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Stiff dovetails on mill

Discussion in 'QUESTIONS & ANSWERS (Get Help Fast Here!)' started by Hukshawn, Mar 19, 2017 at 11:34 AM.

  1. Hukshawn

    Hukshawn Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    I have the standard mini mill most guys have. There is a seriously fine line between no play in the dovetails/gibs, and too tight to operate. Which is especially becoming an issue now that I'm trying to build a power feed with a 12v motor. It just won't run sometimes. Also, when I get near the end of the travel on either side, it really tightens up... so, uneven grind, and poor quality gibs?

    Suggestions? It makes for poor cuts when I have to crank the wheel if I'm at the end of the travel.
     
  2. Ulma Doctor

    Ulma Doctor Infinitely Curious H-M Supporter-Premium

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    the first check is for the flatness of the gibs and ways.
    get a sharpie (or other permanent ink pen) and color the contact areas of the dovetails in both axes
    move both axes through full travel and inspect the colored areas.
    upon inspection, the absence of color in those areas will show where the dovetail/gib interface.
    any ink left in those areas will indicate a low spot.
    if you were to happen to have adjusted the gibs on a low spot, the high spots would really become apparent by binding.

    as a suggestion, remove and inspect the gibs
    lap the gibs as best you can on a plate of thick glass or surface plate with 400 to 600 grit wet/dry sandpaper ( if you wet the sandpaper it will stick to the glass without adhesive)

    clean, reassemble, and re-apply ink to the areas of travel, and recheck with full range movement and close inspection

    if the dovetails are still having a hard time working smoothly, you may need to scrape the gibs and/or the dovetails to correct the situation
     
    ericc, mikey and Bob Korves like this.
  3. ghostdncr

    ghostdncr United States Active Member Active Member

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    Scrape them and be done, is how I do it. I've yet to buy anything like this that had even usable ways, often being only rough milled and having gibs that appeared made on a belt sander or from sheared bar stock. Scraping these ways produces a dramatic increase in smoothness and accuracy and it's not that big of a job.
     
  4. tertiaryjim

    tertiaryjim Active User H-M Supporter-Premium

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    Dovetails work best when the surface is rough enough to hold oil and contact is 60% or less.
    Blue and scrape anything you can for best rigidity and preformance .
    Makes a huge difference.
     
  5. Ken from ontario

    Ken from ontario Canada Active Member Active Member

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    Shawn, I don't have that problem with loose /uneven gibs in X or Y axes but I did have little problem adjusting the Z gib,it would get either too loose and slide off or I had to tighten the grub screws so tight that the head would be too hard to move up and down, after fiddling with it for a while I finally removed one of the grub screws (the top one) looked through the screw hole with a flashlight and found the indentation on the gib is not in the right spot and it was also too shallow, so I checked the other 3 screws and found the same thing.
    I removed the 4 grub screws, ground the "dog points" to make them slightly smaller in diameter, also worked on the matching indentations on the gib by grinding them a bit deeper. doing this gave more flexibility in adjusting the gib, the screws can now go a bit deeper and still they can engage the gib and let it slide freely.

    I'm not saying this is what your problem is but it might help if you spend a good hour or more in re-adjusting the screws on the axis that gives you problems,and by doing it one small adjustment at a time ,you may need to take the gibs out and flatten them on 400 Grit sandpaper(slightly to get rid of the bumps) and or do what I just explained above to fix the problem,Frank Hoose has a youtube video on how to adjust the gibs on his lathe, it's a good video to watch,good luck:
     
    Last edited: Mar 21, 2017 at 12:17 AM

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