Bolts for Linear Rail?

[Tenson]

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!

[Desertboy]

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

[Nickhofen]

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.

[Tenson]

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.

[Ger21]

The holes are not countersunk. Use standard 4mm socket head cap screws.