Playing with Skeinforge

I ran into some user comments on reprap.org that stated the volume of plastic extruded per mm travelled did not change with W.O.T. This would mean that if you did two prints with the only variable changed being W.O.T that one of 1.1 would have a lot of extra plastic extruded compared to one of 1.9. So here are my results for exactly that:

The first photo shows the 1.1 and 1.9 W.O.T. prints side by side. It is obvious that the width of the plastic has changed, so I know that skeinforge is adjusting for my desired W.O.T. The 1.9 print shows a lot of blobs on the outer edge- this is because my perimeter flowrate ratio is higher than 1.0, done to compensate for a different W.O.T. A ratio may not be linear when changing the thickness like this...

The second photo shows a pereimeter of 1.3 and infill of 1.9 W.O.T. It is difficult to see in the photo, but the infill lines are not actually touching each other, implying that maybe skeinforge is usinge the extrude volume of 1.3 as a default across the whole print. I was hoping to print the perimeter on a fine W.O.T for accuracy and a high infill W.O.T for speed but I may need to rethink how I do this.

I will make some test prints next to see what effect changing the packing density variable has, I think I will end up homing in on a set of variables for working with one layer thickness, and have a subset of variables to change when I change W.O.T. I wish there was a way to save multiple profiles for printing PLA - I'll have to do some more searching.

First usable part, and more improvements

Today I tried to print the modular spool hub again- this time with the heated bed.

I first changed some Skeinforge settings based on what I learned yesterday - mainly turning on comb, and increasing my perimeter flow rate over operating flowrate to 1.15 from 1.10. I noticed a couple of the perimeter layers of my minimug were not quite fully atached, so the perimeter adjustment should theoretically help that. I also upped my width over thickness ratio to 1.5 in both skeinforge and repsnapper to hopefully reduce the printing time.

Speaking of the minimug, it may have been watertight, but it definitely didn't hold alcohol. I'm guessing PLA is fairly hydrophobic. Good thing I decided to use some cheap rum instead of the good stuff. I'm thinking that my printer should be called Kraken in honor of that...

I was running into some issues with the X axis skipping steps on the first couple of tests, so I readjusted the trimpot a few times, and also adjusted the tension in the X belt. It had become a bit loose over time. On to the printing!

Excellent! I didn't have to fiddle with any other settings than the 2 W.O.T settings in Skeinforge and the corresponding values in Repsnapper and it still prints well! The heated bed worked really well to keep the part stuck down. I used a bed temp of 55 C, although since my thermistor is taped directly to the PCB instead of the top of the glass the actual temp was probably a bit lower. A few quick squirts from a can of compressed air cooled the part quickly and allowed it to pop right off the glass. Now back to the drawing board to design up some of the crazy ideas I've been having for new parts.

Edit: changing the repsnapper settings doesn't actually change anything. I'm thinking that by changing my W.O.T. to 1.5 reduced the apparent amount of extra plastic being extruded. I will print up some more test cubes later this week to see what else needs to be adjusted...

Success!

I got some help on IRC yesterday with my issues of extruding too much plastic. It turns out there is a printer settings tab in repsnapper buried in the edit menu. This settings tab has info for layer height, width over thickness, and even an extruder multiplier. Once I changed these settings to match skeinforge everything fell into place. Here's a quick rundown of what I think are the important settings that is making this work for me:
Skeinforge:

• layer height = 0.3
• feed and flowrates = 25mm/s
• width over thickness (both in carve and fill) = 1.3
• filament diameter = 1.78 (measured directly with calipers)
• Filament packing ratio = 1

Repsnapper:

• layer height = 0.3
• extruded material width = 0.39
• multiplier = 1

I tried building a central disc of a filament spool holder and was having great success until it started lifting somewhere around halfway through. I should have known better than to try something that large (~80mm diameter) before getting my heated bed installed. But all the fill was looking beautiful and the holes were printing quite well.
I then tried printing my own version of the minimug since I figured it was about time to toast a successful printer. It came out quite nicely, although there are a lot of thin strings on the inside where the inner perimeter finished. I think I need to tweak with clip, and activate comb in skeinforge. There is also a vertical ridge along the side of the mug where the outer perimeter began each path. Despite all of this the mug is watertight, and I'll see if it holds scotch tonight. I'm thinking a mini shot of Laphroiag would make a great toast...

More calibration

I spent more time calibrating the settings today- I fine tuned the e_steps in firmware to give me a decent print, and then realized that my x and y step settings weren't yet right, making a 36.3 x 47.5 plate instead of 30 x 40. Doh. So I fixed the x and y steps, which screwed up the esteps again. I have read that esteps is supposed to be mm of filament INTO the extruder, and the same people have then said that in skeinforge you should set flowrate equal to feedrate. This results in WAY too much plastic being extruded. What settings besides esteps(firmware) and flowrate(skeinforge) control how much plastic is extruded?? Here is a shot of my before and after plates, with the esteps written in sharpie on them:

Mt current settings are 1000 for esteps, 25 for flowrate and feedrate, and a decent width over thickness ratio comes out at 1.3.

setting esteps for proper mm into the extruder is around 1406

Too hot...

I'd love to continue messing with skeinforge settings and printing more, but right now the temp in CA is about 90 F, which means my apartment is about 95 F, and the room with my printer setup is damn near 100 F. It's just too hot to be in there for more than 10 minutes without starting to sweat badly, and I don't want an errant bead of sweat to hit my RAMPS and fry it. I'll have to wait for the weekend when I can work in the morning before it gets too warm...

Printer regression

Well I haven't been able to print anything today. I messed around with skeinforge settings too aggressively and now none of my prints work at all. I worked through a few iterations but my work room got too hot (95 F) to continue. I was having big problems with even getting the first layer to stick to the bed, and when it did the individual strands were not sticking together to create a cohesive layer. I think I've figured out why things went pear-shaped, but will wait until tomorrow to test my theories.

Process for printing

Here's the process I use to make a print. I had some trouble figuring it out from other blogs and the reprap wiki.

1. Slice up an STL using skeinforge with the settings I want to try.
2. Turn on the printer, move the head away from the bed and start heating the nozzle to 185C.
3.  On the GCode tab of repsnapper, delete all but the first 3 lines of GCode from the box
4. Load the skeinforge GCode
5. Once the file is completely loaded, move the print head down so it is just barely above the glass bed.
6. Move the head in X only to get it off the glass bed, test run the extruder to make sure everything is working, then move back to where we want the origin.
7. Send a manual GCode G92 X0 Y0 Z0 E0 to set the origin
8. Print!

I suppose I should just add the origin GCode to my skeinforge preface code, add that to the list of things to work on...