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Installing an ER32 Collet holder in a fixed spindle


Sep 28, 2002
Salinas, CA USA
I am working on a project which bears some relationship to the thread on collinear center drilling, but rather than hijack that thread I thought a new thread was in order.

The project is to replace a worn out chuck on a Sioux valve facing machine head with an ER32 collet holder. The chuck had worn to the point of .004” runout. That is *after* replacing the rollers in the chuck. The goal of the replacement is under .0005” runout 2” in front of the collet. I’m not there yet, but I’ll keep going until I get it done. Before I get suggestions to look for an aftermarket solution, I did. This is a 60 year old machine (model 645L) and the aftermarket solutions are only for recent models.

First, the spindle bearing surfaces were not perfectly coaxial, so they were ground between centers (this is a plain bearing machine so changing the journal diameter a few thousandths is o.k. The head casting is slotted and clearance is adjusted with capscrews. Also, a new center was ground at the tail end of the spindle.

So the next task was to bore the spindle to take a collet holder, to be held in place with RC609. So the spindle was chucked in a 4-jaw chuck, painstakingly aligned to be both on center and on axis, then bored oversize for the collet holder, using a steady rest to support the outboard end of the spindle.

Next the collet holder was cemented into the spindle. This is the setup used in the lathe for alignment: a ¾” dowel was turned in the lathe collet chuck and left in place for alignment, the new ER32 collet holder was clamped onto that dowel. The modified spindle was fitted and glued to the collet holder using a spider to get the spindle front bearing located true to the lathe axis. A second spider was used to get the rear bearing surface coaxial and support the weight of the assembly, then the spindle was left overnight for the glue to set.

So after all that, the new collet holder had .002” runout. What a disappointment. But I thought, no problem, I will regrind the spindle parallel to the work in the ER32 collet holder. Before I got that far, I found that the work (the 3/4” dowel) was moving in the ER32 collet! I verified that the work was not moving in the lathe collet, since there are two collets involved here. The ER32 collet was as tight as I could get it, but with only a medium push at the rear end of the spindle I could change the spindle runout to anything I wanted and it would keep the set. Lesson learned: you get what you pay for when you buy a cheap set of Chinese ER32 collets and holder.

Its a work in progress, I will post more when I get some new results. Before I remove the collet holder I plan to try a new high quality ER32 collet and see if that changes anything. If that fails I will install a high quality collet holder.

Suggestions always welcome…
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Steel dowel, 3/4”. Actually .748”, since it was turned to make a good alignment pin. 2” Protrudes to mount the ER32 collet on. The lathe I am using is a 10EE with a 5C nosepiece and collet.

Update: I used a Rego-Fix (Swiss) 3/4” collet in the Chinese collet holder, and the problem persists: if I tap the side of the rear end of the spindle it introduces runout. Or if I loosen and retighten the collet the runout and location of the high spot changes. The spindle only weighs 2-3 pounds and its about 14” long, so shouldn’t an ER32 collet be able to center that much side force repeatedly My experience is with 5C and 2J, and nothing moves in those collets, comparatively.
Fwiw there's quite a few videos on YT about high rates of run out with those off shore ER collet chucks. Attempts to lower what there getting go up to regrinding the chuck taper and with generally poor returns. The collets them selves also have pretty poor run out as well, but your Rego Fix replacement would remove that. ER colets and chucks are a bit more complex than they seem because there a combination of multiple areas that all have to be correct or you'll have poor run out. Myself I suspect a lot of the problem is poor concentricity and fit on the collet nuts nose taper, it's thread alignment to the chucks threads, and possibly that extraction ring inside the nut if it's tilting the collet as the nut goes tight. All of it fairly hard to verify and even harder to re-grind if any of those areas are part of the problem. If you can get the chuck taper and it's threads concentric and true to the spindle C/L, I think I'd try at least one of Franks ball bearing nuts over at MariTool.
You're looking at it backwards to begin with. See if it repeats with the spindle fixtured, on it's bearings, whatever.

The other factor is the collet itself. An old Sioux we had floating around had 3 ball bearings for jaws, so it didn't force alignment off the stem. The tip seated in a taper in the spindle.

Using an ER collet isn't going to let it float that way. You need line contact in the collet so the valve can 'swivel' in it. But I have no idea what sort of concentricity you'll get without full support inside the collet.