Didn't expect to see this

[WobblyHand]

So I'm finishing up a set tru back plate for a Shars ER40 set tru chuck. All that is left to do is to true the TIR (using the ER taper) and to slightly turn the OD of the back plate to get it slightly closer to that of the chuck. Don't have any ER40 collets yet, so that's as far as I can get for now. Lightly installed the chuck on the back plate. Bolts not tightened but partially snugged. For the first time (that I remember) I unscrew the collet nut. This is so I can get a DTI in to measure the TIR. Look in the ER taper and see that it's scored. Rub the back of my fingernail down the taper, yes, it catches a lot. It is rough. Well, I feel kind of dumb. Why didn't I notice this before? Did I assume that since it was new, it would be ok? Kind of flabbergasted and a bit low at the moment. Should be a smooth ground surface, right? My ER32 chuck taper is ground.

My original photo shows scoring. I do not know how bad this forum will blur the picture.

I will call Shars today. This isn't an email kind of conversation. The scoring seems to increase the deeper into the taper one goes. Can't tell if this was a return or not, everything else looks rather pristine. It's like a collet spun in it. I don't know that, of course, but what could cause something like this?

 

[rabler]

Looks to me like it was turned on a lathe, and then ground with an ID grinder. Either the ID grinder didn't go to finished size, OR the lathe cut was over finished size so that the ID grinder didn't have enough stock left to clean up appropriately.

 

[WobblyHand]

So effectively a factory reject?

Can't see how this taper could ever have consistent TIR. The surface really catches the back side of my finger nail. Not subtle at all.

Gee, seem to be in taper h3ll. Got several different ones that are not good.

 

[jaek]

The fact that your fingernail catches is unfortunate, but the part of the collet that engages with the taper is incapable of catching on anything. It's hardened, perfectly flat, and has a corner radius at each end.

I'd be curious to see what kind of TIR you actually get with an ER collet in the chuck. Maybe it's terrible or inconsistent, maybe it's actually fine. When are your collets arriving?

 

[mikey]

If it was me, I wouldn't care what the TIR of this chuck was. I would send it back for a replacement. The inside taper should be ground smooth and even so that it interfaces cleanly with your collets. Bummer but yeah, send it back.

 

[WobblyHand]

The fact that your fingernail catches is unfortunate, but the part of the collet that engages with the taper is incapable of catching on anything. It's hardened, perfectly flat, and has a corner radius at each end.

I'd be curious to see what kind of TIR you actually get with an ER collet in the chuck. Maybe it's terrible or inconsistent, maybe it's actually fine. When are your collets arriving?

I hear what you are saying, but the surface is not flat, it is rough, and it is not uniform in it's roughness, therefore it will never have consistency. I didn't buy a collet chuck to have crappy consistency.

 

[WobblyHand]

If it was me, I wouldn't care what the TIR of this chuck was. I would send it back for a replacement. The inside taper should be ground smooth and even so that it interfaces cleanly with your collets. Bummer but yeah, send it back.

That's my plan. Inconsistent surfaces on the taper mean it either wasn't made right or it was damaged prior to delivery. It's rough enough that I wouldn't want it to scar my DTI.

 

[mmcmdl]

This was how a new product was received ??????? That finish looks like a plowed field and a bad one at that . Send it back , you have too much effort in your project to put a reject part into . JMO .

 

[WobblyHand]

I've had this a while... Since early February. Never took off the collet nut, assuming a brand new taper would be fine. Apparently a poor assumption.

Here is an ER32 chuck that I had mounted on my mini-lathe. Bought it from Little Machine Shop. It's not perfect by any means, but it's a whole lot better. Minor machine marks deeper in. Barely anything to catch a nail. Very low runout, 0.0001", no zero set. Just made to fit a LMS mini-lathe. Very pleased with the ER32 chuck.

 

[WobblyHand]

I have heard from Shars. They will send me a replacement with a pre-paid return label. They apologized for the issue, and the inside finish. They said, "We have never seen an er40 collet chuck with a finish like that." Me either. Hope to get the new one soon.