Friday, 27 October 2017

MPCNC Machine - Part 1

Mechanical/Electrical Parts

The parts needed are pretty well documented on the MPCNC website.
I went with imperial bolts since they are easier to get in Canada.  Go to an actual supply store like Brafasco, not Lowes or Home Depot for the nuts and bolts – they will be much, much cheaper there.  Home depot wanted $3 for a 6 pack of nylock nuts.  Brafasco was around $5 for a 100 pack.

The Dewalt 660, bearings, stepper motors, belts, pulleys, and leadscrew all came from Amazon.  Most of them can be gotten cheaper from Chinese websites, but I’m impatient and had an Amazon gift card to use up anyways.

I already had the RAMPS board and Arduino as spares for my 3d printer.  The entire kit from FastTech was around $40 USD.

The EMT came from Lowes.  Also needed a shop vac, a couple types of squares and some clamps.
Altogether, I spent a little under $500 Canadian.  If I had been patient and shopped around I could have probably gotten the parts for under $400.  Without the shop vac and Dewalt 660, I could probably do it for $250.

Printed Parts

Printing all the parts took a lot of time and filament.  I'm using a Wanhao i3 printer.  I tried to work out the printing order to use up as much of the partial spools I had lying around as possible.  Altogether, it took roughly 2.5 spools and a week or so of printing time.

Misc Stuff

I used some 3/4" laminated particleboard I got dirt cheap from the Restore store.  While I was there I got a huge sheet of T slot board for $8.  It had a big crack in it, but since I just need small sections of it its perfect for my use - that will be my spoil board and let me slot clamps into it.

Sizing Considerations

I went back and forth on this a few times.  The machine can easily be any size up to 42x42 (even bigger with reinforcement in the middle). But bigger isn't always better.

Some considerations I had to think about:
  • I want the work area to be at least 24" in one dimension. It's easy to get 2'x4' sheets of various boards, and that way I just need to cut them in one direction before putting them in the machine.
  • Smaller means the frame is more rigid and should give better results
  • How much table/room space am I going to dedicate to this thing?
  • How big is the board I am mounting it on?
  • Will I be able to move it around without having to completely disassemble it?  Can I get it through the door in one piece?
I ended up going for an approximately 25"x16" working area.  That required a base of at least 36"x27".  The particleboard I had was 30"x60", so I could easily cut it down to that size.  It fits on my workbench nicely.

Mechanical Assembly

Basically I just followed the guide on the MPCNC website.  Not much special here.


Here I deviated from the instructions.  I want to use ethernet cables to connect the control box so I can easily disconnect it.  People had made brackets for previous versions of the MPCNC to add keystone jacks, but they are no longer compatible.  So I've created some of my own.  

I also decided not to wire the steppers in parallel or series, but rather run each one back to the control box separately.  This will let me add individual end stops later if the firmware ends up supporting it at some point.  It also means I'm spreading the load for the stepper drivers across 5 drivers instead of 3.  Downside is that means there is no room to add an extruder or anything later, but I already have a 3D printer.

I was hesitant about using a single wire in the ethernet cable for each stepper wire, but after testing it for awhile it seems to work ok.  That means I can just use a single jack for each axis.

Z Axis

For the Z axis, I created a holder that will fit inside the EMT and have a keystone jack pop into it.  Drill a hole in the side to feed the wires in, and punch it down to the keystone jack.

Z Axis holder with hole drilled.

Stepper wires cut and punched down.
Slack wire shoved down the EMT, and jack inserted.

X and Y Axes 

First decide which side you want the control box on.  Then on the front and opposite side, run the wires for the stepper motor through the tube to the other side.  Mine were a little too short, so I extended them with some 4 pin male dupont headers, and taped the connectors together so they didn't come apart in the tube.  To feed the wires through, I taped them to the end of an ethernet cable and pushed the ethernet cable through.  The stepper wires aren't stiff enough to feed through on their own.

Far side from control box
I printed some nice end caps (be sure to put them on before feeding the wire through the tube), and some wire loom to keep the cables tidy.  Make sure the wires end up with a loop that won't interfere with the belts once they are installed.  Run a zip tie through the bottom of the bracket (yellow in my picture) to hold them in place.  If you put the zip tie around the top of the bracket it will rub on the belt.

For the back and side near the control box, I wanted to mount keystone jacks.  I printed this part only to realize it won't work with the newer version - the bracket between the two bearings is in the way, so it can't be inserted in the tube.

Instead I created a part that mounts above the stepper and fits a keystone jack.  This requires replacing the two top M3 screws with slightly longer ones to hold the stepper in place.  I think the ones I used are 16mm long.

Back side showing wiring.

Bracket for keystone jacks. Don't put the zip tie on the top like I did here.
Each stepper is punched down to one side of the keystone jack.  The slack wire from the close stepper is shoved in the wire loom to keep it out of the way.

I'm still printing the parts to do the other axis, then I can install the belts.

Part 2 will cover the control box.

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