Friday, December 2, 2011

Stay small my friends!

Having migrated from Skeinforge 40 to SFACT and print print a couple of small calibration objects things were looking up for SFACT.  The first printed object started okay, but as it came time to lay out the exterior shells of some small diameter holes Mach 3 began to stutter.

Initially it was thought the problem stemmed from an overly detailed STL file, which did help with the symptom, but not on every print.  In order to keep the buffer depth at a reasonable level print speeds were dialed back to 25 mm/s and even then there were problematic spots.  Which is real disappointing given it was printing smoothly before at 70 mm/s with out breaking a sweat.

As it turns out, the motion buffering algorithm in Mach3 gets a little hung up if there is an F parameter in a G1 instruction.  Comparing old SF40 to SFACT g-code, the old SF40 only set the the velocity every time it changed.  SFACT, and SF40, will add the speed to every line by default.  Turning on 'small g-code' in the export plugin removes the redundant F parameters.

With a queue depth hovering around 1000 and building almost instantly, things are back to their old screaming selves.  So keep your g-code small!

Thursday, December 1, 2011

SFACT impressions

Having a lot of time invested in tuning Skeinforge 41, I wasn't keen on trying something else.   Print quality still suffered a few issues, mainly hole dimensions, but the parts were strong and were very close to the intended dimensions.

A couple of months ago in #reprap on IRC there was some buzz about  a modified version of Skeinforge. Previous experience has taught me that the 'latest and greatest' is always the former but rarely the latter.  Having switched nozzle sizes and not wanting to go through the tuning process again it would be a good time to at least try something else.

SFACT installs the same as Skeinforge without over writing any previous profiles.  Made the same changes to the Skeinforge modules as outlined here.  Followed the directions from the SFACT webpage and was getting better quality prints out the door.  The author has really taken the time to go through all the python modules to understand how the myriad of ratio-metric parameters interplay and distilled them into a few, easy to understand and, intuitive parameters.

It is as simple as measuring the diameter of the extrusion, picking a layer height slightly smaller than the measured diameter and a width slightly wider.

For example;
extrusion diameter = 0.37mm
layer height = 0.34
width = 0.40

The only way it could be more simple is if it let you enter the measured diameter and then set a single +/- value for the height and width.

Take a quick measurement of the diameter of the raw stock filament and you're in business.

Can't emphasize this enough, you must use a very precise measuring tool like a micrometer.  Calipers don't cut the mustard for these measurements.

My recommendation on SFACT is simple.  Go get it!
Bookoo kudos to the developer(s)

Thingiverse - SFACT