Bed levelling

This is an excerpt from the Mendel90 build instructions, which are work in progress, but it can be applied to other machines.

The best way I have found to level the bed relative to the nozzle is to use a dial gauge mounted in place of the extruder using this clamp. If you don't have a dial gauge you can roll a rod or slide some film under the nozzle and feel when it is just touching.



The two pillars at the back of the bed have a washer under them to ensure the front can be made both higher or lower than the back. Those pillars are tightened and not adjusted. Front - back adjustment is achieved by adjusting the two pillars at the front. Left - right adjustment is done by turning the Z lead screws. Ideally there would be only one mounting point at the front as only three points are needed to mount a stiff sheet like glass. Having four makes the adjustment more tedious as they tend to bend the sheet and interact with each other.

Start by sliding a washer under the front pillars to set them to the same height as the back. Move the gauge or nozzle to the middle of the back of the bed. Note that level on the gauge, or nudge the Z axis to just touch your feeler. This is the level that we want the whole bed to be at.

Move to the back left corner and adjust the left lead screw to get the same level as the middle. Move to back right and adjust the back right lead screw. Moving the gauge all the way across the back should now read the same height.

Now move to each of the front corners in turn and turn the pillar until the height is correct. Lock them in place by tightening the top screws through the bed.

The whole bed should now be level but usually you need to repeat the procedure a few times due to the interaction of the four points.

Ooze free unattended start

Normally plastic oozes from the nozzle during warm up due to thermal expansion and gravity. It is then necessary to prime the extruder by running it for a few seconds to fill up the now empty barrel. Any oozed or extruded plastic then needs to be removed, typically with tweezers, before the build can start.

This procedure is inconvenient because it means you have to stay with the machine during the warm up sequence rather than simply starting a build and letting it get on with it. I discovered a simple solution which I now use on my Mendel and Mendel90.

I remove any filament hanging from the nozzle while it is cold and then start the machine and leave it. My software moves the nozzle to the front edge of the bed and parks it 0.05mm above the surface. It then warms up the extruder and the bed. As soon as the plastic starts to ooze from the nozzle it meets the relatively cold bed and sets. That seals the nozzle and prevents and more ooze. I leave the small gap to ensure the bed does not take heat away from the nozzle.

When the bed and extruder reach their operating temperatures the software waits for two minutes to allow the nozzle to expand to its full length, otherwise I find the first layer height is inconsistent. The extruder is then run for a couple of seconds to prime it before doing a rapid move 50mm along the edge of the bed to wipe it. It then lifts to 1mm and moves to the start of the build. I always start that with a blob and an outline.

Here is a video of the sequence on my Mendel90:



So now I can start my machines and leave them to do their own thing. I use Python scripts but it should be easy to do the same thing in G code. The technique works with PLA as well as ABS shown above.

ABS Fudge

Many months ago I put some HIPS, ABS and PLA in a jar of limonene. The HIPS dissolved completely fairly quickly and the ABS and PLA were seeming unaffected. I then forgot about it until yesterday.

The PLA is still completely unaffected but the ABS has become soft like fudge.

I assume that given long enough the limonene removes the styrene content from the ABS.

It looks like it is feasible to use HIPS as a support material for PLA and then remove it with limonene. Limonene isn't cheap though and it remains to be seen how much HIPS it can dissolve before it becomes too dilute.