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jitsbuild-z-axis

jit's build: Z axis

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This page pertains to the Bukobot v1. Some portions may be useful to v2 owners. For more information, see here.

Parts

Find these in bag 10, bag 16 and various other places:

The eight M3x10mm button-head screws come out of the Z axis kit, along with most of these other things.

Attach Two Stepper Motors

Use these screws to attach the remaining two stepper motors to the underside of the Z axis motor mounts:

The wires go out toward the back.

Z Couplers

Note: New kits are being shipped with lengths of vinyl tubing that fit tightly on both the M6 rods and stepper shafts. These have been found to make simpler and more robust couplers. You should screw the M6 rod 1/3 of the way down the tube, then push it onto the shaft and squeeze and pull it down to constrict on the rod like a finger trap.

If you have the new vinyl tube couplers, you can ignore the following section.


Take out the four Z coupler halves, which are used to attach the stepper motors to the threaded rods. Half of the holes have hexagonal outlines, indicating nuts go there.

Widen all of the holes to 2.5 mm (a 7/64” drill bit will do). Put nuts into the holes that need them - note there are hexagonal shafts for nuts on one side, and round shafts for screw heads on the other. If the fit is tight, use screws to pull the nuts into place. Be careful; it's not difficult to drive the screw heads through the plastic, which is not desirable.

Look at the flat sides of the coupler halves. Each of the four pieces is identical, and each has the same asymmetry:

The upper cavity, for the threaded rod, is wider than the lower cavity, for the motor shaft.

Match up a pair of coupler halves, making sure the larger cavities are at one end and the smaller cavities are at the other end. Insert screws, and tighten them just until the ends of the screws are flush with the nuts. You should be able to spread the two halves apart a few millimeters. Do this for both pairs of coupler halves.

couplers-assembled.jpg

Put one coupler on top of a X axis motor shaft, with the larger cavity pointing up. Tighten the two lower screws, a little at a time, keeping them matched. After every tightening, spin the coupler around on the motor shaft, feeling how much friction there is to the rotation. When you spin the coupler and it catches on the flat portion of the shaft, leave it in that position and tighten the screws a bit more. The coupler should no longer rotate freely on the shaft.

Do this for both couplers:

Z Slides

At this point, loosen the M5 screw holding the Z endstop holder onto the right frame piece and move it down to the bottom of the slot. Tighten the screw.

Now get out the Z slide kit from bag 16 and the X Axis Idler Block we made earlier:

(Four pieces of tape are shown above. You may have eight.)

If the sliders have a hole in the center, widen that center hole in each piece. We won't be using the other holes, if any. Widen to 3 mm (a 1/8” drill bit should do).

(If the sliders don't have a hole in the center, they are an older type that attaches differently, and you should also have an older style of X axis end blocks. Don't widen any slider holes, but widen the pairs of matching holes in the end blocks (to 3 mm). The screws go in from the outside, and then self-tap into the sliders. The lower screws are inaccessable when the long steel rods are installed.)

Pick up a slider piece and place its tab into a slot in an aluminum extrusion. Look at it from the end and see how the four plastic surfaces contact the aluminum. Those four plastic surfaces need to be covered with tape, as described below.

Put a nut into the hexagonal center hole in each slider piece. Pull in with a screw if necessary. Leave a screw in each nut as shown below, with the end of the screw flush with the nut (you will use the screw as a handle for now). This hardware should be below the surface of the slot tab for the next step:

We will be applying special self-adhesive UHMW tape to this part (the upward-facing surface in the above image). The tape will be adhered to three sides of the tab (or two if you have the newer style tape described below), and to the other two upward-facing surfaces. For best results, these surfaces should be clean, so clean them with isopropyl alcohol and a cotton swab. Let the alcohol evaporate completely.

