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Adjusting Bridgeport Table Gib

Rick_B

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#1
I am in the process of reassembling the table on my Bridgeport - is there a good way to know when the gib is adjusted properly? I was thinking of running it in as far as it would go and then backing off - but to where? Table tight but smooth movement with the lead screw? It seems if the table is too tight then there may be excess stress on the lead screw and nut?

Thanks
Rick
 

Richard White (richardsrelics)

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#2
I have never worked on a "new" Bridgeport, so everyone I have ever used ends up have good movement in the middle and little to no slop out near the ends of the travel range..

Keep in mind after having used these machines for over 30 years, maybe only 2 dozen times have I ever needed the full length of travel, so at work I snug it up so the middle is snug but not tight, and if I need to go outside 16 inches or so, I loosen it up.... Also remember when you loosen that screw for the gibs up, your table will NOT track in a straight line, the slop created by loosening the gib allows it to move, beware of that should you need somewhat accurate machining.
 

Rick_B

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#3
So Richard - how do you measure "snug" - this is an older machine so I am sure I would have the wear you describe. Is snug simply that you can't wiggle the table by hand but it still moves with the lead screw (one extreme) or is there a more scientific way to do it. I'm pretty new to this so patience is requested :)

Rick
 

Bob Korves

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#4
If you want to run it to the ends, set it at the ends to something that is not too tight to move, and then live with the slop in the center, or set it nearer the center and understand that the ends of the travel will be unusable unless readjusted. Grabbing the end of the table and shaking it to the front and rear will give you an idea of how much slop you have. A dial indicator in the middle of the table, attached to the spindle or other stationary parts of the machine, will tell you nearly nothing about this. You need to indicate from the stationary parts of the machine to the end of the table to get useful results.
 
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Rick_B

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#5
I did find a fairly useful YouTube video that describes the process using a dial indicator. I may give that a try/

Rick
 

Rick_B

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#6
I just checked my table with a dial indicator and was getting .010" + play but then I locked the saddle and got next to nothing. So then I locked the table, unlocked the saddle and got .010" play. The saddle gib is as far in as it will go. Based on this I assume I need to shim the gib at least .015" - does that sound right or should I go a little bit more - maybe .020" or .025"? Unfortunately I don't have any shim material in of those sizes so another delay while I figure out where to get some.

BTW - I also checked the knee and it seemed very good as well.

Rick
 

Bob Korves

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#7
I just checked my table with a dial indicator and was getting .010" + play but then I locked the saddle and got next to nothing. So then I locked the table, unlocked the saddle and got .010" play. The saddle gib is as far in as it will go. Based on this I assume I need to shim the gib at least .015" - does that sound right or should I go a little bit more - maybe .020" or .025"? Unfortunately I don't have any shim material in of those sizes so another delay while I figure out where to get some.

BTW - I also checked the knee and it seemed very good as well.

Rick
If you found .010" play at the end of the table, the actual play in the gib is much smaller than that. Start with a thinner shim (.005"?) and see what you get. I have never shimmed gibs, so perhaps others will chime in here as well... I guess as long as you can insert the thickness in there along with the gib, it could do the job.
 

Rick_B

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#8
Bob - you must have been looking over my shoulder this afternoon :) I had some .012" aluminum flashing that Itried just to see - it was way too much. Then I tried some .005" copper I had laying around - that was just about right. I did notice that the saddle was tighter in the front so I compromised and adjusted the gib with the spindle in the center of the table. Currently in that position I am getting less than .001" looseness in the saddle.

Rick
 

Bob Korves

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#9
Bob - you must have been looking over my shoulder this afternoon :) I had some .012" aluminum flashing that Itried just to see - it was way too much. Then I tried some .005" copper I had laying around - that was just about right. I did notice that the saddle was tighter in the front so I compromised and adjusted the gib with the spindle in the center of the table. Currently in that position I am getting less than .001" looseness in the saddle.

Rick
Did you check on how tight it gets toward the ends of the travel?
 

Rick_B

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#10
Bob - I did check the front side for tightness - its definitely tighter but still moves (I don't need to use two hands to turn it :)). I did not check the back. Is there a fix for the variation in tightness which I am assuming is due to wear other than rescaping? I was thinking the best approach is to adjust the gib base on where the majority of work is beng done.

Thanks
Rick
 

Bob Korves

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#11
The correct repair is to scrape or surface grind the ways until they are parallel and geometrically true. I think is possible to use a adhesive plastic shim material that is similar to Rulon to fill the low spots to fill part of the wear, but I have no experience with it and know little about it. It is a stopgap repair. I think McMaster-Carr sells it, and perhaps others as well. Perhaps something like this:
https://www.mcmaster.com/#ptfe-tape/=16doh7f
It is a huge precision job to scrape in a mill correctly. It is an expensive job to have the parts ground or scraped by professionals, and often the work is not done to high standards. Usually the practical answer is to live with it or replace the machine...

You can adjust the gib, but any adjustment on a worn machine will be a compromise between too loose in the worn areas or too tight in the areas with less wear. Do check the fit in the other direction. It might be quite different depending on how the mill has been used.
 

Richard White (richardsrelics)

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#12
Turkite is used to repair the way to bring everything back to specs.... I have a mill, at work, that has had that process performed. H & W Machine is the company that performed this service. They measured the table, determined how far off it was and made the appropriate repairs. I have more issues with the lead screw half nuts than with the Turkite.
 
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