Need a diagnostic with problem on leadscrew assembly on Bridgeport Series 1 please?

[Randalthor]

The X axis leadscrew seems fairly acceptable on the machine (backlash about .012 to .015) However, there is a spot where the X axis crank moves, but the table doesn't. It sort of feels like something in the crank "jumps".

At that spot where the crank jumps, I noticed the graduated dial jumps out away from where it normally sits. In other words, while moving the table to the right, it has normal movement, but hits a spot where the table doesn't move, but instead the graduated dial moves a little away from the table, then for the rest of the travel, the table moves normal, without any hitches.

Here is a pic of the dial close to the table.



Here is the same dial the moment it jumps out away from the table If you look closely between the two photos, you can see a small gap. (If you click on the photos, you can get a pretty good closeup.)



Here is another photo where I have stuck a feeler gauge in between the gap. When the dial jumps out, the gap is about .020", otherwise it runs a gap of about .010"



Anyone have any idea what could be causing this?

 

[Paolo_MD]

It's hard to understand with your description.
Do you feel any more resistance when that happens? Is it something that happens at every revolution of the crank, or only at one spot in the whole movement of the table? If the second, where? Near the middle, or at one of the ends?

We likely need more detail in order to diagnose it.

Paolo

 

[Richard King]

If your mechanically inclined take it apart and figure it out. It's a super simple device.

Leadscrew Assembly

 

[rons]

Easy, clean the screw and nut.

 

[M K]

As mentioned, it’s very simple to take apart and remove the leadscrew to inspect it so worth doing and giving it a clean while your there,

Has it always done this or not or is this machine totally new to you

Thanks
Marc

 

[Technical Ted]

Lead screws need to be "captive" thrust wise, with only minimal end play to allow free rotational movement; maybe a couple to a few thousandths of an inch. Sounds like you have more than that. This could be caused by something being loose (end cap, hand wheel, etc) or wear. On mine, when I was fine tuning the end play for the power travel, I made sure that the left side of the lead screw and hand crank eliminated all of the unwanted lead screw end play. Then I shimmed the right end where the power feed goes. Whether you use power feed or not, you need to eliminate the unwanted end play you have. So, you probably either have some component loose or you'll have to shim someplace to correct.

Ted

 

[Randalthor]

Sorry for the poor description. I hope this helps some. This machine is new to me.

The problem just happens once, when the table is toward the left. As I start to crank it toward the right, it goes along smoothly for about a foot, then I can feel what feels like a little "bump" in the crank. At that very moment the dial moves away from the face of the table.

It's like at that point, the screw moves the dial, instead of the table.

As Ted mentioned, I don't think the leadscrew is "captive" at that point. I do plan to take it apart, but thought I'd post about the problem, so I know what to look for during disassembly.

Thanks.

 

[Clive603]

I've seen similar more than once, albeit not on a Bridgeport. Take everything apart, clean it all up carefully, inspect everything for damage and odd wear patterns, lubricate properly and put it back together. No more problem. Result!

Darned if I know what was actually wrong.

Over the years have had more than a few such odd problems bought to me and fixed by similar simple disassemble and put back together right procedures. Inclined to think that such are the result of attempted partial fixes which get things going well enough for a while and eventually run out of gas third or fourth time in. Doing the whole job right obviously sorts it.

If it were mine I'd pull both screws and the dog-bone feed nut carrier to give everything a proper go over. Heck I'd do the lift screw and drive assembly too whilst I was at it. But then Clive is anal about such. My argument is that similar things last similar amounts of time before attention is needed so when one sticks it hand up for attention the others won't be that far behind.

Your little bump feel suggests there may be an issue with slideways or gibs too. More careful inspection.

Clive

 

[Maschine]

Not exactly sure what the problem is, but as the others have said, take everything apart, thoroughly clean and inspect everything and then lubricate and reassemble. I have a HF hydraulic motorcycle stand that made it easy to slide the table off. But I could have also used my HF 2 ton lift as well (albeit more cumbersome). There's a big cast iron X-Y nut under the table that holds an adjustable brass split-nut for each axis. It is secured with a set screw that can be tightened or loosened to adjust runout. If it were loose, it might cause the problem you are describing. Or if the cast iron X-Y nut somehow came loose, maybe that has something to do with it? Or maybe some chips are stuck in the threads that is causing some strange movements? Hard to say.

One thing I do recall after cleaning and reassembling both of my leadscrews and X-Y nuts is that I still had what I considered excess play, especially in my Y axis. It ended up being caused by all the hardware associated with the function of the knurled nut and the baseplate shown in the pics above. It was dry and sticky and not adjusted properly and was preventing the proper lash adjustment at the crank handle itself (instead of the adjustable brass nut under the table). Taking all those parts apart, thoroughly cleaning, lubricating and reassembling everything fixed it and really reduced the total lash to very acceptable levels.

 

[Maschine]

Items 3-10 are mostly what I'm talking about. Also keep in mind the ball bearings present in these cranks could go bad or be dry and "notchy" too.

