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  1. #261
    Quote Originally Posted by John McNamara View Post
    Rails are never straight out of the box they always need to be bolted down. The bolting should be done with a torque wrench for uniformity. If you can get hold of this book or find it at the local library you will see a large section on mounting rails and other components.

    https://www.amazon.com/Precision-Mac.../dp/0872634922

    I got my copy at Foyles many years ago for a lot more, A great book if you build machinery.

    In it he explains the way the rail distorts when tightening it down. Chasing microns is great fun to me! they hide in every corner of your design.

    I would not be concerned about a small amount of movement when you rotate the carriage axially on the rail. If it is a brand name rail you should find the type number engraved on the rail and the bearing blocks. By looking up the manufacturers website you should be able to determine the bearing clearance or preload and accuracy for the particular combination you have. typically around 3 clearance levels may be offered in addition to different accuracy levels. If you are ordering a new rail and bearing set for a project it is tempting to order the maximum preload, this is not necessarily a good idea at all. maximum preloaded bearings are often rated for a shorter life span and more importantly they require more accurate mounting surfaces, using the wrong clearance type can seriously reduce the bearing life and greatly increase the force required to move the bearing placing a high load on the drive system. Fortunately all the bearing manufacturers offer excellent manuals available for free download.

    I ran this Google search today and it yielded some interesting results.

    precision machine design slocomb mounting linear rails

    Or use the link below.

    https://www.google.com/search?rlz=1C...4dUDCAw&uact=5

    Regards
    John
    Mine are medium preload (ZA) mate not high preload, rail is now straight enough for me, although huge fun (not!) there is no point chasing down +/-2um when I can deflect 300mm of 80mm box section that the rail is mounted on between uprights by 5um just by leaning on it. I listed all those example measurements to show what the system is capable of, e.g. obviously the carriage will twist on the rail when twisted, if it didn't then it wouldn't move, but in reality this is only a problem if you have a microscope bolted to the carriage as in actual use two carriages would be used mounted to a rigid plate, I was highlighting this as a source of error with how I mounted the microscope not a criticism of the hiwin system. Possibly a better (although more work) microscope fixture would be to register to the reference edge machined on the hiwin rail rather than use a carriage at all, couldn't be bothered though...
    Last edited by devmonkey; 26-05-2020 at 11:49 AM.

  2. #262
    Hi Joe
    I agree medium preload is a good choice, and when the carriage is installed there will be 4 bearing blocks distributing the load, as they are spaced apart any axial twist will be much reduced. I suspect that if you ran the test with the microscope mounted in the carriage running on your already precision aligned rails You may get even better numbers due to some of the residual errors in the rail alignments averaging out.

    Hi Kitwin
    You mentioned that you were working with round rails, Maybe if you first fit both rails with the mounting screws just tight enough to allow them to move sideways then after sliding on the bearing pairs onto each rail you fit the carriage plate on the bearings in the same manner just tight enough to move you will be able to align one as a master rail using wire alignment and the microscope before setting up the other.
    It may take a couple of cycles of this procedure but it will iron out any errors.

    This worked for me when building a small All laser cut CNC router with a mate for a Men's shed in Bright Victoria in 2012 It is still in use daily apart from the Covid shut down.

    It uses round rails, and yes timing belt drives apart from the Z axis which is a ball screw. Remarkably the accuracy is a lot better than you would think. After wearing out 2 Makita routers due to the high usage It now has a Chinese 2.2kw high speed spindle.

    https://www.google.com/search?q=Brig...%3Apinterest.*

    Regards
    John
    Last edited by John McNamara; 26-05-2020 at 04:37 PM.

  3. #263
    Click image for larger version. 

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    Will use gantry to space slave rail correctly, progress on this particular machine will continue in my build thread:
    http://www.mycncuk.com/threads/13178...-started/page8

  4. #264
    Quote Originally Posted by devmonkey View Post
    I would say it says that standard hiwin rails and carriages are pretty good, would you agree?
    That was my meaning, ' a few um' detected by the microscope is not much movement at the carriage. These rails are known to be intollerant of poor alignment, non-straight frames etc. and that's what you'd expect where there is so little play. When I decided to go for fully suported round rails on my machine part of the decision was that I was unsure I coud make the frame accurately enough for the more expensive Hi-Wins not to bind.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  5. #265
    Quote Originally Posted by John McNamara View Post
    Hi Kitwin
    You mentioned that you were working with round rails, Maybe if you first fit both rails with the mounting screws just tight enough to allow them to move sideways then after sliding on the bearing pairs onto each rail you fit the carriage plate on the bearings in the same manner just tight enough to move you will be able to align one as a master rail using wire alignment and the microscope before setting up the other.
    It may take a couple of cycles of this procedure but it will iron out any errors.

    This worked for me when building a small All laser cut CNC router with a mate for a Men's shed in Bright Victoria in 2012 It is still in use daily apart from the Covid shut down.

