Where to get knee gib?
Close
Login to Your Account
Results 1 to 18 of 18
  1. #1
    Join Date
    Dec 2017
    Country
    UNITED STATES
    State/Province
    Rhode Island
    Posts
    140
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default Where to get knee gib?

    Well I was reinstalling my knee gib for a general test fit of everything before likely tearing down the machine for cleaning and overhaul, and tapped it lightly and the corner broke off. I had no idea these were cast iron!

    It measures 15" long, .220" lower end thickness, .450" thick at the top, 503 stamped on it as well.

    Are any of these made of steel?

    Any advice on replacing this appreciated.


    20191114_220245-busted-gib.jpg

  2. #2
    Join Date
    Jan 2010
    Country
    UNITED STATES
    State/Province
    Arizona
    Posts
    50
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    11

    Default Where to get knee gib?

    H & W carries them. 1158 - Knee/Column Gib. They require some, possibly extensive fitting/grinding. Looking at your broken part, I wonder if you could get it tig welded and re-use it?


    Sent from my iPad using Tapatalk

  3. Likes HWElecRepair liked this post
  4. #3
    Join Date
    Dec 2017
    Country
    UNITED STATES
    State/Province
    Rhode Island
    Posts
    140
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default

    Thanks. Can you give a short description of this fitting process? I wouldnt even know where to begin, but I guess I'll have to. Can also check on welding it but it's cast iron which is pretty brittle.

  5. #4
    Join Date
    Jul 2006
    Location
    Hillsboro, New Hampshire
    Posts
    7,496
    Post Thanks / Like
    Likes (Given)
    1766
    Likes (Received)
    5216

    Default

    Check into brazing or even hard silver soldering for the broken bit. Easier than nickel welding in cast iron, and about as strong.

  6. Likes Newman109 liked this post
  7. #5
    Join Date
    Dec 2017
    Country
    UNITED STATES
    State/Province
    Rhode Island
    Posts
    140
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default

    OK. I just watched some videos on scraping, and also shimming gibs, etc. Also searched here and found that any new gib will likely need to be fitted that way. Actually, technically, the dovetails should be scraped straight and parallel. I'm not even close to equipped for such work. This is an old, beat BP.

    I guess I can try to braze the gib piece. (this is apparently a common breakage point) So I also read about repairing it by scabbing on a new end piece and grinding below the surface so as not to damage the dovetail surfaces.

    But I think I may try to braze it on. Others have. Doesnt sound like the gib screw applies too much force.

    Also learned about not letting the knee drop to the bottom with the broken gib in (it's out anyway) because the knee and gib can get badly stuck.

    Well if nothing else this will be a good machine to learn about a Bridgeport Mill!

  8. #6
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    27,243
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    8492

    Default

    Quote Originally Posted by FlyinChip View Post
    Doesnt sound like the gib screw applies too much force.
    Sometimes no "extractive" force at all.

    Presuming you can simply back-off the "push" screw, apply a nudge from the opposite end with a Bronze or Brass drift... then go back to pushing.

    More than a few machine-tools out in the world with busted-off hook-ends on their gibs being adjusted that way, "other priorities" such as earning a crust, etc..

  9. #7
    Join Date
    Dec 2013
    Location
    Fort Wayne, IN
    Posts
    668
    Post Thanks / Like
    Likes (Given)
    737
    Likes (Received)
    247

    Default

    Any gib you buy will be oversized and need to be ground/scraped in to get it to fit. We have repaired them before, can you post pictures of your broken gib? Depending on the damage, can give ya some ways to go with this.

    Jon
    H&W Machine Repair

  10. Likes jhruska liked this post
  11. #8
    Join Date
    Dec 2017
    Country
    UNITED STATES
    State/Province
    Rhode Island
    Posts
    140
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default

    Quote Originally Posted by HWElecRepair View Post
    Any gib you buy will be oversized and need to be ground/scraped in to get it to fit. We have repaired them before, can you post pictures of your broken gib? Depending on the damage, can give ya some ways to go with this.

    Jon
    H&W Machine Repair
    hi john if you scroll up the picture is there in my first post... I just realized a I subscribed to your youtube channel last night. great videos. I also found on other channel some on scraping a gib. I dont have the equipment to even try it as I think I need a scraper and a flat stone, not to mention never having done it.

    There is also some posts on here that technically should straighten the dovetail surfaces and parallel them al though on an old machine like this one not sure that would be worth it.

  12. #9
    Join Date
    Jul 2009
    Location
    Munster, In. USA
    Posts
    2,318
    Post Thanks / Like
    Likes (Given)
    471
    Likes (Received)
    700

    Default

    I have a ground fixture used to mount gibs for milling to size. The taper per foot I recall is 1/8". To bring a gib to size requires a calculating the amount of drive - the distance the gib has to go to engage the adjuster. To cut a new knee gib you will need machine table travel that is greater than the length of the gib.
    A good braze may be adequate and your best choice.
    With the gib removed the table and saddle can be centered and moved towards the column. This will allow a gap in the dovetails for cleaning.
    Adjustment:
    Oil the gib and the ways with heavy wt. oil.
    Set the knee height about the middle of travel before installing the gib.
    Insert the gib and raise the knee (with table and saddle centered to avoid side loading) and screw in the gib at the same time.
    If too tight drop the knee and back out the gib screw at the same time. This is the best way to remove any gib.
    If a gib will not back out do not force the adjuster screw. Set a piece of material the appropriate dimensions in contact with the bottom end of the gib and drop the knee to apply upward pressure.
    John

  13. #10
    Join Date
    Dec 2017
    Country
    UNITED STATES
    State/Province
    Rhode Island
    Posts
    140
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default

    This is all interesting. I will see about just having the gib brazed.

