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A major problem with the Prusa Mini is that you have to mess with the hotend so often.

This by itself is not so bad, but the three (3) grub screws you need to remove each time, are simply not made for it.

A known problem on the Prusa Mini is the heat break slips down. The only thing holding it in place are three (soft metal) grub screws. You can’t tighten the grub screws they tend to round off really easily if you’re not careful. If your heat break lowers even by a fraction of a mm it creates a gap between ptfe tube and heat break. This gap area can fill with retracted filament which then cools. The gap creates a plug. The filament can’t go forwards or backwards and the extruder drive gears just grind the filament to dust. So you end up having to get in there and pick filament out of the hob gear’s teeth as well as clearing and reseating the heat break and resetting the pinda probe.

Just remember don't try to screw them in flat against the heat sink, there should be a 1mm or so gap. Finger tight then a smidge more, I am sure you can snap that heatbreak, but don't. If you do, you are on your own.

I fit these cap heads bolts when the printer is warm so everything contracted when cooled. Follow the guide on prusa*. There are a lot of wrong YouTube videos out there that just push the heat break up and tighten and forget to unwind the connector at the top half a turn first. So after you pushed the heat break up and tightened it you can then screw down half a turn on top connector to remove any last gap and squish the ptfe tube a fraction of a mm.

* Link to Prusa guide

Ignore the dirty Heatblock! Remove these 3, cheap, soft grub screws.


Ignore the dirty Heatblock! See no crummy grub screws here!

Ignore the dirty heatblock! Screw in the three machine tool steel cap bolts. Gently!

Finger tight and a slight smidge more. Don’t gorilla it down! Should be a mm showing of thread!

This guide references the Prusa mini+ Z axis lead screw aligner that is located here.

This printed part snaps in place to keep the lead screw aligned in the middle of the Z-bottom hole on the Prusa Mini.

It takes care of the wobble in the Z-axis lead screw. (Check yours yourself, grab the z-axis leadscrew near the bottom and give it a wiggle, you’ll see what we mean). It improves your print quality.

Step 1

Raise your Z-axis up to give yourself some working room. Halfway is more than enough!

Step 2

Position the Z-Axis Lead Screw Aligner as shown on your Prusa Mini Lead Screw.

Step 3
Push down on the right hand side of the Z-Axis Lead Screw Aligner and firmly snap it into place. You will note that it is now parallel to your Z-Axis.

Step 4

There is no step 4, Print long and prosper! Wasn't that easy?


For references sake:

Front: Looking over your Prusa Mini Control screen.


Rear: If you were seeing it from the back of your Mini.

Ultimately terms like XZ skew and XY skew are confusing, and it's simpler to explain skew in terms of the problem it creates than in these terms.

  • X axis - the horizontal arm where the print nozzle travels (left and right).
  • Z axis - the vertical arm, that holds the horizontal arm (up and down).
  • Y axis - the rods where the print bed travels along (forward and backward).

Skew Fixes


Squareness Skew

What is it?

This occurs when the horizontal arm of the printer is not perpendicular (at at 90 degree angle) to the Y axis below (which the print bed travels along). It is either pulling forward towards the front of the printer, or backwards towards the back of the printer.

Issue

This will affect if a print is square, specifically how a line of filament is printed from right to left (or left to right) on the bed. A line of filament printed from the front to back (or back to front) will be unaffected as this is reliant on the Y-axis.

What do you need?

  • Calipers for the most accuracy OR a set square

Measuring

You can test this by printing something square and then either using a set square to check if all 4 corners are square, looking for any visible gaps. OR if you have calipers, you can measure corner to corner inside the square (both diagonals) and compare the values. If it is perfectly square, the values will be the same.

Fixes


Bed Level Skew Left/Right

What is it?

This occurs when the horizontal arm of the printer is not parallel on the X axis with the print bed below. It is either tilting downward towards the print bed, or upwards towards the ceiling. As a result, your printers bed will be sloping from left to right or right to left.

Issue

This affects the first layer calibration, the left hand side of the x-axis will be either too close or too far away from the print bed causing a slant. The printer can only compensate for an uneven bed so much, so depending on how severe the slant is, it may or may not affect your prints.

What do you need?

