I am building the ShapeOko following the instructions, with these exceptions:
- Longer Y rails (495mm);
- Dual Y drive (two motors);
- Modified Z drive (more on that below);
- Yet another zip tie method of belt attachment.
Cutting the Makerslide. I cut I cut 1m of Makerslide in half. Getting two pieces of the same length with a clean, straight cut proved a little more difficult than I would have guessed. My chop saw, even though it's perfectly adequate for wood, flexes a little too much when cutting aluminum, so the cuts aren't perfectly straight and flat. I got decent cuts in the end, and I wasted only about 3mm of Makerslide.
Enlarging the holes. As with everyone's Makerslide, mine did not fit the plates. The entire profile was slightly misshapen, with the smaller edges not quite parallel, but that didn't matter: the only real problem was the hole in the core with the three inner walls, which had migrated about 0.5mm diagonally, toward where the fourth wall would have been -- so it wasn't only too close to the other hole, but also further away from the plane of the V-rails. To work around that, I drilled the two top holes in the motor plates to 5.5mm. While at it, I also enlarged the motor mounting holes to 3.3mm. Then I tried to use the same 5.5mm drill bit to enlarge the oval holes in the end plates. That worked, to an extent, but I ruined my drill bit and I would not recommend this approach to anyone (too dangerous). I got jagged edges, which I cleaned up as well as I could with the Dremel.
Removing the nubs. My motor plates had nubs (little molten metal droplets) on the lips of every single hole, and they did get in the way: the eccentric spacers didn't fit on the side with the nubs, and it looked like the washers and screws were not going to sit straight. So I removed all the nubs with my Dremel, even those in holes I wasn't going to use.
Tapping the Makerslide. I tried to use mineral oil -- of the kind you buy at the pharmacy (as a laxative, in the US), or at Ikea to oil wooden cutting boards. It wasn't very good, because it helped the chips stick together and create a mass clogging the flutes. I tried WD40 (the only other oily thing I had), and it was better but not by much. By the time I finished experimenting and decided that neither the laxative mineral oil nor WD40 were good cutting fluids, I had finished tapping all the holes. I tapped them all to the length of my tap; about half the holes went all the way in one go (backing up half a turn every two or three turns), for the other half I had to back out midway, clean the tap, and resume.
Second Y motor plate. I ignored the idler Y plate instructions and built a mirror copy of the motor Y plate instead. I had bought two idlers and one MXL pulley from buildlog.net, extra M5x30 and M3x8 bolts from Boltmax, and a belt on eBay.
Motor mounting. I used M3 washers as spacers on the motor attachment screws. Four washers on each screw were almost enough, so I used five of them (for a grand total of 60 extra M3 washers).
MXL pulleys. I had the unpleasant surprise that one of the MXL pulleys had a bore that narrowed toward one end, so it wouldn't fit on the motor shaft. I drilled it out carefully, from the side that did fit, using a new 5mm bit and holding it with locking pliers. After that, it fit snugly (the other one was fairly loose). The grub screw on the pulleys from Inventables takes a 1/64" Allen key, not 1.5mm as advertised, and they are of worse quality than the one I had bought from buildlog.net (slightly eccentric, coarser finish, some mold flash). The grub screw of the buildlog.net pulley takes a 1.5mm Allen key.
Flipped X rail. I installed the X rail with the Vs to the front, and I reversed the order of everything on the M5x55 bolts holding the X motor plate and the carriage plate together.
Threaded rod and Delrin lead nut. The threaded rod looked rather nasty -- a little rust and lots of debris in the threads. I wasn't going to put it into my precious Delrin lead nut looking like that. I put the grubbier end in my battery-powered drill, grabbed an M8 nylon insert nut ("Nyloc"), held it with locking pliers, and ran it up and down the threaded rod several times. Lots of icky stuff accumulated on the nut. I got a new nut and ran it again up and down the threaded rod; it collected much less dirt this time. I then ran it through the Delrin lead nut, which collected yet more debris. It was easier to turn than the nylon insert nut, but not by much. Running it up and down several times loosened it somewhat, but not enough, in my opinion. I lubricated the threaded rod with Boeshield T-9, but that helped only a little. Seeing that this wasn't going anywhere, I said to heck with it, and took my M8 tap and re-tapped the lead nut. I was afraid to back out the tap, in case it made the thread too loose, so I threaded the tap all the way in and through the nut, only once. This created only a little very fine Delrin swarf, but the nut was just right, or maybe even a little too loose.
