(TUTORIAL) Butt-joining profile linear rail with limited tools

Hi All,
After seeing the question raised recently and having seen it asked many times before, I've thrown together a small tutorial/guide for butt-joining linear rail without having access to a mill or lathe. If you've seen this method before, please ignore me. This is purely for beginners new to the CNC addiction who may have sourced several offcuts off of ebay or similar and wish to make use of them.

I recently needed to join some INA rails together to make an X axis for a small CNC router. I had nine short pieces of 20mm rail, each 160mm (6.3") long. On their own, they were pretty useless, because once you factor in the length of a single carriage, you're left with around 80mm (3.1") of travel, so unless you are using it for a very short Z axis, it serves no purpose.
https://live.staticflickr.com/65535/...8c8c8b44e3.jpg

Now, most if not all manufacturers of rail place a chamfer/bevel on each end of the rail. This makes it safer to handle, easier to get the bearing trucks on to the rail, and stops the rail's sharp edges marking or scraping the bearing trucks. If you want to butt join these rails and not have the trucks bumping as they pass over the join, you will need to remove the chamfer.

I figured if I'm capable of building a CNC router that can hold 3 thou tolerances, then surely I can find a way to remove this chamfer, even if it is case hardened steel, and keep the edge nice and square.

So without further ado, you will need:

A pillar drill (drill press for you heathens across the pond)
A pillar drill vise or some method of holding the rail still and rigid.
https://live.staticflickr.com/65535/...45bdf9db_z.jpg
A grinding disc from a 4 1/2 grinder.
An adapter to hold a grinding disc in a pillar drill. These can be had for around 5 bucks on ebay. If you're really short on cash, you COULD use a bolt, nut and some washers to improvise an adapter. Just try to get the bolt as centered as possible in grinding disc hole.
https://live.staticflickr.com/65535/...4390dffa_z.jpg
Two small pieces of scrap wood
A square.

Mount your grinding disc and adapter in the pillar drill. RPM shouldn't matter too much. I ran mine around 900 rpm and it was fine.

Place your blocks of scrap wood into the vice with the rail vertically between them. The wood protects the rail from the vice jaws.
https://live.staticflickr.com/65535/...c907e41061.jpg

Place your square against the rail with the outer edge of the square touching the bottom of the grinding disc. Adjust your rail until it is perpendicular to the grinding disc.
As the disc is hollow in the middle, you'll be doing your grinding on one side of it. Make it square and don't move it from here. You don't want to introduce any variations in slope or angle by moving it around on the drill press table. Tighten your vice, check for square again, and you're ready to grind.
https://live.staticflickr.com/65535/...d3bca1c4_b.jpg
Lower your drill SLOWLY onto the rail. Take your time here. If you press too hard you will probably introduce deflection into the grinding disc. I did. You are only removing 0.5mm-1mm of material, so don't rush.
You'll see the grinding marks that the disc leaves. As you progress, you'll see more and more until they cover the whole end of the rail. Keep an eye on the chamfer. Once it disappears, stop and check for square. If its not square, you've probably deflected the grinding disc. Try again.

Once you're done, let it cool down for a bit then softly brush the end with some 250 or 400 grit sand paper to remove any burr. If you leave any behind it will catch on the bearing truck.

Join your rails together using a known straight edge placed against one side of the rail. Once again, lightly run some sand paper over the join. You're not trying to remove the case hardening here. Just a slight burr.

And if all has gone well, you should have something like this
https://live.staticflickr.com/65535/...a0c5bd9b61.jpg
https://live.staticflickr.com/65535/...e33d460d5b.jpg

...and movement like this.

https://youtu.be/vEpuSwagamc

I think thats about it.
Thanks for reading

Neal

Nice idea and job you did on them!

For longer lengths you could use a bench disk sander, one with slots for a mitre fence not the other type obviously, one like this (https://www.axminster.co.uk/jet-jsg-...-sander-510390) but with-out the price tag of that unit lol.

I got mine on eBay for £40 second hand, paid for its self with-in a week, there such handy tools to have in the shop I couldn't be without mine now!

Very handy. I was offered a series of short rails for an X axis rail upgrade a while back at a very low cost. In the end I dug deep and bought 2 complete long rails but your method looks good.

Quote:

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Originally Posted by Lee Roberts

Nice idea and job you did on them!

For longer lengths you could use a bench disk sander, one with slots for a mitre fence not the other type obviously, one like this (https://www.axminster.co.uk/jet-jsg-...-sander-510390) but with-out the price tag of that unit lol.

I got mine on eBay for £40 second hand, paid for its self with-in a week, there such handy tools to have in the shop I couldn't be without mine now!

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Yes that is a great idea. Honestly I didn't even consider that the offcuts might be longer than the drill press height could accomodate. That price is ridiculous for a sander, but even with a cheap one you could just rig a fence at 90 degrees to the disc and push the rail into it while keeping it against the fence. Would probably be more accurate than my method too!

Quote:

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Originally Posted by routercnc

Very handy. I was offered a series of short rails for an X axis rail upgrade a while back at a very low cost. In the end I dug deep and bought 2 complete long rails but your method looks good.

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Thanks. Yes for the price of proper rail, its worth trying other methods if you have the offcuts.

Side note, do you know where I can get replacement ball bearing...balls. One of my carriages has a few missing.

Quote:

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Originally Posted by Nealieboyee

Side note, do you know where I can get replacement ball bearing...balls. One of my carriages has a few missing.

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Ask Lee Roberts, I've seen him mention recently that he has some spare!