    It uses round rails, and yes timing belt drives apart from the Z axis which is a ball screw. Remarkably the accuracy is a lot better than you would think. After wearing out 2 Makita routers due to the high usage It now has a Chinese 2.2kw high speed spindle.
    John,
    My main concern with the round rails was that a single carriage will rotate around the rail so some form of 'gantry' going accross both will be required to mount the microscope. Probably not a real problem in fact, especially if the slave rail is quite losely mounted. Nearly all the error seen will be from the nearest rail and a few iterations should sort things out as you say.

    I'm not sure you can fully adjust round rails in practice. The steel rail must be far more rigid than the aluminium support and whilst shims may well sort out vertical errors, I suspect any attempt to nudge the thing sideways will more likely distort the support than the rail. I don't speak from experience however.

    One day I might decide to do a serious upgrade and build a mostly-new machine in which case I will be using all the wisdom gathered from you and Joe to chase down every micron I can. Alternatively somebody with better coding skills than I will come up with a method that can detect all the errors on my machine and writes a dedicated post-processor to take them out in software. Oh No! Not another rabbit hole to head down!!!

    Very amused by your last comments, my version reads "After wearing out 2 Makita routers due to the owner being being stupid it now has a Chinese 2.2kw high speed spindle"

    Kit
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  6. #266
    When we built the router in 2012 it was for a community men's shed. we were on a parts budget, My mate and I put our time in for nothing so there was no cost there. A Makita router was available, from memory it was donated.
    The Chinese spindle. Is much quieter than the Routers with their brush type motors. I guess I should of put this in a separate thread, it is a bit off topic. This thread is about Alignment and software.
    Last edited by John McNamara; 27-05-2020 at 03:39 PM.

  7. #267
    Quote Originally Posted by devmonkey View Post
    Afternoon all.

    [...]

    Anyway the purpose of this post is to describe a new app I put together today for laying the master rail straight. I decided it would be easier to use a taut wire rather than the laser for this and a cheap USB microscope.
    [...]

    The microscope is attached to a hiwin carriage and the new app accurately locates the wire allowing you to zero the tool then reports the error as you slide the carriage back and forth.
    [...]

    Nothing new in the process that other people have performed other than the app that lets you achieve excellent accuracy with little effort.
    [...]

    The wire locating algo is quite different from the laser gausian model and seems extremely robust.
    [...]

    Cheers, Joe
    .

    With apologies for absence ... it's been a while since I was here :

    That sounds like a great development, Joe
    I obviously need to read the next couple of pages, but please let me join those requesting that you share the App

    MichaelG.
    .

    Edit: Just off to grab that code
    Last edited by Michael Gilligan; 20-07-2020 at 07:46 PM. Reason: I've now read those pages, and found your link to the App

  8. #268
    Quote Originally Posted by Michael Gilligan View Post
    .

    With apologies for absence ... it's been a while since I was here :

    That sounds like a great development, Joe
    I obviously need to read the next couple of pages, but please let me join those requesting that you share the App

    MichaelG.
    .

    Edit: Just off to grab that code
    Hi Michael,

    I actually wrote a different app for the taut wire method, I don't think I uploaded it anywhere. It has been a while but I think it made use of the wire not crossing the sensor exactly parallel to the pixel rows to gain excellent sub-pixel resolution and it also took a bisector of the line edges as the line shadow is not gaussian when lit from above by a microscope. This also takes care of the converging or diverging wire edges which you can see under high magnification and are caused by the wire stretching more in the centre of the span than at the edges as it flows.

    Unfortunately I wont have access to the machine with the code on for a few weeks. Thanks for the offer of some wire but I don't really need it, I found that black fishing line worked perfectly since the app is tolerant of an imperfect wire as described above.

    Edit:
    Actually it turns out I did upload the code, fill ya boots!
    https://github.com/betzuka/laserleve...uilds/wire.zip

    Cheers, Joe
    Last edited by devmonkey; 20-07-2020 at 11:13 PM.

  9. #269
    Thanks, Joe

    Yes, that’s the one I found

    Opened it on the old MacBook Pro [just using the built-in camera] and it appears to run fine
    ... But it wouldn’t close
    Then I remembered that I had the same problem with your laser App, and fixed it
    Java had done another update today, so : Once again, I deleted Java completely and re-installed.
    ... All seems fine now

    MichaelG.
    .

    P.S. __ The wire is a bit special, but if you’re happy that’s fine.

    @ John McNamara ... I will send some to you.


    .
    Last edited by Michael Gilligan; 20-07-2020 at 11:41 PM.

  10. #270
    Hi All

    The past couple of months have been pretty busy around our place, Time to get back to the workbench! Glad to see your input Micheal and thanks Joe I just grabbed the updated software. I am moving the workshop so soon I will have more room :)

    Regards
    John

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