Congratulations on becoming a BX owner. You have in your posession one of the most capable 3D printers in its class with some unique features that you will not even find on other, more costly machines.
Despite the capabilities of the machine, it will only be able to perform well if you take the time to carefully ensure that the mechanics are well put together. Fortunately the BX is a very simple machine to assemble so if you follow this guide carefully you will not have any problems.
The BX comes with the frame already pre-assembled. All you will need to do is align it with the base and insert four bolts to hold it in place. Unfortunately the process involved in trimming the aluminium extrusions to length at the factory does not always result in a perfect, 90 degree cut. This means that after you fasten the uprights in place they may not be at 90 degrees to the base.
It's really important that you measure this angle and follow the recommendations to come because if you do not, it may result in x-sled rotation as is covered later in this gist.
After tightening the bolts which connect the uprights to the base, use a miter-square (or any other tool capable of measuring 90 degrees with precision) to measure whether the uprights are at 90 degrees to the base as shown in the following picture. If they are not then take note of whether the upright is leaning away from the miter-square edge or towards it (measuring from the front of the machine).
In the image you can see that my uprights are already at 90 degrees. That's because I have already applied the trick that I am about to explain. Let's assume that your uprights are leaning slightly forward, loosen the bolts holding both uprights in place but don't remove them completely. Pull the upright that you are working on up a mm or two off the base and insert a piece of paper under the side which is leaning forward. Tighten the bolts again and repeat the measurement. You will notice that even a thin piece of paper makes a large difference! In fact I could not use two sheets of normal printer paper as it over compensated on one of the uprights. I needed to use one sheet of normal printer paper and then 1 sheet of notepad paper which was much thinner.
Repeat the process iteratively for both uprights until they are sitting at 90 degrees when the bolts are tightened. Once you are done you can tear away any excess paper so that it is hidden completely under the base of the upright.
With the uprights at 90 degrees to the base you will now need to make sure that they are laterally parallel to each other. Before you tighten the bolts the final time, make sure that both uprights are pushed as far back as possible. Since there is a small amount of play in the longitudinal positioning of the uprights this will ensure that they are both positioned in the same relative location. Now you can measure whether the uprights align with each other correctly. To perform this measurement you can use any tool with a straight edge. Place the tool flat against one of the uprights and then run it to the other upright. It should run flat up against the face of the other upright. If it does not, then you may have some rotation in the uprights. You need to get rid of this to prevent undue strain on the x-axis gantry and z-rollers. The two images below show how to perform the measurement.
As you can see in the second image, there is a minor gap on the unit where this measurement was taken. In order to eliminate this gap you would need to loosen the four bolts at the base of the uprights (without allowing the paper to slip out) and loosen the four bolts at the top of the uprights. Sandwich the uprights in between two flat surfaces that are free from bends and warping and also long enough to reach both uprights and then ask a friend to tighten the bolts at the top of the uprights while you hold them sandwiched. Once done, tighten the bolts at the base of the uprights again. Your frame should now be perfectly aligned!
X-gantry twist causes many a nightmare for novice and experienced users alike. Chances are you have never heard of it before because it is not something that is spoken about often. Hopefully this section will help you to learn something that you will in turn be able to share with others.
X-gantry twist happens when the left and right uprights are are not at 90 degrees to the base. Let's say that the left upright is leaning slightly back and the right gantry is leaning slightly forward. After you have bolted them tight into the base they are not likely to want to straighten out. Then let's say that you now go and bolt the X-gantry to the two uprights using the z-rollers. Obviously it has a flat face on either end that is supposed to sit flat against each upright but it can't because the uprights are not parallel with each other. So what happens? You tighten the bolts on the one side of the gantry and the gantry twists slightly so that the face on that end is flat against that upright. On the other side of the gantry the face is definitely not flat against the upright because the gantry has twisted to accomodate the end that you just tightened. Still, you need to tighten those bolts too so you tighten them and as you do the gantry twists in the opposite direction so that it can sit flat against that upright. The net effect is that the gantry has been twisted as if it were a rag and you were trying to twist it to get water out of it. How does this affect your print? Massively!!! Watch the video below to find out:
https://www.youtube.com/watch?v=rPU4ZAPJTNc
Now that you have watched the video you have a better visual understanding of what is happening. In the video, imagine that the red tip is your nozzle and the blue tip is your probe. Watch the video again and see how the z-distance between the tips of both varies as the print head moves across the x-gantry. At one point the blue is slightly below the red, then they are even and then the red is below the blue. This is exactly what will happen if your uprights are not parallel with each other. Your z-offset will simply not be constant over the whole x-range and there is no way that Marlin can compensate for this regardless of how fine a mesh you have.
