roughing it in, you loosen jaw 4 when you tighten
jaw 2.  If 1 and 3 are in contact, you can move the part over a long ways
as 2 pushes on it, without dropping it.  This method is used up to within
a couple of thousandths, at which time you circle around just pushing on
the high spots, not loosening anything.  If you find perfect center before
the jaws are tight, just circle around again.
 
John Morton					University of California
jmorton@euler.berkeley.edu			Mechanical Engineering
{decvax,cbosgd}!ucbvax!euler!jmorton		Machine Shop

Newsgroups: rec.crafts.metalworking
Subject: Re: 3-jaw vs 4-jaw (was too smart, too long)
From: Robert Bastow <"teenut"@ hotmail.com>
Date: Fri, 03 Dec 1999 07:48:57 GMT

It is only you John ;^)

A four jaw chuck has WAY more gripping power than any three jaw.  

Tweaking out the last thou or so of runnout without ensuring that all the jaws
have close to the same "tightness" is simply asking for the job to go off center
during machining..especially if there are any interrupted cuts involved.

It just takes a little extra patience and practice to get it right..but it does
help to treat the jaws as opposing pairs.  

If you have to back off say number two jaw to twitch number four..go back then
to number two and re-tighten it to the same torque as no. four.  Then do the
same thing with numbers one and three.

8^)

teenut

John Hofstad-Parkhill wrote:
> 
> Chuck:
> 
> >In general, 3 jaw chucks do not have the gripping power of 4 jaw chucks
> 
> I find the opposite is true, and I'm shooting this out to see if it's only
> me. What happens is that I'm so focused on centering the work that I forget
> that I also need to hold it securely. Squeezing the last .001" of runout
> turns out to be an exercise in adjusting _one_ jaw's torque ever so
> slightly. Once I get it set, I'm loathe to make any further adjustments.

Newsgroups: rec.crafts.metalworking
Subject: Re: Centering square stock
From: Robert Bastow <Tubal_cain@hotmail.com>
Date: Thu, 28 Jan 1999 18:59:21 GMT

The quick way to get PDC (pretty damn close) is to first set a ROUND bar of the
same dimension to run true in your four jaw.  The back off ONLY two ADJACENT
jaws to remove it.  Put in your square piece and retigten ONLY the aforsaid two
jaws.  Most times it will be close enough for "Govmint" work.

Quick tip for setting work true in a 4 jaw in two revolutions!

(I learned this, setting up roll turning lathes with 108" swing and a jogging
speed of two to four MINUTES per revolution.)

1. Revolve the work through one revolution..noting the TOTAL swing of the
indicator needle. Bring the spindle to a halt at the MIDPOINT of the swing and
ZERO the dial to the needle.

2. Revolve spindle to bring jaw one to be "on the plunger".  Adjust jaw one and
jaw three to ZERO the needle again.

3 Rotate 1/4 turn and adjust jaws two and four to re-zero needle.

Job is done!

Robert Bastow

Felice Luftschein & Nicholas Carter wrote:
 
> On 28 Jan 1999 14:10:02 GMT, fidln1@aol.com (Fidln1) wrote:
> 
> >    Recently when trying to center a piece of 1 inch square stock in a 4 jaw
> >chuck what had seemed like a simple chore turned out not to be. If I set the
> >indicator on the flats I would have to move the indicator (mounted in the
> >toolpst) back out of the way with the crosslide to turn the work to opposite
> >flat then crosslide back in to the cross- dial setting.
> If you take up all the backlash in the slide screw each time, this
> will work. It helps if you can zero the crosslide dial.
> > I tried making a center mark on the end of the bar and
> >eyeballing it with the tailstock center which got that end pretty close but
> >when I went back and indicated close to the chuck that was off about 20 thou.
> For this method, use a wiggler, with an indicator bearing on the
> wiggler shank.
> This is a hard job.