Spiffcow published a new build:

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Thanks! Hoping to have it done in the next couple weeks, but who knows how long it'll really take

 

I'm expecting it will hold pretty well -- it's all PETG, 50% infill with 3 perimeters and a concerted effort to have the stress points align horizontally and transfer most of their force to the extrusions. You can hit the side of this thing with a mallet and it won't move -- I tried it I'm more worried that the holes I tapped in the conduit for the supports won't hold -- it's only 16 gauge steel, so that's not even 2 full threads per support, and right now I only have 5 supports. Of course I can always add more, but that'll mean partially dismantling the machine to do so.

I'll definitely keep it up to date and let you know how it goes -- even if it doesn't go well. This is actually building on what I learned with some previous builds, and all the weaknesses I encountered before are mitigated in this design.. Hopefully there aren't too many new weaknesses!

 

Build is mostly complete and is pretty rigid, but my Chinese spindle is struggling to keep up.. I'm going to put a Makita compact router on it this weekend if all goes well. It's very rigid on the long axis and Z axis, but the plastic shows its limitations on the short axis.. It flexes in the YZ direction. Currently it's still pretty rigid, but it does flex if I put a lot a pressure on it. I plan to mitigate this by fixing an aluminum plate to the back once I have the capability to cut aluminum.

I have posted the parts at Plastic Monstrosity -- The 3D Printed CNC for 4x8' Plywood by spiffcow in case anyone else wants to print and build one.

 

First cut with a Makita router...

 

Absolutely, I just haven't had time.. I have (accidentally) cut more than 24mm deep and it handled the cut just fine. I'm making this specifically for making 2.5D furniture, and the first few "real" things are going to be OpenDesk chairs The only issue I'm still working out is how to best handle surface mapping -- even if your cutting surface is flat, a 4x8 sheet of plywood won't be. I've got a little endstop mount for the Z axis printed, but haven't tested it out yet.. I'm thinking I'll just do a firmware bed height mapping before the cut. I'm not going to be able to use it for the next 2-3 weeks though, so I can't promise a date on that.

If you're looking to start building it, off the top of my head you'll need:

- The plastic parts in the Thingiverse entry I mentioned in an earlier comment
- 3x high torque NEMA 23 motors
- 1x NEMA 17 motor (70 oz. in. or higher)
- 14x 625 bearings (I'd get more just in case)
- 14x 608 bearings (again, get more just in case)
- ~200x 12mm M5 screws
- ~25x 70mm M5 screws
- ~30x 30mm M5 screws
- ~30 25mm M5 screws
- 1x anti backlash nut block
- 1x 250mm T8 leadscrew
- 1x 250mm C beam extrusion
- 1x 1500mm C beam extrusion
- 2x 2" 10ft conduit pieces from Home Depot (they're actually a little more than 2", but listed as 2")
- ~30x 5/8" bolts
- 10 meters of 10mm wide steel-reinforced GT2 belts
- A bunch of lumber and Simpson ties for the table
- A spindle or router (I use a Makita compact and it works great.. I still need to add the STL for it. I also have one generated for the DWP611 that I need to add)

 

Oh, I meant to write 5/16" for the bolts btw.. 8mm should work as a substitute for those.

Here's the conduit I used.. If you can't find anything within a couple mm of it let me know and I can generate the parts based on whatever you can find nearby

2 in. EMT Conduit-101592 - The Home Depot

 

Oh and the router is RT0701C. If you need something different just let me know the diameter

 

Cool, I'll try to get that generated tomorrow. As for mounting sideways: I had originally intended to mount it at a 45 degree angle, but I was eager to get it done and didn't want to complicate things. I think it would do well mounted at an angle, but if you do you will want to get thick wall conduit.

 

I have a 500W generic Chinese spindle.. It does alright with 1/8" bits, but it's really just too under-powered for wood, and it doesn't have an automatic speed control. I plan to reuse it in a smaller build for cutting soft metals, which it might be better for since it tops out at 12000 RPM.

 

Should be mm.. It's all done in OpenSCAD.

This project requires a lot of 3D printed material.. Around 2kg or so, and I recommend using PETG.

 

@MKD
The 60.3mm OD parts are now posted to Thingiverse (Plastic Monstrosity -- The 3D Printed CNC for 4x8' Plywood by spiffcow)

 

Yep, it really is a great material! It's not the most rigid, but there are ways to work around that

Can't wait to see how your build goes! Let me know if you need clarification on any of it

 

Going through printing services gets expensive pretty quick.. As much as I would love to have someone try out these parts, I'm not sure it's the best fit for someone who doesn't already have a 3D printer. That said, a decent 3D printer kit can be had in the ~$200 range, and PETG goes for $15-30 (in the US, don't know about NZ).. Might be a good way to maximize value

 

Thanks!

And yep, here's the chair link..

Opendesk - Valoví Chair

 

I did a couple small test pieces to measure the right diameter, but when making the entire piece I actually got it "good enough" on my first try. Maybe someday when I build another one I'll tweak the wall thickness a little, but I think I lucked out on this one to a large extent

So what I ended up doing is to undersize the expected opening by about 5%. The bolt through the center can tighten or loosen these a little bit, but the design is reliant on the flexibility of the plastic to pull against the rails. It's a tight fit, but it rolls smoothly and doesn't grind. I haven't used a pressure gauge, but it's pretty hard to get any flex on the side pieces from pushing on the tool head. I think a large part of the success in that respect is due to the very low center of gravity and low amount of leverage on the Z axis.