Configuring Skeinforge: Tuning a new profile with the amazing Dave Durant!
Dave Durant’s latest guide to configuring Skeinforge is probably the most valuable post so far. This post tells us more about the nuts and bolts of his method for dialing in Skeinforge settings to get the best possible prints. What I like about Dave’s method is that although he’s using some counter-intuitive methods and assumptions, he’s clearly thought all of this through and got the results to back it all up. Once again, Dave!
This article’s the second of two on making up a new profile. If you didn’t read the first one, you probably should do that before reading this one. Or at least scan through it. Even if you’re not making up a new profile and are just trying to get an existing one to make nicer prints, you might find this useful.
WordPress.com tells me I’m close to 2000 words here - yikes! – but if you’re having problems getting nice prints and aren’t sure what to do about it, I think it’s worth wading through. You’ll be amazed at how much quality a Makerbot is capable of – I know I was, once I started understanding the calibration process.
The key to just about every aspect of dialing in a profile is being able to recognize when you’re getting too little plastic or getting too much plastic.
I’m going to try to avoid using actual profile numbers here because I’m using a 0.35mm MakerGear bighead nozzle instead of a stock 0.5mm MakerBot nozzle. Profiles with this nozzle are a bit different and if I just spit out numbers and you try to use them, you’re probably not going to get the same results that I get. That’s not to say, not even a little, that you can’t get fantastic prints from a 0.5mm nozzle – you absolutely can.
Enough talk! Here’s a picture of two 20mm calibration cubes taken from two different views:
On the top half of this picture, notice how the threads aren’t touching – you can even see down to the previous layers. The profile that made this cube isn’t putting down nearly enough plastic to make a solid print. If you put any stress on this cube, it’d likely crumble.
On the bottom half of the picture, it’s blob central. This object is supposed to be a nice, square cube (or 1/2 a cube anyway.. it’s 20x20x10mm). On the left side of this one, you can see how the threads aren’t nice and straight – they’re sorta wavey – because the extruder is pushing too much plastic into too little area and shoving the existing lines around. On right right side, you can see how this eventually makes the top bulge up. If you used this profile to print an object that required nuts & bolts or multiple pieces fitting together, you’d get pretty frustrated, pretty quickly.
(note that if you’re using a stock MakerBot nozzle, it won’t look like this – those nozzles, when the profile is wrong, tend to scape up and push around the extra plastic so you sorta get little chunks of goop in random places. It’s a bit of a trade off – the MakerGear hot ends are rock-solid and more tolerant of blobs but the MakerBot ones make a slightly smoother finish on top, when they’re really dialed in nicely. Both are good but they do produce different results. )
Test & Tweak
I had wanted to do a bunch of pictures for this article, showing a gradual quality improvement and ending with a beautiful print. Sadly, these really didn’t show up well. Black ABS in particular never seems to show up well for me.
So, instead of a series of pictures, here’s the end result you’re looking for. It’s not perfect but it’s not bad at all:
The big thing to take note of here is that the infill lines are nice and tight against each other without any plastic blobbing up between them. There is a small dip between each line which I could lessen by dropping the feed rate by another 0.25 or 0.5 mm/second but this is pretty good as it is. There are some gaps between the infill and perimeter noticeable on the right-side cube but that’s because my build platform is overdue for leveling – you can see it’s just fine on the left side.
The whole “Test & Tweak” thing is really easy to do. From the previous article, you should have a target layer height and width over thickness (“w/t”) that you’re aiming for. You should also have at least a general idea of the feed rate that you’ll be using.
To do the test & tweak thing, pick a starting feed rate (and, again, aim high here – better to aim too high than too low) and print out a cube. Once you’ve got the cube, take a look at the top of it and decide if the feed rate is too high or too low.
If the cube seems blobby, the feed rate is too low - raise the feed rate a bit; if it’s looking anemic, the feed rate is too high - drop it a bit. Print out another cube at the new feed rate, take a look at the top and tweak the feed rate again. Keep doing this until you’ve got yourself a cube that’s really, really nice.
How much you should tweak the feed rate each time totally depends on how far off the print is. If it comes out like the pictures up near the top of this article, the 2 views of 2 cubes, you’re going to want to change the feed rate by 10; those cubes are way off.
- Add to the feed rate if too much plastic is being laid down
- Subtract from the feed rate if too little plastic is being laid down.
I usually go by halfs when I adjust feed rates.. If it’s horribly off, I tweak by 10. Once I think I’m within 10 of the right value, I tweak by 5. Once I’m within 5, I tweak by 2 or so. Then 1 then 0.5.
