I did search for anything similar but maybe my search parameters weren’t adequate to find anything previously so here goes.
I printed all my parts for my Primo, bought conduit and a large piece of MDF for a base and then health issues stopped the build. While thinking about the build (if possible I’d like a 3’ by 4’ useful area) I understand that longer runs of conduit will sag. However, what if I designed 3D tube pieces with interior inner wall support structures to keep the piece from bending or flexing, that fit very snuggly (possibly needing to be gently hammered in) in to the conduit and were glued on end (epoxy ?) as they were inserted to continue the idea of one continuing piece of support? Would it be plausible that the extra interior support would eliminate the sag?
Has anyone tried this? If so, did it work or was it a waste of filament?
Thanks for any ideas or suggestions!
Somewhere around here there’s a post about filling the tubes with concrete. There’s a bunch of maths in it showing that putting anything in the tubes is basically a waste of time.
I remember reading the same! Lr3 may be the ticket for you if you need it that large
I agree with Riley. A Primo that big isn’t really feasible. Mine was 55x75cm and had chatter in the middle that was impossible to get rid of.
Totally agree. Mine has a 2x3 foot working area. There is considerable flex. I’m making mine smaller. Go with the lowrider instead.
Thanks for all the great info! I’d never considered the LowRider but maybe that’s what I should consider.
I’m retired and thought it would be fun to make entry doors with customized scenes. I’d use the CNC to get a decent rough cut design and then carving chisels for details. At 3x4 I could do a full panel in two setups using precise registration marks. However if even 2x4 has deflection (I’d turn the door 90 degrees and do 3 or 4 setups) I guess I’ll abandon making a large Primo. Maybe 2x2.
I guess two CNCs are in the future. I already play with FDM and resin 3D printers and am about to go down the laser engraver rabbit hole 
Thanks again everyone!
I tried filling some tubes with spray foam and testing that.
Never did post definitive results, and it made running wires through a real pain.
Off the top, it did improve the flex of the tubes, but didn’t damp vibration much, was very light for extra mass. If you just need a very little extra, maybe it would help, but in general, more trouble than it’s worth.
Increase rigidity cheaply, street racer trick?
I know it produces measureable results in a unibody car chassis, which has relatively thin metal rails, but the metal to void ratio of steel tubes combined with the more ideal shape of round tube makes it a questionable upgrade at best, and a waste of time and money being more likely.
Still waiting for someone to pressurize the tubes.
If I wanted to lessen sag I’d probably look into stressing. Similar to what we do in hi-rise concrete builds on a smaller scale
I think that’s been tired too.