    Brings up a few questions like what if a gib is not ground or scraped properly? Does this simply result in thousandths of slop in the knee of what other issues? What equipment is required to scrape in a gib properly (besides the skill)? How important (or not) is it to true up the dovetail surfaces?

    In my case of course it looks like I'll have the piece brazed back on and reuse this gib, see how things are with the whole machine I've never run it no idea how good it really is yet. It's old, and dirty and a little surface rust here and there thats all I know!

  14. #11
    Join Date
    Jan 2007
    Location
    Flushing/Flint, Michigan
    Posts
    7,776
    Post Thanks / Like
    Likes (Given)
    390
    Likes (Received)
    6470

    Default

    It's very common to find this brazed on a used B-port.
    Remember that after brazing the inside wall needs to be recut to be somewhat flat as there will be a big ole blob of braze in the slot.
    This can be a problem if you own only one mill and it is apart. I've seen it hand worked with a die grinder when no other options.
    Bob

  15. #12
    Join Date
    Aug 2014
    Location
    bainbridge island
    Posts
    1,147
    Post Thanks / Like
    Likes (Given)
    219
    Likes (Received)
    270

    Default

    Quote Originally Posted by FlyinChip View Post
    .450" thick at the top
    where that corner tab broke off, remove 1/4" from the end of the gib.

    drill and tap a hole in the end of the gib, probably 1/4-20. take a 1/4" plate of steel with a hole in it and bolt it to the end of the gib. Cut the steel down so its flush with the gib on all the critical surfaces. --no stress risers, no tab to break off again.


    or just braze it.

  16. #13
    Join Date
    Mar 2008
    Location
    Huntsville, AL
    Posts
    53
    Post Thanks / Like
    Likes (Given)
    71
    Likes (Received)
    10

    Default

    As others have said, braze it. I brazed mine on my bridgeport when I got it in 2006. It's still going good 13 years later. We don't use it every day but it gets used several times a week.

  17. #14
    Join Date
    Sep 2016
    Country
    UNITED STATES
    State/Province
    New Mexico
    Posts
    18
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default

    I have mended several small cast iron pieces with Harris Safety-Silv 45 brazing rod. I degreased them and painted the broken faces with white Stay-Silv but got much better wetting when I sprinkled "Hot Max 24000" granulated flux on when they were up to temperature. I lightly clamped things together with some flat bar bent into a "C" shape and put two MAPP gas torches on the parts sitting on fire brick. I augmented that with a third propane torch on the largest piece, which was an old broken solid mill vise handle. If you have a good torch you will probably have an easier time of it. Heat and flux are your friend. One piece was the broken spindle brake ring from my Clausing 8520 mill, and I was especially pleased with how that turned out. I shimmed the split side to keep it round when clamped up, and it turned out nearly perfect. When I filed it down I was rewarded with a beautiful silver hairline where the break had been, and it's been holding for nearly two years now.

    Good luck!

  18. #15
    Join Date
    Dec 2017
    Country
    UNITED STATES
    State/Province
    Rhode Island
    Posts
    140
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default

    I have an oxy-acetylene setup. I can throttle back the welding tip pretty well. what braze rod should I use? any other flux if the rod has a coating? does it have to be that safety silv silver rod? I wonder if thats available at my local welding supply...

    also I should add, the cutting off, and drilling/tapping for a new steel top piece is interesting too.

  19. #16
    Join Date
    Sep 2016
    Country
    UNITED STATES
    State/Province
    New Mexico
    Posts
    18
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default

    At the time I did a lot of searching on brazing cast iron and the Safety-Silv 45 was recommended, but I don't remember where now. I bought the rod and flux from Amazon at the time, and I see that flux-coated rod is available now which I don't remember seeing then.

    That said, someone with a TIG setup might be able to build that small broken bit back up for you to the point that you could regrind it to shape. Interesting advice here for using aluminum bronze filler.

    If you do a little searching I'm sure you can come up with other recommendations. There are a lot of welding forums.

  20. #17
    Join Date
    Dec 2017
    Country
    UNITED STATES
    State/Province
    Rhode Island
    Posts
    140
    Post Thanks / Like
    Likes (Given)
    3
    Likes (Received)
    2

    Default

    Well I misplaced the little broken piece so I cut one from steel and used ordinary flux coated 1/16" bronze braze rod. Seems to be working fine hopefully it holds. Thermite mentioned that there's not much extractive (upward) pull on this, so maybe it will be just fine.

    I did heat the entire end of the gib with less as I moved down, thinking it would smooth out the temperature contrast a bit. Then let it air cool. Not sure if that would help in any way to prevent a stress crack.




    20191126_144008.jpg

    20191126_144247.jpg

    20191126_152230.jpg

    20191126_154016.jpg

    20191126_155425.jpg

  21. #18
    Join Date
    Mar 2007
    Location
    England UK
    Posts
    1,831
    Post Thanks / Like
    Likes (Given)
    764
    Likes (Received)
    751

    Default

    There can be a lot of extractive force if you don't keep up with the way lubrication. If that gib end snaps off due to excess drag from lack of lube the gib will pull itself into the taper so tight when you reverse direction that you'll have a hell of a job getting it out.
    Personally I would cut a piece of steel plate to back that up and bond it to the end then drill and tap through into the undamaged part of the gib, just to make sure it doesn't snap again.
    Also be advised that the adjuster head has to be a very good fit in that gap. Any gap and the gib can jam as above.

  22. Likes HWElecRepair liked this post

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
  •