DIY CNC Linear Rail Design

For my CNC machine I decided that I would try and make my own linear rail system using 608 skate bearings and flat steel. This was to try and save money, and I must day that my design, which made the best of the equipment I had on hand, failed miserably. Luckily I decided to try making a prototype with a 1m length and half a carriage before diving in and buying metres and metres of steel and wasting my time building any further.

Here's a drawing of the rail with a carriage riding on it:

This is one side of that carriage made and put together, to get adjustability and thus make up for lack of tolerance (had to do this by hand), I drilled the holes a bit large on purpose so I could (in theory) get the bearings pressing tightly against the linear rail and then just tighten up the bolt:

These are the four pieces of SHS cut and drilled, two of them have cuts which allow for access to get at bolts which have to be tightened. It turns out that there was not adequate room to get at bolts with this design anyway:

The linear rail I put together, it is made of two pieces of steel bolted together, namely 50mm SHS with 3mm walls, and also steel flat which was 5mm thick by 75mm wide if I remember correctly.

For the prototype, I only used construction-grade steel and this showed in the surface finish, in the final design I planned to replace the steel flat with precision-ground steel flat and just use structural SHS for support and rigidity.

Another problem with the overly large holes which I hoped would allow me to get adjustability was that the nut would have less flat area to sit on and thus tend to skew off at an angle easily and not be all that rigid, this problem was exacerbated by the fact that the square tube had very thin walls. Also I couldn't get a washer into the tight space to help the nut. This led me to trying to mill slots for adjustability, since I don't have a milling machine or a milling attachment for my lathe, I just clamped the piece to the tool post which was very finicky, also not very rigid when all the milling force was on the clamp rather than the tool post. It sure did mill fairly well though.

In the end I decided against this method of making home-made linear rails even if I could get easy adjustability and rigidity which were major challenges with the tools I have. The final reasons I decided against this design were: the carriages were too bulky, making the carriages was way too time-consuming given the number I would have to make in total and also the fact that precision-ground steel flat for the bearings to run on would cost a lot and negate any cost savings of going homemade. Bottom line: you're going to get what you pay for and your labour is not worth wasting when the products out of China are so cheap.

Instead I've been considering 16mm supported linear rail mounted on a frame made out of 50mm SHS or larger with thickest walls I can get and the linear bearings to go with it. Lucky for me it turns out that the supplier of the linear rail is a short drive away from me.