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  1. #1
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    Question Need Bridgeport mill table advice

    I bought myself a Bridgeport mill, series 1. I'm in the process of rebuilding it. Not in bad shape but was coated with cosmoline and everything has to come apart. Today I slid the table off and cleaning it up I thought I would just sight down the ways and low and behold it has a bow to the table. Top of table and ways are bowed close to .010 on a 42" table, end being down and the middle high. The saddle shows wear on the outside not on the center, matching the table bow.
    To me this indicates that the table has been bowed form the beginning, hard to imagine from Bridgeport. The power feed circuit board is dated Mar 15, 1974, so not that old.
    Any sound advise would be greatly appreciated!

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    that doesn't sound good! one thing that comes to mind, cast iron, even a decent casting, is something of a "live" material, being non-homogenious and multi phase (not electrical phase, crystal structure). It is possible that a particular casting may change/warp in the months following manufacture.
    I would also look for signs of impact or other damage that could account for that.

    I think you are best off getting another table, trying to fix that sounds liken a terrible idea.
    would double check everything however to be certain, how are you checking? do you have a surface plate large enough, or are you using a straight edge? is it one end or both? guess it doesn't mater that much, but do triple check.

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    Someone here did some testing to prove that tightening, or for sure over tightening the tee slot nuts will peen the metal in the groove, expanding the top of the table lengthwise, causing the bow you see.

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    Thanks for the reply cyanidekid,
    I used a straight edge and feeler gauge and you can visibly see it by line of site. No signs that the table was hit, just normal usage.
    The bow is from end to end and like you said it probably warped after it was milled.
    Wonder if I take a day and a big torch to the top side, would it pull it straight or at least scrapable.

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    That I can believe, that would mean that most old Bridgeports have this bow, hmmmmm

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    Most BP tables are bowed. Unless you are doing long parts it does not matter, and if you are you should be using a bed mill. The tables get bowed because the saddle is so narrow the table does not have any support on the ends. It is thought that the edges of the t slot get distorted from use and this contributes to the problem as well. You can grind the table top flat if you want and scrape the dovetales to tighten up and align them. The saddle will naturally show wear at the ends, this is normal and is caused by the table being used near the end of it's travel.

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    a torch? good god no, don't even waste time thinking about that.
    if it is in fact the T slot nut over tightening, you could theoretically relax it with a heat soak, but if you can't get the whole table up to a uniform 1350-1500 and slowly cool, again just so not worth it. if it was the last BP table on the planet, why not, go ahead.

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    Moonlight Machine you have probably saved me a lot of wasted effort. I had no idea that most of these tables are bowed or even that it was possibly for them to sag over time. I'm still and always learning. Long work is not in its future! Thank you.

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    Quote Originally Posted by Gungaree View Post
    Moonlight Machine you have probably saved me a lot of wasted effort. I had no idea that most of these tables are bowed or even that it was possibly for them to sag over time. I'm still and always learning. Long work is not in its future! Thank you.
    I've just measured mine, it looks to be 0.008" higher in the middle along the length of the 42" table - never caused me any problem

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    Just went back to our grinder operator and was looking over his notes from the past 2 years on table grinds. Machines that came in for full rebuilds, the average bow seemed to be between 3 and 7 thou with most of those numbers being ad 5 and 6 thou. I did see a 9 and 2 10 thou tables, but I also saw a 1 thou and a 2 thou. After talking to him, 10 is definitely on the higher end of bow on the machines that we rebuild.

    Ontop of that, you can definitely get the table top and ways ground and then the ways re-scraped to get it super tight.

    Jon
    H&W Machine Repair

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    Now the money question, How much and were?
    I guess this is on of those personal preference things but I would like to be able to do cylinder heads.
    I am located it the far NW corner of the US. Probably the worst place for machinist tools as far as prices and repair.
    I will do some calling today and input my findings. I greatly appreciate all the feed back.

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    Quote Originally Posted by Gungaree View Post
    Now the money question, How much and were?
    I guess this is on of those personal preference things but I would like to be able to do cylinder heads.
    What kind of heads are you thinking about? 1 cyl or maybe 2? straight 6? Old flathead straight 8?

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    I just rescraped a 42" Bport table back to better than 3tenths and 20ppi that was bowed 5thou on top of table, more on worn part of ways. If you have time this is something any scraper hand can do. Got to admit, next time I have to do a table I'll just pay the momey and get it ground.

