aluminum "collet insert" for 3 jaw that is about .004" TIR

madmachinst · May 24, 2020

OK I have this 3 jaw all banged up, too embarrassed to name names. Part I need to flip over and machine on other end to within say .0005" TIR is 5/8" diameter. I was thinking can I get a 2" Inscribed circle piece of hex aluminum, drill bore and ream and make a slit. will this work as a collet? Will I get repeatability after I take out the " collet" and put it back in of course the sides will be numbered to correspond to the jaws. Is make it out of hex a waste of time or I should just use the tried and true method of making it out of round stock just never removing it from the chuck? Maybe I just get myself an MT4 ER40 colet holder and stick that in the spindle taper? That is in my budget.

plastikdreams · May 24, 2020

Do it all the time when I need accuracy....make a shoulder on it so it does5 slide into the jaws.

AlfaGTA · May 24, 2020

If ya got two piece jaws, just run some soft jaws....Bored to the part size. Eliminate the stack up.
Cheers Ross

gustafson · May 24, 2020

Buy a cheap 5c collet block?

madmachinst · May 24, 2020

solid one pc junk. no 2 pc here.

madmachinst · May 24, 2020

gustafson said:
Buy a cheap 5c collet block?

gota a cheap 5c collet chuck and that has to constantly be shimmed in one end. I am beyond certain part sits in there cockeyed.

dian · May 25, 2020

good luck with 0.0005 tir on an er-40 also. maybe make an adjustable backplate for the chuck?

Limy Sami · May 25, 2020

madmachinst said:
solid one pc junk. no 2 pc here.

get a set of soft jaws for it.

madmachinst · May 25, 2020

dian said:
good luck with 0.0005 tir on an er-40 also. maybe make an adjustable backplate for the chuck?

so what kind of TIR you think I can realistically expect?

michiganbuck · May 25, 2020

For the part that has a through hole one can hang it out far enough to bore and do all the OD work from one end, then part it off.. then stand it in a v block and finish the other end if needing change of hole...

Other trick is to leave a little OD stock and bore from one end ...then put the part between centers to skim OD.

Your collet bushung plan may work better if you scap a drill-start position with a tool bit for a drill bore and ream.

I used to OD tickle parts back at the big shop for toolmakers who could not make parts true at bothe ends of a lathe.. < 15 minuet job an a good OD grinder.

5 tenths is the average collet error and .0002 the better ones..add a litthe lathe error and so very difficult to get .0005 with good machines...That is where the between centers OD tickel shines.

Yet another trick is to put the part hole/bore on a head stock end center...the out end in a steady..place a ring on the part ..perhaps a heater hose clamp..then stack a bunch of rubber bands to pull the part tight to the head stock center...yes your dog on a marked jaw.

You can put a soft center in any lathe chuck..turn a ^) with a tool bit and that center will run dead true. Use your fish to check 60*

dian · May 25, 2020

difficult to say, especially not knowing how long the part is. on my lathe and using a regofix holder and ultra precision collets (which i dont have in this size) i would expect half a thou at the collet and another thou for every 10" out. for run of the mill tooling easily triple that, if you have a perfect spindle.

i would start by putting an adapter in the taper. how much does it run out?

gustafson · May 25, 2020

madmachinst said:
gota a cheap 5c collet chuck and that has to constantly be shimmed in one end. I am beyond certain part sits in there cockeyed.

no hex collet block. If you get lucky you might be able to close and open it without opening the chuck, using the ring closer and a pin to open and close.

Here is the problem with your 3 jaw. Depending on 'how' it is screwed up, it may or may not open and close to the same position, or hold an object in the same place.

Thus anything that involves opening the chuck at all is not going to be repeatable.

If the part is fairly short and has a through hole you can make an expanding stub arbor with a piece of random round stock a band saw and a socket head flat head screw.

Trueturning · May 25, 2020

madmachinst said:
so what kind of TIR you think I can realistically expect?

How do you think they can even check that close? Seriously .00005 tir?

thermite · May 25, 2020

madmachinst said:
solid one pc junk. no 2 pc here.

Save a shiney-wood tree. Grip even a TRASHED 4-J in the 3-jaw.

Dig the half-tenths - or better-yet 20 millionths - DI out of the back of the drawer. Adjust out yer TIR. Take light cuts.

YOU NOW ARE the "repeatability" mechanism.

Payback for running a fool scroll-operated chuck when yah shudda KNOWN better.
Invest in a primo high-repeatability collet system when budget off saving enough shiney-wood trees accumulates.

I harbor both of a 5C "key operated" nose-closer and an ER 40 "plate mount" that have no spindle mount. (Also others as DO have.. D1-3)

Ditto BOTH of hex-body and square-body collet blocks, 5C and an ER-40 "other PM member fabbed".

Any of those are run... gripped in a 4-J.. for the very purpose of adjusting where their center be.

And now? Yah can even rapidly DUPLICATE intentionally eccentric parts.

Cheap enough.

And not even ONE shiney-wood tree had to die! First time. Nor ever again.

Red James · May 25, 2020

Since all 'stores' are closed today, go ahead with your 'alignment bushing'. I have done similar when I wanted to hold 1/4" stock in cnc that had no way to bore soft jaws (or maybe no desire ...). Made bushing from steel and made one lengthwise slot on band saw. Held parts w/i 0.0005 tir.

michiganbuck · May 26, 2020

Almost any lathe chuck even a decent 4jaw and with the part indicated to .0002 at the out end will likely run out .0005 or more 3” deep into the chuck jaws.
So, for close work the finishing cut, between centers OD skim may be best.

Sometimes one can bore a slug of stock held in any (good or crap) chuck with that bore a snug tap-in size to the part needing to be turned, so that slug bore is acting like a part on a mandrel. Run near dead true this way
with first making a tool-bit scalp to center the start of the drill or center drill when making the slug bore... Yes, you don’t losen the chuck, but just tap in the part in to make near dead straight at enter and at the back end of the part. Yes, you might dog the part so it can’t turn..

Yes the slug can be a slug of aluminum..

Note with not the tool bit scalp most any drill or center drill will not start dead center to the part OD..
Indicated in a 4jaw a scalp will run true only at the point of indicating..deep in the chuck the chuck wobble will make the back or held area run out to the quality of that chuck.

*The bored slug will run true all the way through the chuck and stay that way intill it is taken out of the chuck.

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