Using C-beam for large OX

I’m building a 1000x1500 OX. I understand some of the tradeoffs (I know deflection increases as the cube of the arm) but my purpose for this is relatively large-scale wood projects, like chairs, so that I’m not expecting micron precision…

It looks to me like I could use 1500mm C-beam for the Y rails instead of 20x80 extrusion, at the expense of 40mm of X travel. It should be stiffer, and I can’t see anything in the design that it would interfere with. Anyone know that I’m missing something?

I could even join C-beam to 20x80 for an 80x80 square beam, at a cost of another 40mm of X travel.

I might not even lose that much X travel. Eyeballing pictures, It looks like there’s about 60mm of lost X travel between the spindle and the edges of the X gantry plate, so I might lose nothing with the C-beam and 20mm or so with both beams joined. I haven’t measured, but I think if I lost even 80mm it wouldn’t have a significant impact on the projects I want to do.

You are on target I think. But if you are going to upgrade to Cbeam, then I would look at making it a leadscrew driven build. I have an OpenBuilds Sphinx lead screw machine, and have a 1meter X 1 meter OX currently. I rarely touch the OX because it feels like a toy compared to my 1 meter X 1 meter Sphinx. The belt drive on the OX is very limiting, that being said, cbeam is overkill for a belt drive OX, you cant push hard enough to cause much deflection.

My Sphinx can push around a 1.5kW spindle without issue, even with large depth of cuts, my Ox has a 500W spindle that has to go mimimal depth and fairly slow.

1 meter isn’t long enough for my projects. I would have gone R7 if 1 meter were enough because screw drive.

I’ve realized I could sister the 80x20 pieces to some shorter 80x20 resting on the table surface and also handle the vertical deflection (not worried here about torsion here right now).

If you need any plates cut to be able to run an r7 setup, I’d always be willing to cut them for you. Also for a 1000mm on X you will need to stiffen it up if you plan on cutting much aluminum. If it’s just for wood he’ll be fine, but even on the r7 cutting aluminum with that wide x-axis can run into chatter if you push it with too much depth of cut. your best bet is to make the x-axis stiffener tall, on the r7 it had wheels on the front and top with a plate riding on the back which limits your ability to make the x-axis gantry taller to avoid deflection, if I were going upgrade to my r7 it’ll probably be putting a large 80/20 across X and linear rails on the front.


Thank you! If I end up needing plates cut, I’ll definitely reach out! :slight_smile: