7. January 2018

xBot Medium – Mechanical Parts – (BOM cont.)

By BeTrue3D

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.

I’ve set up a xBot-Medium Github Repository where the files can be found for this project. As I havn’t finished it yet, all the files aren’t there, but they will be! Only the .STP files for the Dibond frame pieces and some a few for printed parts are missing, so it’s pretty much complete allready.

A complete BOM file is in place in the Github Repository.

This post is sorted in the following categories:

  1. Parts for the XY Axes
    1. 200-GT2 Belts
    2. 20-GT2 5mm bore Pulleys
    3. 20-GT2 8mm bore Pulleys
    4. 610-GT2 Belts
    5. Sliders
    6. LM6LUU
    7. Spacers
    8. Flanged 688 bearings
  2. Parts for the Z-liftplate
    1. Anti-backlash nuts
    2. 12mm flanged bearings
    3. 8mm flanged bearings
    4. Fingerscrews
  3. Screws and nuts
    1. Screws for Z-Stage
    2. Screws for the Frame
    3. Motors
      1. Motorshields
    4. Limit switches
    5. Under the machine
      1. Z-Rod brackets
      2. Connectors
      3. Duet WiFi and Duex Mounting
      4. Powersupply
      5. Chamber Heater
      6. SSR

1) Parts for the XY axes

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.

200GT-2 Belts

Price # €0,33 total for 2pcs: €0,66 from Robotdigg

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.

20-GT2 5mm bore Pulleys

Price each €1,33 for both from RobotDigg €2,65

In order for our motors to make use of the 200-GT2 Belts, they each need a 20-GT2 Pulley with 5mm bore.

20-GT2 8mm bore Pulleys

Price for 10psc at RobotDigg: €6,22

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.

610-GT2 Belts

Price for x4 from RobotDigg: €2,98

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.


Price for 4sets €8,6

1 set is made up of 2 plastic parts a spring and a selfgraphite bushing 30mm long 8mm inner 12mm outer diameter

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.



Price for 2: €3,16

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.


Price for a bag €4,7

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.

  • 4x 25mm long
  • 2x 15mm long
  • 2x 10mm long

Flanged Bearings

Price for 8 at RobotDigg €3,32

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.

2) Parts for the Z-liftplate

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.

Antibacklash nuts

Price for 3 from RobotDigg €7,46

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.

Both these images are from the post on Backlash on liutaioMottola.com

12mm flanged bearings

Price for 2 LMK12LUU €4,64 from RobotDigg

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.

8mm flanged bearings

Price for 2 LMH8UU: €4,14

We use  2Pcs of these LMH8UU ellipse/oval flanged ball bearing to support each of the front Z-axis motor.


Price for 3 sets €3,39

We need 3 sets of these to adjust our Heated Bed.

Each set consists of a fingerscrew (which comes in gold and silver) a powfull spring and a m6 washer + 20mm m3 flat head screw to sink into the countersunk holes in the heated bed


3) Screws and Nuts

You can get a complete list of all items needed, included a listing of the screws and nuts from the xBot Medium Github Repository. Look for the xBot Medium-BOM.pdf file

Screws for Z-stage

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.

Screws for the Frame:

  • Right side:
    • 12x m3 16mm Button Head Screws
    • 12x m3 Square Nuts
  • Left Side
    • 12x m3 16mm Button Head Screws
    • 12x m3 Square Nuts
  • Front
    • 5x m3 16mm Button Head Screws
    • 5x m3 Square Nuts
  • Back
    • 6x m3 16mm Button Head Screws
    • 6m m3 Square Nuts
  • Door Hinges
    • 4x m3 10mm Button head Screws (might change)


  • Z-Motors
    • 12x m3 10mm Button Head Screws
  • XY Motors
    • 8x m3 30mm Button Head Screws
    • 8x m3 Metal Spacer
  • 8x m3 10mm Button Head Screws

Limit Switches

You can either use 2.5mm screws + a nut or an m3 screw if you tap the switch first. I like to tap mine.

  • Z-Max Limit Switches
    • 6x m3 10mm Button Head Screws
    • 6x m2.5 12mm Screws
    • 6x m2.5 nuts
  • X and Y Limit Switches
    • 4x m3 10mm Button Head Screws
    • 4x m2.5 12mm Screws
    • 4x m2.5 nuts

Under the machine

Z-Rod brackets

  • 12mm Z-rod Brackets
    • 4x 12mm m3 Button Head
  • 8mm Z-rod Brackets
    • 4x 12mm m3 Button Head


  • Front USB
    • 2x m3 10mm Button Head Screws
  • Rear USB
    • 2x m3 20mm Button Head Screws
  • Power Connector

Duet WiFi and Duex Mounting

  • 8x m3 10mm Button Head Screws
  • 8x m3 8mm Button Head Screws

Power Supply

  • 4x m4 10-12mm Button Head Screws

Chamber Heater

  • 4x m4 20mm Button Head Screws


  • 2x m4 20mm Button Head Screws