An uneven first layer, regardless of the resolution of your mesh, is the first indicator that you have this issue. Another good indicator is that your mesh has a consistent tilt, either positive or negative, along the x axis. To check for a tilt you can connect to your printer using a terminal app like pronterface and run a G29 command (ABL) or G29 T (UBL). Copy the results into a notepad application and remove the column and row markers. Paste the resulting matrix into the bed visualizer website here: http://lokspace.eu/3d-printer-auto-bed-leveling-mesh-visualizer/
So how do you fix it? Your best move is to get the uprights perfectly parallel. However if you have tried and tried to do this and are still suffering from inconsistent first layers then follow the steps below.
- Lower the z-axis to the point where the nozzle is about 1mm away from the bed.
- Remove the tensioner from the right hand side of the x-gantry.
- Loosen the bolts that hold the x-gantry to the plate that runs up and down the right upright. You should see something that looks as follows:
The yellow arrow shows you the gap caused by the uprights not being parallel. You need to release the gantry from the plate enough to shove paper into the gap. The idea is that the paper will fill the gap and prevent the gantry from twisting again after you tighten the bolts. Sometimes the gap is so tiny that you may even need to select a thinner type of paper to avoid over-filling it. Sometimes it is a little larger and you may need to use more than one sheet of paper. Whatever you do, don't rush it and get it right.
After the paper has been inserted, bolt everything back together and test ABL/UBL again.
It's possible that the center of the stepper axis may not align perfectly with the center of the lead screw nut as it comes in the box. If this is the case then the rotation of the lead screw will actually force the base of the lead screw to move in an elliptical shape which creates z-banding on your prints. To remove the pressure on your lead screw you should loosen the bolts on the brass nuts on either z axis so that they have freedom to move within the holes where they are mounted as can be seen in the image below.
While we are on the topic of lead screws now is the time to mention lubricating them. Want to see an instant jump in layer line consistency? Use some quality lubricant on your lead screws. I've done days of research and tried numerous types only to settle on dry PTFE lube. It repels dirt and reduces friction between surfaces to the extent of almost breaking physical laws. Do yourself a favour and try to find some. If it says that it is supposed to be used on bicycle chains then it is probably the right stuff. Apply it reasonably often.
Each axis has eccentric nuts which allow you to adjust the pressure with which the v-wheels roll against the aluminium extrusions. Too much pressure and the wheels will bind and impede movement of the axis. Too little pressure and there will be play on that axis resulting in print imperfections. You need to get these nuts adjusted just right and then continue to adjust them every few prints.
The correct adjustment is one where you are able to hold the axis in place and roll the wheels on that axis against the aluminium extrusion using your fingers, allowing them to slip. You should not have to force them to slip against the extrusion by straining but you should also not be able to turn them so easily against the extrusion that it requires very little effort. The sweet spot is sometimes just a fraction of a turn of the eccentric nut away from a bad spot.
The images below show where you will find the eccentric nuts for the z-axis rollers. For the X roller look on the underside of the print head and for the Y roller look on the underside of the bed. Note that there are two eccentric nuts that need to be adjusted for the Y roller.
Many people feel that if they can't pluck their belt and hear a note then it is not tight enough. As an excercise, please do the following: Tighten your y-axis belt nice and tight. Really, really tight. Now grab the bed and try to move it with your hand. Was it easy? Probably not. In fact it may have even felt so difficult that you could swear that the motor was engaged. That means that moving your bed is getting close to the holding torque of the motor and that is not good. The reality is that tight belts are good but belts that are too tight are going to result in layer shifts and seriously mess with your sensorless homing.
To figure out the right tightness for your belts, tighten them while moving that axis with your hand. For the y-axis it is likely that the difference between just right and too tight will be no more than a quarter of a turn. The x-axis is a bit more forgiving and can go a bit tighter without putting too much frictional force on the motor. Still, test with your hand on the print head while you tighten the x tensioner to be sure you are not going too far. If you get to a point where it becomes difficult to run the print head along the axis then you have gone too far.
With your belts at the optimal tightness you are now in a position to calibrate the sensorless homing. This is not strictly mechanical but is so closely related to the mechanics of the machine that it belongs in this section.
