[sgspenceley]

I'm in the process of building a CNC machine which is made from rectangular mild steel tube, aluminium extrusion for the X axis, ballscrews and Bosch 20mm linear bearings.

Electrics
48V 12.5A switching power supply
Gecko G540 4 axis stepper motor driver
4 High-torque Nema 23 380 oz-in stepper motors
I have built a custom electronics enclosure.


Feedback is most welcome because this is my first scratch build. I recently finished at OpenBuilds OX, but found this design was not strong enough for my purposes.
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My idea is to bolt 1/2" cold rolled steel to the rectangular tubes, in the hope that the colled rolled steel will be straight enough for the linear bearings to be mounted to.

[louieatienza]

You shouldn't need two LM rails on each side...

[sgspenceley]

Thank you for the input...

I have been thinking the same thing since my Bosch linear bearings arrived a few days ago.
I originally purchased SBR16 from China and thought 2 per side was required because they are not very precise. Then I came across a good deal on 20mm rails and bearings.

I also wondered if 4 carriages are really required for the Z axis, given the bearings are 3 1/2" long.

So will update the design with just one bearing per side. I have also noticed this forum has lots of machines built from steel tube and less built with gantry side plates.

Lots to think about waiting for the ball screws to arrive.

[sgspenceley]

I updated the side gantry plates to support just a single linear bearing on each side.

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This makes me ask another question. Is there any advantage or disadvantage to linear bearings being on the side VS on the top of the Y axis rails?

[louieatienza]

If they're 4-way linear rails then they can carry equal load vertical and horizontal, provided they're mounted solidly. These rails by the way are capable of loads we'll likely not see with most all DIY jobs...

As to the Z carriage I prefer to have two blocks per rail, since there is likely the most "levering" force.

[sgspenceley]

Thank you for responding, so quickly, yes they are 4 way running on 20mm rails. So should be more than strong enough for my little DIY machine.
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[louieatienza]

Thank you for responding, so quickly, yes they are 4 way running on 20mm rails. So should be more than strong enough for my little DIY machine.
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Yes, if your frame is strong enough the rails and blocks will carry a small car!