Help me with extruder calibration?

[RTLdan]

Hello everyone!
After finally completing my machine, working through my mistakes and getting it to actually print the first calibration cube (exciting moment!) I'm in need of some extruder calibration help.

I'd read through another post about printing the 20x20x10 mm cube, 0% infill, extrusion width .55, etc...

I've printed a few of them and here is my dilemma -
At 100% flow My prints actually looked fairly good, except that when measured with digital calipers the walls were were much thicker than the requested .55. I used the technique I read on the forums (divided .55 by my actual thickness and then used that as my flow multiplier... 86% in my case). With the newly calculated flow rate my wall thickness actually was coming out pretty close to .55, however the print visibly looks too sparse...occasional holes in the perimeters, and when held up to the light I can see through the cube in many patchy areas sort of like mesh. Tried Slic3r, Kisslicer, and Cura all with similar results.
What could cause this?

Also, I have been messing around occasionally with layer heights (switching between .2 and .3 mostly depending on how much time I have for the print) and it occurred to me that I have not thought about what compensation I might need to make between layer heights! What sort of other numbers should I be looking at altering when I change layer height?

I'm away from the workshop at the moment, but if it helps to see some cube pictures I can post them up later.

Thanks in advance for all your help!
-Daniel

[lordbinky]

Extrude into the air, and measure the filament thickness. Take that diameter and multiply it by .66, and that use that as your upper limit for layer height. You're trace thickness that is laid down by the nozzle should be between the nozzle hole diameter and the diameter of the nozzle tip, the trace thickness increases with lower layer heights. The trace width can also decrease with faster speeds, so you have to adjust extrusion width accordingly. Mostly these are generalized rules that you can compensate for with various slicer settings, that's why we like people to post all their settings when asking these kind of questions.

[RTLdan]

Hi Lordbinky!
Thanks for your reply.
Yes, sorry for not posting exact settings and photos. I was on my way out for a birthday and thought I would at least ask the general sort of question, but I definitely get how difficult it is to help without more info and pics. I will get some of those up after messing around more with the advice you gave.

For my reference though (because I have a hard time internalizing information without knowing "why")
where are we getting the .66 to multiply our extruded diameter by?

Thanks!
-Daniel

[lordbinky]

I explained it better here as to where that comes from : http://forum.seemecnc.com/viewtopic.php ... 740#p20724

In that thread they are right you shouldn't need to set you extrusion multiplier to anything but 1.0, if you need that for things to be correct there are several things you can try. You should try something like this fine tuning calibration http://reprap.org/wiki/Triffid_Hunter's ... ine_Tuning but when I tried that my default EZ-struder step value was trivially different. Another thing that does help in keeping your settings consistent is getting the filament diameter correct. You need to measure several places of the filament over a couple meters and use your average value. When you do each measurement you need to measure the diameter of the filament twice, take a measurement twist the filament 90° measure again and use the average of those two since the filament are not perfectly round. A tenth of a mm on your filament diameter setting can make a big difference.

Since you want to know why, here's a link to a post of more useful links

http://forums.reprap.org/read.php?178,2 ... msg-262485

enjoy studying