I have bought some SBR12 rails and bearing blocks in an attempt to make a fancy flattening jig for my router.

I haven't been able to see 100 % everything that other people have done on the YouTubes due to camera angles etc., but I went ahead and bought some to fit the table I currently have.

The idea is to have two rails attached atop another two rails perpendicularly as to act as an X and a Y axis to move the router across the workpiece easily.

The issue I have found now the rails have arrived is that the holes in the rails, designed for fixing them to a tabletop, etc., don't align fully with the threaded holes in the tops of the bearing blocks...

Is this something that is normal, or was I just naive to the idea that they would fit perfectly? Also, is there something you can suggest I do to attach these securely?

Close up of misalignment - top view

Close up - isometric view

View to the side



1 Answer 1


That doesn’t sound very unusual to me unless you purchased materials that specifically purported to be predrilled and compatible. Sounds like you may need to manually mark out, drill and possibly tap or countersink the holes you need.

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    $\begingroup$ Thanks for the advice @Rowan. Yes I've seen elsewhere that you have to buy specific rails/blocks etc. However this was a bit of a measured impulse buy from Amazon so no technical info supplied. I suppose I'll Have a go and then return them if I can't get them to work $\endgroup$
    – physicsboy
    Jul 21, 2021 at 9:59
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    $\begingroup$ You’re welcome. Drilling, tapping, countersinking are not particularly hard to do. Just need the right tools, and to measure twice then act once. If there is a community maker’s space near you they may have the tools and experience to share. $\endgroup$
    – RowanP
    Jul 21, 2021 at 12:25
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    $\begingroup$ I'll second what RowanP is stating @physicsboy - no need to return these, just drill the appropriate holes and bolt them together. If the thought of drilling into the rails is making you uncomfortable then consider making a block to sandwich between the lower slider and the upper rail. The block would mount to the lower slider through the four holes and the upper rail then screws to the block. I'm assuming that, by the fact that you own a router, you're comfortable doing some DIY projects. You could use lumber or maybe PVC if you want something more dimensionally stable. $\endgroup$
    – Chuck
    Jul 22, 2021 at 12:37

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