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Bridgeport Self Feed Gearbox

G3TDM

Plastic
Joined
Apr 16, 2006
Location
Cornwall, UK
Hi All,

I have only recently discovered this excellent forum, so please bear with me if I commit some terrible mistake due to ignorance!

I am slowly (very slowly) getting a UK made Bridgeport up and running. I have recently got three phase power from an inverter to the little motor on the self feed device. This particular self feed device is Bridgeport designed, it is the one with the gearbox which has six speeds, with a high/low selector (12 speeds in all).

My problem is that if I apply a bit of resistance to the rotating handles there is a bit of a "clunk" and the handle stops turning (the motor is still rotating). Does this gearbox have a slipping clutch in it? If so how do I adjust it? If not - what is likely to have sheared?

As far as I can see it is not the dog clutch associated with the bevel gears connected to the feedscrew.

Any ideas would be appreciated.


Cheers,


Roger.
 
Hi Roger

Firstly there is a shear pin connecting the lead screw to the drive box output, you can see it quite clearly if you look up under the table, sometimes the pin shears but drops back into partial engagement until loaded.
Secondly, if it is the old type table drive the end of the spring loaded locking knob wears & no longer locks the speed selector arm in the indent at the end of each track, in this case it jumps out of engagement under load.

regards

Brian
 
Roger, take the cover that haas the oil cups off. You can then get a better idea how the power feed works. You will see the spring loaded pin (shaped like an arrow)that engages the handle via a small falt plate with three "V" grooves (that is where the spring loaded arrow engages the "V" grooves).

The plate with the grooves has this "shear pin" going in the underside. This pin sits down into a collar that, when shifted, engages the gears forward and reverse.

Check to see if the pin has sheared. If so, replace it and then try to use it. You might also try to find the broken piece that may have lodged itself somehwere in the gears.
 
Take the six speed handle off and turn the key around. When the table hits the end of travel the key warps a little, turning it over fully meshes the gears again.
 
If the motor is running backwards, it can blow up the insides, breaks off the idler....guess how I know........can be brazed tho
 
Hi All,

Thanks for the input on this topic.

Inspired by your ideas I have further investigated the problem.

Brian (1) - When the drive stops, the bevels which are connected to the feedscrew, and the bevel on the vertical shaft from the gearbox are not rotating - so the problem is in the gearbox.

Brian (2) - the gearbox is of the type that has a spring loaded locking knob. This seems to be quite a good fit and although the speed selector arm "twitches" there is little significant movement.

jackalope - The dog clutch on the bevels stays engaged. As I mentioned above all three bevel gears stop rotating when the problem occurs.

notillr - The arm is quite difficult to remove - the large nut is a very tight fit on its threads! The key is rather strange in that it is stepped - fatter in the arm than in the hollow spindle that goes into the gearbox. I wonder if this is because of a problem, like you describe, in the past.

keithg - Thats interesting. As I am driving the motor from an inverter (it is a three phase motor) it is easy to get the motor rotating in either direction - when going backwards it is much quieter - I wonder if this is because the thrust from the worm is in the opposite direction and onto unworn parts of the motor bearings? However it seems quite happy to work when rotating backwards - the only problem is the table won't automatically knock the drive off at the end of the travel!!


Anyway thanks for the ideas folks - will continue to look for the problem - I am sure there must be a springloaded clutch with a detent hidden somewhere in there!


Cheers,


Roger
 
I don't recall that the key is stepped. If the handle hasn't been recut, is there a possibility that the shaft side is worn? It doesn't take but a little bit of play to make the engagement too loose to pull. When I bent my key, it would almost pull in the slowest speed, but wouldn't reach far enough to touch in the other 5. There is a lot of leverage from the key to the swing gear. A tiny bit of slack translates into a lot of disengagement. I wonder if the key is unusally soft for safety; mine sure bent easily;maybe it is soft enough to wear down rapidly too.
 
Hello Roger,
I'm also working to get an old mill with a gearbox like yours going and will watch out for any findings or thoughts from the forum on my situation thru your questions as of right now I found that the Pin connecting the gearbox to the main shaft had sheared and was letting the hand wheel slip after a short turn. the gearbox looked in tact and except for the spring being bad on the three position detent for the for/rev handle all seems well. My problem now is that the motor has a couple of broken windings and I either need to convert or have this motor rewound! I too have just built a 3 Ph conveter to use on the mill and am hoping to keep everything 3 PH. Good luck with your mill and hope to get some power to my gbox soon.
 
Just a though on wiring up the mill (not an answer to your question)

When I wired my mill, I configured the wiring so if the main motor trips, the 3 phase power to the power feed is also killed (removed). I am using a home made phase converter, and I was not sure it would work reliably. I did not want the spindle to stop, and the power feed to keep feeding. The is a lot of mechanical advantage between low gear and the feed screw.

Good luck with your project,

Vince
 
I have the same gearbox wired for 440 volt. I need to re wire it to low voltage, 220 volt. does anybody have the wiring sequence for the motor from hi volt to low?
 
Bridgeport feedbox clutch/sheer pin

Hi Roger

I realize this is a super old post, but I now find myself in the same position asking the same questions. Yes I agree there seems to be a clutch system with a spring followed by a ball bearing.
I am looking for a detailed drawing for this setup and also what diameter should the sheer pin be and can one buy a sheer pin off of the shelf ?
George
 








 
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