PCNC1100 Spindle Rebuild

Hello from New Zealand!

A little while ago I purchased a used PCNC1100 here in NZ and have been happily and patiently learning how to use it. Getting some good results now with custom made parts out of aluminium and mild steel. I had a little accident where my work holding wasn’t sufficient and the endmill jumped to the back of the part it was milling slightly shifting the part in the vice jaws. Hit the e-stop immediately.

Spindle sounded noisy after this. I assumed I had damaged the bearings so decided to do a rebuild as I can only assume it had never been done to this machine before. Had a local engineering shop source the bearings (cross referenced the Tormach P/N), check spindle shaft runout, install bearings, seat and torque as per Tormach specs in the spindle rebuild guide.

The lower bearing preload washer is loose (I can turn it with my fingers) when everything is tightened up, has the shop not seated the bearings correctly? I don’t want to crank down on it in case I damage the super expensive bearings. Can you just crank down on the bearing preload nut to achieve the correct seating then back off and tighten as per the rebuild instructions?

Any suggestions are much appreciated.

When we have rebuilt our 1100 spindle we usually seated the bottom bearings with a press by supporting the housing and pressing the R8 end of the taper tube. This removes most of the friction from the system and lets you easily tell when you are in contact. If you don’t have a press, you should be able to crank the nut down to seat the preload washer without issue. I don’t remember offhand what the thrust rating for the pair of bearings are, but especially with all the additional friction you have to go through pulling from the nut side you shouldn’t be able to Brinell the bearings unless you really go crazy with the torque.

If you try to torque it in and don’t see the washer lock up before you get out of the hand torque region I would find a press and seat the bottom bearings that way. Just remember that especially with a hydraulic press the shaft should basically move with zero pressure and you don’t want to apply and significant load. If you get any resistance and the washer isn’t tight I would disassemble the cartridge and make sure that all the parts are correctly installed.

Also, make sure if you pull the bearings into contact with the nut to back it off, spin the spindle to make sure it rotates freely and then reset the nut with the extra 5 degrees for the preload.

One other tip for when you reinstall the cartridge is don’t put anything on the cartridge body. We once made the mistake of putting a light coating of grease on the outside of the cartridge before we slid it into the head casting. The next time we tried to remove the spindle we had to fabricate extraction tools to get it out.

Good luck finishing your rebuild. If I can be of assistance let me know.