The UHMW tape is actually transparent. The blue stuff is the backing that must be peeled off. Separating the two can be fiendishly difficult. Basically, abuse a corner of the tape until you see the transparent layer starting to separate. Grab the two layers with the edges of your fingernails and peel the backing off. Throw the blue backing layer away immediately, otherwise you might later confuse it for another piece of unseparated tape.

abuse-tape-with-allen-wrench.jpg

If you have the new style tape (eight pieces altogether instead of four), yours are described a bit farther down. Skim through the following.

four pieces of tape

Lie the transparent layer, sticky-side up, on a flat surface. Try to get it to lie flat.

Pick up one of the Z slides by its screw and set it down right in the middle of the tape:

Press down firmly on the back of the slide, along the centerline only. Then pick it up by the screw and look at the other side:

(The alligator clip seen extending to the left is not part of the build.)

The tape should be stuck along the tab, but not anywhere else. If it is stuck anywhere else, pull the tape away from there.

eight pieces of tape

Newer kits have thinner tape that's half the width, and twice as many pieces. Apply them as follows. The rest of the procedure is similar.

Try to completely cover all of the plastic surfaces that will touch the aluminum.

(When you install these parts with the narrower tape on the extrusion, make sure you don't catch the edge of the tape on the edge of the slot and peel it back from the face. This is something we didn't have to worry about with the wider tape.)

four or eight pieces of tape

The tape needs to completely cover the four plastic surfaces that will be in contact with the aluminum. The best way to accomplish this in a symmetrical way is to push the tab into a slot in an aluminum extrusion. Use the top slot in the frame bottom piece. Lower the Z slide straight down into the slot (if you have the narrower tape, don't catch an edge and peel it back) and press it down firmly. Press the Z slide against one edge of the slot, and then the other. Then push down firmly again.

Pick up the Z slide and examine it:

Leave that Z slide sitting in the slot. Repeat the above procedure with a second Z slide.

Attach X Axis Right End

Remove the screws from the two Z slides, and insert them into the holes in the X axis right end:

Make sure the ends of the screws are flush with the surface of the idler block.

Pick up the two Z slides, and press them into the front and back slots of the right frame piece (don't catch any edges and peel back the tape). They should be at the same height. Hold them there with one hand, and pick up the idler block with the other, being careful not to move the two screws. Slide the idler block in from the right, enclosing the Z slides.

Holding the Z slides in position with one hand, hold the idler block with the other hand by pressing in on the two screws. Slide the idler block up and down relative to the sliders until the two screws find the center holes (not any other holes!) in the Z slides.

Holding the whole assembly and pressing the two screws with one hand, and pushing the idler block to the left against the frame, pick up the 2mm hex driver with the other hand and tighten the screws. (If a screw goes all the way in but doesn't stop tightening, then it hasn't caught the nut – the nut may have gotten tilted, so take the assembly apart and straighten the nut and put the screw through to verify you can catch the nut.)

Slide the X right end up and down and verify that it moves easily and isn't trying to fall off the frame. It may rotate a bit in the X-Z plane, but don't worry about that, it will be stabilized when the X axis steel rods are installed later.

If the slides aren't gripping the frame firmly, you may need to install a shim. For a small gap then you could use a couple of rectangles cut from the rigid, clear plastic “clamshell” packaging they use just about everywhere these days or thicker “takeaway” plastic containers (both normally PVC). Drill-out a 3mm hole, trim to the size of the Z slide (remembering to remove any sharp corners - this stuff is lethal) and then stick them to the back of the Z slides when satisfied. This is not shown here.

Attach X Axis Left End

Now do the same on the left side with the remaining two Z slides and the X left end. This is much easier if the motor and endstop are not installed while you do it.

Verify the movement of the X left end as before.

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The contents of this page may be re-used under any of the following licenses: The Creative Commons Attribution-ShareAlike 3.0 Unported License (CC BY-SA 3.0), or the GNU Free Documentation License (GFDL, version 1.2 or later). Nothing on any of these pages is there to tell you what to do, only what other people have already done.

jitsbuild-z-axis.txt · Last modified: 2014/01/25 17:43 by jit