CNC Router Build I am a new member, Gordon a retired farmer 70 yrs young.

I am re-designing a CNC Router I saw on the net, RHS Steel 65x35x3mm is the basic material , I have an 16mm offcut of Aluminium for the z axis mounting plate and the router plate . Linear Rails 20mm sq Solid with square sliding bearing blocks, Drive screws are 16mm SFU 1610 two step with antibacklash nuts. The Spindle is a 2.2 kw water cooled 20 Collet and with its bracket weighs just on 6 kg . X axis is 1000mm Y axis is 940 mm and Z axis rails are 325 mm.
X and Y gantry design I am fairly happy with but Z axis I have no idear at all what dementions at all regarding , distance between Y linear rails , and same for Z rails, the ally plate when laser cut will be 280mm wide so am wondering if that will be ok or should it be a bit less for the z axis mounting plate.
I saw somewhere that the router plate linear rail bearing blocks should be about half the length of the router plate apart , which should be kept as short as possible but retain desired travel. Am I anywhere near knowing anything about all this . will be very interested if someone can help me . Many thanks , Gordon WA

Distance for the rails on the gantry make sure you get the maximum distance feasible as that way you reduce the moment applied due to cutting forces axially against them. So say for instance at the very edge of the gantry plate or even better on the top/bottom and that way you get an even larger distance to reduce the moment.

The 2.2kw WC spindles are really good, mine is super quiet. The water pump creates more noise on idle!

Rob

Gordon,
Nice to know there's another DIY CNC builder here in WA! I'd love to see some pictures of your progress.

Two sections of 65x35 welded together will give you a flat (if only!!) face 130mm high which might give an acceptable separation for the rails. Then you have to work out where best to place the ballscrew. I'm considering using something like 2 lengths of 100x50 steel box section on their sides at top and bottom for holding the rails, with an upright section between them which is set back to make room for the ballscrew to run between the rails and directly behind the Z-axis baseplate. This would be good and rigid (at least for my wood-cutting machine), eases the design of the Z-axis unit but is not something I've seen used in practice. Maybe the experts can see a flaw in this idea that I can't!

Kit

Sounds like my design are similar for the gantry, I will have one main gantry upright bolted to X axis bearings, Back of this another RHS at the top length to suit Z axis 12 mm aluminium plate , Z Linear Rails will be mounted on 2 more RHS placed horizontally across behind the vertical uprights these rails will be approx 300 mm apart ,and this setback will go towards centre of gravity of the whole gantry , the 2.2 kw Spindle is quite heavy. I invisage the Z axis linear rails to be around 230 - 250 mm apart , does that sounds about right or should they be more or less , thats where I am unsure. Thanks Kit Regards Gordon .

Gordon,
My practical experience is limited, I'm in the process of upgrading from a wooden framed machine to a steel version, so I would defer to the more experienced builders on this site, but the rail spacing you describe is on the high side of what's common I think. Not that that's a bad thing.

One issue I have with my current design is that the width of the Z axis assembly and the design of the gantry ends restricts the available travel and hence cutting width. I get less than 400mm cutting width from a machine that is over 800mm wide in total. I can raise that to 600mm in the next upgrade with a new gantry design and remoddeling the existing frame (I'm so glad I bolted it together rather than welded it!)

Have a look at pictures of commercial machines and other DIY builds. The fixed rails tend be on the sides of the machine or at baseboard level with the uprights as far apart as possible. This alows the Z axis assembly to travel as far as possible over the width of the bed and beyond. Sorry if I'm preaching to the converted but I actually restricted my cutting area more than I realised while I was concentrating on making the gantry as rigid as possible.

There is a video of the current machine in action at the link below (cutting a wooden gear prototype for a wooden clock. Lots went wrong during this cut but I learned a lot for next time). The current gantry is very much a bodge using many components from the old wood-framed machine and what steel components I could scrounge from the tip (freight costs to Outer WA are horrendous for anything heavy) but it cuts wood reasonably well which is all I want it for.

https://vimeo.com/284841202

Kit

Thanks Rob Everything I read says maxamize this or minamize that but does not give any examples in actual measurement ie 200 mm or 300mm or whatever as a starting point , from where one can try to design Y axis distanced between linear rails , and same with Z axis
linear rails .it needs to support a 2.2 kw water cooled spindle. Sorry if I appear a bit bewilded its because I am . Any help in this regard would be much appreciated Gordon