Hi All,

I recently purchased a collet chuck to use in my mill.  I have a lathe/mill combo and the distance from the mill head to
the cross-slide is just a bit more than an endmill mounted with a collet directly in the spindle.  The collet chuck adds
another 1.5" or so and comes with tiny collets to hold some engraving tools (3/32") that I want to tinker with.
Unfortunately there appears to be a great deal of runout in the chuck itself.  If I mount an endmill in any of the
collets and run a dial indicator at the non-fluted based of the endmill there is as much as .005" of runout.  By the
time this is extended to the end of the cutter, there is a noticeable wobble that makes the cuts much wider than
the tool bit.  I assumed it was a poor quality chuck (eBay  ), but I see this set from Smithy http://www.smithy.com/ecom/detail.asp?n=Spring+Collet+Chuck+Set&sc=MILL+%26+DRILL+SETUP
says concentric to .005".  That's pretty crappy even for my less-than-perfect equipment. 

I would try to true this one up a bit, but I'm not sure how to go about it since I can't clamp it true in my lathe
(no taper in my spindle, just a 3" jaw chuck).  I thought about mounting a cutter upright and bringing the mill head
down on it to center the taper, but if the collets are also bad I see no way I am capable of fixing them.

Does anyone know of a source that sells a more accurate collet chuck?  It seems like a great solution for me as it makes
tool changing relatively quick, doesn't requiring hammering on the drawbar against my Z-axis drive, and gives me my
needed extra length to reach thin plate directly on my machine bed.

Thanks for any input!

Have a look here :-

http://www.jlindustrial.com/Toolholding_Workholding/Collis/Collet_Closers,_Chucks_and_Headstocks/COL-63922K/SEARCH:CATEGORY/Y/product.html

Or

http://www.jlindustrial.com/Toolholding_Workholding/Kennametal/Collet_Closers,_Chucks_and_Headstocks/EKN-14984B/SEARCH:CATEGORY/Y/product.html

Thanks very much for the input Graham.  The quality of those units looks good but there are no specs on the runout.
http://www.jlindustrial.com/catalog/product.jsp?id=ERI-90052H&origin=SEARCH:KEYWORD&backtosearchpage=Y
I'm going to e-mail and see what they say.

In my hunting around it seems like .005" concentricity is a common level of accuracy.  That seems bizarre to me in the
world of even amateur machining.  It certainly makes cuts a lot wider than the tool used.   

Thanks

I use these and have found them to be .0005" TIR, when checked between my lathe centers.

I did it like this :-

Turn a 10mm dia 25mm long on a bit of bar and centre drill with a BS2 centre drill, part off.

Grip this in the collet chuck, center facing out!

Put a bit of scrap bar in lathe chuck, turn a 60 degree angle on end of bar. Do NOT remove from chuck!

Put fixed or running center in lathe tailstock, mount collet chuck between centers with just enough pressure to allow it to turn,

With clock on mag base you can now check runout by spinning collet chuck and clocking the shank.

Ignore the collet outer body as it don't matter.

Graham.

Thanks for all the info Graham!

I did a little fussing about and am pretty sure I've got the problem figured out.  I would chock it up to bad design on the unit I have.  For the small engraving cutter I have (1/8" shaft), if I put the cutter in the collet and force it into the taper (not using collet chuck nut), it runs dead true.  As soon as I try the nut it ends up whipping all over the place.  The threads on the nut are so sloppy that when it tightens the nut "leans" one way or another and forces the collet off centre.  I fiddled a bit looking at re-cutting the nut to be on-center, but it moves around differently every time you tighten.  The other significant problem is that all the collets are bored large at the "back end" (narrow end of the taper) so the gripping length is only about 3/8" instead of the full length of the collet.  Time to buy a real one 

Just an update...  I bought another collet set & holder on eBay, this time ER40 and quite a bit more $ than the last one.  First time out of the box the 3 different collets I used are deadly true -- better than my measurement capability anyways.  Works fantastic.  I was starting to worry that maybe my spindle wasn't that great (an $1800 Canadian lathe/mill combo).  Seems to be doing the job now and the repeatability/accuracy amazes me for the relatively small cost and crude tools I had to perform the CNC conversion.

Thanks again for the tips & tricks Graham!