If you follow the Prusa solution below, they suggest simply moving the print head from one side to the other and visually checking the height from the bed. In all honestly, I think that is a waste of time as it will never be anything close to accurate. I highly recommend setting up a Raspberry Pi with Octoprint and the Bed Visualiser plugin. I also highly recommend that you should have a mechanism to measure belt tension (for Solution 2 below). Without this, you will be completely in the dark as to how tight your x-axis belt is, and if you are messing with those screws, you would want to know. This is what I recommend, it's very good. I verified its accuracy on a MK3S(+), which can give you a belt tension reading which I then compared to the meter.

Measuring

As above, I suggest running the Bed Visualiser plugin on Octoprint. This makes it very clear to see if you have an issue or not. This is a good example of what to look for, in this case you'd need to lower the arm, by tightening the top screw. Once you have run the visualiser you will know whether the arm needs to move up or down. Ensure you turn on "Descending y axis" if you are looking at the "Current Mesh Data", this orientates the data as it would be if you are looking at your printer from the front. Do not worry about any dips or raised areas you see in the corners when running the visualiser, there is a separate fix required for this. The aim here is just to get it as level as possible from left to right.

Fixes

There are two potential causes for this...

  1. The Z axis arm is not perpendicular to the bed
  2. The X axis arm is not perpendicular to the Z axis arm (and therefore not parallel with the bed)
  3. Both

Solution 1 - Z axis arm not perpendicular to the bed

You can loosen the three screws holding the Z axis arm and adjust it to ensure it is at a 90 degree angle from the print bed. I did this by placing a small set square on my print bed, adjusting the position of the arm, then retightening the screws in the order specified. Unfortunately if you have the print bed positioned such that you can place a set square on it and touch the arm, you won't be able to reach the main print arm, you'll just have to keep checking it until you get it right. Another option would be a digital level e.g. Klein Tools 935DAG Digital Electronic Level. You can hold the level against the Y axis while you are tightening the screws and try and align it at 90 degrees. One thing to consider though, is unless your print bed is perfectly level and it may not be, you may want to factor in any discrepancy into how you align the Z axis. Refer to Prusa's guide to see which screws need to be loosened source. There are also some mods that may help here, I have not tried these

Solution 2 - X axis arm is not perpendicular to the Z axis arm

Follow the steps as provided by Prusa. Remember, if you tighten the lower screw, this moves the arm upwards, towards the ceiling. If you tighten the upper screw, this moves the arm downwards, towards the bed. This is counterintuitive, so it's worth mentioning. Once you have made the adjustments, check that both of the horizontal bars are straight and not twisted. Look at your printer from the top and check the two bars are perfectly aligned. If you need to adjust turn the orange piece with the screws a little to correct. If they are not aligned your print nozzle will turn slightly as it moves along the x-axis. If you loosen the belt tension screws, you should push the orange piece that holds the screws inward towards the z-axis arm, while holding the other end with your other hand. This is not mentioned in the Prusa's, but is mentioned in a video I watched and you will feel the orange piece move inward when you do this. Otherwise loosening the screws may not have an effect. Once you have made an adjustment, you should check the belt tension! See "What do you need?" above.


Bed Level Skew Corners

What is it?

This is the skew that occurs when your print bed is not level. With the "Bed Level Skew" fixes above, you should be able to achieve a level bed from left to right in the very center of the print bed (or at any single point on the Y-axis). However the print bed itself may not be consistently level from front to back and as it moves backward and forward on the Y-axis, the level changes. In my particular case, my print bed actually droops in the front right and back left corners, and is elevated in the back right corner. As the bed moves forward or backwards the level will change since the leveling is not consistent.

Issue

Depending on the severity this may or may not cause you issues. The Prusa Mini (and MK3) both have auto bed leveling, which detects any variance in your print bed, and accomodates this by raising or lowering the nozzle height accordingly in those areas. However if the variance is too high, your printer may not be able to compensate for these differences. The other potential issue, is although the nozzle compensates for an uneven bed, the bottom surface of your print will follow the contours of your bed.

Measuring

Your only option here is Octoprint with the Bed Visualiser plugin, this makes it very clear how level your bed is. Before going any further you should decide if this is worth the effort. If your differences are small I honestly don't think you should worry about it. How small is acceptable? I'm not sure I can answer that. I feel like I read somewhere up to 0.5mm from corner to corner is acceptable, but don't quote me on that. In my case my front right corner was -0.16mm and my front right corner was +0.38mm, so just over a 0.5mm slope. I can't say I can definitively attribute any issues I've had to my print bed, but I decided I wanted it as level as possible as that's the kind of perfectionist I am.

Fixes

Solution 1 - Masking Tape Mod

Someone recommended to me to perhaps try the masking tape mod. This was actually an incredibly quick and easy way to level the print bed at a very low cost. Using octoprint each time I made an adjustment I focused on getting the front left and back left corners the same height, and likewise with the front right and rear right. I then leveled the bed almost completely using the XZ skew adjustments by Prusa. One caveat with this fix though, is this "may" affect your print bed temperature as the masking tape will insulate the heatbed from the steel sheet. If you are printing PLA that should not affect your first layer, as you can technically print on a cold bed (I believe), but it may cause warping if your bed is not evenly heated. It's hard to say if this is an issue and probably depends on how much masking tape you use and where you put it. You'll need to experiment for yourself. Solution 2 - Silicone Mod So what is the ultimate solution? It's this and while it is the perfect solution it's also pretty involved and requires a lot of care to execute.

Getting the Prusa MMU2 work is about removing friction and pinch points on the filament.

First – Watch this You tube Video:

Prusa MMU2 Multi Material Unit - Tips and Tricks - Chris's Basement
Link to Youtube Video

Two Primary items to review when working to get reliable prints for your MMU2.

1) Checking the filament paths to make sure there is as little friction as possible. From the spool to the extruder here are the steps to take.

a. Make sure you have the latest selector printed from Prusa.
i. Print the selector out at .15 with Quality layer height out of PETG.
ii. When you assemble make sure the filament path is clear, Use a drill to clean it up a bit. Also, when you set your finda height make sure the filament can pass through WITH MMU THE FORMED END. When changing filaments, the MMU forms an end that has a larger OD.

b. Updated M10 Pass Through connector to get filament tube all the way to the bond tech gears.
i. https://www.thingiverse.com/thing:3541897

c. Prusa MMU2 PTFE Holder M10 Passthrough Adapter.
i. Supports the PTFE tubes as they enter the MMU with much less resistance.
ii. https://www.thingiverse.com/thing:3233579

d. Gravity Auto – Rewinder
i. I have tried 4 types of buffers, 2 rewinders and this so far is the best I have found.
ii. https://www.prusaprinters.org/prints/3729-multiple- mechanism-auto-rewind-spool-holder

2) Tension on the MMU and Extruder can cause issues. There is a sweet spot for both that can cause miss feeds. Specifically, that the filament would index to the extruder. The extruder would grab it, pull it in and then retract. Not sure why it does this but sometimes it retracts too far and loses the filament.

3) Signal and Power cables between the MMU and Prusa. I kept having the MMU fail with both Red and Green flashing lights. After I separated power and signal cable, re-routed then along the frame to the MMU it solved the issue.

Leadscrew induced Z banding.

Leadscrew induced Z banding is primarily caused by lateral displacement of the bed arms by the radial movements of the lead screws. In a perfect situation the Z linear rails and the carriages fixed to the bed arms would be able to resist this lateral movement.

Many 3D printers describe their bed mounting system as being a Maxwell kinematic coupling. According to the Wikipedia definition, “Kinematic coupling describes fixtures designed to EXACTLY (my emphasis) constrain the part in question, providing precision and certainty of location”

At first glance these bed mounting systems look like perfect Maxwell Couplings…but they are not, because the fixtures (balls sitting in pins and arms bolted to linear rail carriages, mated to the linear rails) do not solidly and EXACTLY constrain the bed, simply because there is a very small amount of movement between components in this restraint chain.

Under good circumstances the weakest point in this restraint chain is the clearance tolerances between the carriages and the linear rail. The clearances could be reduced by using higher grade, but more expensive linear rails/carriages. The effects of these clearances could be reduced by using wider rails and/or longer carriages, again at some increased expense. Prusa for example uses two linear bearings stacked one above the other to increase their effective length as part of their solution to Z banding.

Money can help solve a lot of problems, but so can clever design with cheaper components, and the aim with a hobby/prosumer printer is to get the biggest bang for buck.

In practice, because the large cross section of these is able to withstand bending from the applied forces it is very unlikely that any flexibility in the printed bed arms contributes to Z banding. However, a small amount of movement between the bed arms and carriages is possible and does occur if one or more of the screws that hold them on to the carriages work loose due to plastic creep or vibrations backing off the screws. Checking the tightness of these cap crews should be part of periodic maintenance.

Other issues such as loose grub screws on both X and Y motors and the Z lead screw flexible couplings can also cause artefacts that look like lead screw Z banding. In addition, the beds are not fully constrained against the pins by more than the weight of the bed assembly and sometime with the added assistance of quite weak magnetic force.

