Strange collet interference on Rusnok clone

[stoatmax]

Hi all,

I recently picked up a Taiwanese clone of a Rusnok milling machine, circa 1980s. Cool little mill, and everything seemed in order. The previous owner reported that the spindle possessed an R8 taper, and by all accounts that would seem correct, but I'm encountering a weird issue when trying to install R8 tooling.

Thinking it might be interference with the indexing screw, I removed the screw, only to find that the interference is happening on the rear bearing surface for the collets. As indicated in the first photo with an arrow, the diameter of the bearing section is a good bit too small to accept the back end of my collets. Thinking the collets might be the issue, I tried to install my jacobs chuck, again to no avail.

Third photo shows the depth to which a collet will seat before encountering the interference. Second picture shows the annoyingly-recessed 32mm spindle nut. I can only imagine the annoying wrench I'm going to have to make to loosen that.

Any ideas as to how to resolve this issue? Are there super short R8 collets I'm unaware of, or some other, very similar collet system perhaps?

Thanks in advance,
Max

 

[4ssss]

There should be 2 screws. 1 tightens against the other to stay in place.

 

[stoatmax]

There should be 2 screws. 1 tightens against the other to stay in place.

Are you referring to the alignment screw that indexes into the keyway on the collets? If so, I already removed that screw, and there was only one on this mill.

 

[4ssss]

Yes, there should be 2. Put your finger up in the head and make sure there's not another one sticking out.

 

[stoatmax]

As far as I can tell, there's just the one. Upon further inspection, it appears as though the bearing may be eccentric to the rest of the shaft, as though it's drifted off-center.

 

[stoatmax]

Made some progress. Got a 32mm socket, cut it in half so that it could fit over the spline shaft, and ground some flats in. Removed the spindle from the quill and was able to fully remove the indexing screw.

With a bit of playing around, I got my drill chuck to seat. I took some measurements, and the back diameter of the chuck's shaft is .9475. The collets I have are .9495, so a mere 2 thou seems to be preventing them from seating. Seems like a tight fit on that bearing to me, given that I though .9495 was the nominal dimension for the back of an R8.