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paulsv
01-29-2012, 01:37 PM
I started to get a bit of a grinding noise in my 10" Atlas Quick Change Gear Box. It happens for a part of each revolution of the lead screw. It is bad enough that it shows up on the surface finish of the part I am turning. I took it apart this morning, and the problem seems to be with the keyed gear that the leadscrew fits into, part number 10-1530. That gear has an integral shaft. The leadscrew fits inside the shaft, and the outside of the shaft rotates in a bronze bushing in the gearbox housing. (The bushing has a .875" ID, 1" OD.) The OD of that shaft, where it goes through the bushing in the QCGB housing, is nominally .875. On mine, the portion that rides in the bushing has worn to .865, on the outboard (leadscrew) side, to as small as .840 on the side towards the gearbox. The surface looks scratched and scored. You would think that they would make the gear harder than the bushing, so the bushing would wear rather than the gear!

Clausing's parts list does not list this part as available, and SearsParts on line shows it as unavailable from the supplier, so, I may give Clausing a call tomorrow, but I assume they will tell me it is unavailable.

So I'm thinking that I will try this: Get a 3/4" ID 1" OD bronze bushing, and bore the ID of the bushing to around .830, and turn down the shaft portion of the gear to around .830 to match. Perhaps leave a little meat on the bushing, and adjust final fit with a brake hone, to get a close fit and a smooth finish. I've never tried to bore a bronze bushing before- any problem with that? Use a lubricant? Any other thoughts? Suggestions?

vpt
01-29-2012, 02:04 PM
Hey Paul, Like I posted on the other forum I pressed in a bush and then used a reamer to clean it up and get it to the near exact right size. I didn't have any trouble reaming the bushing at all. Not sure how one would turn on a lathe. I am sure others will chime in with some insight.

http://img40.imageshack.us/img40/9455/qcgb019.jpg

Tony Ennis
01-29-2012, 03:16 PM
My only insight is for you to post a link to that thread, VPT. It has the best pictures of an Atlas QCGB I have seen.

mf205i
01-29-2012, 03:56 PM
Use a standard SAE 841-Oilite sintered bronze bushing as they are impregnated with oil and are somewhat self lubricating. True up the shaft to fit an undersized bushing or sleeve the shaft back to the proper dimension, sleeving is preferable. Do not hone a sintered bushing and though not recommended, if you must bore one, be careful to use a sharp tool, as you do not want to smear the pores of the sintered material closed. To avoid dimensional problems with the crush fit of the bushing, install the bushing first and then fit the shaft.

The sintered bushings in our old tools fail because the oil in the pores of the bushings turned to oxidized crap decades ago. All of the bushings in your lathe are standard sizes and are available at any bearing house for a total of about 20 bucks.

If you decide to go for it, don’t forget the spindle pulley bushings. Because they don’t usually spin, they are usually beat to death. These worn bushings are often the cause of the bull gear-back gear pin walking out and finish problems.

SAE 660 bronze is more durable but it requires a constant source of lubrication.

Have fun with it, Mike

paulsv
01-30-2012, 10:27 AM
Thanks for the tips, guys!