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jitsbuild-x-leftend

jit's build: X left end

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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

Some of the items shown above may differ slightly from the ones you get in your kit (this is bag 15).

Clean Part

The printed plastic part shown in this image has a significant overhang in the large circular opening (this is the opening on the underside where the UHMW nut, the white object at lower left, will be inserted). The printing technique used to make this part cannot produce a sharp clean profile with this kind of overhang, so the part must be trimmed before you attach parts to it. The trimming and clean up of this opening is non-trivial. It can take some work and some time. A 1/4” (6mm) sharp wood chisel and a X-ACTO knife help a lot. Larger material will crack and break away, the smaller bits of plastic deeper in the circular opening can be cut and scraped away with the 1/4 wood chisel. Just make sure you don't poke a tool through the hole and cut your hand holding it on the other side. If there is concern about how much material is to be removed, consider the fact that the UHMW nut should be sitting flat against the bottom of the opening, so if there are chunks that prevent this then they need to be removed.

Note, however, that you don't have to make the bottom surface of the UHMW nut flush with the bottom of the X end block. Some people do this so that the machine looks nicer, but it's not really important to the function of the printer. What's most important is that the UHMW nut is level, and doesn't shift around. So try to make that rough printed surface reasonably level and flat. If it was really important that the nut fit precisely and completely into that hollow, the parts would have been designed differently so that the nut fit that way right out of the box. Deezmaker never intended you to engage in hard manual labor with sharp instruments just to fit the kit together.

whosawhatsis says:

I punch out the bridge and then run my pocket knife along the inner edge of the circle around where the nut goes to taper it and allow the nut to slide in a big easier, but that's it. The underside of the UHMW nut trap should not need any additional cleaning.

ncorison says:

I used a 5/8” deep well automotive socket lined with emery cloth to flatten the bottom surface and clean up the sides and a smaller one to clean up the sides of the top hole.

Assemble Part

Make sure the UHMW nut goes in straight and fairly level. It doesn't have to go all the way into that hollow, but it should definitely go in far enough so that its attachment screw has a firm grip on the end block:

(Some other parts seen in this image will be added later.)

Note that the attachment screw for the UHMW nut is there primarily to keep the nut from rotating in its holder. Don't tighten it so much that you can't pop the nut out of its holder with your thumb. If something goes wrong and the printer tries to drive the X axis down into an obstacle, the UHMW nuts should pop out to prevent further damage.

Check that there are no protuberances in the channels that will hold the long steel rods. Get out a steel rod and check that it fits snugly into these channels. It needs to rest on the bottom of the channel. See Cleaning up printed parts.

Also check the two small holes that will hold the screws that attach the Z slides inside the arms of this part. Widen them enough so that M3 screws can pass through these holes easily. A 3mm or 1/8” drill bit will work fine. (If you were an “early adopter”, you may have four holes to widen. Look at the Z axis page for more details on this. If it's not obvious what to do, ask for help.)

Sometimes you will find that a screw will not easily fit into a hole in the printed part. This printing technology cannot produce holes of a precise size, so parts designers try to adjust the sizes of holes so that variations in the printing process are unlikely to produce a part that is unusable. This means that sometimes you have to widen a hole. If a screw is intended to be self-tapped into a hole (with no nut on the other side) it is important that the hole not be too wide, so the designer will specify a smaller hole than really needed for that screw. If you have a lot of trouble self-tapping a screw into a hole, then widen the hole, but not too much. (If you use so much force to drive a screw into a hole that the screw gets really hot, hot enough to burn your finger, then you probably melted the plastic around the screw too. Don't let it get that hot. Widen the hole a little bit first.)

On the other hand, if a nut is to be used on the screw, the hole can be widened until the screw easily passes through. Be very careful to determine which holes use nuts and which don't, as it can be a big hassle if you remove too much plastic from a hole that needs it to hold threads.

Sometimes a designer will indicate which holes need nuts by printing a nut-shaped depression at one end of the hole. In some cases you can press the nut into this depression and it will fit there, and sometimes even stick there. But if this depression is printed on the bottom of a part, its shape will not be very accurate and the nut may not fit into it. In this case, it may not be necessary to adjust the size of that depression to actually fit the nut; try adding the screw and nut to the part, then check to see if the protruding nut will interfere with anything. Often there is no potential interference, and no need to do anything else. Consider the nut-shaped depression to be just a hint that a nut goes on that side of the part, and not an actual required feature of the part.

Note that there are no lock-washers in this design. Vibration during operation may cause nuts to unscrew. You can use a dab of threadlocker (the blue removeable type) to hold nuts in place. Many nuts and screws are left loose throughout much of the build process, so that the position of various parts can be adjusted in later steps; don't apply threadlocker until these adjustments are made. If you are worried about nuts working loose during the build, apply a small dab of threadlocker near the end of the screw, far from the nut; the nut may work itself toward the end of the screw, but it won't leave. (Jit's build never did use any threadlocker.)

Stepper Motor

Now get out one stepper motor and one synchromesh pulley (in bag 11) and put the pulley on the motor shaft. Align the setscrew with the flat on the motor shaft and tighten it with your 1.5mm hex driver.

At this point you can use four M3x10mm button-head screws to attach the motor to the printed plastic part. However, unless you have particularly large hands, this motor can make it harder to attach this assembly to the Z axis later on, so you might want to defer this step until later. If so, put the motor and its four screws in a bag and set it aside. The images to follow assume the motor is installed now.

(bottom view):

Note that the two M2.5 nuts near the bottom of this image are sitting on top of nut-shaped depressions, but may not fit precisely into them. They don't need to. There is room on the bottom of this part for the nuts to protrude from the surface. Threadlocker can be used later to keep these nuts from wandering if you are concerned about it. An M3 washer should be threaded on the top side of each of these M2.5 x 16mm screws (the washer is screwed down against the steel rod going through the channel to hold it in place).

(Almost) top view:

The screws with fender washers on them should be quite loose. The long steel rods will be inserted under the fender washers later.

The wires for the stepper motor have been threaded through the oval hole near the motor.

End Stop

In this section we describe how to install the X-axis endstop; however, you may not want to install yours now as it tends to be in the way and the wires can be easily broken. Instead you can wait until final assembly of the printer before attaching this subassembly to the X left end. Many of the images from this point on will however show the endstop already installed.

From the endstops kit (bag 5):

Some builders have positioned the switch on the other side of its printed bracket. It should work either way; however, the depicted orientation places the wires in a more protected position and the end-stop switch is triggered by hitting the side of the front-left bearing holder rather than trying to catch the aluminum plate edge (this means that the importance of the endstop up/down position is far less).

Check to make sure stray strands of wire aren't shorting across the switch terminals. Also one mounting hole of the endstop microswitch is smaller than the other. The smaller hole can be drilled out with a 2.5mm drill so that the screw easily passes through it.

Thread the endstop wires through the same oval hole near the motor, wrap all the wires around the assembly, and set it aside, along with its Z-slide sub-kit.

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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-x-leftend.txt · Last modified: 2014/01/25 17:38 by jit