What happened here and how can I keep it from happening again?

This evening I cut some of the spikey bits for my knitting machine. My first run came out just as expected. I pulled that sheet and the cut pieces out, put in a new sheet of acrylic, made sure it looked ok on the screen, pressed the flashy button, then set about peeling the masking off of the first batch.
Then I heard a Thunk, which was the print head running into the lower right corner. I pressed the button to stop it, turned it off, and pulled the plug (which I always do anyway). That was at about 10:45 pm 3/14/21. Since it is really past my bedtime I didn’t do any further messing about.
So, why is the second one misaligned? I think I have printed one job after another before, but I am not positive that I have. Should you always go back to the dashboard before each print?
Thanks for your help.
This is what the Glowforge interface on my PC showed

This is what was printing

Most likely you accidently moved the head when you pulled the first sheet. That happens when the head thinks it’s in one spot, and it’s actually in a different one.

If you confirm the head is all the way in the upper back corner before opening the lid, and before hitting go it’ll never happen again.

If it’s not - don’t move it with the machine on.

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The head started in the back left corner as usual.
The job appears to have been printing about 4 inches towards the front and 2 inches toward the right.

The machine should “re-home” at the start of every job. For there to be this kind of offset, there has to be a bug in the algorithm that figures out where “home” is, or a problem with the hardware.

I’m assuming there’s a limit switch in the back left corner to tell the printer the printhead has reached that location. Perhaps one of those switches is sticky or (if optical) dirty…

The head finds home by placing the logo on the top of it under the camera at the beginning of each job.

You know, I knew that… duh on me. :slight_smile:

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Because I was removing masking and straightening my area, I didn’t watch what it did before it started, but it didn’t make any unfamiliar noises. I was using the top of the Glowforge for the unmasking so I was watching / not watching what was going on. The previous run of this same file, the Glowforge started at the bottom, which on this run would have put that part of the file outside the Glowforge. For this run, it seems to have started at the top. Sometimes I am amazed at what it comes up with as the easiest path - it will jump all over the place :slight_smile:

The machine does NOT re-home the head before each job. It only does it on bootup after a power cycle - on power-up, or after an update is applied. Your UI will show “homing” during that time.

There are also no limit switches in the mechanism. It detects a stalled motor. Unfortunately, this also sometimes leads to the “bumped” error when it wasn’t.

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Today I moved the camera to the center under the logo, turned every thing on and the Glowforge did it’s thing. The first print came out great, I pulled that out, put in a new sheet of acrylic and it came out great as well. I seem to have had a one time issue.
Thank you all for the input!


Oh no, I’m sorry to hear you’ve hit a snag.

Often, when we see an offset this large, it occurs because the head was physically moved or accidentally bumped, which affects the current calibration. I extracted the logs from your Glowforge to investigate the print you reported trouble with, and it looks like the printer head did not start from the “home” position. The head may have been inadvertently moved or bumped while preparing a print.

I’ve extracted your logs to investigate further and can confirm your Printer Head didn’t start at home for the second attempt you performed on Sunday.

I’m glad to hear you were able to resolve the trouble by rebooting your Glowforge!

Should any additional questions or concerns arise, please feel free to create a new forum post or email us at support@glowforge.com!