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Thread: I need a 3 jaw chuck
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7th Feb 2010, 04:44 PM #1Boilermaker
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I need a 3 jaw chuck
The chuck that came with my lathe is really crap. Best I can get is 0.3mm tir so I want to buy another one. Yes I know I can use the 4 jaw when I need to be accurate, but the 3 jaw on the lathe at work (pratt bernard) has about 0.01mm tir.
Been looking at the Fuerda that H&F sell. I know they are still chinese but their website seems to focus on their quality goals etc - which is a lot different to a lot of the manufacturers.
I would be happy with <0.03mm tir if I can get it. Is this a reasonable goal in a $250 chuck? They do have a adjustable 3 jaw that can get 0.001mm tir but it is also $770 so a little out of the price range.
Anyone got any thoughts on this? Needs to be a D1-4 camlock. Would look at used but I would imagine the majority of chucks out there would be 6 pin rather than 3 though...
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7th Feb 2010, 04:54 PM #2Most Valued Member
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Is the Chuck itself running out (the Body) or is it the jaws.
If you decide to buy a chuck why not use your existing cam locks and make your own backing plate.
You may even find that you will be able to machine the existing back plate to suit a new chuck.
I think that finding a mass produced chuck of chinese origin that is around.03 might be pushing it but you should be able to find something around .05.
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7th Feb 2010, 05:22 PM #3Boilermaker
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Haven't checked but I assume its the jaws/scroll. The nose of the lathe spindle doesn't move the indicator by anything much at all, but I haven't checked the chuck body.
To machine a new backplate would also be a solution to the current chuck run out yes? There doesn't seem to be a backplate though, the camlock pins are threaded into the chuck body.
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7th Feb 2010, 05:57 PM #4Member
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I bought a TOS "precision" 3 jaw from H&F a few years ago. The salesman told me at the time that the precision ones were no different to the ordinary ones and come off the same production line. They just measure the specs of every chuck, and those that are better than some benchmark are graded "precision" and the others are ordinary.
This implies that there is a runout standard for the precision chucks. H&F should be able to say what that is.
Graham
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7th Feb 2010, 06:00 PM #5Golden Member
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I bought 100 mm 3 jaw and 160 mm 4 jaw Fuerda chucks recently. These are the separate backplate version, not the D1-4s.
FWIW the spec. sheet which came with the 3 jaw if I am reading it correctly quotes radial runout of a test piece 50 mm from the jaw as a maximum of 0.08 mm for the 160 mm chuck and 0.100 mm for the 200 mm and 250mm chucks. The maximum runout for the 315 mm and 400 mm chucks is quoted as 0.125mm 75 mm from the chuck.
No runout figure was quoted for the 100 mm chuck which I bought, but if you assume the 0.08 figure quoted for the 160 mm chuck should also apply to the smaller one, it will achieve this minimum runout using only one of the three chuck key holes. The runout using the other two holes exceeds this figure. I don't know whether the same specs are quoted for the D1 series chucks.
FWIW again, the hole sizes on the drawing for the 4 jaw backplate were shown as 10mm and the PCD for the mounting holes as 142mm instead of 148mm. I picked up the PCD error, but the chuck back is tapped for the 8mm cap screws supplied with the chuck, so I now have 4 spare oversize holes in the backplate. Yes, I should have opened the packet and checked the cap screw size first before drilling the holes!
Frank.
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7th Feb 2010, 06:05 PM #6
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7th Feb 2010, 08:14 PM #7Boilermaker
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Measured tir of chuck body - 0.065mm
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7th Feb 2010, 08:20 PM #8Pink 10EE owner
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That seems similar to what my el cheapo 10" 3 jaw says... But in reality it's runout is around 0.06 or so... It is a turkey shoot as to what you end up with... I bought a 100mm 3 jaw TOS years ago and it's runout was horrendous..
I got a 320mm four jaw here brand new and it is shocking You cannot hold anything straight with it..
I would keep an eye out for a Pratt or something similar...I have gone right off cheap chucks..
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8th Feb 2010, 02:11 PM #9Senior Member
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The 160 mm TOS 3 jaw chuck I have came with a signed certificate of accuracy and a separate table of accuracies for the different sized chucks. Those graded as "precision" have half the runout of the "standard" chuck. For the 160 mm "precision" this is .025mm radial and .015mm axial for test pieces gripped in the jaws. Chuck OD radial runout spec is .05mm.
Chas.
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8th Feb 2010, 08:35 PM #10Boilermaker
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Maybe I should look at a 5c collet set for the repetitive accurate set up stuff rather than trying to chase a perfect 3 jaw? Majority of what I turn is under 25mm anyway!
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9th Feb 2010, 09:28 AM #11
Collets are probably the way to go, a 3 jaw will never really be consistently accurate over it's entire range of openings.
I'm considering the 5MT-5C adaptor for my lathe as well but the one from H&F seems quite expensive once you factor in the cost of a full set of collets (albeit cheaper than the adjustable 3-jaw and a hell of a lot lighter).