Look for the endstop switches on the BX. OK now stop looking because you won't find them. At least not on the X and Y axes. That's because the BX uses sensorless homing which is both a neat feature but also needs calibration. The TMC 2209 datasheet (TMC2209/2226 is the model of the stepper drivers used on the BX) says:
"The StallGuard4 value SG_RESULT is affected by motor-specific characteristics and application-specific demands on load, coil current, and velocity. Therefore, the easiest way to tune the StallGuard4 threshold SGTHRS for a specific motor type and operating conditions is interactive tuning in the actual application."
TLDR; For sensorless homing to work correctly you are going to need to tune it for your exact application. Change the load on the motors by tightening the belts, you'll need to tune it again. Change the eccentric nuts so that the carriage sits tighter on the axis, you guessed it, more tuning.
Before you start trying to tune the sensorless homing it is recommended that you update to the firmware that is maintained within this repo: https://github.com/looxonline/Marlin
We will tune each axis one by one. We are going to use the terminal on the TFT as well as the homing menu. First, navigate to the terminal and send M914. The result will show your current sensitivity levels for the X and Y axes. Now you have a starting point. Next, navigate to the homing menu and start with the Y axis by hitting the Y homing button. The Y axis will retract by 3mm and then start moving towards the home position. If it stops before it gets to the home position then your sensitivity is too high. If it makes it to the homing position but grinds once it gets there then your sensitivity is too low. To stop it grinding just grab the bed and pull it towards you.
Depending on the outcome of the above test, return to the terminal and either increase or decrease the sensitivity on the Y axis by typing M914 Y (e.g. M914 Y95). I recommend only increasing or decreasing by 1 each iteration because the difference between just right and unreliable can be as fine as a single level.
Once you have a value where the Y axis is homing reliably I always recommend stress testing it before moving on. To stress test it, go to the homing screen and repeately home it. If you can get 10 successful homes in a row then you have probably found the right value. During your stress testing it is good to disarm the bed so that you can move it to a random location and test that the homing works from anywhere along the axis.
Repeat the same procedure for the X axis except if it starts to grind just pull the print head to the right and it will stop.
Finally, from a mechanical standpoint, you will need to level the bed. This is good practice even for a machine like the BX which has ABL. This guide does not touch on that since there is already extensive information available on the internet to help you to get it done right.
In order to be sure that your ABL probe can accurately probe the bed without crashing the nozzle into the bed you need to make sure that it is the correct height above the nozzle. The probe should be no more than 2mm above the nozzle, less is often better. If you are getting a probing failure message when the probe dips for some points then it is too high. You can either use a spacer which measures less than two mm to get this right or you can fold a piece of paper over around 4 times and use that as a spacer and it should get you into the general ballpark.
To adjust the height of the ABL probe you'll need to unscrew the nuts on the top and bottom of the probe so that it has free vertical movement. With the nozzle already just touching the bed, place the spacer underneath the ABL probe and then drop the probe down onto the spacer. Tighten the nuts back up so that the probe is well secured in place. It's always best to send M851 Z0 after this to ensure that your z-offset is reset to 0 and the nozzle will not crash into the bed during the next calibration.
If you don't have a spanner that is the right size for the ABL probe nuts then you can use a pair of pliers and that should be enough to get them loose and tighten them again.
The remainder of the process required to calibrate the z-offset is mentioned in this gist: https://gist.github.com/looxonline/94510f433c0f40ddcacbbecc384e844f
DANGER WILL ROBINSON The connector to the TFT is not keyed. This means that you can put it in the wrong way very easily. I'm unsure why BIQU never went with a keyed connector but since cost is not really a factor with a piece of plastic I would have to assume that availablility is the issue.
The net out is that you need to be careful when installing the connector onto the TFT. The connector should have a white marking which must face the print bed. Also be sure that the pin alignment is correct. Many people install the cable offset towards the top of the connector. This is easy to do if you have already bolted the TFT to the chassis and are trying to install the connector. Instead, install the connector first and then flip the TFT over and bolt it to the chassis. Always check that you have exactly the same gap on either side of the connector to be sure that you have the correct pin alignment.
If you want to install a pi then the connection part should be very straightforward. However you will still need to do some work on the software side of things to get it to output correctly. You can't just smack octopi and octobtt/octodash on it and expect it to work. You need to tell it what resolution and HDMI type to output. Follow the config guide in the octobtt repo to understand how to do this:
https://github.com/bigtreetech/OctoBTT
Coming soon...
