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jit's build: Y axis

Prev: Y carriage < Up to Jitsbuild > Next: Frame

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


Note: The models smaller than 8” have a different carriage design, and some of the images on this page won't match exactly.

Find these:

The three metal parts on the left will be shorter if you have a model smaller than 8”.

Look at all four of your steel rods (not the threaded ones). If they are not all the same length, then the longer ones are for the other axis, so set those aside for now. The ones you need here are just slightly longer than the extrusion, as seen above.

Attach the Y Front

Start with attaching the Y front end (the printed part without the motor) to the extrusion. It goes on the end furthest away from the two holes drilled in the extrusion. Loosen the two M5 screws until the nuts are flush with the ends of the screws, and then loosen them a bit more (but not enough so that the screws fall out of the nuts). If the nuts fit tightly into their niches, you may have to force them outwards by pushing on the screw heads. Insert the aluminum extrusion the only place it can go (check image below for which end to use) and slide it all the way in.

If it doesn't want to go in, trim the plastic. Use a file or a sharp woodworking chisel to remove enough plastic at the end so that you can get the extrusion started. Once the plastic part is inserted a little into the extrusion, you may be able to use the extrusion itself to remove the excess plastic. You might be able to get the part the rest of the way in by hand, or you may need to use a rubber or plastic mallet; use one hand to keep the parts lined up, and tap gently:

(This image actually shows a different set of parts, and the screws and nuts are missing, but the principle is the same. The image below is also from a different part of the printer.)

You may have to adjust the height of the nuts to clear the edges of the channel, or press on the screws to push the nuts into the proper position.

Tap the piece in a little at a time, so that you don't accidentally tap on it when a nut is caught against the end of the extrusion. Make sure there is never any gap between the bottom face of the extrusion (the face with two slots) and the plastic part; it must be flush.

When the extrusion is fully inserted, tighten the screws.

Insert Y Axis Screws

Next, prepare the hardware that will attach the Y axis to the frame bottom. Get two M5x8mm button-head screws and screw one nut on each, just until the nut is flush with the end of the screw. Slide the head of one screw into one of the channels on the bottom of the extrusion, and then slide the head of the other screw into the other channel. Move them in toward the middle of the extrusion.

People have found that when you later strongly tighten the Y-axis M5x8mm screws that they can hit the bottom of the channel of the bottom frame extrusion (even when using the 8mm screws rather than the incorrect 10mm screws). This limits the amount of tightness you can get for the Y axis connection. You can prevent this by placing an M5 washer (not included in kit) under the two screw heads when inserting them into the Y-axis extrusion channel.

If the M5x8mm screw is not bottoming out, then the screwed-in metal-on-metal joint is very extremely strong in the important Y-Z direction. Unfortunately the join is not very strong when rotated, that is, it is not too difficult to bump/move the Y-axis out of perpendicularity with the X-axis. One thing that seems to aid the rotational strength of the joint is to ensure that the M5 screws are held in the middle of the extrusion channel so that the nuts are held evenly across both sides of the extrusion channel. One simple way of achieving this is to carefully cut a long 3mm-wide strip of tape (can be cloth, gaffer or electrical tape) and wind it tightly around the M5 screw until the tape is around 7mm in diameter. It should be thick enough that you need to compress the tape when inserting it into the Y axis extrusion channel and there is a reasonable amount of resistance when sliding it along (you can also use a 3mm slice of plastic tubing with a 5mm internal diameter). If the tape is too wide or wrapped sloppy, then it can get sucked into the nut or washer when tightening causing it to slip. Both approaches of preparing the Y axis screws are shown below.

y_axis_screw_with_washer_and_tape.jpg y_axis_screw_with_washer_and_tubing.jpg

Deezmaker have said that they are looking to include T-slot nuts for the Y-axis screws in future kits. In this case the tape preparation is not required. You can also improve the rotational strength of the joint by later installing printed Y axis braces such as this.

Attach the Y Back End

Insert the Y back end into the extrusion, fully seating it on the extrusion, just as you did with the front end. Tighten the screws.

While installing the Y back end, be careful that you don't damage the endstop or its wires, if you have already installed it.

Using your fingers to hold up the screws as shown may help in inserting the extrusion. Note that in this photo and some of the others below, the pulley is upside down; the setscrew end should point down.

