Scraping tapered gib problems.
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  1. #1
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    Default Scraping tapered gib problems.

    Hello.I need Your advice with scraping tapered gib.I glued 1mm steel plate to the gib nonworking side because ,it gets too thin after ways scraping.My problem is that iv scraped this gib to 70% lenght and there is still wiggling on the top .Down side is fine but it looks like that my scraping is useless.Berfore I'v started to scrape gib with surface plate to get both surfaces flat.Then installing gib by rubber hammer into dovetail,and removing by hammering the saddle.

    Iv marked on the photo what's going on.




    20210422_180821.jpg
    Attached Thumbnails Attached Thumbnails 20210422_181001.jpg  

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    With the material you added to the shim, how did you determine how thick it should be? If you needed to fill a 1mm gap for example, your shim would be much less than that because of the angle it's sliding along. You can experiment with different thickness's, or do some trig to calculate the thickness.

    How did you glue the shim in place, and did you confirm that there were no burrs or raised edges before gluing?

    If you remove the saddle from the way and place the gib in place, can you confirm that it sits evenly in there? The taper of the gib and the taper under the saddle should be the same. If they're not, something was cut wrong or wore funny.

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    Iv added full lenght shim 1.01mm .Gib was going all through the dovetail.Iv checked and scraped both sides of gib before scraping and the shim was scraped to get good contact between them.No burs-removed with grinding stone...

    Main problem is that the shimmed gib(before shiming too) has wrong taper angle.My job is to fix that without surface grinder.
    Every gib in this machine has different angle . Old russian 675P

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    Check for interference between the acute angled edges of the gib and the inner corner of the dovetails. If it's interfering, you'll just be making it worse trying to scrape it. You need to take off those sharp edges with a file first.

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    Before you glued the shim to the gib how far did it slide in past the new machine location? When I rebuild a machine and machine and scrape the ways Flats and dovetails I only glue steel shims to the back sides of gib's if it is an emergency. I glue Turcite or Rulon the the worn side. All worn gibs bend. I straighten them first and I also test the dovetail or positive side of the gib and scrape it so it has about 2 to 5 PPI, Then check the surface where the back of the gib rests as 90% of the ones I check with a dovetail straight edge it is high in the middle, has burrs on the ends where the gib screws are. Then before shimming it I slide in the gib and use plastic ship stock or 2 feeler gage sets on both ends of the gib to be sure the taper is the same. If the gib is tight on one end with the loose shim I scrape the gib wear side so the taper is the same before I glue on the Turcite to the old worn gib. You can buy Rulon 142 in size 0.76mm, 1.2, 1.5 mm plus the glue thickness is 0.127mm. Check 5:27 minutes of this show and see how I straighten gibs. Richard King scraping class Norway August 2014 - YouTube

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    The corner of your gib looks like it is hitting. Your shim looks like it is to wide and it could be hitting on the width. Did you check the taper before hand? On many gibs in the USA the gibs are tapered .008" or 0.203mm per 1" or 25.4mm.
    I would check width issues first and see if that helps. If you asked me to do the job now, I would strip off the steel shim and glue on some Turcite B or Rulon 142 on it. Where did you glue the steel shim on the gib and why did you choose that thickness?

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    When I glue a shim on a gib, I install the gib in the machine after gluing and tighten the gib good and tight while the glue sets. Is that what you did? Otherwise, you may not end up with a good fit, and you have a lot of extra work.

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    Iv glued steel shim experimentally.Problem is fixed.After scraping fail the gib was grined with surface grinder and scraped again.Now i have about 0.02mm clearence.Taper was measured by trigonometry and the angle was perfect.Main problem was that i had wear in the middle of gib and that caused all issues

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    rimcanyon Unfortunatelly not. Iv glued and clamped gib with shim to camelback.I have used cyanoacrylate glue.That was bad idea because it unglued on magnetic table during grinding.

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    The way Ido it, I scrape the gib taper before I glue on the turcite and on you case the steel shim. I only use steel on emergency breakdowns.

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    Quote Originally Posted by alien97pl View Post
    rimcanyon Unfortunatelly not. Iv glued and clamped gib with shim to camelback.I have used cyanoacrylate glue.That was bad idea because it unglued on magnetic table during grinding.
    Most likely it came loose from grinding heat. That thin strip of shim more or less thermally isolated by the glue line from the gib will heat extremely easily. Keeping it cool using a sharp, freshly dressed 46 or coarser stone, flood or generous mist coolant, and light cuts would probably have kept it in place as long as your surface prep and glue line were good in the first place. On that kind work I check the work temp often with my finger. Then again, maybe you did all that.

    Denis

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    hi i really admire you for having the balls to have a crack at it .i will one day be up to your standards.do not give up cheers

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    I usually use feeler gages and Starrett taper gages to determine thickness needed, then try out with 12" feeler gagees stacked up, then I put Turcite on the gib.


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