Tribed: a fully automatic bed leveling and tool height adjustment, with FSR and 3 Z screws

This post is the continuation of my preliminary analysis regarding bed tramming and automatic tool height adjustment. So far I never made the step to redo my bed, even though it was on my wish list for years. Now it is a reality :)

Early testing of the complete setup : starting with a properly calibrated bed,

corrupting it manually, and letting the system auto-calibrate it again.
A faster / realistic movement is here, since speed was not a concern above.

So why now? A few months ago, someone came and talked to me about his wish to design a new, open source, user-friendly printer for the prosumer market. Please check this as your opinion counts!

All in all, it was an excellent reason to realize my idea of a fully automatic bed leveling. And since the new printer will also be opensource, here is the work, design and my analysis. How nice: not only I was given the possibility, but I was asked to do so!

As said, this improvement is part of a longer effort towards a user-friendly printer, for more reliability and less manual tweaking. My Ultimaker itself may eventually be ditched one day. Huh. No, I am joking. Well.. unless the new one is really is obviously better... Damn, that's exactly what it is all about :/

Sensors and issues for automatic bed leveling and height adjustment

My printer eventually has a fully automatic and hardware bed leveling (aka tramming), and bed height (aka Z-offset). Yes, it now handles any tool height without any user action, in addition to a long-wished automatic leveling of the bed.
This is part of preliminary studies for a prosumer open-source printer, for which you are more than welcome to give your opinion! The entire bed structure was entirely revamped, as one important point in my former wish list.

Revised heated bed with automatic tramming and tool height compensation.

Since I wanted to document both the new bed but also why I wanted it this way, this first post addresses usual sensors and strategies used to deal with the bed calibration. The deal is to make a bed level and to start printing at a proper height, and there are many ways to do so, but not as conveniently as I wanted (which will be documented in a subsequent post). The second post will show more precisely what and how I did it.

Rollerstruder: a filament feeder / driver / extruder

The rollerstruder filament drive system on an Ultimaker

Almost one year ago I got rid of the plywood Ultimaker filament drive mechanism. It is an extremely important part of the FDM process as it pushes the (cold) filament towards the (hot) end. Any malfunction at this stage systematically leads to a bad print. So when not reliable, you have to stay close and react quickly to fix troubles, for example by feeding the filament further manually (btw check this if you are still doing it on an Ultimaker).

As for me, most of the trouble came from the old bolt that was shipped with my printer: it was grinding my filaments a lot, sometimes to the point it would stop moving completely and ruin the hour-long printable kalashnikov. It also lacked Bertho's addition of a ball bearing on the "idler arm", which soon became part of the official design.

In fact I just don't know about the new official drive mechanism (which seems way more reliable given the forum feedback), because I designed my own feeder that has to match my more efficient but unsual hobbed bolt. It suits me completely: months of intensive usage without a failure. And I learnt a lot of openscad and industrial design by the way.

Short belt tensioner for NEMA 17 stepper motors

How to tension the Ultimaker short belts once for all?

Upside version of the tensioner

The short belts that drive the main rods from the X and Y steppers must always be kept tight. Otherwise the print quality really gets bad. Two symptom that are easy to spot is non-round cylinders or "bouncing" waves in the surface of the print.

The usual fix is to unscrew the 4 bolts, push the motor downwards with a thumb and tighten the screws very hard while keeping the pressure...

I just could not stand this anymore, so I designed this thing and this derivative (with an additional spring).

Removable filament feeder : add a plug to the stepper motor cables

Add a plug to the extruder stepper motor cable !

The case slot design let me thought it would be easy to remove the filament feeder for transportation, good idea. But... did they forget that the stepper cables are going through the case with no way to unplug them ? Note that the unusual feeder itself is described here.

Heat sink on the stepper motors

Clean passive cooling on a stepper motor

Cool down your steppers : active or passing ?

For some time I was developing a new filament feeder, made out of PLA plastic, and finally, after a long print, I stumbled upon a feared issue : the motor gets hotter with work, and since it was over-extruding it got hot to the point it started to melt the pla around its screw mounts...