Bottom view:

Top view:

Install the Steel Rods

Examine the ends of the rods. One end may be smoother than the other, as if it had been prepared for what follows. The smoother end is the one to be inserted through the linear bearings.

Clean the rods by applying a small amount of WD-40 (spray it on a rag and wipe with that), and then wiping them completely dry with a clean cloth. Be careful to keep the WD-40 spray away from all other parts (it can damage them). Be very thorough about getting all of the WD-40 off of the rods, as it's very bad for bearings. For more information see Clean and lubricate.

Once the rods are cleaned and dry, pop two linear bearings out of their holders on the Y carriage, and carefully insert one of the rods through them, starting with the smooth end; don't bang the end of the rod against the bearing balls inside, do it slowly and right down the middle. Move the bearings apart a bit; you can use them as a handle when handling the rods in the next step, which helps to keep the rods and your hands cleaner. Do the same for the other rod.

Install the rods under the fender washers, using whichever technique works best for you. You may have to loosen the fender washer screws; don't lose the nuts on the other end. It can help to hold the assembly with the washers facing down to make room for the rods. Once the rods are under the washers, make sure they are fully seated into their curved seats.

Attach the Y Carriage

Loosen the bearing holder screws a bit on the Y carriage, so the holders can be rotated. Snap the carriage in place, and check that it moves smoothly:

Peek under the carriage and check that there is plenty of clearance between the bottom of the tensioners and the aluminum extrusion.

Make sure all of the linear bearings are fully inserted into their holders. When everything is well aligned, carefully tighten the holder screws without rotating them. Check once again that movement is smooth.

Install the Synchromesh Cable

Next, we install the Y axis synchromesh cable. Get out both of the synchromesh cables, and compare their lengths. One of them may be shorter. If so, set the longer one aside, and use the shorter one.

Now find that last tiny, semicircular part from the Y tensioner sub-kit.

Remove the Y carriage, and turn it upside down. Place the small semicircular Y tensioner on the end of the Y tensioner screw, hold it in place, and retract the screw until the Y tensioner is fully retracted:

There is a nut between the two plastic parts. In some images it is hard to see.

Thread the synchromesh cable through the tensioner as shown:

Then thread the cable through the right part as shown, making sure the long part of the cable has no kinks or twists between the two tensioners.

At this point, pick up the carriage by one rail and let the carriage, and the big loop of cable, dangle. The big loop should be flat. If it hangs in a shape like a figure-8 or a saddle or a pretzel or worse, then it is twisted. Pull the cable back out of the part on the right and take the twist out, then re-insert it. The cable should be dangling in a plane.

Insert the free end through the last tensioner hole, leaving a loop big enough to grab:

This smaller loop should also be flat.

Snap the carriage onto one rail, as shown below. The carriage will be acting as an outrigger and will try to tilt the whole arrangement over, so support the far end of the carriage with some object. Arrange the cable as shown.

Take the slack out by pulling it through the tensioner into the smaller loop. Make sure the cable goes onto the two pulleys; you only need enough tension right now to keep the cable on the pulleys. If the smaller loop gets out of hand, shrink it by pulling excess cable through the tensioner; the free end of the cable may be getting rather long by now.

Rotate the carriage over and snap in the two remaining linear bearings. Make sure all four bearings are fully seated.

Take in more slack, keeping the cable on the pulleys. Peek under the carriage and make sure the cable is still seated on the small semicircular part. Carefully examine the synchromesh pulley (on the motor) and make sure the helical winding on the cable is lined up with the matching indentations in the groove of the pulley.

The tensioner parts need to be adjusted in the X direction (up and down in these images) to make the cable parallel with the steel rods. (However, the portion of the cable between the two pulleys doesn't have to be parallel with anything.) Loosen the three screws (the ones shown here with three washers under the head of each) just enough so they can be slid along their slots. Slide each tensioner along its slot until the bit of cable between that tensioner and its nearest pulley is parallel to the steel rods. There is a groove in the aluminum extrusion that can be used as a guide, as the groove is already parallel to the rods: move your head until the groove lines up with the cable.

Adjust the tensioners in this way, then pull on the small loop to tighten the cable some more, then adjust the tensioners again.