You can go down to tweaking it by 0.25 if you want but any more than that is overkill, IMO. Other variables (ambient temperature, filament inconsistencies, how well X/Y rods are oiled, etc) can effect the print more than tweaking that much. If you can get it to 0.25, you’re going to be really happy with the prints.
This is another one I wanted pictures of but they look a lot better in person than in picture so you get words instead of photos. While the 20mm cube is printing, keep an eye on the surface of it.
If your feed rate is perfectly right or too high, the surface of the print (even if it’s still in the middle of the print) will look uniformly shiny.
If the feed rate is too low, it will not be uniform – there will be parts that look shiny and parts that look sorta dull.
This makes perfect sense, too.. Go back up and look at the 2 view of 2 cubes near the top of this post. On the top-right one where there’s not enough plastic being laid down because the feed rate is far too high, if you were to look in from the front of your ‘bot while this is printing, each of those identical lines would reflect light the same way and it would be nice and uniformly shiny.
On the bottom-right part of the picture where it’s blob city because the feed rate is far too low, it’s not consistent. Because too much plastic is being laid down, extra plastic is pushing up from semi-random places which causes the light reflection of those places to be different from the more normal parts.
Watching the print while it’s printing, especially once you get down to tweaking feed rate by 1 or less, is going to be enormously helpful in figuring how where to go next on the feed rate - if you get to the point where it’s all nice & shiny up until the last couple layers, you’re within 0.5 or 0.25 of it being perfect. If it’s fine until around mid-print, you’re probably within 1 or 2.
All that said, I generally ignore the first 5 layers or so unless they’re hugely, painfully obviously off. It’s hard to get the Z stage perfectly positioned at the start of a print and that can throw things off a bit. Once you get 5 or so layers done, it will have worked out any of those types of issues.
One thing I learned pretty early in my calibration cube printing days is that with each cube taking 10-15 minutes to cycle through, from starting the print to starting the next print, plus eating and sleeping and answering the phone and maybe a tasty adult beverage in there too, it gets hard to keep track of what’s what.
The easiest & simplest solution to this, at least for me, was to use a razor to carve a roman numeral into the side of each cube when it finishes printing and notes on a piece of paper (or some text editor) the details for each cube.
You don’t have to use roman numerals if you don’t want to but it’s a lot easier to carve I, II, III, IV, etc into a cube than 1, 2, 3, 4. Or use a Sharpie, as long as you’re sure it won’t smear or fade or anything like that.
This doesn’t need to be anything fancy. When I dial in a profile, I just scribble the layer height and w/t at the top of the paper then have lines under that like “I = 33″, “II = 34″, etc, noting the cube number and the feed rate it was printed at.
Once you get close to being dialed in, this will make things a lot easier. You’ll be able to just check out the top of the cubes for too much or too little plastic and make a quick decision on how much the feed rate needs changing.
Infill Solidity = 1.0??
Any time I suggest printing calibration cubes, I say they should be printed with Infill Solidity set to 1.0, which is 100% solid. Fairly frequently, people look at me funny (yes I can tell, even when it’s via text) and say that they never print over .15 or .25 solidity so why waste time & plastic turning it up to 1.0?
The bottom 2-views-of-2-cubes cube shows a bit of an extreme example of why these cubes should be printed at 1.0. If I had printed this one at a lower infill, skeinforge would have left hollow bits in the object and those would have given all that extra plastic somewhere to go – it still wouldn’t have looked great but it wouldn’t have been as horribly wrong as what you see in this picture.
On the surface, that might sound like that’s a good thing – if it hides problems, why not turn the infill down and be happy? The answer is that it probably is fine if you’re never going to print anything more complicated than a calibration cube.
Once you tried a more complicated print like something with some large flat areas and some smaller/narrower areas, you’d run into trouble – you’d either get too little plastic (like the top picture) on the big open areas or you’d get too much plastic (bottom picture) on the smaller areas. Only with a profile that puts out the correct amount of plastic will you be able to handle both types of features in a single print.
So, moral of the story, set Infill Solidity to 1.0 when you’re printing calibration cubes. The goal is not just to get a little cube that looks good – it’s to find the right combination of values that will work at any infill setting…
I know that’s a lot of words and hope you didn’t “tl;dr!” this and jump here to the end. I also know it’s a fair amount of work to dial in a profile but once you go through it a couple times, it really does go pretty quickly. You’ll also, hopefully, get a better feel for skeinforge, which isn’t nearly as complicated as it seems, once you get a handle on the basics.
I really can’t over-state how much your prints can improve if you’ve never really sat down & worked on a profile and go through this test & tweak process . The time & plastic investment you make here are well worth it. Really.
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