Colchester Bantam Mk1 - Eccentric Spindle, damaged rear spindle bearing

Well that was easier than I'd hoped and the bearings look undamaged and pretty darn good to my eyes for almost 50 years.
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No discernible eccentricity in this spindle - can't quite see what's been causing the trouble, but going to rebuild and test it again.
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More about the bearings for any future travellers..

Both are Gamet precision taper roller bearings with a flanged cup - manufactured by 600 Group, Colchester Tools. The bearings are produced in three grades with 1.5-0.5 micron run out.

Front spindle bearing is marked L2350 on cup and X L2350 on inside. Outer diameter is 90mm + 4.66mm for flange. Inner diameter is 50mm.

Rear spindle bearing is marked L7021 on cup and X L7021 on inside. Outer diameter is 85mm + 4.66mm for flange. Inner diameter is 45mm.

The part numbers are not current, but a quick comparison with their catalogue gives front spindle bearing is possibly part 85050 / 85090C and the rear spindle bearing is possibly part 119045 / 119085C (neither of these are definitive and anyone ordering should use the original Colchester part numbers (03-912 Front and 03-913 Rear). I've attached a copy of the current Gamet catalogue if anyone fancies some light bedtime reading!
 

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Hmm, I reassembled this and was getting much better run out at the spindle nose - 1-2 micron. I even dropped the oil and cleaned the sludge out of the headstock gear box.. (refilling with Westways ISO 32 mineral oil - Shell Tellus 27 equivalent).


However, I ran this up gradually through the speeds to 1800rpm, to bed in and allow things to warm up and things loosened up again and I was getting 5-6 microns afterwards.

I tightened up again and eliminated this play, but after a quick run I still see 5 micron run out and if I run at speed for 5 minutes plus the expansion is ceasing and causing the phase converter to trip out. Odd as neither end is getting properly warm.

Infuriating, but guessing these bearings have had their day and need to be replaced....
 
Interesting that you claim a seizure?.....Ive had a bit to do with Gamet bearings over the years,and seen a few ruined too...........Any seizure usually is the rear bearing(,if the oil level falls low,)and the bearing being only a slip fit will turn on the spindle ,often welding itself to the spindle in a few spots.......So far ,the spindle isnt ruined,but when you press the race from the spindle ,bad scoring results......and the spindle will need a hardchrome and grind...........Ive also seen Bantams lock up on the plain bearings in the pulley assy,if the oil fails...............so clean up oil sight windows,and keep the oil level well up..........dont be decieved by dirty sight windows,..............another Gamet fact.....if you take the rollers out,and reassemble them out of order,runout will increase greatly.......I dont know why.
 
I've done some further testing and certain that the motor cutout problem is not related to the bearing seizure - not enough and certainly no adverse heat build up in the bearings and I can still freely turn the spindle immediately after it cuts out. The motor cuts out after 3-5 mins running fairly consistently and then takes a few minutes to cool down before it will run again, so I'm guessing there's some thermal cutout on the Brook Crompton, a twitchy breaker on the rear cover or brake or possibly wiring. I guess it could also be a supply fault, but I run the lathe independently from a static 240V single to 415V 3phase converter and no fault indicated here.

The motor looks original and is filthy, so I dismounted and gave it a bit of a clean. The bearings turned freely, but surrounded by grease that seems to have hardened off - so I cleaned this off and re-lubricated the bearings with lithium grease. Quick shot of the motor plate and wiring for future reference..

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A good opportunity to clean some hard to reach areas and check the belt tension - a good 3/4" play in this, but worn and at maximum extension. I've refitted and run the motor, but will get a new belt (Fenner A34 - A section 8x13mm V belt 34" long).

Everything was refitted last night and I quickly spun the motor up to confirm it was wired back in correctly. Too late for a full test, but hope to get some time this evening.
 
Interesting that you claim a seizure?.....Ive had a bit to do with Gamet bearings over the years,and seen a few ruined too...........Any seizure usually is the rear bearing(,if the oil level falls low,)and the bearing being only a slip fit will turn on the spindle ,often welding itself to the spindle in a few spots.......So far ,the spindle isnt ruined,but when you press the race from the spindle ,bad scoring results......and the spindle will need a hardchrome and grind...........Ive also seen Bantams lock up on the plain bearings in the pulley assy,if the oil fails...............so clean up oil sight windows,and keep the oil level well up..........dont be decieved by dirty sight windows,..............another Gamet fact.....if you take the rollers out,and reassemble them out of order,runout will increase greatly.......I dont know why.

John - thanks for this reply, some really good pointers here and much appreciated. There was some black marking on the shaft where the rear bearing sits - though this cleaned up and doesn't really show in the picture I took before reassembly:
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It also seems a good tight fit. I changed the oil (and cleaned the sludge/swarf!) out, making sure the oil ways were clear for both bearings as they seem to lubricate by capturing sprayed oil from the headstock and circulating by gravity - simple enough but had me a little worried as any blockage would starve the bearings of lubrication.

I didn't take strip out the pully/drive shaft, but it seems to turn freely without obvious play. I did clean out all the oil ways for the other drive/gear shafts.

I didn't strip the rear bearing as this had a nylon locking/retainer washer around the cone. However, the front bearing had a sprung wire which I removed on disassembly and I did strip/clean this one :( - a thin film of black gunge on the non contact surfaces of the cage, but no obvious scoring marks or damage.

Quick crop of the front bearing rollers (focus not great!)

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Spindle looks good.......you would know if it seized,the bearing would be tightly stuck on......Incidentally,Gamet bearings start to seize on the ends of the rollers and the reaction flange on the inner race.........Not a pretty sight on a 8" ID bearing..........Years ago,we bought Students and Bantams in job lots from technical colleges..........the damage to some was incredible,along with parts missing......tailstock spindles were favorites for theft as they come out so easily....I kept a Bantam with all new gears and shafts,and a Master in good nick.(from the airforce,not a college)
 
Microns as in millionths of an inch? Or some other increment?
mark
 
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