Lowcost capable CNC - Make vs Buy?

[Andrewg]

Ah Kitwin, the siren call of ‘just make it a bit bigger’! But I take your point, extra Y length does not change the design or performance significantly.

And thanks for the appreciation Brian, I had hoped this would be of value to others. However others have already steered you away from gantry routers for steel

So where has Jazz left me:

Budget and spec is realistic (Hurrah) but time under significantly! I can live with the greater time commitment, though I expect I will be tempted into stretching the budget when it comes to the motors.and electronics. Definitely worth press on then:

Frame
Wood and plastic cutting router, so aluminum extrusion frame keeps things simpler for me.(avoids welding and steel work) Plates I will definitely be looking to cut/drill my own so will want to keep design simple.

It's also very very important how it's all fastened together and plates etc. Done correctly it's very strong and perfect for wood routers.
.

Sure I will need to come back to what joining methods for extrusions are best once I have a first stab at the design.

Mechanics
Ballscrews all round, but only 3
Single Y ballscrew will save a bit of budget, however I do need to cut ends of boards set vertically. With an under-table ballscrew and cross brace, I will needs to have the spindle sitting forward of the bearings enough to do this. I only need 65mm of cut distance beyond table. Is that a sensible design option?

Gantry

However, it's important that you have a piece of material which is a nice tight fit that goes into the slots between upper and lower profile.

I get the material in the slots to lock the two extrusions together, but see that 10mm aluminium bar is not a standard size so what to use? Options seem to be either machine a ½” aluminum bar down to 10mm slot size on a router table or forget the slot filler and have multiple bolts. By creating a gantry length ‘washer’ with regular clearance holes along it, I could use it as a guide to drill the access holes in the lower extrusion, then install bolts in it to mate with slot nuts in the upper extrusion, so they are bolted every 50mm or so. Avoids having to machine material to tolerance?

Electrics
Tempted by closed loop steppers - looks like for 2nm nema23 steppers it is about £40 stepper plus £20 driver vs £80 for closed loop motor and driver, so maybe extra £20 per axis well spent. Where will I see the benefit besides getting error rather than inaccuracy due to missed steps?


Electronics
There are enough challenged already, UNCNC it is.

Design is VERY VERY important and if done with a forward-thinking attitude then you can have a great machine for not a lot of money.

But still all down to the design, so guess I need to fire up Fusion360 and start designing. Plan to start from the Z axis and work out axis by axis. The Z seems a simple matter of sandwiching 15mm linear rails and 1605 ballscrew between two plates and getting the heights and clearances right...we shall see.