I’ve previously went over the Custom parts and Electronics and Electrical parts in two seperate posts needed to build the xBot-Medium Printer. This included motors and limit switches, so everything with current in it.
In this final BOM post I’ll list the inert mechanical parts.
A complete BOM file is in place in the Github Repository.
Lots of parts going into this contraption. It IS one of the key parts to make this printer design so successfull. It’s not really that complicated once you wrap your brain around how it’s working though.
We basically have 1 motor pr axis. They each use a short 200-GT2 belt to push and pull at the end of one 8mm rod pr axis.
In order for our motors to make use of the 200-GT2 Belts, they each need a 20-GT2 Pulley with 5mm bore.
At the end of each 8mm rods there is a 20-GT2 pulleys connected to the opposite 8mm rod for that axis with the closed 610-GT2 belts.
At the furthest end of 1 rod of the X and Y axis, there is an extra 20-GT2 Pulley, where the belt from each motor is connected to.
It means when motor Y pulls at the end of Rod 1 for Axis Y that entire rod turns around. Via the 20-GT2 pulleys in each end, and the connected 610-GT2 belts makes the corrosponding second Y rod turn synchronized.
Same goes on for the 2x 8mm rods for the X axis.
We have 4 of these 610mm closed/endless GT2 belts which are used on each end of each pair of 8mm rod for X and Y axis.
Sliding along each 8mm rod, there is a “Slider” which slides along the rods by utilizing a 30mm long 8id/12od mm self graphite bushing.
Each Slider can be split in two in order to run one side of the belt through the middle of it. The belt is is fastened in the middle using a small spring, which also helps ensuring the right tension and even makes up for some small inaccuracies you might have in the axes.
Each slider then runs along/on an 8mm rod. Pulled long by its own 610-GT2 belt. Each axis consists of 2 sliders connected with a 6mm rod where the Carriage with hotend is located on the cross-section between the 6mm rods of the X and Y axis.
The rods rotate as part of how they pull the sliders, which is the reason for the bushings as ball bearings would break down here.
The bushings also means extremely quiet running, which is just awesome.
Contrary to the sliders, the Carriage uses 2x LM6LUU ball bearings as the 6mm rods aren’t rotating, and also to provide a bit of compensation for tiny inaccuracies in the construction – ball bearings have build in about 1% give.
It all means there is equal identical directional force being applied on both sides of the carriage, so we do not experience any form of skew on the carriage as with CoreXY.
The bushings are listed as not requiring lubrication, but they really do benefit from a bit of lubrication. Especially if you buy cheap rods with bad tolerance. Many cheap rods are too big, which might be nice for ball-bearings (remember the 1% tolerance), as it gives a tighter fit, but with bushings it just means more friction, noise and potential bad print quality. You might also experience problems inserting the flanged bearings onto the ends of the rods, if you buy cheap rods.
Use acid free clear and thin sewing or cycle oil. Or PTFE spray, which I’m using.
You can get all sorts of upgrades which are mostly relevant if you tend to pick your machine apart a lot.
In those cases the plastc sliders rapidly degrades and after a few times they no longer grip onto the 6mm rods very well.
For such cases, you can get various different Aluminium sliders. I have these linked parts, but other variations also readily available now.
They do cost over €30 though for a set. Beware the dimensions for rods as some of these use 8mm cross rods instead of the 6mm we use.
As decribed above, we need 2x long 6mm ball bearings for our Carriage. You might be tempted to use Bushings here, but if you have the slighted misalignment they are going to make grinding noises and ruin the print. These bearings also help compensate a bit for misalignment, as the balls have a build in 1% give.
You might want to buy extras, as you need to change them now and then – when they begin to rattle.
We need some accuracte plastic spacers M8,2x14x5 (inner, outer, height) at the end of all our 8mm rods for the X and Y axes. They go between the 20-GT2 pulleys and the outer flanged bearing in the side of the frame.
It’s important they are uniform in size, so I really prefer to buy these instead of printing them. Especially since a bag with 200x spacer 5mm thick costs less than €5. Such a bag has served me in multiple builds. You can’t use a spacerset from Ultimaker 2 as we use more spacers than they do. It wouldn’t save us any money regardless if we could use it though.
I don’t even know if you can get them in pieces 15 or 25mm long, but this listing shows the fewest, longest pieces possible.
It is 150mm total, so if you get a back with 5mm long/wide spacers, you need 30 of those.
Our 8mm rods are inserted into a single F688 Flanged Bearing at each end, so we need 8 of those.
If you find you can’t get them onto your 8mm rods I’ll wager it’s due to bad quality rods and you should demand the money back.
We allready went over the Z-liftplate and the heated bed itself in the first 2 posts, and we’ll look at the bits and pieces here.
We are going to be using 3 of these nuts for our Z-stage. We use these as they are cheap and direct replace for standard lead scerw nuts. The reason for using Anti-backlash is to avoid issues with Backlash which might show some, especially when doing Z-lift during prints, but also after a while, when the nuts and/or rods are a bit worn.
The Anti-backlash nuts compensate for the wear and tear and also for bad quality the lead screws, and even the nuts themselves, might have.
The partnumber is B-ABN88 where the 88 is 8diameter and 8mm travel pr rotation. Also call “Lead”.
You might wonder about what Backlash is, so you should head over and read this nice post about it.
We use 2 of these to for the rear end of our Z-liftplate. They provide a nice large surface area to use as stabalizer for our plate as it goes up and down.
We use 2Pcs of these LMH8UU ellipse/oval flanged ball bearing to support each of the front Z-axis motor.
We need 3 sets of these to adjust our Heated Bed.
A complete listing of screws for the Z-stage. I’m not listing price for these.
Only thing of note here is the fact that we are using m3 square nuts for the frame as these sits better in the cutouts. Aside from this, all parts are totally standard.
You can either use 2.5mm screws + a nut or an m3 screw if you tap the switch first. I like to tap mine.