Design stage of 4030(ish) for wood and plastic

[andy586]

Hi,

After a bit of CNC hiatus, I am back on track with funds all ready to go. I am aiming for a small machine (around 40cmx30cm cutting area) for mainly wood and some plastic (if it cuts thin alu at all then great but not important…I am planning to make toys, games, and light-based gadgety design items).

I have no workshop and live in a tiny flat so minimal machining is required (as it will all have to be paid for at silly london prices).

Any general advice would be great before I go too far with my current design and I also have a few specific questions.

I have attached some images of the design as it stands (still a work in progress but think one can get the idea).

The base is two 700mm lengths of 60x60 series 6 profile extrusion sitting on three 600mm pieces across. Then sbr16 bolted straight on to this with plates (all plate in machine to be 20mm ecocast) at front and rear to provide mounting for motors and screw supports and reinforcement.

The gantry is a 600mm length of 120x60 series 6 with a 140mmx600mm plate stuck on the front, plates at sides to reinforce, sitting on bearing plates.

So…

How bad is it to mount the Y rails on front of gantry rather than top and bottom (more concerned by mechanics rather than exposed screws and bearings issues) ? It seems to make the z axis so much simpler.

With regards to z axis, should I have the y bearings outside of the z bearings (as it is currently) or should I swap around?

I plan on snipping off any excess on the gantry sides once I have added in holes for motor and screw supports. Is it worth trying to save weight elsewhere (e.g. few holes in either of the z axis plates)?

Fitting metal parts together…at the moment I have a couple of bolts on either side connecting the 120x60 extrusion directly to the bearing plates and then the gantry sides are also bolted to both the extrusion and the bearing plates. Can one use finger joints or similar to attach plate parts at right angles to each other (as well as bolting)? I have had a little read about interference fits etc…I can see issues in trying to build a precision machine that requires a hammer to put it together. Maybe just a reasonably close fit so it assists a bolted joint?

Was planning on using 1605/1610? ballscrews all round, twin x, nema 23s. Is it possible to have a versatile machine without use of belts?

I could ramble on for a while but think that is enough to hopefully get the ball rolling. As always, any advice is much appreciated. I know the machine is full of compromise but such is life.

Notes:
The spindle was grabbed from 3d warehouse…I will go for something which protrudes less if possible.

Need to resolve positioning of gantry sides in relation to ballnut mount (can only attach one or the other but not both at moment!)

I will start enquiring about prices for getting the plate parts done. If I get them milled then I will create pockets for bearings (left it all flat for now as one possibility is a university nearby that does waterjet cutting).