    Lucky7

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    To start with my Toyota v6, so I'm guessing 20" and maybe pushing it a straight 6.

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    I would love to scrape this one in and like you said, only once would I say that.
    How long did it take you?

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    Well, first you need to learn how to scrape, then get/make surface plate, straight edge, right angle, etc...

    Personally, with a table bowed as much as you say, I'd either sell it and get a better condition mill, or get it ground.

    The top of the saddle always wears on outside. You'll also need to scrape the knee (maybe column), the saddle, and refit or make new gibs in addition to however you deal with the table. You'll need to fit and scrape Turcite. Pros who grind the table talk about 60 hours to rescrape the rest. I'm no pro...

    Thankfully a Bport is simple. Imaging the amount of work with a universal K&T?

    Lucky7

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    Thanks Lucky7 for the reality check!
    I talked to H&W and for 3k they will rebuild the bottom end, Barry took the time to explain they whys, hows and what ifs. Basically if you do one surface your committed to do all the surfaces, everything needs to be parallel and square including the lead screw as it will move down with the table grind and be high in the center.
    I think I need more time money and tools

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    That's less than assembling the kit to do a rescrape, assuming you use a second hand Biax. OTOH, once you have the knowledge and tools, all sorts of other tuning up jobs in your shop become possible.

    Suggest, if you haven't, peruse the threads in the rebuilding forum in PM. Lots of good info and inspiration. Also suggest hand scraping, without a Biax, a short straight edge to see if you enjoy scraping before plunging into a Bport re-scrape. Denis Foster, who is active on PM, lives in your state and casts and scrapes very nice straight edges. For info, watch Stephan Gotteswinter and Keith Rucker's youtubes on hand scraping and rebuilding.

    L7

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    Quote Originally Posted by Gungaree View Post
    Thanks for the reply cyanidekid,
    I used a straight edge and feeler gauge and you can visibly see it by line of site. No signs that the table was hit, just normal usage.
    The bow is from end to end and like you said it probably warped after it was milled.
    Wonder if I take a day and a big torch to the top side, would it pull it straight or at least scrapable.
    Actually yes, IMO is IS possible to straighten a table with a torch. I have done it twice so far. I got a BEAT bridgeport last year, marked out the table in 6" increments and heated up a section on the side of the tee slot 2" wide, to just short of glowing rapidly with a rosebud, and let cool, and repeated across most of the table, I think I had five lines of them, so a total of 30 spots. It went from sagged .002" per foot or perhaps worse, to clear the other direction about .0007" per foot initially,I then slightly panicked at the overcorrection and hammered around the spots a bit and beat the table generally to relieve some of that stress, and it straightened somewhat, after a week settled to .0002" per foot concave.
    After a year of weekend work, it's now sagged back to probably .0003" per foot convex at the moment.

    I've just done it to a series II, and it seems to be about the same story. initially OVER corrected, but at the moment almost straight, at least to the point I can't determine how much is bend and how much is wear. As far as I can tell all the tables sag, and it's a shame, And I think we need to invent some way to deal with it.

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    Quote Originally Posted by Glenurban View Post
    Actually yes, IMO is IS possible to straighten a table with a torch. I have done it twice so far. I got a BEAT bridgeport last year, marked out the table in 6" increments and heated up a section on the side of the tee slot 2" wide, to just short of glowing rapidly with a rosebud, and let cool, and repeated across most of the table, I think I had five lines of them, so a total of 30 spots. It went from sagged .002" per foot or perhaps worse, to clear the other direction about .0007" per foot initially,I then slightly panicked at the overcorrection and hammered around the spots a bit and beat the table generally to relieve some of that stress, and it straightened somewhat, after a week settled to .0002" per foot concave.
    After a year of weekend work, it's now sagged back to probably .0003" per foot convex at the moment.

    I've just done it to a series II, and it seems to be about the same story. initially OVER corrected, but at the moment almost straight, at least to the point I can't determine how much is bend and how much is wear. As far as I can tell all the tables sag, and it's a shame, And I think we need to invent some way to deal with it.
    Glenurban, Nice job, I was hoping it would work but got scared off and had no idea how cast iron would act.
    Just to clarify the area you heated was not the full width but just the area on each side of the tee slots.


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