Bridgeport Constantly Loses Accuracy - Page 2
Close
Login to Your Account
Page 2 of 2 FirstFirst 12
Results 21 to 34 of 34
  1. #21
    Join Date
    Sep 2006
    Location
    Sacramento County, California
    Posts
    3,460
    Post Thanks / Like
    Likes (Given)
    1954
    Likes (Received)
    1042

    Default

    Quote Originally Posted by CarbideBob View Post
    "I have a ProTram from EdgeTechnologies. I tram the BP with it."
    I will not touch the many reasons this type system does not and never will work or repeat.
    It all looks good on paper but ..... I live in the real world.
    Your head may in fact be moving, I don't know but this is a terrible method to check it.
    Bob
    You said the magic word "repeat". A very important factor in any measuring method, device or system is the ability to repeat or its "repeatability". I wondered about accuracy and repeatability when I first saw the ads for the ProTram unit. With two dial indicators, I just don't see how it could ever repeat when checked over and over again.

    I have a big Webb mill and regardless of whatever anyone might say or think about Taiwanese machines, I can guarantee that it doesn't move when I'm not using it.

  2. #22
    Join Date
    Oct 2010
    Location
    Dewees Texas
    Posts
    1,884
    Post Thanks / Like
    Likes (Given)
    24
    Likes (Received)
    479

    Default

    First thing I thought of is the table is worn, with some low spots. The OP might put some pencil marks on table and saddle and always tram at that location. Swing the indicator on the same radius also. Tightness of the of the knee gib could cause that also (mentioned already). The OP mentioned tightening the head bolts very tightly, supposed to be 50 foot pounds to bring the quill casting back round, no reason for overdoing that as it is machine abuse.

    Added thought worn quill? Especially with over torqued bolts, maybe check the quill with different amounts of extension?

  3. Likes Newman109, Oldwrench liked this post
  4. #23
    Join Date
    May 2009
    Location
    Canandaigua, NY, USA
    Posts
    2,592
    Post Thanks / Like
    Likes (Given)
    115
    Likes (Received)
    1046

    Default

    Ours does the same thing. I think it's a BP "feature". You just have to check it on a regular basis. We've used the ProTram without trouble until I broke it, and also the traditional single indicator. No problems with the measurement, the head just moves with use and time.

  5. #24
    Join Date
    May 2003
    Country
    UNITED STATES
    State/Province
    Iowa
    Posts
    10,410
    Post Thanks / Like
    Likes (Given)
    3530
    Likes (Received)
    4189

    Default

    Quote Originally Posted by Conrad Hoffman View Post
    No problems with the measurement, the head just moves with use and time.
    If you're pushing an insert mill, yes. Under normal use, you shouldn't have to worry about the head moving. That's if the thing was put together correctly and you torque the bolts.
    JR

  6. Likes Matt_Maguire liked this post
  7. #25
    Join Date
    Feb 2005
    Location
    Hatch, NM Chile capital of the WORLD
    Posts
    8,650
    Post Thanks / Like
    Likes (Given)
    12358
    Likes (Received)
    9865

    Default

    Had an old Wells Index years ago. The head kept coming out of square..

    Square it up, tighten it up, and with a little use, it was out of square again,
    and the bolts/studs that held it were kind of loose.. Square it, tighten it, a few
    days later they were loose again...

    The problem. The studs that held the head had been OVER tightened SOOOO MANY!!! times over
    the years that they had reached the yield point.. Crank 'em down tight, and over a short
    amount of time they would slowly stretch and loosen.. When I finally pulled them out, they
    were nicely hour-glassed (<--- that can't be a real word)...

    New grade 5 studs and all was good again.

  8. Likes JRIowa, Oldwrench, CarbideBob, AlfaGTA liked this post
  9. #26
    Join Date
    Mar 2009
    Country
    UNITED STATES
    State/Province
    California
    Posts
    4,375
    Post Thanks / Like
    Likes (Given)
    82
    Likes (Received)
    748

    Default

    Quote Originally Posted by Bobw View Post

    The problem. The studs that held the head had been OVER tightened SOOOO MANY!!! times over
    the years that they had reached the yield point.. Crank 'em down tight, and over a short
    amount of time they would slowly stretch and loosen.. When I finally pulled them out, they
    were nicely hour-glassed (<--- that can't be a real word)...

    New grade 5 studs and all was good again.
    Get a torque wrench and tighten almost to spec. Then use a manual wrench and tighten the last small bit and get a feel for the fit. Recheck with the torque wrench. Process takes less than a minute. Then over-tightening damage can be avoided.

    Also put a sign on the mill, "NO GORILLAS WITHIN 10 FEET".

  10. Likes JRIowa liked this post
  11. #27
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    20,254
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    6465

    Default

    Quote Originally Posted by rons View Post
    Also put a sign on the mill, "NO GORILLAS WITHIN 10 FEET".
    You must be single to risk that?

    If not, and yer blanket-sharer asks to measure you for a gift of clothing, then runs a measure from knuckles to the deck, your shop is about to be sold-off for scrap and replaced with treadmills, flower pots, yoga mats, tennis rackets, pottery kiln, paint easels, or such girlie stuff.


  12. #28
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    20,254
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    6465

    Default

    Quote Originally Posted by Bobw View Post
    Had an old Wells Index years ago. The head kept coming out of square..

    Square it up, tighten it up, and with a little use, it was out of square again,
    and the bolts/studs that held it were kind of loose.. Square it, tighten it, a few
    days later they were loose again...

    The problem. The studs that held the head had been OVER tightened SOOOO MANY!!! times over
    the years that they had reached the yield point.. Crank 'em down tight, and over a short
    amount of time they would slowly stretch and loosen.. When I finally pulled them out, they
    were nicely hour-glassed (<--- that can't be a real word)...

    New grade 5 studs and all was good again.
    Beginning to wonder if half the horror stories ever told about overly-flexible Bridgeport mills were due to operator headspace error rather than slippery design.. but never mind..

    Size of the bolts used on the Quartet, I'd need a longer cheater bar to damage than they left room enough to get into place and swing. More than one definition of "clever design feature", one supposes.

  13. #29
    Join Date
    Jan 2007
    Location
    s w NH
    Posts
    227
    Post Thanks / Like
    Likes (Given)
    138
    Likes (Received)
    71

    Default

    Quote Originally Posted by Newman109 View Post
    I have a big Webb mill and regardless of whatever anyone might say or think about Taiwanese machines, I can guarantee that it doesn't move when I'm not using it.
    I can say for my Acra based cnc, in 10 yrs of daily use it didn't move even when using it. using insert tooling, ie 1" iscar 3 fl apkt, or 2" lovejoy hi rake 3 fl octagon, possibly a little movement after a lot of hard work. maybe out of tram .003 in 8" from ctr sweep using a .0001 indicator and a jo block to table surf. and this with a speed, depth and per tooth load that had made more then one person who considered "bridgeports" flexible look and say "WTF?"


    far as a torque reading for bolt tightening, it was always snug, tighten medium, then tighten the shit out of em. id guess way in excess of 50 ftlb.

    never understood need for the 2 indicator tramming aids. a bent rod, .0001 indicator, jo block. easy. do x or y, then the other, then repeat to fine tune. to move the last little bit, forget the worm, and tap around with a no mar hammer.

  14. #30
    Join Date
    Jan 2007
    Location
    Flushing/Flint, Michigan
    Posts
    6,500
    Post Thanks / Like
    Likes (Given)
    273
    Likes (Received)
    5287

    Default

    I'll run 6, 8 and 10 inch milling cutters on a B-port or clone and stall the spindle on a regular basis.
    The whole machine/spindle does twist under such loads so you intentionally tram off square for this use.
    But in my experience they don't move on their own from the hammering if your bolts and nuts are in good shape.

    Not much substitute in my world for an plain ole Indicol and a tenths or 50 millionths DTI but you do need a mirror.
    Pushing a bit sideways on the inside of the taper or top of the head with the indicator in place gives you an idea about how flexy this system is.
    Everything bends, everything moves when loaded so you comp for that.
    Point a laser interferometer at your building's concrete block wall and then lean on that wall............
    Yet people will indeed hold a handful of tenths on these machines.

