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  1. #1
    dsc's Avatar
    Lives in Lincoln, United Kingdom. Last Activity: 2 Days Ago Has been a member for 5-6 years. Has a total post count of 248. Received thanks 1 times, giving thanks to others 9 times.
    Gents,

    this is mostly for the people who used or use Hiwin rails.

    Looking at the Hiwin technical manual:

    http://www.hiwin.com/pdf/lg/QE/QE-Li...ay-%28E%29.pdf

    page 11 , there's a whole section on how to mount the rails and carriages.

    I've seen many machines which use Hiwins and only a few times I've seen the rails mounted against a datum line, even rarer with side plates used for securing the rail. Curious how many of you followed the Hiwin manual and how many simply slap the rails on a flat plate and bolt it when everything is aligned? Am I correct to think the suggested mounting methods are for high loads, not normally seen on home built machines?

    Regards,
    dsc.

  2. #2
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Current Activity: Viewing Has been a member for 9-10 years. Has a total post count of 1,837. Received thanks 192 times, giving thanks to others 5 times.
    It's to do with ensuring the blocks/rails can't move, and allows easier assembly.

    Relying on bolts alone means that under high loads (especially shock loads), the blocks/rails could slip. By ensuring they're mounted firmly against an edge ensures they won't move.

    Also by using datum edges, it makes assembly quicker and more accurate. Most machines using linear rails will be getting machined anyway, so adding a datum edge isn't a major issue, and saves quite a bit of time in mounting and adjusting the rails/blocks. For one offs, it's probably not a major benefit, but if you're producing multiples of the same machine, that additional time mounts up.

  3. I always incorporate a datum edge when i build a new machine i have done ever since i built my first machine.. and always used hi-win gear.

  4. #4
    Quote Originally Posted by AdCNC View Post
    I always incorporate a datum edge when i build a new machine i have done ever since i built my first machine.
    Where are they on the first machine, they look well hidden to me...
    http://www.mycncuk.com/forums/router...tempt-cnc.html

    To make a datum/reference edge you need a milling/grinding machine with as much travel as the length of the rail or maybe a long precision straight edge to use as a reference. Either way it's not realistic for the vast majority of people on the forum.
    Last edited by Jonathan; 17-03-2013 at 01:56 AM.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  5. #5
    GTJim's Avatar
    Lives in Coventry, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 8-9 years. Has a total post count of 110. Received thanks 3 times, giving thanks to others 20 times.
    So how do people get around this problem. I'm very interested as I will be facing this problem soon.

  6. #6
    dsc's Avatar
    Lives in Lincoln, United Kingdom. Last Activity: 2 Days Ago Has been a member for 5-6 years. Has a total post count of 248. Received thanks 1 times, giving thanks to others 9 times.
    Gents,

    thank you for the replies.

    Looking at the manual, you can do without having a datum edge for the rails (ie. use the edge of the plate as datum), but the carriages still need a 'lip' and side bolts to secure in place.

    Regards,
    dsc.

  7. This is how i mount my rails..
    Click image for larger version. 

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  8. The Following User Says Thank You to AdCNC For This Useful Post:

    dsc

  9. #8
    dsc's Avatar
    Lives in Lincoln, United Kingdom. Last Activity: 2 Days Ago Has been a member for 5-6 years. Has a total post count of 248. Received thanks 1 times, giving thanks to others 9 times.
    Few things I still don't get:

    1. mounting against an edge assumes the edge is perfect, otherwise things go wonky. Surely there will be errors when machining the edge every single time.

    2. with no side plates pressing the rail against the edge, I don't really see the point of the edge. Surely if the rail moves under load, it will move anyway. Sure the edge will spot the movement towards the edge, but the other way is still unsupported

    3. the manual suggests simply bolting the rails down (ie. no edges) if there's no side space, but shows the carriages supported and mounted against edges. Again point 1 comes into play.

    Regards,
    dsc.

  10. #9
    Quote Originally Posted by dsc View Post
    1. mounting against an edge assumes the edge is perfect, otherwise things go wonky. Surely there will be errors when machining the edge every single time.
    Its for registration . A machined reference edge to butt up against makes getting your rails level far easier than without.

    2. with no side plates pressing the rail against the edge, I don't really see the point of the edge. Surely if the rail moves under load, it will move anyway. Sure the edge will spot the movement towards the edge, but the other way is still unsupported
    I'd love to see you bend a hardened steel rail that's fixed every 80mm lol Rails bending is the least of your worries when you constructing your machine out of only aluminium or steel box section. It ain't the weak link.

  11. 1. It all depends on what machine you use to mill the datum, so I'm fortunate enough to have a VMC at hand. (when i use this method i get a parallelism of 2um)

    2. That would be true if you could exert a serious amount of side force to dislodge the rails, but in this instances its highly unlikely to happen.

    3. Its tried and tested and works fine; all depends on the application and I think it would be necessary for the large machines that are doing heavy milling or moving heavy loads.

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