Calculating your feedrate to get awesome prints!

Use science to increase the quality of your prints! By finding the actual feedrate of your machine, and dropping that into skeinforge, you can get much better prints!

The DC motors used in the MakerBot are the cheapest possible solution to getting the torque you need to drive a MakerBot but they are DC motors so they don’t all run at the same speed. Speeds can vary from 17mm/sec to 32mm/sec. That’s a huge range and so it makes sense that each bot needs to be tuned. With the current default settings in ReplicatorG 23, we’ve been able to get great results by calculating the actual feedrate of the motors, changing that setting in Skeinforge from 32mm/sec to the actual feedrate and rocking great prints.

One of the easiest ways to get frustrating prints is by having a feedrate that is too fast. If you’re machine extrudes at 17mm/sec and you’ve got it set at 32mm/sec, the filament will get stretched as it comes out of the nozzle and stretched ABS wants to shrink and so you’ll get cracks. If you stretch the filament, you’re objects will get much more shrinkage in prints. My personal MK5 plastruder extrudes at 22mm/sec.

How do you calculate your feedrate? Here’s a way I’ve come up with that works.

1. Raise your extruder nozzle 100mm off the build platform. You can use the control panel to make this happen… or a ruler!
2. Get the plastruder to extrusion temperature. We keep it locked at 220.
3. Start the plastruder by setting the speed to 255 and pressing the forward button. This will make plastic come out.
4. Get a stopwatch ready. Most phones come with stopwatches these days.
5. Use tweezers to pull away the plastic from the nozzle as it’s running. Start the stopwatch at the exact same time.
6. Stop the stopwatch when it hits the platform.
7. Repeat 10 times. Ignore any results that vary widely and average them by adding them up and dividing by 10. You should have a number between 3 and 6 seconds.
7. Divide 100 by your number to get the mm/sec.
8. Drop that into skeinforge under the speed tab and try a print!
9. Win!

Here is another skeinforge tip that we’ve been playing with that seem to be very helpful in dialing in good prints. Up your travel feed rate to something like 40mm/sec. It’ll make the whiskers between objects much thinner. If you’re feeling adventurous, increase it to 100mm (untested!).