Sizing Advice Requested

Mostly Printed CNC - MPCNC Advice
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Hi - I have all my printed parts done and I’m ready to start cutting my tubing. I just would like a little advice first.

I originally had in mind using this to cut a wing rib out of 1/4 plywood for an ultra light project. The rib would be quite large, 48” long and 10” tall.

I printed all my parts out of PET-CF and it’s very strong, very stiff stuff.

I purchased 1/8” wall 4130 tubing and so my rails are very stiff as well.

I’m thinking about trying for a 49” x 25” x 8” workspace, but I see all the comments that doing that would be way too big.

Is there any chance that the stiffer materials I have planned to use with let me make this larger than recommended? Has anyone tried to do this before? I have no problem adding mid span supports if that’s what it takes.

I figure if it’s the much to big and there is no accuracy, I can always cut down the tubing with minimal waste. If I start small, I’d have to re buy everything to make it larger.

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Are you thinking about that workspace for the 3d printer or for a CNC? MPCNC or Lowrider v3/v4?

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For the MPCNC. Al parts made from PETCF and 1/8” wall 4130 tubing.

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I can’t remember if it’s v3 or v4. I started printing it in 2023 if that helps date it. I can check when I’m back at my computer.

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You need to be more clear. There is no v3 or v4 MPCNC.

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That size is too big for an MPCNC. A LowRider V4, on the other hand, would be really stout in that size.

One reason that you’re confusing folks is you posted this in the MP3DP section of the forums, and a MP3DP is Ryan’s design for a flying Z 3D Printer.

As others have asked, exactly what are you thinking of building?

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Is there any chance that they use the same hardware pieces or the same kit I purchased for the MPCNC? Apologies for posting in the wrong spot.

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The electronics are the same. 5 stepper motors, control electronics, switches.

The nuts and bolts have some crossover. 608 skate bearings, 5/16" x 1.5" bolts, nuts… some of the M5 hardware.

The problem with the LR4 is that the rails are different. The Primo uses 23.5 (3/4" conduit) 25mm, or 25.4" (1" tube). The LR4 uses 1" conduit, 30 or 32mm tube.

You could use the same tube for a LR3, which would still be excellent at your target size. 25"x49" would make a very nice LR3 still very capable.

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I’ve thought about this for a while… I’m going to build the kit I have. Is 24x24 a good build size? I think my system should be more rigid than not with the better plastic and tubing but I’ll just enjoy that on the normal size MPCNC.

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24x24 should be fine. I wouldn’t go much bigger than that for a MPCNC.

The smaller you make it, the faster and more rigid it can be.

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11

Just to not start another thread I also have a question about the sizing. I need to mill 8 inches thick foam. Is there a mod that people already did to accomplish this? I prefer to do a 8" depth from one side instead of doing 4" from one side and turning it over to do the other side. Mostly for convenience but also for precision and alignment reasons.

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Where are you getting an 8+ inch endmill? Other than that, the solution is typically using a drop table.

Edit: Plus there’s not that much Z travel. I don’t think I’ve seen anyone here cut a full 8 inches. It’s one thing to cut into 8 inch thick material, it’s a completely different problem to cut all the way through it, especially without flipping it.

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They sell even 10" router bits. I don’t think this is the problem. I think the limiting factor is the 200mm lead screw. If it can be replaced by a longer lets say 300mm screw, it would be able to travel 12".

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You can’t replace the whole sides with plates that big, you need to create a drop table of some sorts then. :slight_smile:

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Just FYI for the future. Our preference is for you to start another thread. They are free, and often turn into a much longer thread than you expect.

Plus we want to see this machine once you make it :slight_smile:

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