This page pertains to the Bukobot v1. Some portions may be useful to v2 owners. For more information, see here.
Move the X left and right end pieces all the way down and rest them on top of the Z axis couplers.
Get out the two remaining steel rods (not the threaded ones). Clean and lubricate. Note which end is the good end, as described before.
If your smooth rods have signs of surface rust then you should also try to deal with this if the surface of the rod no longer feels smooth. Don't use steel wool. You can try to remove the rust with a non-ferrous buffing pad or similar. You can also try a “rust converter” product which works for stainless steel - ask at your hardware store (and of course use gloves with this stuff). Once the rod is installed and properly lubricated then this should prevent further rust development.
Yours may be shorter than those depicted here.
Insert the smooth end of one of the rods through the X right end, from the right. You may have to lift up the fender washer so that the rod goes under it. Slide the rod over until the X right end is at the center of the rod.
Do the same with the other steel rod.
Get out the X carriage. Loosen the screws holding the linear bearing holders. The bearing holders must all easily rotate, and the rear one(s) must freely slide along their slot(s).
Carefully slide the X carriage onto the steel rods, and all the way to the right; do it slowly, and don't bang the ends of the rods against the bearing balls that live inside the bearings. The carriage is oriented as shown below, with the terminal block at the rear.
Slide the steel rods to the left, and through the X left end. Make sure the rods move far enough to the left so that they go completely under the fender washers. Make the right ends of the rods flush with the right end of the X right end. Tighten down all four screws and their fender washers to securely hold the rods down onto the left and right ends. Check to make sure the rods are all the way down in their channels.
Make sure the X carriage is securely seated on its bearings. Tighten the two bearing holder screws in the front, a bit at a time, sliding the X carriage to the right and the left each time; it should slide smoothly. Then tighten the one or two rear bearing holder screws the same way.
If you haven't already secured your X carriage linear bearings on with cables ties then it can be easier to just remove the bearings from the bearing holders, thread the linear bearings onto the X axis rods as you install each rod, fit the X carriage onto the bearings (tightening the screws as described above) and then add the cable ties in-situ (not difficult).
Get out the two threaded steel rods. Screw one down into the top of each UHMW nut (the white plastic piece attached to the bottom of the X left and right ends). They may not go in perfectly straight, relative to the X left and X right pieces, as the UHMW nuts may not be sitting flat in their hollows. Screw them in until they are flush with the bottom of the UHMW nuts. Let them rest on top of the couplers:
They need to be parallel with the frame side pieces. Loosen the small button-head screws holding the UHMW nuts in place, and see if you can straighten the thread rods by shifting the UHMW nuts. Get them as straight as you can, and then tighten the small screws to lock the UHMW nuts in place.
Grab the top of one of the threaded rods and start screwing it down through the UHMW nut. Guide it into the top of the coupler, without lifting the UHMW nut above the coupler. Screw it down until it bottoms out against the bottom of its channel in the coupler:
Tighten the coupler onto the threaded rod, keeping the distance between the two halves of the coupler roughly the same. Check that the coupler is tight on the motor shaft.
Do the same with the other coupler and threaded rod.
Now the bottoms of the UHMW nuts should be the same height above the frame bottom. However, that's not what we need; we need the horizontal rods to be parallel with the frame bottom. You may not have this yet, because the UHMW nuts may not be sitting in the X left and right ends at the same level (as you recall, the holes for the UHMW nuts are not precisely formed).
The easiest way to make the X axis level is to use a spacer. In the image below, a pad of sticky notes was used (but, see the following paragraph). With this method, the spacer should be 5 mm or less in thickness, so it fits between the frame side piece and the heads of the Z motor mount screws, and at least 1.5 inches or 38mm tall. The pad is placed under the X left end piece (not under the UHMW nut) and against the side of the frame side piece. The pad should not be on top of the button-head screws that hold the motor onto the motor mount. Turn the coupler to move the X left end up or down until the pad fits perfectly between the top of the Z motor mount and the bottom of the X left end. Move it a little at a time, and each time move the X right end up or down to keep the rods roughly horizontal.
A superior method is to use a spacer on the other side of the frame side piece, between the frame bottom and the two horizontal rods. A common soup can, the 10 3/4 ounce size, is a good fit; these cans are about four inches or 102 mm tall. Check that the can isn't dented or distorted anywhere. You need to increase the height of the X axis until the can fits exactly between the top of the frame bottom piece and the bottom of the horizontal steel rods, on both sides, as close as you can get it to each frame side piece. Move the X carriage up evenly, moving the can from one side to the other to measure the height. When the can just fits under the horizontal rods on both sides, the rods are parallel with the frame bottom and you're done. Don't leave the can balanced there, otherwise it might fall over and break something.
Now we add the X axis cable. First, loosen the two screws on the X tensioner and rotate it to the position shown:
Put one of the M3x10mm button-head screws through the eyelet at one end of the cable, and put the nut on. The nut should be against the flat side of the eyelet. Slide this onto the slot at the right back end of the X carriage:
Pull the free end of the cable to the right, until it is straight. Try to take any twist out of it. Loop the cable around the X right end pulley, from underneath to over, and pull it to the left. Loop it over the X left end pulley, making sure it meshes properly, and bring it to the X tensioner. Pass it through the loop in the tensioner, and run it away toward the lower right:
Temporarily secure the free end by passing it through a hole in the carriage. Let out enough slack so that you can get the cable off of the two pulleys.
Set the printer on the edge of a table and lean it over the edge, backwards, so the cable dangles toward the floor. Don't drop the printer. Make sure the cable hangs flat, with no twist. Set the printer back on the table and put the cable back on the pulleys.
Take all the slack out of the cable. Make sure it is meshed with the pulley on the left. Jam the remaining M3x10mm button-head screw in next to the cable, and screw it in tight, as shown:
Getting that screw started might be tricky.
Move the two cable attachment points along those slots until the cables are parallel with the steel rods. (As before, the length of cable between the two pulleys doesn't have to be parallel with anything.) Turn the tensioner clockwise until the cable is as tight as the other one. Tighten all three screws, without losing your adjustments. The nuts on the bottom like to freewheel when you do this, so stop them from doing that somehow. An extra hand or two is handy for this.
When everything is tight, find a place to tuck the free end of the cable where it won't snag on anything.
Now is a good time to apply at least one cable tie to the linear bearing holders on the X carriage, as described here. Apply to the rear holder(s) only. That way, if you manage to collide your extruder into something, the front of the X carriage will pop up and possibly save something from damage.
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