rimcanyon
Diamond
- Joined
- Sep 28, 2002
- Location
- 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…
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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