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  1. #131
    The long rails on my machine are 1.8m, 100x50x3 box steel. One dipped in the middle by about 1.5mm, the other side a little bit more. Like you, don't know if that was welding or how it came, but in my case epoxy filled the hole

  2. #132
    diycnc's Avatar
    Lives in Manchester, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 6-7 years. Has a total post count of 66. Received thanks 2 times, giving thanks to others 11 times.
    I appreciate the concerns about the measurement method.
    Did some more measurements today to check the repeatability and accuracy of the method.
    I deliberately rotated by plywood platform 180 degrees, and positioned the surface plate differently to really test the approach, and pretty surprised to the 1st and 2nd measurements vary by only a max of 0.1mm, that more than good enough for me.
    I also used the same method to measure the polished edge of a piece of granite upstand, its the straightest thing I have to hand. I got less than 0.1mm deviation along its 500mm length. Again I'm happy with this.

    All in all im very happy with the measurements, and im confident they are accurate enough for me.

    Click image for larger version. 

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    X and Y axis are 750mm.
    Intended for wood and plastic, and hopefully aluminium. I know ill have to take it easy with aluminium, and I'm not expecting it hog out anything more than the smallest of cuts, or the highest of surface finish quality.

    Going back to shims, my concern is will there be a noticeable lack of stiffness with the rails supported on just a handful of points?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by diycnc; 27-05-2020 at 09:27 PM.

  3. #133
    HI diycnc

    I can say epoxy is a bit of a mess, result is excelent.



    But i do feel when you do 2 pours like 1 to get in to plane where thinnest film is 3mm thick or so and then do a final pour of another 3 or 4 will give you excellent results.

    Please read up on best practices on this forum.

    I had about 3 mm of warp over 1850mm
    i did a single pour 4 to 7 mm

    I did ignore the reports about epoxy shrink differences where layer thickness is different, which is solved by a second pour.
    Maybe I will do a second pour some day...

    I have no jobs that need such accuracy yet.

    Grtz Bert




    Verstuurd vanaf mijn SM-A505FN met Tapatalk

  4. #134
    Quote Originally Posted by diycnc View Post
    Going back to shims, my concern is will there be a noticeable lack of stiffness with the rails supported on just a handful of points?
    No problem if you use epoxy putty. I have never tried it but if you think of mounting the rails and then pouring epoxy, i believe it will be difficult to take the air out, though probably will work if you use West System epoxy as its quite thin.

    To be 100% sure, best method is pouring the epoxy 5mm deep and 40mm wide, you could use only one channel to connect but make sure channels extend additional 20cm from the frame, there is a lot of info on forum. In my second build from signature i have explained in great detail how to do it properly and most economically for that matter. It cost me a couple of hundred $$ to understand the process in detail.


    Another cheap option is use calibrated steel bar like 40x5mm or something, put epoxy putty on it and straighten it on place with straight edge. When dry, dill and mount. Its precise and cheap flat surface

    At the end all depends on what shape you rails are in, in most of the cases they are perfect and easy to mount and shim, plus its a small machine, so easier




    But epoxy makes that even easier, if you do the epoxy right . Most of the people i am 100% sure do the epoxy in the wrong way or have no way of measuring the result. As funny as it seems i went to that conclusion, measuring my results on a 3m rails and reading the build logs at that time





    Similar machine like yours done with 100x100x3mm box , 40x100cm x/y , was well under 0.05mm frame bend when finished.
    project 1 , 2, Dust Shoe ...

  5. #135
    diycnc's Avatar
    Lives in Manchester, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 6-7 years. Has a total post count of 66. Received thanks 2 times, giving thanks to others 11 times.
    I have persevered with the shimming approach, and after a couple of evening measuring then shimming, both my Y and Z axis are planer to within 0.05mm.
    Measurements are 100% repeatable too, and I have no reason to believe the method has any error at all. For example, after adding a 0.1mm shim to under a bolt, the measurement increases by pretty much exactly 0.1mm at that location.

    Only slight tweak to the method is I now do the leveling of the measurements in excel, rather then physically moving the surface plate.

    Iv tried to solve the amount of support under the rails issue by adding more bolt, lots more bolt! I have 50mm spacing between bolts now, rather than 150mm as they arrived.

    I initially started aiming for a 0.25mm deviation over the Y-axis but blew past that on the first attempt, so just did 1 more iteration to see how good I could get it, and ended up at 0.05mm deviation from a flat plane. It was almost 3mm when I started.
    At the moment I reckon the play in the cheep bearings, and maybe even the deflection of the frame under the gantry weight will be more than this, so its total overkill!

    Shims are just small pieces of aluminum sheet, cans, and foil. Nothing special.

    Im pretty chuffed with the results, it's one of the few things that's gone better than expected.
    I painted the frame too, blue Hammerite spray paint, and the paint is so soft I can scratch it off with my fingernail! I clearly didn't do a very good job of cleaning it before painting.
    Click image for larger version. 

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    Any suggestions for how to measure straightness of these round rails?
    Last edited by diycnc; 02-07-2020 at 09:24 PM.

  6. #136
    [QUOTE=diycnc;118473]
    I painted the frame too, blue Hammerite spray paint, and the paint is so soft I can scratch it off with my fingernail! I clearly didn't do a very good job of cleaning it before painting.
    /QUOTE]

    It may not necessarily be your fault - over the years I've had very mixed results with Hammerite - it's never dried particularly quickly, but some coats/colours have hardened OK after a week or so, other were still soft months later even with lots of care with surface prep. I don't know whether temperature is an issue in your case, but I've heard other people say it's best to keep it warm to accelerate the drying.

    Well done on the shimming BTW

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  8. #137
    diycnc's Avatar
    Lives in Manchester, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 6-7 years. Has a total post count of 66. Received thanks 2 times, giving thanks to others 11 times.
    Paint does really seam to have got any better, and can still be scaped off with a finger nail. What a waste of 2 tins of hammerite!

    Think im going to take the opertunity to repaint it now before I fully assembly the rest of the machine.
    Any recomendations for paint?

    Also just finishing off the design of some covers. Would some thin 0.7mm galvenised sheet steel be okay?
    Little concerned about it rattling.
    Plan is to print out some paper templates, cut with a jig saw or scroll saw when sandwhiched between some scrap MDF to stop it bending to much, then fold and pop rivit into shape.

  9. #138
    Paint?, I'd use some of the hard enamel paints used on the machines of old - check out Paragon paints for something as reassuringly expensive as hammerite, though altogether better!

  10. #139
    ...and covers?, for what?, belts?, etc? 3D-printer can be a friend here for complex shapes.

    0.7mm a bit thin - they'll quickly attract, erm, character :) Stainless might be prettier (though altogether harder to work well). Why not standard MS and paint in sympathy with the machine?

  11. #140
    Think im going to take the opertunity to repaint it now before I fully assembly the rest of the machine.
    Any recomendations for paint?
    I find Hammerite paint very good even without a primer but you have to clean any oil off with a solvent first.

    I have never used the spray tin version
    ..Clive
    The more you know, The better you know, How little you know

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