    Unsure the OP's actual problem.
    The base test is a gauge R&R using different clamp ups and orients varying as much as possible on everything possible you can think of.
    This gives you a "trust" number.
    Out of the box I trust no gage no matter the name or other's experience, It has to prove it to me and my shop's use.
    Bob

  15. #31
    Join Date
    Sep 2009
    Location
    Apex, NC
    Posts
    1,209
    Post Thanks / Like
    Likes (Given)
    1
    Likes (Received)
    577

    Default

    I would be interested in an explanation of why the "easytram" widget approach is not accurate. I made one from two old high-quality Federal indicators and it seems to work well (within the expected tolerance of a BP). Assuming you have two decent indicators, I place a 246 block on the table, rotate one axis to get a reading (usually with quill locked and moving knee near where most of the work will be done if possible), zero that dial,mark the spot on the 246 block with a marker, rotate 180 to the spot and zero the other dial, take reading and adjust head to same readings; repeat for other axis; recheck both axes. And I do some fairly piddly work on the BP at times (stepped boring precise holes, deep holes drilled from two ends of a part hanging off the edge of the table with an angle-block, dowell-pinned fixtures, etc., never noticed an issue with the "widget". A single DTI is not foolproof, besides using a mirror, have to make sure the setup is rigid enough and that it does not move during the entire process of monkeying with it (not an issue with the "widget").

  16. #32
    Join Date
    Dec 2008
    Country
    UNITED STATES
    State/Province
    New York
    Posts
    8,752
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    2321

    Default

    double indicator setup for tramming bridgeport always worked fast for me but. if it takes more than a few minutes you got problems
    .
    1) table surface not perfect. you check different spot and if .001" different wouldnt surprise me
    .
    2) as machine warms up and cools down. alignment can change. .001" change not unusual
    .
    3) heavy milling can easily knock a bridgeport head out of tram, i have often had it happen especially if a cutter like a end mill is broken. i always check tram usually daily as if drilling holes and head is leaning as quil is extended it changes XY position cause of the head leaning. many a hole or milled surface can be easily off .002" if head not tram....... flycutter with the slow speed high force wack wack wack can easily knock head out of tram
    .
    4) make sure gibs are 1/2 tight on knee and X and Y. if loose your whole vise and table can be moving around cause its loose

  17. #33
    Join Date
    May 2005
    Location
    AZ
    Posts
    2,214
    Post Thanks / Like
    Likes (Given)
    193
    Likes (Received)
    737

    Default

    One thing to check if the machine is an older unit, from my personal experience:
    The circular T-slots in the head mounting surface can be a source of never-ending drift, if they are chewed up on the internal bearing surface that the T-bolt heads clamp on. I have a 1958 J-head machine that I bought about 10 or so years ago, and had almost zero success tramming into alignment. Finally removed the head and found the T-slot surfaces completely cratered at the "normal" orthogonal positions where head would be set square to table. I had to replace that part before I could really do any decent work on that machine.

  18. #34
    Join Date
    May 2003
    Country
    UNITED STATES
    State/Province
    Iowa
    Posts
    10,410
    Post Thanks / Like
    Likes (Given)
    3530
    Likes (Received)
    4189

    Default

    Quote Originally Posted by car2 View Post
    I would be interested in an explanation of why the "easytram" widget approach is not accurate.
    Did you look at my pic of how I tram a head? I'm probably out there with a 4" radius while the "widget is 2-3". I don't need no stinkin' mirror!

    For those of you that lock everything down to tram, is that how you mill? I try and mimic the milling condition the best that I can. maybe tight Z & Y and loose X. It depends! If it's taking you longer than 15 minutes to tram a head, you've got problems. I've seen the same thing as Bob described with stretched bolts, but on a SuperMax.

    It's akin to mounting stuff in a 4-jaw. If you do it enough, you get damn good at it.
    JR


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
2