Hi all.

I'm an absolute beginner with CNC, but have been that impressed and blown away by some of the home builds out there that I feel I must have a go at it. Of course, I'd like to set my sights high, but even if all I manage to cut out is a circle or a square then I'll be very happy..! My engineering experience is very limited but, in my favour, I'm reasonably good with my hands and like to do things 'properly'.

I've got a whole heap of questions (somehow answers seem to lead to more of 'em...) but I guess I have to start somewhere so here's my proposed concept (feel free to tear it apart..!):

The build will be based around 50mm square section aluminium extrusions (3mm wall).

I mostly intend to cut wood.

I'd like the cutting area to be around 450x550mm with a minimum plunge of around 60mm.

I'm fairly aware that I may well end up 'over-engineering' this, but would rather end up with a machine that's sturdy, even if it costs me a bit more. I'm budgeting on around £1-1.5k for the parts (extrusions/motors/spindle/rails/lead-screws/support bearings etc.) +electronics +software on top of that.

I'm more interested in repeatability and precision than outright speed.

Motion will be via 12mm lead screws (3mm pitch) ACME nuts (possibly pillow block ACME nuts for the Y & Z) all driven directly by steppers.

The gantry will ride on blocks/rails.

You can see what I'm thinking in the following clip:



Both the gantry and the Z-box will be made of chunky aluminium u-channel with side plates held in place by the tension from the nuts holding the guide rails in place. Again, here's a clip to illustrate what I mean:



I think it'll work, but you may well think otherwise! The reason I took this particular approach is that I can be reasonably sure that the aluminium channel will be sturdy and manufactured to a fairly tight tolerance. I also know that I can very accurately cut and mill the side plates for both channels on a friends ShopBot. This approach also saves me having to drill and tap into narrow edges!

If possible, I'd like the gantry to be driven by a single lead screw, but this would mean that the screw sits quite far down from the gantry with the ACME nut attaching to some sort of bar which in turn is bolted to the back of the gantry. Is this madness? Will the ACME nut working this far away from the load introduce prohibitive torque at the base of the gantry/blocks?

Where do I start? I guess a bench and frame would be a good place, but after that? I'm thinking that I buy the lead-screws, ACME nuts, rails and support bearings and then begin to design in greater detail... Would that be an acceptable approach?

The electronics I'll most likely leave until a later stage. I'll be using standard (easily available) stepper motors, I'd like to be able to use a bit/probe to zero the machine and the control software I'll go for will more than likely be Mach 3. Although I'm fairly good with computers, this part's a bit of a mystery to me... More research needed...

Finally, if you're in the Manchester/Stockport area and you wouldn't mind talking me through and showing me your build in exchange for a fine bottle of wine, then I'd welcome the chance to do so.

Thanks for sticking with me this far, let me know your thoughts.

Once I start I'll be sure to keep a diary.

Warmest.