 

[Technical Ted]

Why does it do it in just that one location??? Wild guess on my part, but maybe for some reason there is a little more restriction in table travel at that location. This could be caused by wear, gib adjustment, etc.. Loosen the gib up and see if it does the same thing in the same spot. Could be the extra play in your lead screw doesn't shift until more resistance is encountered by more drag on the X travel???

Just a wild guess. But, yes, the answer is obviously to disassemble, clean, inspect and repair and/or make adjustments. It's a very easy machine to work on.

Ted

 

[Danny VanVoorn]

There are only two things that will cause the condition you describe. First is the thrust bearing is bad and has some slop in it? Second is the bearing mounting has some play in it? It's as simple as that but finding it is up to you; requires taking the assembly apart and looking for an adjustment or a gap in the mounting that needs tightening by what ever means necessary.
Dan

 

[Randalthor]

There are only two things that will cause the condition you describe. First is the thrust bearing is bad and has some slop in it? Second is the bearing mounting has some play in it?
Dan

Thanks.

I discovered tonight that #8 double bearing (in the schematic that Maschine posted above) has some axial play in it. It shouldn't have that should it?

I had mentioned the problem happens in one spot, but I couldn't always get the problem to duplicate in that spot. Just most of the the time.

 

[jhruska]

The table bearing on the left side is held and should not float. The bearing on the right side is not held and is allowed to float/slide into it's position.
The gap you see is because there is some axial play in the left side bearing and it floats left and right. When the table is all the way to the left and then advanced there is some resistance between the x-screw and the nut that results in a push against the bearing until it slides far enough to hit a stop. This pushes out the dial and is the gap. It occurs at variable locations because the screw resistance builds in a random way.
The resistance is typical of older machines that have less wear on the screw at the extreme end of travel. When the nut is adjusted for wear the screw will be much tighter at the full extent of travel, left and right. Forcing the screw into the area of least wear hastens wear on the nut.

John

 

[rons]

Thanks.

I discovered tonight that #8 double bearing (in the schematic that Maschine posted above) has some axial play in it. It shouldn't have that should it?

I had mentioned the problem happens in one spot, but I couldn't always get the problem to duplicate in that spot. Just most of the the time.

Get a piece of nylon cord or rope and wrap it around the screw from underneath. Turn the screw while holding onto the cord to clean the threads. Use different parts of the rope as you turn the screw. Clean it all up then see what happens.

 

[Maschine]

One more thing I was thinking about in case you haven't heard about it yet: It is common for Bridgeport owners to cut the brass split nuts in two in order to gain better control on lash adjustment. If this was done to your machine and the nut is loose or not properly tensioned, maybe it could cause a problem similar to what you're having? Here's a video where a guy goes through the process...

 

[Danny VanVoorn]

Get a piece of nylon cord or rope and wrap it around the screw from underneath. Turn the screw while holding onto the cord to clean the threads. Use different parts of the rope as you turn the screw. Clean it all up then see what happens.

If you read the OP he has a gap it the collar that changes. The change in the gap of the graduated collar has nothing to do with the screw threads, that can only be the thrust bearing set up. Now if he showed some back lash: the collar rotating .020"-.060" then that would be play in the screw/nut combination.
Dan

 

[Paolo_MD]

I think that what you observe is the consequence of something else, like a bur or galling on the ways that increase the resistance of movement in that particular position. Of course, the thrust bearing at the left side of the leadscrew needs to be adjusted. BUT the major issue is the condition of the way of the table.
I bet that, if you slide the table back and forth after removing the leadscrew, you will feel one or more hard spots. Stone carefully any bur or any sign of galling from the ways and clean all the oil passages. If it has a one-shot oiler, make sure that oil is being delivered to the ways and not a single oiling orifice is clogged.

Paolo

 

[Randalthor]

Thanks to everyone for all the great help. I have removed the screw and it looks good so far. I plan to clean it thoroughly and examine it closely. The table seems to move freely on the ways. If I get some time today, I will pull it completely off and feel for any galling or burs on the ways and table.

I do plan to clean the ways of the table, saddle and knee thoroughly and make sure all oil passages are open to the one shot oiler, as suggested.

The gap you see is because there is some axial play in the left side bearing and it floats left and right.
View attachment 224692View attachment 224691
John

John,

Should there be axial play in the left side bearing? In other words, does the axial play I'm feeling in the bearing exist when the bearing is brand new.

Your explanation of the resistance in the screw pushing out the dial makes the most sense to me. But, I'm a little unclear as how to remedy the situation.

Are you saying simply tightening the screw nut will prevent the dial from being thrust away from the table, or that replacing the left side bearing will prevent it, or is the fix something more drastic like replacing the longitudinal screw?

 

[Randalthor]

One more thing I was thinking about in case you haven't heard about it yet: It is common for Bridgeport owners to cut the brass split nuts in two in order to gain better control on lash adjustment. If this was done to your machine and the nut is loose or not properly tensioned, maybe it could cause a problem similar to what you're having? Here's a video where a guy goes through the process...

Thanks Maschine. I will check to see if the nut is split after I remove the table.