Skeinforge 40+ volumetric calibration
Wednesday, June 8th, 2011
n this article I want to help you with SF40 calibration.
Main difference over older version is volumetric flowrate.
It basically means that SF counts how much of the plastic its should extrude for given layer height and width of trace (height*width*lenght = volume).
Most confusing on all this is to realize SF uses the length of filament which goes in instead of extruded thread which goes out. For that you need to set your e_steps_per_mm in your Firmware to count with filament instead of extruded thread. And I’ll show you how.
Tools you need:
- Some permanent marker which can make visible marks on your filament
- My RepRap calculator http://calculator.josefprusa.cz/#ExtrusionSF40
So how to do it?!
- Set your e_steps_per_mm to some nice value. Lets say 50. You can do that either by re-flashing FW or simply by sending “M92 E50” G-code (Works only on tonokip based FWs = Tonokip, Klimentkip, Sprinter, …) (See note 1)
- Heat up your nozzle to temp you normally use for the print. (Or you need to remove nozzle. But we are lazy, right? Or atleast I am :-D)
- Find the speed at which it can safely extruder without skipping steps. E.g. hit the extrude button in Repsnapper, if the filament extrudes, you are fine, if not, reduce speed.
- Mark some length on the filament with the permanent marker and calipers. I use 3cm, but longer it’ll be more it will reduce our measurements error. Then mark another segment right after the 3cm one. Let it be 1cm, this will later be used for validation of our new settings.
- Extrude just enough material to get the first mark on filament aligned with intake of extruder.
- What we will do now is extruding of the marked 3cm. So hit extrude button as many times as it needs and count how many times you pressed the button. DON’T CHANGE THE EXTRUDED DISTANCE DURING THIS. (You actually can, see note 2)
- Now we have all the info we needed to count our new e_teps_per_mm 🙂 Which you can count ( (extrude button clicked times)*(extruded lenght per click in host)*(e_steps_per_mm we set ) ) / (marked length on filament in mm we have ) Or you can use interactive calculator athttp://calculator.josefprusa.cz/#ExtrusionSF40 Explanation: ( (extrude button clicked times)*(extruded lenght per click in host)*(e_steps_per_mm we set ) ) Counts how many steps we used to extrude our marked distance on filament. When you divide it by the distance in mm, you’ll get number of needed steps per mm.
- We should test the new e_steps_per_mm. So send “M92 E???” to your printer, where ??? is the number you’ve got from calculator.
- Now we want to move the filament for exactly 1cm (we marked it before) so do it in your host SW GUI. For example in Repsnapper set distance to 10mm, and speed somewhere around 60. If it’s exactly 1cm, you’ve won! “G1 E10 F60”
- This still doesn’t have to be exactly right. You’ll need to tweak it sometimes a bit. If the lines aren’t fused in solid layers, just add 5% to the e_steps_per_mm 🙂 It’s not rocket science 😉
Setting up Skeinforge:
- In dimension tab, set precise filament diameter. Filament packing density leave at 1.
- In speed tab. Set same Flow rate as feedrate.
There are few alternative ways how to do it. Best alternative is calibration script written by Nathan shipped with Kliment’s amazing Pronsole. Or araspitfire’s posthere.
You don’t have to change the e_steps_per_mm during the experiment at all, you just need to be sure what number you use now, and at the end use your number instead of 50.
Note2: You can use multiple distances during the 3cm lenght. What you really need to know after this is the overall length you extruded. But interactive calculator wont allow you to do this, you’ll need to use your brain and this formula ( (extruded distance in mm)*(e_steps_per_mm we set ) ) / (marked length on filament in mm we have )