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BP quill power feed selector gears not mating

ETI2K

Plastic
Joined
Oct 11, 2020
This is on a 2J head from a True-Trace Speed Selector.jpg s-l640.jpg (not actual photos). This mill has seen very little action as it came from a tool and die maker, not a production shop. EVERYTHING inside the housing is in first rate condition, but the two shafts (Cluster Gear Input Shaft and the Cluster Gear Shaft) appear to be too close preventing the gears from meshing when operating the 3-position speed selector. I can force them to mesh, but they are very, very tight. This problem exists whether the speed selector is installed or not.

I have removed and disassembled the two shafts completely. Every tooth on every gear shows very slight wear and the gears are in excellent condition otherwise (no nicks or banged edges), the bronze bushings are not worn (holes are round), bushings were oriented as originally installed by BP, nothing obvious with the casting (no cracks or hammer blows evident). The only thing worth noting is the Worm Drive Gear key has a very slight shearing indent, but fits comfortably in the key slots of the gear and shaft. All other keys and keyways are straight and true.

I chucked up the shafts (less than 2 tenths runout each) with gears to visually inspect while turning slowly to look for runout of the gearsets with nothing evident. Last night I thought I might remake the bronze bushings for the Cluster Gear Shaft with the bore slightly offset from center to provide some clearance between the shafts, but that would affect the relationship of the bevel gears to each other - not sure if I could adjust the bevel bears clearance afterwards.

I've been chasing this problem around for several hours. Did BP provide any sort of clearance adjustment for this assembly? Any ideas would be appreciated.
 
... the two shafts (Cluster Gear Input Shaft and the Cluster Gear Shaft) appear to be too close preventing the gears from meshing when operating the 3-position speed selector. I can force them to mesh, but they are very, very tight.
If you can force them to mesh, it's not a large amount.

If you are sure everything else is correct, then careful use of an abrasive blaster is the easiest way to fix this. I had access to a bead blaster with silicon carbide beads, they worked fast, but something else would do, too. Just rotate the part evenly under the nozzle, check it, do some more, check again until they fit.

You aren't running 100 hp through these at 3000 rpm, they'll work fine reduced by hand. There are other methods but almost every one is much more expensive than this and requires specialized tools or equipment.

Or, generally it's not good practice to run lapping compound through the mesh but maybe in this case, since the material removal will be very small, you could try that. Making a little fixture would probably be smarter than trying to clean out the Bridgeport's head afterwards ...
 
Good ideas. I can lap or blast, but I'd think lapping would produce more uniform results.
Also, I am working on building a vapor blaster which would be a great way to polish it up after lapping. Trouble is I am way off from having it ready.
So I'll lap them in and report back with results. If it works well, maybe I'll pop them out after the vapor blaster is up and running and tune them slightly.
Thank you for your help.
 
@EmanuelGoldstein
Your idea worked - like a charm.
Chucked the Cluster Gear Shaft in the lathe, and mounted the three-gear set on a 3/8 shaft which was held in a boring tool holder on the quick change tool post. Used the cross feed to slowly mesh the gears while adding lapping compound. They mesh clean and smooth now.
Thank you again for the idea!
 








 
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