When one arm moves laterally, the balls in the other two arms can either slide on their respective pins which allows the bed to rotate fractionally or climb up on one pin in the pair to accommodate this, which if/when achieved would/will fractionally lift the bed. Both these options cause imperfect layer stacking, which can be viewed as Z banding in the prints.

Contributing to the issue is that the length of the bed arms amplifies any lateral displacement caused by the lead screws.

Before trying to engineer a new solution it is best to ensure that your printer is as mechanically fine-tuned as possible. It may be after doing this tuning you deem you do not have a problem that needs solving.

What causes the lateral movement of the lead screws?

1. Radial misalignment of the stepper motor shaft and the lead screw. Radial misalignment is when the centre of these two rotating ‘axels’ is not perfectly aligned.


2. Angular misalignment. This is when an extension of a line drawn along the two axial centres of two shafts intersect each other.


3. Angular misalignment of the lead screw with the linear rail. I have published sturdy lead screw alignment tools on Thingiverse to assist with reducing this misalignment.


4. Bent lead screws. Lead screws may not be straight to start with, but are also likely to become bent over time.


All of the above cause lateral (sideways) forces to be present at your lead screw nuts which are attached rigidly to your bed arms.

The only thing constraining the lateral movement of the bed arms is the chain of restraint from the from the linear rails to the carriages to bed arms through to the lead screw nuts

In attempting to move the arms sideways the printers lead screws are a competing with this chain of restraint…and you definitely want the chain of restraint to win this argument.


Squishworx, LLC stands by every product we manufacture and we truly want our equipment to be the last you'll ever need to buy. Many of our products carry a lifetime warranty against defects and even normal wear and tear.

Our warranty is simple - Send us an email, let us know you are unhappy and we take care of the rest.

The warranty specifics on a per product basis are as follows:

Any Squishworx Manufactured product carries a lifetime, no questions asked warranty.
All 3rd party equipment carries manufacturers warranty.
Consumables (Nozzles, print surfaces are meant to be used, sometimes abused, and as such, are not covered except for original product manufacturing defects. Rust - outside of warranty and not covered
Loneliness - Send me an email, I'll talk with you.

January 2021 Update: All shipping carriers are experiencing delays, so please expect an additional 1-16 business days beyond the estimated delivery date, and possibly longer, depending on your location. Some packages are arriving right on time, but it seems to depend on the distribution center it is routed to, which unfortunately we cannot control.

Please note that both UPS and USPS have suspended their service guarantees on all shipment services, so the delivery date of any expedited service you purchase is not guaranteed.

We have spoken to a USPS customer service rep, and they have confirmed that some post offices have stopped scanning packages, so packages will only get tracking updates when they reach a major hub. They also said that they are seeing delays of about 10-16 business days for Priority Mail, but it may be longer.

If your tracking says "Shipment Received, Package Acceptance Pending" or "In Transit, Arriving Late" please know that your package is still in transit. We have yet to see any packages be lost, just extremely delayed.

Ammon and I are shipping in-stock items within 6 hours during weekdays. Our UPS and USPS pick-ups are usually early in the morning, so items placed after 9am EST may not ship out the same day. UPS pick-ups are M-F and USPS pick-ups are M-Sa (not including holidays).

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Ammon and I are shipping in-stock items within 6 hours during weekdays. Our UPS and USPS pick-ups are usually early in the morning, so items placed after 9am EST may not ship out the same day.

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We hope that you love everything you order from us, but we understand that when shopping online, occasionally returning an item is unavoidable. Other than the exceptions listed below, all unopened and unused items may be returned within 30 days of purchase.

To start a return, log into your account, find the item in your order history and chose the return option. After you submit your return request, we will then be in touch via email with return instructions and your RMA#. Items received without an RMA# will not be refunded and will not be returned to the sender.

The following items are not returnable for any reason:

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The following items have a restocking fee of 20%:

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Due to the technical nature of 3D printing, it is our policy to first troubleshoot any items that are thought to be defective, as we have found that usually other variables are causing the issue (settings, poor quality/damp filament, etc.) and most of the time we are able to resolve it through troubleshooting.

If, after troubleshooting, the item still isn't working, we will send you an RMA# to return the item to us and we will send you a replacement at no charge.

If an item is suspected to be defective, we ask you contact us right away, as after 30 days from your order date, you will have to go through the manufacturer to make a warranty claim.

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