Advice on Mammoth CNC Router Build - Steel Framed - 2440mm x 1220mm cutting area!

[Wejjmeister]

Next round guys Mk3!




Removed steel form sides and changed bed supports. Any better? Saves a lot of excess steel.



Started on ideas for rails etc... let me know your thoughts please.





Think this should provide a strong setup, also thinking about using BK blocks to mount Ball screws? Will these be suitable?

Thanks!!

[Jonathan]

The covers round your ballscrews will fill up with swarf and cause the ballnut to fail prematurely.

Think this should provide a strong setup, also thinking about using BK blocks to mount Ball screws? Will these be suitable?

Best way is to use a rotating nut. If not, then at this length you'll want two angular contact bearings at both ends to get a respectable speed. Search on Google 'ballscrew critical speed' for more information.

[Wejjmeister]

Thanks for that, as for the former comment, I would have covers all along the open section to prevent swarf ingress, would this suffice?

[Jonathan]

Potentially - depends on the covers.

[Wejjmeister]

Potentially - depends on the covers.

Could always put the slot in the outer sides and make it so the gantry overhangs a little more and they attach on the side? Was trying to keep the rails and screws as close to each other as possible thats all.

[Jonathan]

Was trying to keep the rails and screws as close to each other as possible thats all.

That is a sensible priority.
I'm being intentionally vague here since, as you've realised, you've got to weigh up the factors and if I just say how I'd do it, then you might miss out on finding your own better solution. Ideally you need to minimise distance mentioned for rigidity, not allow swarf to build up on the ballscrew (especially if rotating nut) and not cost an unreasonable amount.

[Wejjmeister]

Exactly what I feared!! I will do some more thinking, need to research rotating nuts first as I'm not at all familiar with these, then I can hopefully come up with something. The covers are pretty resilient though and will stop most foreign bodies, with those plus regular cleaning I think it may be the best option as it gives the most strength.

I'll give it some thought! Any other glaringly obvious mistakes in the design??

[JAZZCNC]

Best way is to use a rotating nut. If not, then at this length you'll want two angular contact bearings at both ends to get a respectable speed. Search on Google 'ballscrew critical speed' for more information.

100% Agree I wouldn't use rotating screws at this length.

Thanks for that, as for the former comment, I would have covers all along the open section to prevent swarf ingress, would this suffice?

Could always put the slot in the outer sides and make it so the gantry overhangs a little more and they attach on the side? Was trying to keep the rails and screws as close to each other as possible thats all.

The covers will still fill up the way you have them now. The little extra the Gantry will extend to make it so slots are on outside won't make any differance to how this machine performs so it will be worth doing no matter if rotating screw or Nut.

Don't get caught up in the over analysing the machine because while important your only talking a very small differance which won't a make a JOT of differance to the cut quality or speed needed for cutting woods, plastics and even for the level of Aluminium cutting this machine will be capable of dealing with.

Shit in the Screws or Nut will make you REGRET NOT doing it EVERY DAY were has you'll never even notice the screw being closer to rails.!!

[JAZZCNC]

Any other glaringly obvious mistakes in the design??

Not glaring but you have gone too far with removing the diagnols but not far enough in other places.?

I would have diagnols at each end of the sides. But would remove the central upright and re-space others on all the Bed support frames.
Would also have a Bed support frame on each side upright and not laid flat in like you have in centre.

The rest looks ok.

EDIT: I would also on the outer End bed supports have diagnols on inside lower beam which fastens to the sides to help hold frame square while setting up and bed frame is fastened. Like this but larger and to suit your design.

[Wejjmeister]

Will make the recommended changes tomorrow in sketchup, im getting square eyes now and RSI from that software, its good but frustrating!!

Also done some research on the rotating nut idea and like it a lot, need to make a few mods to allow it to work. Can you guys tell me which Blocks you use to hold the ballscrews in situ tho, are they FK blocks?

Also where do you get the actual rotating nuts from as I can only see the manufacturers, not any suppliers etc, Zapp dont seem to list them??

Any help would be very much appreciated!

Thanks again!!