Slow down, you move to fast. You've got to make the moment last.

Over the weekend I was experimenting with really really fast feedrates for my Thing-O-Matic. ¹  What I discovered was that if I start even a complex object off very slowly, I could run the Thing-O-Matic pretty darn fast. ²  The tricky bit was getting that first layer to print slowly enough.³

After some poking and prodding in Skeinforge, I found the settings here:

• Raft -> Object First Layer -> Object First Layer Feed Rate Infill Multiplier (ratio)
• Raft -> Object First Layer -> Object First Layer Feed Rate Perimeter Multiplier (ratio)
• Raft -> Object First Layer -> Object First Layer Flow Rate Multiplier (ratio)

I set each of these settings to the same value.  However, my target range was between 10 and 15mm/s.  So, I look the Feedrate from the Speed settings, and discovered that I would have to reduce my Feedrate to 30% of it’s normal speed in order to get within that range.  Thus, I entered 0.3 in each of the above settings.

The result was an almost agonizingly slow first layer – but a print that adhered well to the heated build platform, did not deform as the infill was applied, and provided an excellent base layer for the rest of the print. ⁴

1. Feedrate is the speed of the X and Y axes.  Flowrate is the speed at which the plastic comes out of the nozzle. [↩]
2. More on the speed stuff in a later post. [↩]
3. Photo courtesy of Jakob E. [↩]
4. If you’re curious, I was printing the 27-to-1 gear toy [↩]

Obsolete 40mm Cube Test Object by bre

As some of you may know, I’ve been working on a Skeinforge calibration projected called, “ProfileMaker.”  I released v3.0 last month over at MakerBlock.com. ¹  My goal was a web-based cross-platform easy-to-use Skeinforge setting calculator.²

Calibration by cube is essentially a trial and error process.  Print a cube, examine the results, take some notes, change a setting, and LRR³ until you have a satisfactory result.  There’s nothing wrong this this, but it is time consuming and can be frustrating.  ProfileMaker uses the same math and formulas as Dave’s Profileinator to derive the flowrate (or speed at which plastic comes out of the nozzle) based on the few settings you choose.  There are also some advanced options, for the more adventurous.

When you calculate some new profile settings, ProfileMaker will generate the settings and tell you exactly where to enter them in Skeinforge.  Or, if you wish, it can e-mail a zip file containing those settings as part of a complete profile.  Just unzip into your directory and start slicing!

As always, I’d appreciate feedback!

1. In that time more than 200 people have generated nearly 1000 profiles.  I see this as a good trend.  If people weren’t happy with the profiles they’re getting, they probably wouldn’t come back to generate five profiles on average. [↩]
2. In fact, if this isn’t the easiest Skeinforge calibration system you’ve EVER used, I’ll give you your money back! [↩]
3. Lather, rinse, repeat. [↩]

Another kind of feed rate

I’ve been a MakerBot operator for about 18 months now, and only just now am I really coming to understand Skeinforge’s nomenclature. ¹  Dave Durant did an excellent job of explaining the most important settings and terminology for Skeinforge in his series on configuring Skeinforge.  “Flowrate” is the rate of plastic exiting the extruder’s nozzle.  With a little math and science the flowrate is a function of the extruder motor speed and the volume of filament.  “Feedrate” is the rate of speed of the XY platform.  There are several different methods proposed on Thingiverse for configuring Skeinforge, and most of them involve solving for the proper flowrate or the proper feedrate for a given profile.

When using a MK5 or other DC motor powered extruder, there’s a very narrow range of reasonable flowrate settings.  The MK5 DC motors had a maximum speed of 255 PWM and a functional minimum of around 230-240. ²  Much less below 240 or so and the motor just wouldn’t turn.  The MK6 stepper motor extruder, on the other hand, has a much wider range of speeds – from around about 0.0 to up to about 3.0 RPM or so. ³

What values, then, is a 3D printer operator supposed to modify to get the best profile?

If you’re using a MK5 or DC motor extruder, I would recommend calibrating Skeinforge as you hold the DC motor speed at 255 and the maximum reliable flowrate you are able to obtain.  You’re going to want to adjust the other variables that are easier to control – the feedrate⁴ , the layer thickness⁵ , and thread width⁶ .  Since I like choosing my resolution and there’s not much choice in flowrate, I like to vary the feedrate since it’s easier to control.

If you’re using a MK6 or other stepper extruder the flowrate, feedrate, layer thickness, and thread width are all easily adjustable.  I prefer to choose the layer thickness and thread width, hold the feedrate at a level I know my robot can handle without problems, and vary the flowrate.

Here’s the interesting thing about solving for flowrate: the nozzle size ends up not being super critical.  As long as you’re choosing sane numbers for layer thickness and thread width, the amount of plastic going in will always equal the amount of plastic coming out.  While a 0.5mm nozzle would be capable of up to about 0.36mm thick layers and 0.75mm wide threads⁷ , these numbers might not make sense for a 0.4mm nozzle⁸ but could still work for a 1.0mm nozzle.

What settings do you like to vary when you’re configuring Skeinforge?

1. Photo courtesy of MadBuster75 [↩]
2. My understanding is that a PWM of 255 equates to about 2 RPM [↩]
3. A few disclaimers are in order.  You can set your RPM in the control panel to whatever you want and try to extrude – with no guarrantee it’s actually going to extrude at the mathematically calculated flowrate.  Additionally, the maximum effective RPM will be a function of the nozzle aperture. [↩]
4. XY platform speed [↩]
5. The thickness of each layer as it is laid down.  0.25mm/layer to 0.36mm/layer are reasonable ranges [↩]
6. This is the width of the filament as it comes out of the extruder nozzle. [↩]
7. Since they’re getting squished as they’re laid down [↩]
8. Since it would be tough to squeeze a 0.75mm thick layer out of a 0.4mm filament [↩]