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RichTes
02-03-2015, 11:58 AM
I can see a better quality 3 or six jaw scroll chuck being better (or a 5C collet chuck) but does better make any difference on a four jaw independent if you're always dialing in anyway?

Need one and thought I'd go used and cheap as I can find. Thought I'd ask if I'm missing something.

Thanks,
Rich

Old Hat
02-03-2015, 11:59 AM
No Cheap, Sir!
for several reasons.

#1, Jaws need to be well fitted in the channels. A poor fit allows kick.
......Kick means as you tighten the jaw tilts away from the part.
......This complicates 'finding truth', and grips poorly.

#2, Cheap is cheap, will wear out sooner, and will wear-in in a random fashion.
......Or in a non-uniformity, one jaw worse than another, and different still from the prior.

Used can be good, but not cheap-used.
Stick to the old faithfulls as to brand.

Carm
02-03-2015, 12:50 PM
Consider what size work you'll do...a large four jaw vs. small will have different curvature to the gripping teeth, and large might not grip the work without resort to other measures.

Old Hat has points worth noting, generally speaking if you're buying sight unseen, you're less likely to get a boat anchor with a four vs. three. I can think of mebbe 5 people that use four jaws, I'm one. I see them behind lathes covered with you name it.

If you work centers a lot, the jaw print won't matter, and it isn't hard to rectify for much the reason in your post.

Make sure it's rated for your intended RPM.

Forrest Addy
02-03-2015, 01:08 PM
With respect for the shrewd and savvy Old Hat, my take is a little different. Over-all quality in a 4 jaw is not as much of an issue as in a three jaw. So long as the jaws fit half way decent and the parts work smoothly a cheap 4 jaw is about as good as a high quality 4 jaw other things being equal over the short term. The difference will tell in years to come where better materials and heat treating are manifested by lower wear.

I say this because I've held small tenths tolerances in a-worn out Skinner far looser and sloppier than the Third World's saddest equivalent. Having four independent jaws means the beast is universally adjustable making fine, accurate work positioning possible over the chuck's entire working life. Compare with a three jaw chuck which has a finite life before heroic measures have to be taken when work-holding to close concentricity - different animals.

Jaw splay on a 4 jaw chuck is of small consequence. Most work you grip with three or four jaw serrations so you can knock the nutation out of the work's extended axis. The only time you bottom the work against the chuck face is if you have to drill from the solid with a big drill so the feed thrust doesn't push the work back in the jaws - particularly if the jaws are un-serrated.

Abom79 is a good hand with a 4 jaw chuck. Watch his videos where he puts his Monarch through its paces. He doesn't go into his technique but his MO is in line with the way I was taught back in the '60's.

Old Hat
02-03-2015, 01:14 PM
I say this because I've held small tenths tolerances in a-worn out Skinner far looser and sloppier than the Third World's saddest equivalent.
Having four independent jaws means the beast is universally adjustable making fine accurate work positioning possible
over the chuck's entire workig life whereas a three jaw chuck has a finite life before heroic measure have to be taken
when work-holding to close concentricity.


Abom79 is a good hand with a 4 jaw chuck. Watch his videos where he puts his Monarch through its paces.
He doesn't jaw much about his technique but his MO is in line with the way I was taught back in the '60's.

Agreed!
On both accounts + use of H.S hand grinds.
https://www.youtube.com/watch?v=vtS4or4lykY

If you watch Adam, see how he needs little effort to key in the jaws.
Cheap sometimes = a free moving jaw opposed by a sticky or dragging jaw.
So worn yeah OK, but cheap, may be a gamble. And a frustration.

rbregn
02-03-2015, 01:44 PM
I have a 4 jaw that came with our Summit. It won't hold a part perpendicular to the chuck to save my life. I can dial it in, move down a few inches and the part is out .005". Our last "machinist" used a 4 foot cheater bar on the tee wrench to tighten a part in it. He doesn't work here any more. I have looked and looked and I can't find anything out of whack on it. Pisses me off every time I use it. So just beware of used chucks!

