Y ball screw issue

[Threadkiller]

Hey all. I have a Bridgeport with ball screws on the x and y. The x is silky smooth but the y has always been somewhat of a bear to turn, more so towards me (in the negative direction I guess that would be). I figured it was just wear in the ways but today I noticed that turning the handle so the table moves towards me in the negative direction the screw goes inward towards the machine and the dial collar makes contact with the knee and that’s what makes it so hard to turn. Going the other way is much easier because the dial moves slightly away from the knee so I’m not fighting the friction of the collar metal on metal. I’ve attached some pictures. It seems as though I’m missing something that would help capture/connect the screw to the bearing in the bearing housing. There’s a shoulder that the bearing rides against in the easy direction but in the negative direction the screw unthreads itself and that’s when the collar makes contact with the knee. Anyone have a similar setup that wouldn’t mind taking some pictures for me or something it would be greatly appreciated.

 

[projectnut]

I don't know of any manual Bridgeport that came from the factory with ball screws. I'm guessing it was either an early servo operated machine converted back to manual operation, or something the previous owner did in an effort to make table movement easier.

I think your best resource for information and possible parts or repairs would be H&W Machine Repair and Rebuilding. Over the years I've talked with them on several occasions and bought a few parts for my Series I Bridgeport. They're very friendly, easy to talk to have extensive knowledge on the machines, a good parts inventory and good prices. If anyone can help you, they can.

Home

Your trusted source for Bridgeport Machine Replacement Parts and Services. We're the best place to get metalworking parts & services online!

machinerypartsdepot.com

 

[RJSakowski]

My guess, definitely a thrust bearing issue. It sounds like either a misadjusted thrust bearing or missing part(s). If this was an OEM setup, I would take @projectnut 's advice. If this was an upgrade by a PO, then all bets are off.

My Tormach mill. uses angular contact bearings and a pair of nuts and washers to adjust preload on the thrust bearings. the ball shaft has a shoulder as a stop and is threaded for the nut as the second stop. If the nuts were not adjusted correctly, would pull the table in would tend to pull the lead screw into the table further as you describe. In my case it would just pull my stepper motor deeper in and I would just have an increased backlash problem. In your case, your collar is rubbing.

The solution is to remove the excess backlash by adjusting the retaining nut(s) or add a shim to take up the backlash. You might want to pull the x axis apart to see how that is configured. That should tell you if you are missing parts.

BTW, you should be seeing a serious backlash problem with y axis too.

 

[Threadkiller]

My guess, definitely a thrust bearing issue. It sounds like either a misadjusted thrust bearing or missing part(s). If this was an OEM setup, I would take @projectnut 's advice. If this was an upgrade by a PO, then all bets are off.

My Tormach mill. uses angular contact bearings and a pair of nuts and washers to adjust preload on the thrust bearings. the ball shaft has a shoulder as a stop and is threaded for the nut as the second stop. If the nuts were not adjusted correctly, would pull the table in would tend to pull the lead screw into the table further as you describe. In my case it would just pull my stepper motor deeper in and I would just have an increased backlash problem. In your case, your collar is rubbing.

The solution is to remove the excess backlash by adjusting the retaining nut(s) or add a shim to take up the backlash. You might want to pull the x axis apart to see how that is configured. That should tell you if you are missing parts.

BTW, you should be seeing a serious backlash problem with y axis too.

This was an upgrade from a previous owner. It sounds like the same issue im having. There is definitely a backlash issue as well. Thank you

I don't know of any manual Bridgeport that came from the factory with ball screws. I'm guessing it was either an early servo operated machine converted back to manual operation, or something the previous owner did in an effort to make table movement easier.

I think your best resource for information and possible parts or repairs would be H&W Machine Repair and Rebuilding. Over the years I've talked with them on several occasions and bought a few parts for my Series I Bridgeport. They're very friendly, easy to talk to have extensive knowledge on the machines, a good parts inventory and good prices. If anyone can help you, they can.

Home

Your trusted source for Bridgeport Machine Replacement Parts and Services. We're the best place to get metalworking parts & services online!

machinerypartsdepot.com

I am going to try to contact H&W today and see what they say. It would be nice if they know what im talking about and its a relatively easy and cheap fix. I thought about drilling a hole in the leadscrew and putting a pin to keep the bearing against the shoulder on the leadscrew so it no longer moves back and forth. Id rather not do that if theres an easier fix.

Thank you for the replies/input.

 

[RJSakowski]

The primary reason for upgrading from a lead sacrew to a ball screw is to eliminate (or virtually reduce) lost motion or backlash. The conversion should have had some means of doing that. A pin should not be necessary.

Backlash will occur in three places, the ball screw bearing, the thrust bearing(s), and in windup due to increased torque due to drag in the ways. caused by an over tightened gib or rough surfaces.

 

[sdelivery]

This is a common problem with brisgeports with or without ball screws open up the BP manual. Make sure you have all the parts and adjust it by the factory procedure.

 

[Threadkiller]

This is a common problem with brisgeports with or without ball screws open up the BP manual. Make sure you have all the parts and adjust it by the factory procedure.

Oh wow I didnt know that. Than you. I will find a manual.

The primary reason for upgrading from a lead sacrew to a ball screw is to eliminate (or virtually reduce) lost motion or backlash. The conversion should have had some means of doing that. A pin should not be necessary.

Backlash will occur in three places, the ball screw bearing, the thrust bearing(s), and in windup due to increased torque due to drag in the ways. caused by an over tightened gib or rough surfaces.

Thank you for the reply. I am going to call up H&W machine today. I emailed them and Barry thinks the bearings could be the cause.

 

[RJSakowski]

Ball screw conversions usually use opposing angular contact bearings to minimize lost motion aka backlash. If one or both of the bearings is reversed, it won't be possible to eliminate lost motion. You should be able to adjust out lost motion even if a bearing is totally shot. I would check the thrust bearing assembly for wrong assembly or missing parts first.

 

[sdelivery]

It takes about ten minutes to disassemble. I don't see a bearing number on this bearing and I am not near the manual.

 

[sdelivery]

If you need or want you can just take the entire screw assembly off with just four screws and take it to the bench....you can see the dark section behind holds the bearings....