McWire Motor Coupling

The Structure Is Built
The basic McWire cartesian structure has been built. The last step was to couple the drive screws to the motors. I was undecided on the way to do this.  The stepper motors I have a D shaft. I was a little concerned about using the suggested aquarium tubing with them. I was in the hardware store on my way to find some tubing and I came across the PEX pipe. It's a semi rigid plastic pipe.  It was cheap and very sturdy. It's even rated for hot potable water so I though i would give it a try. I meant to pick up some tubing as well as a fall back incase this didn’t work but, I was so focused on making the PEX pipe work, I forgot.

The Coupler
It's 3/8" OD and ID about 7/32". At first, I tried to slide it on the the motor shaft with a good amount of pressure but it was a no go. The motor shaft diameter is a 1/4" so I drilled it out to 15/64" and tried it again. No joy there either.  Then I tried  a 1/4"drill. Finally the motor shaft slid in - but not without a significant amount of pressure.

I decided to use a 2"  piece for the coupler. This would allow 3/4" for the motor shaft and 1" for the threaded rod with a 1/4" gap between.  On the drive screw side I tapped it about 3 turns worth of 1/4"-20 and then using a jam nut configuration screwed the threaded bar into the pipe about an inch. Looking back I think 1/2" would have done but the wheels were already in motion.

On the final assembly I kept the jam nuts on the rod to help get the pipe off if ever I need too.

Yet Another  Spacer
I discovered another place a spacer is needed. When I attached the coupling nut using the 1/2" conduit strap to the X and Y platforms, the added assembly was running into the end support.  I lowered the end support from the rails with 1/4" of PEX pipe for a spacer. This was only a problem on the X and Y as the Z coupling nut assembly is not at the end of the platform.

Another option was to take off the end support completely as it seems it's only function is to hold the opto-endstop and I think that could be done in a different fashion. For now I will leave it.

McWire and Opto-Endstops

So I didn't have as much build time yesterday as I normally do but did manage to get the opto-endstops built and mounted. These came along with the GEN3 electronincs that I got from MakerBot. At first, when I poured the contents of the bag O opto-endstops out, it looked like I was in for a bunch of work.

I called up the link that was on the outside of the bag that had the assembly instructions and no problems with assembly except inserting the 5 leads of the optical sensor into the hole. Lining up all 5 spindly leads at the same time was a challenge for me so I trimmed each of the leads at a different length so that they would go in one at a time.

I stuffed and soldered in all of the components except for the connector which I left unsoldered. I wanted to do a fit check at each of the locations before committing to having it on the board. It's a good thing I did because it would have definitely interfered with the Z motor shaft. Given that I decided to go with a right angle header solution.  This option was smartly designed in so it was easy.

After the boards were fully soldered I tested them using the Arduino board I got from Adafruit Industries.  It was a simple cut and paste of the code from the MakerBot sight and the program was running on the board. I did have one problem while testing. At first it didn't work. I checked all my wiring and hookups and made sure that the board had power and ground.  I thought, ok I'll just move on to the next one and get back to this one. Well, none of them worked! Then I was suspicious. I noticed in the photo on the assembly and test web paged used a thick piece of  cardboard so I changed the piece of white printer paper I was using to a piece of cardboard and it worked. In fact now all tested good. I then colored the piece of paper black with a marker and tried that. That seemed to do the trick as well.

Once the boards were working, I started mounting them to the McWire.  Some location were fine and some were iffy. I think I will end up moving one or two of them. I will see as the build progresses.  The one closest to the Z motor had the highest probability of interference.

McWire Build Session 5

I am approaching the end (for now) of the Mcwire build effort. Just a few small things to do and I'll be tackling the extruder. The things on the list before the extruder are:

• Solder up and mount the opto end stops.
• Mount the rest of the motors (2)
• Couple the motors to the drive screws
• Attach coupling nuts to the platforms

I came across another challenge this session. There was a large discrepancy between the laser cut holes in the plexi and the holes in the flange to mount the Z platform to the structure. I thought about using some smaller screw with big washers but I thought that would put too much localized pressure on the plexi that usually leads to cracking.  Instead I opted to make an adapter plate that would interface between the  two. Also it helps distribute the load along the length of the plexi. Adjustments might have to be made for the proper over hang distance. I will adjust that once the extruder is mounted.

McWire Build Session 4

Things progressed nicely to day.  Here are the highlights.

X Rail Spacers (continued)
I finshed the X-Y stack and started the Z sled. I adjusted the spacers between the pipe and the X rails. I cut the inside of the spacer flush with the rail because the nut holding the bearing to the swing arm was hitting it. The outside part still protrudes out and I like that because it's easy to hold with your fingers when lining things up.  I also removed the washer between the rail and the spacer. It wasn't needed as I did not account for the height the PTFE bearing were lifting the platform up.

Y Rail Spacers
Just as with the X, there needs to be a spacer between the Y rail and the X platform. I thought about cutting some U channel to do this just as with the X but that would have made a spacer longer than the 5/16"x3/4" screws could handle.  The final solution was to use a 5/16" nut between the X platform and the Y rails.








Progress: Z Platform
The lessons learned with the X and Y platforms made the Z Axis go smoothly.

McWire Build Session 3

So, my lessons learned the first two build sessions are starting to pay off. I managed to get to the hardware store and picked up the 5/16" washers and some metal blades for the saber saw. That made all the difference. The builds are progressing at a stead pace now and not too many surprises.

So far I have only used 3 screw types.

• 5/16" flat head, 3/4" long ( That I think would be better at 1"long) are used to attach rails, swing arms and bearings using counter sunk through hole and nut.
• #10-24 pan head, 1" long (That I think would be better at  1/2" or 3/8" long)  are used to mount motors, PTFE bearings and the end supports to the rails. These are use with tapped holes in either the plexi or the aluminum.  This is a little more work than the though hole and nut but gives a nice precise fit. 
• #4-40 pan head 1/2" long are used to hold the springs to the swing arms in leu of the small nails suggested. These are drilled and tapped.  

Im sure the nearest metric equivalent would work fine for those who are so inclined but holes in the laser cut pieces should be adjusted. 

Here is the time lapse...