Category Archives: Printing

Marlin – Auto Bed Levelling

A great feature was added to the Marlin firmware last year and I’ve finally gotten round to implementing it on my printer.

There were quite a few hurdles to over-come including designing some new parts to make it work.

I wanted to re-design the whole X – axis for my Mendel-Max as the clamps for holding the X – axis rods were poor and the belt being outside of the 2 rods meant there was a considerable amount of turning force on the parts, especially if you wanted tight belts.

So with the belt now between the 2 rods I had to completely re-design the carriage not only because the belt clamps had to be moved but I wanted to move to a direct-drive extruder on top of designing the probe arm to probe the bed!

With all of the new designs complete there were plenty of adjustments to be made to the firmware.  Moving to a direct-drive extruder meant new E – step / acceleration / speed settings. Enabling the bed levelling, setting up the servo including finding out which pin to assign to the servo for my PrintrBoard.  The biggest hurdle was discovering that by enabling the bed levelling filled the RAM on the PrintrBoard! To make the firmware fit I had to remove parts of the LCD menu.

After you have everything is working you need to set the distance from the hot-end to the micro-switch on your probe arm. Spend some time getting this as accurate as possible makes for the best result and only needs to be done once.

Has it been worth it? YES!

It’s great not having to adjust the bed manually, you can fine tune the distance between the nozzle and the bed in the LCD menu which is far more stable that any screw adjustments.

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Extrusion Calibration v2

After re-reading Triffid Hunter’s calibration guide I was specifically curious about the final comments about volumetric extrusion which makes sense as we are dealing with something that has volume.

You can read up on the process and the rationale behind it HERE

Put simply:

  1. Set the filament diameter to 1.128379 and never change it
  2. Set the extrusion multiplier to 1 and never change it
  3. Divide your E-Steps by 7 for 3mm filament or 2.4 for 1.75mm filament
  4. Multiply your E related speeds, accelerations and retractions by 7 for 3mm filament or 2.4 for 1.75mm filament
  5. In Sli3r multiply the Retraction Length and Retraction Speed by 7 for 3mm filament or 2.4 for 1.75mm filament

Multiply the E settings by 7 for 3mm filament or 2.4 for 1.75mm filament in the Marlin firmware in the following lines:

Configuration.h

#define DEFAULT_AXIS_STEPS_PER_UNIT
#define DEFAULT_MAX_FEEDRATE
#define DEFAULT_MAX_ACCELERATION

#define DEFAULT_ACCELERATION
#define DEFAULT_RETRACT_ACCELERATION

The only calibration you will then make is by altering the E-Steps.  You can alter this mid-print by either sending gcode M92 Ennn (where nnn = the new E-Steps number) or by adjusting it on the printer’s LCD control panel.

You can either calibrate the E-Steps by visual inspection where you’re looking for gaps in the infill at 95% and with no gaps on a solid fill or after slicing a single wall cube with no infill look in the gcode for the perimeter width, print it halfway and then measure the wall width.

 

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Extruder Calibration – [UPDATE]

Until recently I had not found a method of calibrating the amount of extrusion required for a good print which has worked well for me.

Well…. All that has change since I stumbled upon this post: HERE

Of course I calibrate the extruder stepper like most people do (see Slic3r is Nicer) but I still had to fudge around with the Filament Settings / Extrusion Multiplier and the Printer Settings / Advanced to get something that resembled a ‘nice’ print.

I would change the Advanced settings from their default, print something and then change again and again until the print looked right as I had never found a good guide for setting up Slic3r.

[UPDATE:

Since I’ve been using this technique for a few weeks I wish to share what extra bits I’ve learnt.

When Calibrating make sure you set the extruder to slow down when print time is below 0 sec.  I found it difficult to get a good calibration when the walls were made with a slow moving head so this makes sure the head DOES NOT slow down.

Set First Layer to 200% for good adhesion.

Set Infill to 125% to fill in any gaps in the top layer.]

So, from the “Solidoodle Tips” post I know that the Default Extrusion Width should be 1.4 times the layer height (eg. Layer height = 0.3 then Extrusion Width = 0.42) (0.2 = 0.28)

To then calibrate the extrusion:

  • Create or change your settings in Slic3r to use for this test:

Layer Settings: (click the picture for a larger version)

Layer Settings

Infill:

Infill

Advanced:

Advanced

Filament Settings: (obviously don’t copy my Diameter or temperature settings, just the Extrusion Multiplier)

Filament 1

  • Download / design a small (eg. 20 x 20 x 20mm or try this) cube.  Print with the settings as shown above.  We are trying to print a wall which is a single line of filament thick so minimum perimeters is set to 1 and Fill Density (infill) set to zero.  This will give us a single wall hollow cube.  Stop the print when it has printed halfway up the cube as we want to measure the thickness of the wall.
  • Measure actual printed wall thickness will digital callipers.
  • If you’ve printed at 0.3mm layer height this SHOULD read 0.42mm (the width you’ve told Slic3r to print).
  • If not (mine printed 0.55mm!!) then divide what it should be by what you’ve measured.  0.42 / 0.55 = 0.7636363636 for example
  • Copy and paste the total into the Extrusion Multiplier: (I rounded the number)

Filament 2

Print the cube again and re-measure.  If it’s still not quite right then divide the Extrusion Multiplier by the measured thickness, then times by what it should be.  (0.7636363636 / 0.44) * 0.42 = 0.72892561983471 for example.

I know this isn’t that straight forward but I wish I had found this method a long time ago!  Thanks go to Ian Johnson over at Solidoodle Tips, he’s got a great website there full of VERY useful information to help you with your prints.

Hope this helps, let me know if it does or if you’d like any further information. Thanks.

Printing

The First Print

Here are some shots of the first print.

Everything seems to be doing what it should, it’s a bit rough but I’m just happy that a set of bundled together parts can do this!

 

 

 

 

 

 

 

 

 

Printing some more

… and so it grows.  This is a 10x20x40 calibration block.  I think I need to sort my extrusion settings out though.

 

 

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Printing Parts

The printer prints a printer

This build was kickstarted (pun intended) by my fathers purchase of a Printrbot.  With his printer I am able to print parts for my MendelMax (hence the whole “replicating” part of the RepRap philosophy).

A few of the parts needed tweaking due to some different bolt sizes (M6 instead of M5 for the tapped ends of the extrusion).  This leads to being thrown in the deep end with programs like SketchUp, OpenSCAD, NetFabb and ReplicatorG.

With SketchUp STL files don’t come supported as standard and you need to install some extensions to allow you to import and export STLs.

Where SketchUp is a great visual CAD program where you can drag surfaces around with your mouse OpenSCAD is purely code based.  This leads to (depending on the code) a more simple and accurate control over geometric shapes and patterns.

After creating or tweaking STLs in SketchUp I’ve found the “Center” and “Put on platform” functions quite useful for aligning up your objects reading for printing.

Also, after some failed prints I started using the free / basic version of NetFabb as this program has a “Repair” feature which repairs any non manifold parts (breaks in geometry) which would cause issues with Slic3r which we were using to print the parts.  So in total this lead to a SketchUp -> ReplicatorG -> NetFabb -> Print work flow.

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