Original Z drive. The kit included a Delrin Z motor plate, and the bearing was a very, very tight fit, so I decided that the bearing could take the weight of the spindle and other forces on the Z axis and not slide out of the Z plate. In a ShapeOko assembled according to the instructions, the weight of the Z axis does not get transferred to the bearing, because the bearing is free to move down the threaded rod; instead, it is trasnferred to the Z motor, through its bearings to its shaft, to the flexible coupler, and finally through the threaded rod to the lead nut. Even if the shaft and the threaded rod touch, which is what Edward recommends, the weight is still supported by the motor's bearings. When subjected to an upward force, such as when plunging into a cut, the Z axis lifts and the flexible coupler expands until the bottom nut rests again on the bearing.
Modified Z drive. I've always thought that the Z drive design was a weird oversight, so I assembled my Z as follows:
- Insert the bearing into the Z plate, making sure it is flush with one side of the plate. It is important that the bearing lines up and sits horizontally. The side that's flush is the bottom, the side where the bearing sits proud of the plate is the top.
- Find the cleaner end of the threaded rod. Thread a nut on the other end. Thread it until 19-20mm of rod sticks out.
- Slip the bearing, with the Z plate, on the short end of the threaded rod, bottom (flush) side toward the nut. If it's not a tight fit, take it off and put some tape on the rod until the bearing fits snugly. Aluminum tape works very well (I needed two turns of that); plumber's PTFE tape is good too. Tape only the 7mm of rod that goes into the bearing. Work the tape in with your fingers, then try the bearing again. The tape helps keep the rod centered in the bearing during assembly.
- Thread another nut on the end of the rod. Tighten the two nuts firmly, trapping the bearing between them. You should have 8-9mm of rod sticking out of this last nut.
- Slip the flexible coupler on to the end of the threaded rod. If it's not a snug fit, again, tape the end of the rod. Do not tighten the coupler grub screw(s) yet.
- Mount the Z motor to the Z plate.
- Thread the Delrin lead nut about three quarters of the way on to the threaded rod.
- Bring the Z plate and the Z rail together. You'll see that the bottom nut touches the Makerslide. Using a file, notch the inside top end of the Z Makerslide enough that the nut can rotate freely, even with the rail in the closest position to the threaded rod. You need a notch about 12mm wide and 4mm tall, and it's not a problem if you remove a little more material than that.
- Attach the Z rail to the Z plate, but do not tighten the screws all the way yet.
- Mount the four Z V-wheels on the standard carriage plate, put the Z axis assembly in, and adjust the eccentric spacers.
- Line up the lead nut with the respective holes in the carriage plate, and screw it in. Temporarily tighten the screws.
- Looking from the side of the assembly, find the position for the Z rail on the Z plate that makes the threaded rod run parallel to the Z rail. This is easiest if you look from the angle where the edges of the Vs on the rail seem to overlap. The small space between that edge and the threaded rod should be the same at the top and at the bottom of the assembly. Tighten the Z rail screws.
- Loosen the lead nut, then tighten it back again.
- Tighten the grub screws on the flexible coupler.
- Continue with the assembly of the X carriage as in the original instructions.
Belt attachment. Finally, everything else assembled with no further surprises, the time came to attach the belts to the belt anchors. I did it as in the image. I am less than thrilled with the belt anchors themselves: I can't get the belt very tight because they tend to bend. I got it as tight as the anchors themselves permitted. I had to add a second zip tie head on the end of the zip tie that goes through the hole, because one of them had begun to slip back. These zip ties aren't the best around; good zip ties should hold. The same method works even better if you have holes or slots that line up with where you want the belt to be (for example, Edward's new X plates), because the zip tie attached to the belt does not have to bend around. Just poke it through the hole and slip two zip tie heads on it -- done.
Landing the space shuttle on top of the Z motor. An absolutely necessary step.
To be continued...