Tighten the three screws. The tensioner blocks will probably try to slide around while you tighten the screws, so get a good grip on the block while you tighten, and check alignment again after they are tight.

So far we have adjusted the angle of the cable in the X-Y plane. We must also check the angle of the cable in the Z-Y plane. This can be observed by looking at the cable from infinity along the X axis.

Looking from the side at the portion of the cable between the synchomesh pulley and the tensioner nearest to it:

(Click the image to see a more detailed version)

In this image, the nearby steel rod is visible just below the cable, and is somewhat out of focus. But as you move your eye along the bottom edge of the cable from right to left, you can clearly see that the distance between the cable and the rod increases. This is because the synchromesh pulley (out of frame to the left) is too high. If you move the carriage to the left, this angle will increase.

If your cable is already parallel, you don't need to adjust the pulley. Otherwise, adjust the pulley by first moving some slack from the small loop back to the big loop, and then use your 1.5mm hex driver to slightly loosen the setscrew on the pulley. Shift the pulley up or down on the motor shaft until the cable is parallel, then tighten the pulley setscrew. Tighten the cable once more, making sure the cable is fitting onto the pulley properly.

(If you have already gotten rid of all the slack in the smaller loop, as described below, you can get enough slack to get the cable off the pulleys by loosening the tensioner screw, the long flat-head one.)

Next, check the portion of cable between the Y front end pulley (the one without the motor) and its nearest tensioner. If it needs adjustment, you have to remove the M8 bolt and nut and bearing/pulley and adjust the number of washers. You need at least one washer there, but you can add more. On this build, two were needed to get the cable flat. (Make sure you relieve the tension in the cable before you start to loosen that bolt!)

After checking the cable alignment in that plane, you need to go back and check the alignment in the first plane again. Every time you adjust in one plane, you have to go back and check the other plane. This is because the procedure described here uses visual cues such as the edges of parts, or that groove, which means you are looking along a direction which is almost but not exactly parallel with one of the axes; therefore, each measurement will be not quite orthogonal with any of the axes, and will be affected by both adjustments.

So go back and forth between the planes, iteratively, until everything is close enough. After each step, make sure the cable is tight, as tight as you can get it by pulling on the small loop with your hand.

Now take a careful look at the entire Y axis. Double-check everything: how the bearings fit into their holders, how the cable fits, and so on. Slide the carriage back and forth and check the angles of the cables. When you are satisfied, take the slack out of the smaller loop. Grab the loose end of the cable and pull. It will take a bit of force to get the cable completely into the slot on the tensioner:

There is a lot of cable hanging out of this assembly. Don't cut all that off. If you ever need to completely disassemble this, you will need some of that slack to get it back together again. And if you ever decide to switch to longer metal parts to get a larger build volume, you might be able re-use the same cable if you haven't cut it. For now, wrap the cable around the carriage:

Now you can tighten the tensioner adjustment screw as shown above to tighten the cable further, until it is as taut as a guitar string. Plunk the portion of the cable between the two pulleys and adjust the screw with the 2mm driver until it produces an audible tone.

Adjust Endstop

If you haven't installed the endstop yet, do that now, but don't completely tighten the screws that hold the endstop holder onto the Y back end. If you have already installed the endstop, loosen those screws enough so that the endstop can be slid back and forth.

Slide the endstop holder all the way back, away from the carriage.

Move the carriage all the way back toward the motor until something stops it. Then back away a little bit. Move the endstop switch toward the carriage until the switch is fully depressed:

Tighten the two screws, then move the carriage away from the endstop, listening for the click the switch makes when it opens. The signals the switch sends to the controller should prevent the carriage from ever moving that far back again.

(If you have come back here from a later step, and have already installed the extruder(s) and a heated bed, then you should adjust the Y axis endstop so that it will stop the hot end(s) from ever hitting the connector on the top of the bed. Move the carriages until the hot end(s) are above the middle of the front of the heated bed, then slowly move the Y carriage until the hot end(s) are almost to the connector hardware. Move the Y endstop until its switch closes, then tighten it there. Go back to where you came from.)

Secure the wires so nothing will snag on them while you work with the Y axis, and set it aside.

Prev: Y carriage < Up to Jitsbuild > Next: Frame

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-y-axis.txt · Last modified: 2014/01/25 17:42 by jit