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Gib refurbishment

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  • Gib refurbishment

    I am trying to resolve an issue with my KX3 machine. I have had it for a while and recently discovered the Z gib is undersized and one issue in some surface finish issues.

    Its a tapered Gib with a ~1 degree taper. I measured it at 0.97 degree.

    To get the gib to lock one has to remove the lower Gib screw and move it about 3/8 to 1/2"" further than what the factory set it at. :-(
    Of course the adjuster screw is too short.

    Looking for suggestions on how to fix it.
    I have two suggestions so far:
    1) Crazy glue a piece of shim stock to the backside of the Gib. My calculation is I need a 0.006" shim to lock in the centered location. I would try that today but my inventory of shim stock suitable is a piece of 0.014" too thick for sure. Mondays task unless I get a great idea from here.
    2) Make a longer adjuster. I had to get a 55 mm SHCS and machine up a washer to remove the locked gib. I don't favour that as the solution because with the adjuster hanging out that far it flexes.

    If I was really skilled I could make and scrape a new gib. I don't have any stock today and looks a little daunting. I know how to scrape thanks to a course from Forrest and Don a few years ago.

    Right now #1 (Sir John) idea is the front runner.


  • #2
    Making and fitting a gib can be daunting when you think through the process and envision all the steps

    Tapered gibs in the metric world are tapered 1 in 50. In the normal (Imperial) world, 1/4" per ft (1 in 48). That's about 1 degree 11+ minutes. Dovetail gibs have no "handles". The beveled edges don't lend themselves to bein gripped by a vise and since their surfaces are 100% machined there's apparently no way to hold them for the final machining except maybe a magnetic chuck.

    Getting the angles right and the proper fits is a trick all by itself. My favorite solution is to silver braze an extension to the thick end and contunue the existing furfaces, fit it, scrape it in to full bearing. then crop the ends to length. If the gib is headed, accomplish all the machining and fitting, then silver braze the head. Cast iron silver brazes as well as any othe ferrous material but the surface graphite inhibits fluxing and wetting in the flow out phase of brazing. I've found a light bead blast of only the joint area in clean media removes the surface carbon (which nothing sticks to) eaving the tougher iron matrix.

    If the piece you add on adds several inches to the gig lenght you can machine it and scrape it to a continuation of the original gib surface. At the joint there will be the bright line of the braze otherwise the surface will be continuous. The joint may be a plain butt and be plenty stron enough. Some people like to get fancy with scarf joints or half laps or bridle joints. While indicative of careful fitting and care such joints are very little stronger than the simple butt.

    Whatever people may have told you cast iron will not absorb oil except for the very surface. One scraping pass to clean up and the oil is gone.

    Straightening a crooked gib is tricky. Cast iron is brittle and will fracture with little warning when press straightening. The trick is to straighen without bending. Bending a ductile metal stretches one surface and compresses the opposite. The same effect can be attained in a far more controllable fashion by peening.

    Now you have to train your ears. The "tap tones" of matal laying flat to a surface is subtley different to the same metal bowed slightly above it. Practice with a piece of keystock.

    Polish up the ball and face of a 4 to 6 oz hammer. Using the face of the hammer, tap gently along its length on a flat surface like a cleaned and stoned milling machine table. note the difference in tones. If the keystock is flat on the table the tap tone will be more of a "tick"; if there is a small space the sound with be distinctly different. You have to experiment to understand the difference. These tap tones are indicators sensitive into 0.0001" in thin small work.

    Develop your technique with taptones untl you can determne the convexity or concavity of the surface and the locations of bends and kinks. Use a feeler to verify your observations.

    Next comes learning to peen scietifically. Peening indents the surface producing a small zone of compressively stressed deformed metal The compressively stressed matal make the work "bow up into the hammer". A small area of peening applied at a kink can remove it. A sparsely peened area over a gradual bow will correct it. A line od peening running diagonal can correect a twist. Thus you can tweat a near-straight cast iron gib into near perfection - once you develop the skill.

    More later
    Last edited by Forrest Addy; 11-26-2011, 06:32 PM.


    • #3
      So what do you think about crazy gluing a piece of shim to the back side?


      • #4
        Originally posted by DFMiller
        I1) Crazy glue a piece of shim stock to the backside of the Gib. My calculation is I need a 0.006" shim to lock in the centered location.
        maybe worth a try, or epoxy.....there is a really no movement on the side you'd shim so it may a lot less work for you

        how big is the gib? might be able to set you up if you want to make one...I bet you're more than skilled enough; like anything else you just have to figure out the sequence . just made a new one meeself for the DSG....



        • #5
          When i got my excello 602 mill and went through it i found that the gibbs were worn and had little adjustment left and the gibb would stick out the other side. So i did as you are wanting to do and used JB weld and glued a feeler gauge to the back of the gibb, careful to make and line up a hole in the feeler gauge to match the one in the gibb for oiling. Has worked good so far.


          • #6
            I've shimmed a gib on the cross-slide of a lathe. No glue, put it on the none working side. It stayed put and worked fine for many years.



            • #7
              On the SB 10L rebuild I just finished I had to add a .006 piece of shim stock to the cross slide gib to get it running smooth. I just scissored a piece to match the dims on the gib and let it slide in on install. Im now working on an Induma mill and I can see Im gonna have to do something similar on the X axis going back together.
              If everything seems to be going well, you have obviously overlooked something........


              • #8
                Cool, thanks for the feedback.
                I will give it a try. Once I get some material.
                Thanks for your vote of confidence, have you tried out the Water soluble dye?
                I tried some out and it looks good, much nicer to clean up :-)
                Yes I could maybe make a new one but I have things to do with the mill.
                Here is a picture. Its not that big. The mill is small also



                • #9
                  You're lucky if you only need .006". Not too long ago I shimmed the cross slide on my Jet 1340. I had to use .020" shims just to bring it back to the middle of adjustment range. I bought two 1/2" by 12" shims from enco and super glued them on to the back side. I had to cut one of the shims shorter with tin snips to get the overall length I needed. If you need long pieces enco sells rolls of shim stock.


                  • #10
                    How thick is a coke can ?

                    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


                    • #11
                      Originally posted by John Stevenson
                      How thick is a coke can ?
                      I wouldn't use aluminum. I tried that and it kept compressing. I went with steel shim stock to avoid that problem. The shims from enco were cheap. Only a couple bucks each.


                      • #12
                        If you do some searching you can get 12" long feeler gauges. I got mine from a snap-on tool dealer.


                        • #13
                          Shim is a good quick and dirty fix for an over extended gib adjustment. Any "hourglass" remaining in the slide left uncorrected will still cause problems. Then there is misalignment between the nut axis and the leadscrew axis. Fixing one thing on a worn slide leads to fixing a half dozen others.

                          BTW steel shim is best if you bond it to the gib. Brass is easier to work with but it has a greater rate of thermal expansion. Bonding the gib to the shim without an instant means of clamping leads to irregular bond thickness. Line the slide surfaces you don't wish to bond with wax paper. Slobber the back the gib and the shim wwith cyanoacrylate glue and quickly slide them together to set in the waxed paper lined gib cavity.

                          If you use soft steel or brass shim you can cut it to width on a paper cutter: Do not use the trimmer that uses a knife erge. Use a roller shear, an old fashioned paper shear, or a guillotine shear. If you hand shear it with scissors, tin snips, or aircraft snips the sheared edge is inevitably irregular. It you are really lucky the needed shim will suit the thickness of steel banding, if you are lucky. Coke cans are often uneven in thickness from the drawing die's slight eccentricity - which is OK if the fit is compensated for it.
                          Last edited by Forrest Addy; 11-26-2011, 10:58 PM.


                          • #14
                            Soda cans (US) are about 3 thou. Beer cans are 3.5 to 4 thou. Imported (German, Danish, Belgian) are 4 to 4.5 thou. Brass sheet labeled 5 mill will be 5 thou +- .0002. These are average measurements taken by me over about 25 imports, ~75 domestic beer and a couple hundred soda cans.

                            To clarify why I know this, I am designing a tool which will work these materials.



                            • #15
                              I can get some 1/2" x 12" feeler gauge shim stock at local supplier. I will get a couple of sizes to try. The shim should be .650" wide and I can replace once I figure out the size.
                              Lots of good suggestions. I will report the results.
                              This is a low hour machine, just not quite right form the factory. I have been cutting mostly plastic on it on letting it sit so there should be no wear. The Gib still has the scraping marks on it.