Large bull gear rubbing on cover plate above it

ophthalmophobe · Oct 7, 2018

Hi All,

I'm a long term lurker, first time poster. I'm having a issue with my new Bridgeport clone mill (it's a varispeed mill, branded a Condor, but has no info plate. I think it is a 2VS or 3VS type).

There is a lot of friction in the system, and i've not been able to get it to start on my rotary phase converter. I initially suspected the RPC, but having tried to turn the mill's motor by hand (it was very very stiff), i realised that there must be a serious a friction related problem in the mill.

Having had the drive system apart, i found two problems, the first was the small bull gear wasn't fixed high enough on the shaft, so when the top bearing plate was screwed down, there was a high side load on the bearings making it hard to turn. This would have caused high friction in low gear, and (hopefully) i have it sorted now.

The second problem (high friction in high gear) has me stumped: The large bull gear is rubbing on the cover plate that sits above it. It was severly crudded up, with hard gunge and metal shards, which i've cleaned off now, but it is still rubbing. I've checked that the gear lever splined shaft is correctly installed (moving to the 'next' cog makes the vertical movement of the bull gear miles off where it should be). It looks like it's only 1 millimetre or so that the bull gear needs to be lowered by to stop hitting the cover plate. I wondered whether the gear shift lever might be slightly off, but there is a roll-pin keeping that in position along with a cap-head screw. (A bodge solution might be to take the roll pin out, rotate by about 90 degrees, then fine-tune the angle of the splined gear select shaft, holding it in position with the screw, then take it out and re-drill a new hole in the shaft for a roll-pin). I'm reticent to do this before i've exhausted any other causes of the bull gear being too high. The other thing that confuses me is that when the bull gear is set to low-speed, it looks to be in a good position to mesh with the small bull gear (if anything it is slightly too low - the top of the large bull gear is about 0.5mm lower than the top of the small bull gear).

Apologies for the tolstoyesque brain dump, but any help would be gratefully appreciated.

Thanks in advance, Nat

PS, i have googled and googled, but can only find one other mention of the large bull gear rubbing on the plate, but there was no suggestion as to why, or how to fix it.

thermite · Oct 7, 2018

ophthalmophobe said:
Hi All,

I'm a long term lurker, first time poster. I'm having a issue with my new Bridgeport clone mill (it's a varispeed mill, branded a Condor, but has no info plate. I think it is a 2VS or 3VS type).

There is a lot of friction in the system, and i've not been able to get it to start on my rotary phase converter. I initially suspected the RPC, but having tried to turn the mill's motor by hand (it was very very stiff), i realised that there must be a serious a friction related problem in the mill.

Having had the drive system apart, i found two problems, the first was the small bull gear wasn't fixed high enough on the shaft, so when the top bearing plate was screwed down, there was a high side load on the bearings making it hard to turn. This would have caused high friction in low gear, and (hopefully) i have it sorted now.

The second problem (high friction in high gear) has me stumped: The large bull gear is rubbing on the cover plate that sits above it. It was severly crudded up, with hard gunge and metal shards, which i've cleaned off now, but it is still rubbing. I've checked that the gear lever splined shaft is correctly installed (moving to the 'next' cog makes the vertical movement of the bull gear miles off where it should be). It looks like it's only 1 millimetre or so that the bull gear needs to be lowered by to stop hitting the cover plate. I wondered whether the gear shift lever might be slightly off, but there is a roll-pin keeping that in position along with a cap-head screw. (A bodge solution might be to take the roll pin out, rotate by about 90 degrees, then fine-tune the angle of the splined gear select shaft, holding it in position with the screw, then take it out and re-drill a new hole in the shaft for a roll-pin). I'm reticent to do this before i've exhausted any other causes of the bull gear being too high. The other thing that confuses me is that when the bull gear is set to low-speed, it looks to be in a good position to mesh with the small bull gear (if anything it is slightly too low - the top of the large bull gear is about 0.5mm lower than the top of the small bull gear).

Apologies for the tolstoyesque brain dump, but any help would be gratefully appreciated.

