Yet another ER40 collet chuck for an Atlas

[JPMacG]

Just completed an ER40 collet chuck for my Craftsman (Atlas) 12-inch lathe. I followed the excellent drawing by Ronald Crowell, Harold Hall's website, and the many YouTube tutorials. This was a real nice learning experience with a variety of operations... boring a precise diameter, internal thread relief, internal threading, external metric threading, boring a taper, and the order of operations was important. I'm getting a TIR of about 0.0005 on a .500 pin gauge. I think this is okay, considering that I am using an economy collet and chuck, and I'm nowhere near the proper nut torque. The repeatability of installation on the spindle is good - that is, I can measure TIR, take the collet off the spindle, put it back on and get very close to the same TIR.

 

[wa5cab]

That looks quite good. Did you cut the internal taper with the compound set around or with a taper attachment?From your third from last photo, it looks like probably the former.

 

[JPMacG]

Thanks Robert. I cut the taper with the compound. To get the angle I installed a collet on a mandrel and adjusted the compound rotation to get a constant indication on a dial indicator as it traveled the length of the collet.

 

[wa5cab]

OK. That's what I thought that the photo showing a dial indicator and ER collet on a mandrel probably meant.

 

[WesPete66]

Did you purchase the collet nut? and, was it a metric thread (or are they available with inch threads)?

 

[JPMacG]

Yes, I purchased the collet nut. It was about $12 from Shars. It is metric - M50-1.5mm.

I did not see any for sale with inch threads but people do make their own. The standard nut design has an eccentric ring and groove that helps to extract the collet from the chuck. I think the ring and groove would be difficult to cut. They could be left out and the collet could be knocked out through the spindle with a brass bar. Then the nut would be straightforward.

 

[wa5cab]

ER collets were "invented" in Europe and are a metric based system. Although it would be possible for someone to make the compression nut with a UNF or UNEF thread, I seriously doubt that anyone ever would.

 

[T Bredehoft]

Sixteen pitch thread, sloppy, will fit.

 

[wa5cab]

As I seem to recall, the required pitch is M1.5. If it is, any Atlas built 6" with the standard set of gears that were supplied with the machines new can cut M1.5 accurate to within at least 3 decimal places. The same is true of change gear 9", 10" or 12". Owners of a 10" or 12" equipped with a QCGB will need to purchase a 44T and a 52T gear and follow the instructions given in a file in Downloads.

 

[Ambit]

Wow, the way you are cross drilling using that boring bar holder is such a smart idea. Can you provide a little more information on what that setup looks like? I have never seen it before!