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

[Wejjmeister]

So I've been planning to build this thing for quite some time now, finally I have taken the plunge and started to finalise the specs. I have read, re-read and read again many of the posts on here looking for advice and ideas, and I am now ready to lay out my designs in front of you guys for some no doubt frank but highly constructive criticism hehe!

My machine will be used for every type of material between balsa (model making) and Aluminium, and must be able to cut 1220mm x 2440mm sheets of the above materials at times. I will type out my specs a little later on as I'm limited on time at the moment, but I have put together the design in Sketchup for the general idea, and wondered before I go any further if you can give me ideas as to whether it will be strong enough or not?

[EddyCurrent]

It looks quite strong but you don't have any diagonal bracing on the ends. Also with a machine this size I would estimate the amount of material and calculate the weight, you will probably find it need to be made in bolt together sections, the bed being one section on it's own. The method of bolting may therefore have a small effect on your current design. It also looks like you have very little depth of cut in the Z direction.

These threads are worth reading.
http://www.mycncuk.com/forums/router...on-please.html
http://www.mycncuk.com/forums/router...t-build-3.html

[Wejjmeister]

Thanks pal, yeah I read both of those threads as part of the planning stage for this build. The Bed will be bolted together in the three sections shown. I will try to incorporate some diagonals too, thanks for that advice. As for the Z axis, what do you recommend? I did think about putting another length off 100x100 between the carriage and the Y axis, to lift it a little further but wasnt sure??

[EddyCurrent]

This is the side arrangement I went for, the linear rails sit on top of the upper blue beam, top of the bed will be flush with the top of the lower blue beam.


The top rail bolts to the bottom section via those red flanges, this allows me to level up the top faces using shims or compressing epoxy putty in the joint.
I'm planning on 150 to 200mm for Z travel, you have to account for your longest and shortest cutters plus your workpiece thickness plus any sacrificial beds you might add in.

[Wejjmeister]

Thanks for the comments. I have made a few adjustments to the design based on comments made and also my own thoughts (dangerous!)

I have added a second 3m length of 100mm x 100mm box along the top, this gives me around 200mm on the Z axis. The plate of Aluminium on the bed will be 20mm thick and surfaced flat. I will set the rails along the 3m steels on Epoxy as in Jonathan's build so they are as true as possible, and the Bed will also be supported with uprights rather than diagonals, purely because the frame must bolt together and it is easier with uprights than diagonals to do so, without hopefully compromising the overall strength, I can add feet below the uprights if you deem it sensible too?

Let me know your thoughts guys as I would like to start on the frame soon. Ignore the frame for the Z at the moment, its in its very very early sketchup stages and will change A LOT from now...

Thanks in advance!

[JAZZCNC]

I wouldn't use that method to build it.? I would drop the extra top rail and just extend the uprights to get your extra height.
It will save on material and resonance because those will be 2 large drums you'll be creating. To be honest I wouldn't use 100mm Box I'd go with 80mm and thick walled.
I'd use the design Eddy showed with top rails sat on plates which can be adjusted into plane much easier. The work involved with Epoxy is quite involved and to be honest a complete waste of effort if your going to use those Cheap round rails has there will be more error in there base than the surface your fastening to.! . . . . I also doubt you'll get it any better with epoxy than using the above method and it will take much longer and not be has flexible, it will also cost lot more money.

Show us the same picture but with out the bed base so can see the bracing etc.

[Boyan Silyavski]

On your last picture it seems you were thinking mainly of cutting aluminum . If you continue with this design, take care that the rails on the gantry should be maximum low, near towards the table and as round rails don't like that position nor milling aluminum something has to change there, for starters -square rails.

[Wejjmeister]

Ok I will spend some time converting it all to 80mm box, what wall thickness would you recommend?

Those rails are only for an idea of where everything will go, in the end I will use Hi-Win rails all round as I have read a lot about there flexibility in use and strength, I just couldn't find a model of then in Sketchup so put the SBR's in just for reference. My main priority is getting the frame completed as I would like to do the build in phases.

If I extend the uprights and use the plate method to true it all, will five uprights be enough/too many? Or should I leave that as is?

Also, should I leave the bed in 100mm box as surely that will need as much strength as possible?

Thanks in advance guys appreciate the time taken to help!

[mekanik]

Hi M8
with such a large machine i think resonance could be an issue, i think Jazz commented on another build and suggested loosing the symetry of the supporting members, i am sure he will comment shortly.
regards
Mike

[Wejjmeister]

Hi M8
with such a large machine i think resonance could be an issue, i think Jazz commented on another build and suggested loosing the symetry of the supporting members, i am sure he will comment shortly.
regards
Mike

Hi Mek,

I considered this whilst planning it all, all boxed sections in the side of the frame would be filled with sand, and then the holes plugged afterwards, including the diagonal braces, would this be enough to damp the resonance?