Thanks in advance, Nat

PS, i have googled and googled, but can only find one other mention of the large bull gear rubbing on the plate, but there was no suggestion as to why, or how to fix it.

You said "new" but the only photos I can find online are of a 1993 Condor mill. I presume you mean "newly resident" rather than "newly manufactured"?

I'd suspect that at some time in its prior life it was mishandled in such a manner as to shift its bits about.

A deeper dig, further back up the chain of the shift positioner, but not-only, may find evidence beyond just the gear being too-high, then too low as might confirm that suspicion.

Hopefully that could also lead to an easier and more enduring "fix", or at least rule out such.

Otherwise, if the cover is structural, I'd introduce a standoff ring or just use the mill to make a new cover from solid plate but with greater clearance.

You have but the one mill on your own shop floor to fix. Not the entire production run as it departs the factory.

ophthalmophobe · Oct 7, 2018

thermite said:
You said "new" but the only photos I can find online are of a 1993 Condor mill. I presume you mean "newly resident" rather than "newly manufactured"?

I'd suspect that at some time in its prior life it was mishandled in such a manner as to shift its bits about.

A deeper dig, further back up the chain of the shift positioner, but not-only, may find evidence beyond just the gear being too-high, then too low as might confirm that suspicion.

Hopefully that could also lead to an easier and more enduring "fix", or at least rule out such.

Otherwise, if the cover is structural, I'd introduce a standoff ring or just use the mill to make a new cover from solid plate but with greater clearance.

You have but the one mill on your own shop floor to fix. Not the entire production run as it departs the factory.

Thanks for the reply. Yes, my bad - I would guess it's 30 to 40 years old. So about as 'new' as I am :-)

I had a good old dig around, and cant find any other cause for the gear sitting too high, everything is seated correctly, nothing else is left up to the assembler too 'choose' where exactly to fix it.

Having started to reassemble it, and experiment with my proposed bodge, i found that i couldn't find a gear-shift lever angular offset where the large bull gear didn't rub on the cover plate in high-gear and was still in neutral when supposed to be (it would partially engage the small bull gear or at least skip over it). It turns out that the small bull gear that i thought had been positioned incorrectly should indeed seat on the shaft's flange, but rather a not-fully-seated top bearing was the cause of the high side load on the bearings. Having seated that bearing properly, and re-seated the small bull gear all the way down on the shaft, i now had enough space to allow the large bull gear to sit in neutral when it should and not rub the cover plate when in high-gear, by introducing a suitable angular offset into the gear-shift lever as per my planned bodge. So, a small success if not a conclusive epiphony type moment with the enduring fix you mentioned.

Whilst i don't understand the ins and outs of the original problem, it looks like i have a band-aid style solution. (Though i have often 'fixed' 'poorly' designed newly acquired tools only to later find that i had just misunderstood how they were supposed to work, so i am still half expecting this to be the case).

That said, i no longer have a crazy amount of friction in the system! Which is good! :-) Though my RPC still doesn't have enough ooomph to start the mill - the varispeed pully setup is quite stiff (That's the only high friction part of the mills drive train now). I guess i'll have to add a flywheel or second idler motor to give the RPC a bit of an inertial boost.

Thanks again thermite for your help. I'll update the thread if i do have that epiphony. If anyone wants to have said epiphony on my behalf, that would also be good (as long as they share it here of course! :-) )

thermite · Oct 7, 2018

ophthalmophobe said:
i have often 'fixed' 'poorly' designed newly acquired tools only to later find that i had just misunderstood how they were supposed to work,

So long ago I even still had hair, I THOUGHT - from a well-executed and colourized cut-away drawing in a glossy publication that I had twigged to War Two US Navy torpedoes being propelled by the energy stored in a flask of compressed air.

Asked a distinguished elderly visitor about that.

The former BuWeps designer of some of those very gadgets just looked at me as if I were a blithering idiot. Which I had, after all, just demonstrated, to be fair.

Dry remark:

"It HELPS if you light the Alcohol."

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