1. #1
    Hi,

    I've got two different brands of 15mm linear profile rail (one Chinese import, one SBC Linear). Both have identical mounting holes that are 4.5mm dia. with a countersunk hole for the bolt head 7.5mm dia.

    I'm not sure what bolts I am supposed to use here?

    M4 would fit through the hole, but all M4 bolts with a countersink are 8mm dia. on the head so they don't fit. An M4 cap head would fit the hole but it doesn't seem right to use that on a countersunk hole because the contact patch will only be on the edge on the head.

    Am I supposed to use some kind of imperial size?


    Thanks!

  2. #2
    Quote Originally Posted by Tenson View Post
    Hi,

    I've got two different brands of 15mm linear profile rail (one Chinese import, one SBC Linear). Both have identical mounting holes that are 4.5mm dia. with a countersunk hole for the bolt head 7.5mm dia.

    I'm not sure what bolts I am supposed to use here?

    M4 would fit through the hole, but all M4 bolts with a countersink are 8mm dia. on the head so they don't fit. An M4 cap head would fit the hole but it doesn't seem right to use that on a countersunk hole because the contact patch will only be on the edge on the head.

    Am I supposed to use some kind of imperial size?


    Thanks!
    15mm I assume is Hiwin style rail, I have original and clone rail and both take M4 A2 stainless steel bolts.

    This is my clone rail
    https://www.ebay.co.uk/itm/15-1500mm...e/202182780858
    Last edited by Desertboy; 01-03-2018 at 04:58 PM.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  3. #3
    I use the 20mm Hiwin rail and had to grind the allen bolt heads a little so they can sunk in the rails with out problem, I know it is time consuming but i couldn't find bolts with the proper head diameter to drop in there .If you look close at the photo, I place the bolt in the chock of a cordless drill and spin it, while I push it on the grinding wheel, this make the bolt head diameter to be evenly grind.
    Click image for larger version. 

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  4. #4
    That's interesting, thanks!

    Here is a photo of one rail (click to biggy). I don't know if you can tell that the bottom of the hole is not 100% flat, it has a very gentle chamfer, like it was drilled rather than milled out with a flat bottom end-mill. I think it is less steep than a standard screw countersink, but also not 100% flat.

    I think what I'll do is just use a soft washer under the screw head to allow it to seat nicely.

    Click image for larger version. 

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    Last edited by Tenson; 01-03-2018 at 07:35 PM.

  5. #5
    The holes are not countersunk. Use standard 4mm socket head cap screws.
    Gerry
    ______________________________________________
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