Sunday, July 5, 2015

CTC printer tuning

So I was printing some stuff on the new CTC printer this evening and found that it was printing a bit small. I tried printing a 50mm calibration square, and it was coming out 46mm.  Well that's useless.

So I looked for the steps/mm setting in the firmware and couldn't find it.  I tried forcing it with M92 X100 Y100 - no luck.

I tried loading the gcode into ReplicatorG and printing from there. Better, it printed 49mm.  Still not really good enough.  But it's weird that the same GCode would print differently.

Finally I looked into gpx.exe, and found that there was a s3g-decompiler python script. I ran that on the x3g file and examined the output, and discovered that apparently Makerbot's s3g/x3g files do the steps/mm calculations in the file generation, and the printer just moves the specified number of steps.

This seems pretty backward to me, it means that the x3g/s3g files are specific to a given printer. It's not really horrible but it's not what I'm used to.

So it turns out that I needed to create a custom machine configuration to get precise settings.  The X/Y/Z are pretty easy, the extruder less so.

I started with a calculation, 16 tooth gears, 3200 step per revolution, 2mm belt pitch, should have resulted in exactly 100 steps per millimeter. But for some reason, it didn't work out.

I eventually used a dial indicator (I gotta get a new dial indicator - the one I have reads in inches. I never EVER want to read anything in inches) and wrote some quick GCode to home, then wait 10 seconds between moving to +10mm and 0 repeatedly. This allowed me to zero in to within about a hundredth of a millimeter.

I did similar for the Z axis, putting the dial indicator underneath.

For the extruder, I wrote some GCode to just heat up, wait 10 seconds, then extrude 100mm of filament. I marked with a sharpie up 100mm from the inlet of the extruder, then let it go. It came up a few mm short the first time, after some adjustments it was fine.

In the end I came up with a config file for this printer that results in good prints:

And here's the file:
Put this in your GPX directory, then when running GPX, use a command line like this:
(gpx directory)/gpx.exe -g -c (gpx directory)/CTC.ini (gcode file) (output x3g file)

Hope this is helpful.


Tom Servo said...


what did your GCode file look like to extrude 100mm? I copied the GPX r1d settings from the source code into a machine .ini to start from. Then I wrote a small GCode file, of which the main line is:

G1 E100 F5

I had several attempts at it, until I dropped the feedrate that low, yet the extruder still seems to spin too fast, grinding the filament.

Thanks for any help.

John Ridley said...

I will check on this when I get home. Also I should post a new ini for this. The one I posted originally had retraction going extremely slowly and the printer would pause for several seconds while it did retraction and extension.

Tom Servo said...

Cool, thanks. It's mostly to get an idea on how to handle the feedrates. People talk about both mm/min and mm/s, but there is no information if and what. Say if I specify G21 Exx Fyyyy, without any axes, what unit is the feedrate in. Or whether the firmware discerns at will depending on the size of the number. Because all my CTC does is rattle when trying to get it to extrude a 100mm, whereas normal jobs print fine.

John Ridley said...

Tom Servo, I've just done a new post with up-to-date config files and everything for the CTC printer used with Slic3r. Figured you might be interested.

With a name like that, I suppose you must be happy about last month's Kickstarter. I was one of the contributors to the Digital Archive project back in the day, and I kicked in to the campaign in December. Keep circulating the tapes!

Tom Servo said...

Thanks for the update. I wrote a GCODE file a while ago to get it to extrude a calibration length of filament without freaking out and it worked out fine. However I'm about to retrofit an E3D V6 and a Smoothieboard. Hope that'll work out well.

The idea of the campaign was interesting, but I don't think something like MST3K in its original form would work again. Kind of like trying an 80ies action movie.

John Ridley said...

Cool. Well I'm excited, they have a fantastic new crew, and IMO making fun of bad movies just never gets old. Also it's gotten me back into watching the old episode again. Hi-Keeba!

New printer: JGAurora A3

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