Pulling the Trigger

Mostly Printed CNC - MPCNC Troubleshooting
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Ok. it is about time to order some parts. My Wanhao Duplicator i3 has been churning out parts for the last week. I have 30 of the 44 parts printed from the 23.5mm set so far. My plan is a 30x30" bed. (one planned project is a carved design in a piano benchtop which measures 14x30" so I need the 30") Since having another 3D printer would just be awesome, I NEED that too. But I’m thinking of having two extruders to do multi-color prints. As for the Z axis, only once did I want to print something that was more than the 180mm height, (~7 inches) but it was decorative so I just scaled the entire model by 95% and it fit. My current software chain is 123D Design -> STL -> Cura -> g-code-> Octoprint (on a Raspberry Pi 2 with camera) -> Di3 over USB. (and I have used Inkscape to produce gears) I rarely use Octoprint’s Cura slicing plugin because I like to be able to tweak different settings and there are too many combinations to save a profile for every combination.

So, of course, I have questions.

As for the Z axis size, is the problem with a larger Z related more to the larger mass of the longer rails, or is it due to the extended length requiring more force (leverage problem) to push through when cutting? Basically, if I always do CNC on a raised surface and drop the work surface (maybe recess the table top for 3D printing?) for taller 3d prints the Z would only be extended when little force is required. Could I get away with a 12" Z? Based on the calculator, the bundle all-thread limits it to 9", but a longer one can’t be too expensive to procure.

If I run two extruders, is there anything extra I would need to order in the way of electronics? I assume for each extruder, I would need to order a “3D Printing Extruder”, a “Stepper Driver DRV8825”, a fan, and possibly some wire to extend everything. Is there a place to plug in the second stepper driver in the RAMPs board? Does the firmware handle it? Is there a universal mount to handle dual extruders? Can the 30A PS in the bundle handle both heads and maybe a heated bed?

The bundle says it has enough belt for 48" total X+Y. So, I need an extra order (6.5 feet) of GT2 Belt to reach 30x30". Is the wiring kit enough to reach?

Can 123D Design be used to design for CNC? I will probably swap out Cura with Slic3r. I have read people have used Octoprint with MPCNC but more so with 3D printing than for CNC. I really like the automatic time-lapse I get for every print.

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Just a quick reply, I have a 5 year old’s birthday to go to. If you need more info let me know and I can give more detail tomorrow.

The z axis is a leverage problem, You are correct. The other issue is long legs also have a similar leverage issue but divided by 4. So the ideal solution is a table that the bottoms drops out of. I am working on making one to show the concept. That way you have short legs as well.

Extruders, you are correct again extra drivers fans and wire. Everything plugs right in. The 30A will work, you need to change the firmware to say 2 extruders instead of 1, literally just a number change.

Yup extra belt for your desired size.

not sure about the 123D, are you talking about the 3d scanning software? If so, yes STL’s will work in estlcam, and other CAM software. Pretty sure octo print will work just fine for cnc, it is basically the same as printing, just sending gcode over.

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123d design can be used to model parts. 123d is an autodesk product and they have since introduced Fusion 360 which is a step between 123d and Inventor. It is free until you make 100k profit from using their software. Fusion 360 has the advantage of having a built in CAM program (HSM) so you can program the MPCNC with 1 program. If you don’t know much about modeling or cnc stuff then 123d and estlcam are probably the way to go.

You will want to build slightly over size say 32 inches if you have a 30 inch piece to cut.

Not sure how you account for the spacing difference by having 2 extruders. I am sure there is a firmware or slicer thing that you can set the distance between nozzles.

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My thought for a drop table is to make a 2x4 framed box like your design, but only attach the center 2x4 to the waste board and put a bottom on the box. Lift the waste and center board out to drop the work surface.

I read somewhere that when doing multiple nozzles, you need to specify the exact X/Y offset between the nozzles. I assume the Z has to be exactly the same or the lower one will hit the model when the higher one is printing.

So, I guess my only remaining question is about mounting two extruders. Does anyone have a design that uses the latest universal mount?