With the machine built and powered on, you'll need to run a PID tune on the hotend and the bed. This will make sure that their temperature regulation is as good as it can be for the environment in which you are using it and at the temperatures you are using it.
You can use the BTT UI to run the PID tuning or you can do it through the terminal. I usually do it through the terminal because I like to have fine grain control over the parameters. Assuming that you are going to do it though the terminal window you can enter the following commands for the hotend and bed respectively:
M303 C8 E0 S220 U
M303 C8 E-1 S60 U
Change the number after the S to be closest to the average temperature that you will print with on the hotend and bed respectively. Each process will take a few minutes to complete as it iterates using various parameters to find the best ones.
Send an M500 once you are done to lock the new parameters in.
Yes, this is mentioned in the list of recommended mods below, however it gets its own, honorary subheading right here because it is such a simple mod to make and yet it has such a major impact.
This is a general axiom that is true for all 3D printers. Never use the spool holder they come with. Always change to a ball bearing based spool holder, ideally, placed next to the printer. This reduces the amount of force required needed by the extruder to pull filament into the melt zone, thereby creating more consistent flow. If the holder is placed next to the printer then it also prevents an upward pulling force from being placed on the extruder during a print which results in uneven layer lines.
A very common spool holder is TUSH but there are literally hundreds to choose from: https://www.thingiverse.com/thing:2047554
Cura has built in profiles for the BX (in progress for the V5.0 release). Don't expect these profiles to be a silver bullet that will buy you perfect performance with all filaments. Essentially they define everything that they can possibly define that is not dependent on the filament that you are using and then leave the rest in your hands. To get the best performance you will still need to tune the profile for each different filament that you use.
The settings that need tuning include:
- Retraction distance.
- Retraction speed.
- Nozzle temperature.
- Bed temperature.
- Flow.
- Number of top layers (filament with good bridging may need fewer top layers to get a good finish).
You will also need to tune the e-steps value but that is not a slicer setting. To help you to tune the profiles you can use the guide made by TT at this link: https://teachingtechyt.github.io/calibration.html
The retraction tuning tool at this link may also prove helpful: http://retractioncalibration.com/
The BX is already such a capable and well outfitted machine that there are very few modifications for it relative to other machines. Nevertheless, there are still some things that users can do which will increase performance or make the printing experience a little better.
- The fan silencing modification - This is a modification which will require you to change two plugs within the machine and install some new firmware. The net result is that your case fans will only turn on when the printer is printing and therefore your machine will be a lot more quiet. See this gist for more info: https://gist.github.com/looxonline/2966862620b831a33cb36340ed73f644
- Part cooling fan modification - Some people desire a bit more cooling. For those who fall into that category there are options available such as this one https://www.thingiverse.com/thing:4682915
- Printing a bearing based spool holder which seats the filament spool next to the printer and reduces the friction in the filament path. Only be sure to install a bowden fitting into the top of the extruder with a small piece of PTFE tube if you are going to run the filament from the side - https://www.thingiverse.com/thing:2047554
- Mini UPS (https://www.bigtree-tech.com/products/bigtreetech-ups-24v-v1-0.html) - Running a mini UPS on your BX will enable you to enjoy power loss recovery which can park the nozzle. On the other hand, if you are running a raspberry pi and are worried about the pi being powered off without having a proper shut down then you can also apply the modification at the following gist which automatically shuts the pi down when the power is removed from the machine. However, note that if you are printing from octoprint you cannot enjoy power loss recovery when using a mini UPS unless you tell octoprint to force the print to happen from the BX SD card. See this gist: https://gist.github.com/looxonline/fd260bfc29c124f22fe7613311ae3a79
- Firmware - If you would like a firmware distribution that aims to stay up to date with the latest marlin release and has a few little extras built in then go back to the repo that led you to this gist (https://github.com/looxonline/Marlin) and follow the instructions.
Above all else, NEVER work on the printer with the power applied. It's very easy to short parts out which can destroy the motherboard or other electronics.
Also avoid removing the HDMI cable from the hotend when the power is applied. Pins could short together and destroy electronics.
If you want to work on the hotend but need it to be hot (removing the nozzle) then rather heat it up to about 20 degrees over the temperature that you need it to be at, turn the power off completely and then start working on it.
If you have a point which is related to getting started with the BX then please feel free to add it in the comments below.
