CNC machine for the London Hackspace

I'm starting a project to get a CNC mill /router at the London Hackspace (a UK maker community). I was hoping that you guys here could give me some advice about what directions we should be looking in.

I've surveyed members about what they want and how much they're willing to donate towards getting such a machine. The results were:
- the biggest group of people - $2500 budget - would be happy with a 12" x 12" that could do PCBs, wood, plastic and softer metals such as aluminum;
- a further smaller group - taking the budget up to $3000 - wanted the machine to be able to do up to 20"x20" or 24"x24", cutting the same materials
- another small group - taking the budget up to $4000 - wanted a 4'x8' wood router.

All of these people want to be able to carve complex shapes, but there was little appetite for undercuts, so we're talking 2.5d.

I should clarify that when we're talking about cutting softer metals, it's not simply a matter of cutting out shapes in 1/8" sheets -they want to sculpt complex shapes with maybe 3" of z travel.

Robustness is a priority as it will be used by people like me with little training who won't know how to mother it and will damage it often if there's a way we can. Speed is not so important as this is a hobby environment not a production one. Machine will probably be running about 1-2 jobs per day.

This budget needs to cover absolutely everything - spindle, software, dust extraction, cutting bed, etc.

Building from scratch or upgrading/converting is realistic option for us. We have in our hackspace metal working tools (mills, lathes, but not CNC) and a laser cutter (wood not metal). We can definitely get plastic parts 3d printed by members who have 3d printers, and may be able to get metal/wood parts CNC machined by members who have a CNC at home.

The way I see it, we have three choices:
1) abandon the people who want 4'x8' and their money, and spend $3000 on 1 good machine 20"x20"

2) get 2 machines for $2000 each: one 12" x 12" for precise work like PCBs that can also cut metals OK, and one 4' x 8' primarily for wood that has less precision/accuracy and can do metals only very slowly.

3) get 1 machine for $4000 that can do 4'x8' with enough rigidity to do metals but good enough on detail to do PCBs.

Which is the right strategy to pursue? Particularly given that we need a machine that is as user-proof as possible.

Any advice much appreciated.

Jonathan

Just curious - why is your budget in dollars?

Apart from that clearly the best value will be DIY - and you'll also know how to fix it if it goes wrong rather than relying on some vendor (or unreachable Chinese manufacturer) for support.

Plus for extra idiot proofing you could build in things like shear pins or friction clutches so that a crash shouldn't result in too much damage.

Read the build logs here and post the designs here too for critique before you start and you won't go far wrong.

if you're a hack space you should team up and make the CNC yourself, or with favors from friends...free labor!

PCBs machine have to be high resolution, slow, very little to no play in the couplings and very very flat.

wood needs to be cut fast otherwise it will burn the cutter/wood

and for doing metal it needs to be rock solid.

I'm sure one machine could do it all but building small machines are much easier

Thanks for the feedback guys.

I'm currently thinking that realistically we might well end up with a 60cmx40cm size. Or even 30cmx40cm

Any ideas for designs/plans for a machine this size that has enough rigidity to perform OK when going through aluminium? Building ourselves would be tempting, but realistically it's just not going to happen unless we have "painting by numbers" good instructions.

The KRM machine Building the KRMx01 CNC looks like it might have this combination of rigidity and detailed instructions. Any other options I should be weighing up?

One possibility I'm seriously considering is the 6040 machines from Yoocnc 3020 3040 6040 series - carving-cnc.com. They're Chinese and used to have awful electronics but now better. You can buy the main body alone which is a tempting option.

A lot of people on cnczone.com seem to think the mechanics on these is good, and that you'd be hard put to get the materials alone for less than what they cost assembled. What's your take on the value-for-money of the frames of these machines?

I get the impression they can mill aluminium, just slowly.

Jonathan