Old Hat
02-03-2015, 01:57 PM
Our last "machinist" used a 4 foot cheater bar on the tee wrench to tighten a part in it. He doesn't work here any more.!

I suspect the body is now cracked in at least one place.
Hence used does NOT = abused.

I should mention for newer members, that when the Forrest posting above, (2 r's).
posts on a matter.........
Pay close attention, and give it good heed!

The other Forest (1 R) whom I affectionately refer to as Forest the Bruce,
the mad man from Texas, now in Germany it seems.... may have things to teach you as well.

Like erasing fence posts from landscapes, and building hydraulic sheep spatulas.

Forrest Addy
02-03-2015, 02:10 PM
I have a 4 jaw that came with our Summit. It won't hold a part perpendicular to the chuck to save my life. I can dial it in, move down a few inches and the part is out .005". Our last "machinist" used a 4 foot cheater bar on the tee wrench to tighten a part in it. He doesn't work here any more. I have looked and looked and I can't find anything out of whack on it. Pisses me off every time I use it. So just beware of used chucks!

I suggest you don't swallow the work. The work will always follow the trend of the jaws. Use the first few serrations. Drive them right into the metal once you've dialed in the work.

If you're nervous about grip for heavy stock removal on rough work, first machine a couple of "death grip" ribs on the end you wish to chuck. Pitch them to match the jaw serrations. Make the ribs a little larger than the serrations so when the chuck bites it moves a little metal. Better do it right the first time because once chucked the extended work axis cannot be moved.

Hat: watch Adam when he handles heavy stuff: he's a gorilla. He holds 60 lb in place with one hand while he twiddles the chuck with the other. He doesn't muscle the chuck key because tight enough requires no great effort for him.

Old Hat
02-03-2015, 02:37 PM
He's fun to watch, and his calm way of speaking is relaxing, but holds my attention.
Cool!

PStechPaul
02-03-2015, 05:44 PM
Some things to consider:

1. Self-centering chucks (most three jaw and some four jaw) use a scroll to adjust the jaws, and will have a variable amount of surface area to contact the grooves on the jaws, so the force needed to get a given tightness will also vary with work diameter.

2. The concentricity of the work depends on the precision (and condition) of the three-jaw chuck components, which may not be very good for some imported chucks.

3. An independent four jaw chuck has four adjustment screws which exert their force directly in line with the tip of the jaw, and the screws will engage fully with the teeth on the jaws over most of the adjustment range, which can provide much greater holding force than a 3-jaw.

4. The screws for a four-jaw chuck can be replaced with ones you can make, and they can be made slightly larger to compensate for wear. I made a set for a good quality but damaged Cushman 6" four jaw chuck I got for my lathe in trade for a new imported self-centering 8" four jaw that would not fit my lathe, and I really need independent jaws.

http://enginuitysystems.com/pix/tools/Chuck_Screw_1356.jpg

http://enginuitysystems.com/pix/tools/Lathe_Chuck_6in_1386.jpg


https://www.youtube.com/watch?v=fO_WpIo5gzs

rws
02-04-2015, 06:45 AM
I not only bought a cheapie 4jaw, but I bought a direct mount, D1-4. As soon as I got it, it took Eck jaw out and sawed the tow steps off of them, so I only have the main portion of the jaw left.

I did this to shorten the length through the headstock for chambering barrels. Between the backing plate and the extensions of the jaws, I saved almost two inches. Plus, I use a piece of #10 gauge copper wire between the jaws and the barrel, so there is no influence of the jaws while indicating the barrel both ends. It is job specific, but I use it for a lot more. I get in such a habit of indicating in a piece, I rarely use a 3-jaw.

J Tiers
02-04-2015, 07:55 AM
Shims always work.... sometimes work loose, but generally are capable of making a loose 4 jaw hold over more length. I've had chucks I had to shim to make them work right... it's generally the same shim in the same place, so not a huge issue, just a nuisance.

What you knock INTO truth is just as easily knocked OUT of truth, unless you take extra measures against it.