How accurate is your 3 jaw chuck?

[Norman LortonParticipant @normanlorton75928]

Would people like to submit figures for the actual run out found for their 3 jaw self-centring chuck? Insert a true piece of 5/8" (or 16mm) round bar and use a dial gauge to record the total deviation seen on the gauge (i.e. total deviation of 0.002" thus out of centre is 0.001" )  .

I ask this because I have no idea what is typical or the best achievable.

My Pratt 3 jaw chuck on my Myford was showing 0.0035" out (total) and not gripping properly because of wear at the jaw edges. So I have re-ground the jaw tips, in situ using paste on a bar between centres, and now the jaws grip perfectly along their full lengths (test with blue).

However, the total run out deviation now reads 0.0025" (i.e. it is holding a 1/2" rod 0.00125" off centre). Slightly better, but I expected it to be nearly perfect after the jaw tips regrind. What would you expect?

 

Edited By JasonB on 17/09/2013 14:25:12

[Norman LortonParticipant @normanlorton75928]

Self-centring error

[JasonBModerator @jasonb]

Just checked mine 0.0009" tir so 0.00045" off ctr measured 20mm from the jaws, not bad for a Chinaman.

J

Edited By JasonB on 17/09/2013 14:28:30

[JAParticipant @ja]

Both these seems very good.

I would not expect anything from a three jaw chuck even when new. They weren't even mentioned during my machine shop training as a mechanical engineering apprentice.

JA

[JoParticipant @jo]

Jason: I thought you had Bison Chucks. If so they are made in Poland.

If I want accuracy I use a collet.

Jo

Edited By Jo on 17/09/2013 15:07:50

[JasonBModerator @jasonb]

The 5" 3 jaw is the one that came on the Warco, the Bison is a larger 160mm 4-jaw

[Sub MandrelParticipant @submandrel]

~0.0005" total runout, with a brand new Indian Zither chuck, backplate turned in place on the lathe.

Very sensitive to swarf on the scroll, as noted elsewhere.

Neil

[Gordon WassParticipant @gordonwass]

I had to go and check mine, for the first time. A bit of silver steel about 30 mm out it was 0. o6mm. Pretty reasonable for a dirty 5 year old chinese chuck I think.

[Anonymous]

I had to have a search for mine before I could check it. The TIR was 0.3mm. But then again I almost never use it. I use collets up to 1-1/2" and the 4-jaw chuck or faceplates over that.

Regards,

Andrew

[mechman48Participant @mechman48]

Hi Norman,

Read my write up on my chuck overhaul at…

**LINK**

Cheers

George

[WALLACEParticipant @wallace]

Yes, but is it the same for a range of diameters ? Even using difference tightening sockets can make a difference.

Personally I prefer a 4 jaw lined up with a DTI even if it takes a few minutes.

Then I know it’s true.

W

[Norman LortonParticipant @normanlorton75928]

Thanks for your thoughts, and thank you George for pointing to the discussion back in August that I should have seen. I assume that TIR means "Total Indicated Runout"?

So the summary results from both threads (for TIR) converted to imperial are:

0.0005" new Indian

0.0009" 5yr old Chinese

0.0015" before overhaul (0.0005" after)

0.0024" dirty (0.06mm)

and I won't event attempt to list the one that has 0.3mm TIR, or the one that was visibly wobbly.

The good news is that I retested my chuck but using a piece of 1/2" precision ground MS. Now I get 0.0005 – 0.0010" so it seems to be performing OK. Using other random pieces of bar would give the good result or larger errors (0.0025" ) which could be fixed by very lightly tapping the high jaw before tightening.

I have also just realised that I should have slip stoned the edges of the reground faces on my jaws. They might be catching on different bar material? I will try this tomorrow.

 

Edited By JasonB on 17/09/2013 20:17:08

[Anonymous]

The 3-jaw chuck with the 0.3mm runout is a Pratt-Burnerd, almost certainly original to my lathe, a Harrison M300. No doubt it could do with a good clean, but I think the basic problem is that the jaws are worn, and do not hold the material properly. I use it so infrequently that sorting it out is way down on the list.

Andrew

[Sub MandrelParticipant @submandrel]

Wallace – the Zither chuck is consistent with 1 1/4" and 1/2" bar. The original chinese 3-jaw chuck (now 15 years old) has a runout (from memory) of about 2 thou but I think it's a bit better now I have given it a good clean.

I think it is fair to say that modern mass production methods probably produce much more accurate scrolls, so even cheap chuck perform better than the economy ones our predecessors of 50-odd year ago might have battled with.

Neil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Apart from simple accuracy of manufacture there is a fundamental design problem with conventional three jaw self centering chucks :

When the jaws are locked on the work the scroll , jaws and work form a solid object but there is nothing to positively lock this against the solid metal of the chuck body – the whole lot floats to the limits of clearances and will in general take up a different position at each time of use and can just occassionaly move under load .

The better the chuck the more accurate he parts are made and the more controlled the clearances are .

The situation is different in and independent chuck where work beds against jaw , which beds against screw which beds aginst chuck body – all in a very positive manner like having four vices acting on a common base .

MikeW

Edited By MICHAEL WILLIAMS on 17/09/2013 22:59:45

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by MICHAEL WILLIAMS on 17/09/2013 22:46:08:

When the jaws are locked on the work the scroll , jaws and work form a solid object but there is nothing to positively lock this against the solid metal of the chuck body – the whole lot floats to the limits of clearances and will in general take up a different position at each time of use and can just occassionaly move under load .

That's an interesting point Michael. Could that be why we are always told to tighten with the same socket each time. I guess that the force on that will push the scroll to one side and lock it there. I have just tried tightening my TOS chuck on a silver steel bar, zeroing the dial indicator, and then slacking it off and tightening it again on another socket and I only get 0.0001" change.

TIR measured on 4" TOS chuck with 3/4" bar: 0.0005" adjacent to chuck jaws, 0.002 at 100 mm from jaws. (SVP excuse the mixed measurements)

Would have measured my 6 1/2" English made chuck but can't lift it while recovering from a hernia operation.

Russell.

[Thor 🇳🇴Participant @thor]

Hi Norman,

you asked for the runout on 3 jaw self-centring chucks, my old Emco and TOS chucks are 0.03 to 0.05mm. The chinese chuck that came with my new 290 lathe has a runout of 0.15mm. I will try and remachine the backplate when I find the time.

Regards

Thor

Edited By Thor on 18/09/2013 17:52:45

[wheeltapperParticipant @wheeltapper]

Hi
I just had a nice surprise.
I checked my 3" 3 jaw chuck that came with my chester Comet lathe.
After stripping, cleaning and reassembling it I bolted it to the flange on the spindle finger tight then clocked the outside of the body, tapping it till it ran true. the bolts were then tightened.

then I put a steel rod from an old printer in the chuck and clocked that.

After trying all three keyholes I found that one in particular gave me a TIR of 8/10ths of a thou!!

The name on the chuck is "TIANPAI"
I'm certainly not complaining about that.

Roy.

[Sub MandrelParticipant @submandrel]

Confession time!

Whilst checking a workpiece in my mill, I realised that the overhung setup I had for my DTI on its magnetic base was flexing, even under the pressure of the probe and was under reading. That I used for teh chuck test was not as extreme, but the seeds of doubt were sown.

I sorted the DTI holder to bemore rigid and repeated the test on my Zither chuck, which now came out spot on 0.0005" runout – spot on, going between two graduations on the dial.

Neil

[Ady1Participant @ady1]

Use a tailstock and centre and make runout irrelevant

[Author]

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