Will MPCNC do what I'm looking to do?

I’ve got two projects I need - well, would like - to use a CNC machine on, for precision, repetitive cuts. I’ve never used a CNC before, but man it sounds like fun to have one in my garage. First, I have a set of dollhouse plans that I’m converting to CAD using Draftsight. They will be cut out of 1/4" 4’ x 8’ “normal” plywood. Second, I have some wooden boat plans, cut out of 3mm or 4mm 4’ x 8’ marine plywood. In the dollhouse, I could use a smaller setup (I think the smallest piece is 2’x3’ or so). The boat uses the full 8’ length of the board, cutting some parts on the entire diagonal.

Am I crazy to think of using MPCNC for this? I’m happy to start with a small 30x30 build to learn the system, but would need to expand after that. In fact, it’d be great if I could collapse to 4’x4’ or so, and just lengthen to the full 8’ the times I need it.

Tangentially related, some super-pro-fancy CNC software I’ve seen at a shop arranged all the parts on the board automatically. I assume with estlcam I’ll have to manually lay all those out in Draftsight before I export it out.

In estlcam you can generate the tool paths then arrange them however you want. It won’t optimize the layout for you. You don’t need to use estlcam though you can use the gcode from any software you want.

Most people are not building aa big as you are talking but some have so it can be done.

Theoretically I believe it can be scaled to the sizes you want, but you’ll need supports to keep sagging to a minimum. Stainless steel conduit may be a better choice than the normal EMT conduit to reduce the sagging. Regardless I’d use supports like this http://www.thingiverse.com/thing:1160962 . I’m not really sure how you could support the gantry x and y rails with it being so long.
As far as the collapsing goes, I think you could swap the 8’ conduit in for the 4’ and vice versa with relative ease as everything can be slid in and out. However a problem that could arise is your machine not being square with the constant swaps. Anyways this sounds like a cool idea and would like to see how it turns out.

Yeah, look into stainless tubing for a build that size, flex will be your nemesis. Keep the Z size to a minimum so little wiggles won’t be magnified. I don’t think you’ll want to try a resizable design, it takes too much effort to re-square if you swap tubes out or slide one end in on the long tubes. It might be feasible to mount the bed on an angle to minimize floor space used, but we’ll probably have to have someone more knowledgeable to weigh in on that.

I was considering stainless tubing, but also looking at solid rather than hollow. I’ll search/post and see who’s done a full 4x8 build and see what tips I can get. Good to know that resizing it isn’t going to be worth it; now I just need to find a place to put the damn thing :smiley:

Hollow tubes are stronger than solid tubes though.

That’s not true if I recollect right. Hollow tubes are stronger than solid tubes when they have the same mass. However a 25mm solid tube would still be stronger than a 25mm tube, but the weight of the solid tube will be way heavier. If you drill out half of the tube, you will lose less than 50% of the strength. So the strength increases related to the mass, but the same diameter rod will always be stronger than the tube. `(And a lot heavier)

I started out dreaming of cutting 8’ x 4’ sheets on the MPCNC, but I now see it’s not the best way to use the technology.

When you think about it, for cutting shapes in those sheets, you only need 2d routing, albeit you need plunge capability in the z axis.

You don’t need the full accurate 2.5d CNC that MPCNC gives you at its intended size.

I now plan to stick to the recommended size and enjoy the true capabilities of the machine with no compromise. That also means no crazy z-heights to create a big build area for 3d printing. For that I think a MP3DP looks good, or some other cut parts Prusa style thing.

The penny dropped for me when someone on here linked to the Maslow CNC kickstarter project, which despite many technical observers claiming it wouldn’t work seems to have some reasonable proof that 0.4mm accuracy can be achieved while cutting 8’ x 4’ sheets. You’re able to then use a more powerful router too, which should in theory make cutting quicker. I think the founder said he uses 3 passes to cut a 1/4" sheet, but I might have that wrong. I don’t know what the cut speeds are. It also mounts vertically in portrait, just like a panel saw, so won’t take up your whole garage.

Tubes are better than solid rods for our use. That kind of weight has a much larger effect on accelerations and would cause a very slow machine. This is either cover under the “sizes” or “FAQ” page. I have also linked https://www.v1engineering.com/forum/topic/stainless-steel-quick-and-dirty-flex-test/

I suggest the .049" walled tubing for a reason if you decide to go stainless.

Wall thickness and strength are not linear. A huge majority of the bending load is on the surface of any tube. compression and tension. The strongest way for us to build this style machine is thin walled larger the diameter tubing the stronger. Solid rods are for vertical compression and tension.

As for a full sheet machine, it is a different beast as James pointed out. I am getting ready to start designing one, discussion in the updates, version 2 thread. The printrbot company, that makes the Crawler, gave me the okay to go similar in design to the crawler.

I’ll hop over to that discussion thread. I’m not particularly eager to wait until late-2017 to have something running (Maslow CNC). I know that I don’t need all the extra features that MPCNC gives me, and certainly wouldn’t plan on much 2.5D work at full sheet size, but MPCNC provides the best dollar value and quality of everything I’ve looked at so far (that’s available today at least). Perhaps it’s not the intended use, but it sounds like it would work overall?

You can make a Maslow now if you want. The plans have been released and are open source. I admit this is probably not an easy route, as there are PCBs to create from scratch, so you’re right, it’s not readily available yet.

My concern is there are a few people who have mention big MPCNC builds on here, but the thread seems to go quiet. I haven’t seen evidence it’s feasible with the current design, and I’m skeptical you would retain the speed and accuracy you get with the standard size.

I hope you do it and prove me wrong.

RE: only needing 2D routing for large pieces

What about fancy joinery and cabinets? My goal (which is far from completion… sadly) is to use my MPCNC to design and cut pieces for large furniture (tables, chairs, cabinets, etc.), and utilize some fancy 2.5D CNC joinery in the process. I get that this is harder to do with a larger build (hopefully still possible?), but I don’t think that obviates the need for it.

I have the same goal you David and probably nloding.

I am excited to hear that you’re starting on something to cater to this need Ryan!

I guess I’ll be waiting until that takes shape, and playing with MPCNC for now.

I am psyched to hear about the crawlbot-like design. I think that sounds way more promising than the Maslow (sorry, I just don’t see it working out in a general case… Following RepRap projects has taught me that there are many potential motion systems that sound great, but ultimately don’t pan out). Now I kinda wish I had waited to pull the trigger…

I’m not sure I have the means to cut my giant stainless steel frame, so I suppose I’m stuck with trying it out :wink: