3XXL replacement bed with integrated Y rail supports

I’ve modified my 3 XXL to make it more robust, reliable, and functional. I made a custom Z axis for my 2.2kw spindle. And changed the X axis to linear rails. Also replaced original steppers with high torque ones. All good! My Z axis has a lot of travel. I’m thinking of making a plywood torsion box replacement bed with integrated high walls to support the Y axis rails. I can’t think why this would be a bad thing… Anyone?
It’s less than three sheets of ply. Obviously pretty crucial that I get both Y rails planar in reference to one another. Getting them parallel is easy using the X gantry.
It would give me a little more than 200mm below the highest Z height to the waste board. My Z axis is very solid and X is much stiffer than stock because of the linear rails.

existing mods.

proposed torsion box bed.


Be careful you don’t go whuppin’-a-dyin’-hoss.

The mods I did, I had to do to make the thing work reliably. It was almost unusable as a production machine when it was stock. It’s good now. Performs solidly. But Z travel is too small for some of the 3D carving I do. It seems 3 sheets of plywood and a 2-day build is a reasonably cost-effective thing to do… I’d love to upgrade to an industrial 2500x1250mm machine with ATC, vacuum bed, and servos that know when missed steps have happened. But I can’t afford it or the larger workshop space I’d need to house it!

I can’t see how it could be a bad thing, the only risk is that…it may not improve anything, if Y axis deflection was not your problem in the first place. One thing I have learned from successful modders here on the forum is that it all starts with characterizing what the limitation actually is in your current setup, and improving that specifically. Rinse and repeat. And when I say “I learned”, I of course mean that while I know this is the right approach, I choose to ignore it and just have fun modding my machine just because :slight_smile:


The problem is not enough Z height.
It’s partly due to how I have my Z-axis set up. The plate that the router is attached to moves up and down with the router.
To do a deep carve, say 70mm deep, I’d like to be able to place the bottom of the end mill 70mm+ down from anything that might collide with the work. (Bottom of the Z axis) Then my toolpaths can go at it. But that means I need 70mm for my stock and 70mm for my tool under the X gantry. My OG Z-height is about 75mm so for anything more than 35mm deep, I have to think very carefully to make sure there are no collisions.
The new table will solve that. But also will cause a larger moment for rotational deflection of the X gantry. Due to the Z axis being generally further away from the X gantry when it is cutting. This is most extremely the case for thin stock like plywood. The new wasteboard is far away from the X gantry. 3/4" plywood doesn’t lessen the gap much.
If deflection turns out to be a problem I guess I can make a torsion box cuboid to bring the thinner stock closer to the X-axis gantry again. Then the geometry is similar to the OG 3-XXL?

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