Tapered way shim / corrosion of dissimilar metals
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    Default Tapered way shim / corrosion of dissimilar metals

    I'm scraping my lathe in and now my cross slide tapered gib is too thin. Of the several ways to deal with this, I thought that bonding a copper or brass shim on the back side of the gib sounded good. Given that I do not expect to replace this gib again in my lifetime, is corrosion of dissimilar metals a concern here? I really don't know my stuff here.

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    Quote Originally Posted by otter View Post
    I'm scraping my lathe in and now my cross slide tapered gib is too thin. Of the several ways to deal with this, I thought that bonding a copper or brass shim on the back side of the gib sounded good. Given that I do not expect to replace this gib again in my lifetime, is corrosion of dissimilar metals a concern here? I really don't know my stuff here.
    Only if a corrosive medium is present, plan on washing down with seawater?

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    Electrolysis requires not only a natural voltage difference, but also a current path in the form of an electrolyte. Oil is an excellent insulator. Unless submerged in water, you have no issues.

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    I've bonded brass shim several times to gibs, it works well, and you can scrape it in once it's bonded, the thing to be careful of is its pretty slick so you need to be sure your prep work is good on the bond side to make the epoxy stick. I have very good luck with bead blasting, also I wouldn't use anything thinner than say .015, that goes for any material not just brass.

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    Quote Originally Posted by ironsmith89 View Post
    I've bonded brass shim several times to gibs, it works well, and you can scrape it in once it's bonded, the thing to be careful of is its pretty slick so you need to be sure your prep work is good on the bond side to make the epoxy stick. I have very good luck with bead blasting, also I wouldn't use anything thinner than say .015, that goes for any material not just brass.

    Thanks to all for the responses. Your advice of not going thinner than 0.015 is interesting. I need about 0.010 right now. Assuming that I will need a few thou for glue and will scrape a few thou off getting things straight again. I suppose that's like scraping on tin foil. I imagine it's prone to denting, tearing, etc. It seems like such a pain to make a new gib from scratch, but if I'm going to machine some off of the old one, I might as well make a new one.

    thanks again!

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    Otter:
    You can put a .010 strip of shim stock on the back side of the gib..
    I've used as thin as .005 no glue.. Brass or stainless both work..
    Cut it 1/16 to 1/8 narrower then the gib and cut a notch were the gib screw
    is, It will adjust with the gib..

    Good Luck
    Steve

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    I will answer next week. I have been teaching a class this week and have been whipped. Rich

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    If you only need .010 your better off leaving it loose as sauerkraut said. Your spot on otter about denting and scraping tin foil, its hard to bond anything without it needing some attention afterward. I would loose shim it or make a new gib.
    Another thing to consider, if it interests you to put turcite under the cross slide, you can easily mill the flats, bond turcite under the slide with extra thickness so it sits higher, you'll have to shim or adjust the nut lower, and your center height will change, not a problem if you have an aloris post, but this will kick the gib out further without needing to thicken it. I've done this several times. You can experiment by shimming under the flats to see how much extra height you'd need to get the gib where you want it, it doesn't take much. Of course you'll want to add an extra .005-.007 turcite than you need so you have material to scrape it in. Something to think about.

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    Chris, it is so nice to see you back and helping here. I was gone last summer, but won't be leaving until I'm in the scraping shop in the sky. I my not be writing a lot in few years, but by then hopefully with our help and others like Tyrone, Cash, Pete, Demon, Bob and those I am forgetting who do machine rebuilding and get or got paid to do it will be able to pass on our knowledge to the future generations.

    To all who don't know IronSmith89 is a Journeyman Machine Tool Rebuilder and he has several YOU Tube shows under his name CG Precision. His real name is Chris German and he is what his PM name on here IMHO!!. Rich

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    Iron smith- I hadn’t considered building up the flat surface with the turcite . Pretty clever. I think I might do that.

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    Thanks for the kind words Rich. I only contribute when no one else has. Most of the time, when I get around to reading through the threads, the questions are already answered by the other fellas out there. I don't feel a need for redundancy just to say something so I don't write much. This forum is pretty well covered
    Otter, if you search eBay for turcite there is a seller with "kits" of turcite precut for the saddle of an Asian Bridgeport clone mill. They run roughly $50 and you get four strips of turcite, I don't know the size of your lathe but it's highly likely one of these kits will cover your cross slide for a lot less money than buying actual turcite. I've used their product before and it is good.

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    Yes - I’ve seen the kits and even already had ordered one. I was going to use it to just experiment, but it looks like it will be put on the real cross slide now.

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    Good idea, but before you glue it on cut some small 1/2 wide pieces and put them on the 4 corners and try to slide in the gib. If it doesn't slide in far enough then buy some plastic shim stock and keep putting in 4 shims of thinner material until the gib is sticking out the right distance. Remember the glue will probably be about .005" bond line. You may have to mill off some iron off the surface you want bond too.

    I have a few more idea's too.

    Im getting a bit tired now...will write as much as I can.

    If you just want to repair the gib and not rebuild the cross-slide, you can do what some of the others said and steel, brass or plastic shim stock and not glue it on. behind.

    You can buy Phenolic grade linen Phenolic as thin as .010". Also some Rulon and sheet platics come in thinner thickness.


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