Can PRU borrowers make modifications to their machines? (evolved into camera focus and material height discussion)

I’m wondering about the policy regarding making modifications to pre-release units.

I’m guessing that destructive modifications (eg. “let’s cut a passthrough slot into this Basic machine”) are out of the question, but what’s the policy on reversible/non-destructive modifications?

I’ll start with a simple hypothetical situation…
Let’s say a PRU was shipped out and the recipient noticed a screw holding the shielding to the case was loose. Let’s say this screw was visibly sticking out a small amount, but obviously wasn’t affecting the performance of the machine. After the PRU user has filed a bug report, would they be allowed/encouraged to grab a screwdriver and tighten-up the screw? Would they be expected to wait to be told to tighten the screw? Ignore it / “deal with it”?

What about repairs to parts that aren’t working right?
“Oops, this thing is bent. I bet I can bend it back using a pair of pliars. Now that I’ve filed a bug report, the next.thing I should do is ___________________.”

I’m assuming I’m near the end of the PRU candidate list, so the answers to these questions won’t help me personally, but I’m curious about the answers anyway.


Are you about to slide down a slippery slope, hypothetical, of course ? :slight_smile:

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No. They’re our machines, and while we don’t put many restrictions on what customers can do with them while they’re borrowing them, we do ask that they not modify them.


So, with the (not affecting performance, non-destructive, reversible, easy to identify, and easy to correct) screw situation, the user would be expected to wait to be told to tighten it up? To put it a different way: anything beyond putting a ring around the button is verboten without the “go-ahead”, right? That is routinely my policy when I lend things out.

As I write this I can see that it could be coming across as a “gotcha question”. That’s not my intent. I’ve just been curious a couple times since the PRUs started being shipped and didn’t want to interrupt other threads to ask the question.

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Really worrying about the minutia. If you get a PRU, and if it’s somehow flawed, in a very specific way, are you allowed to fix it? Dan has already answered but for more clarity about the fix part. You have to ask before hand, they have to answer and give guidance, and surprisingly, even for something that was a simple tweak, the answer to me was no.


I had this exact scenario. Since the purpose of PRU is to debug production I specifically didn’t just tighten the screw, since clearly support needed to understand why a screw with blue-gunk came loose to make sure final production models don’t have this issue. I even ended up bore-scoping to see what happened on the inside since it was behind something so you couldn’t directly see if anything was loose, for support, and then at their instruction simply tightened it back up after all their debugging.


The lid camera on my PRU has a slight focus issue – annoying at times, but still usable. I took a little bit (ok, a lot) of kidding from other PRU users, because I didn’t just reach in and re-focus it.

Instead, I notified support and asked if they would prefer that I adjust the focus myself (trained astronomers are fairly well versed in focusing optics) or leave it as is as a test bed for any potential software/post-processing fixes.

They requested that I leave it as-is, so I have. It’s their machine, after all. :wink:

One of the a-ha! moments with my PRU has been realizing that the effective focal plane of the camera is set by the thickness of the material entered into the UI. If the target surface of the material isn’t in focus (after defining the material in the UI), you have an unmistakable sign that you may have mis-measured and/or mis-entered the depth. Also, the accuracy of optical placement of designs onto materials is directly related to the quality of the focus.


That was an “Oh!, Duh!” moment for me as well…a long time after I got the machine. I caught it when I was watching one of Marion’s demo videos.

It really makes a huge difference in placement accuracy too.


So now I’m confused. If ‘the effective focal plane of the camera is set by the thickness of the material entered into the UI’ then what’s autofocus got to do, got to do with it? Isn’t autofocus supposed to set the focal plane?


This is indeed very confusing, especially when you don’t have a GF to work with. Here’s the workflow for a simple GF job:

  1. Load design into GFUI

  2. Place material on bed

  3. Allow the GF to identify the PG and set the focal plane (or enter the material thickness for non-PG). The camera (software) refocuses to that plane and updates screen display

  4. Adjust the position and cut/engrave/score settings as necessary, then click “Print” in the GFUI

  5. At this point, the GF’s head will move over a single representative spot on the material (you have no choice in where), shine a red laser on the spot and measure the surface height/location/whatever. This is the single-spot auto-focus operation for the laser itself.

  6. Once the head returns to it’s resting location (rear left corner), the GFUI will report that it’s prepping your job. When complete, the GFUI will report the print time and report ready.

  7. The button on the GF starts glowing, and you press it. Burnination ensues.

As you can see above, there are two steps in which focus is critical – In Step 4, the visual/display focus is critical to the correct placement/alignment of the design(s) onto the material. In Step 5, the auto-focus makes sure that the laser focus is correct.


  • Lid focus is to aid the user in placement and alignment.
  • Auto-focus is for the laser itself.

Thank you!

Clear and concise!


My pleasure… You are going to love your :glowforge: when it arrives. It is a joy to use.


@dan why not have an option for the head to come over and measure material height if the user needs a more exact optical placement? Perhaps after step 3 we could select a location on the bed and have it come over to measure and get an updated bed image.


Excellent – very clear and easy to understand. Thank you.


It does that. When you hit print the gantry moves ‘roughly’ in the area that the op is going to begin and measures then. Then uses those values.


Yes but that is after you have positioned your work and design file right?


I believe adding an escutcheon to the button is the only acceptable modification (albeit a temporary one) :grin:

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Yeah, not sure why I tell it the height, then it focuses based on my determination. Then when I start the job (when placement is now fixed) only then it moves the head out and determines the “actual” thickness… Seems a tad weird.


I haven’t spent a lot of time examining the actual bed image but have read the overhead camera focusing claim a bunch of times. I know the S/W corrects the bed image based on your material thickness, but is the overhead camera actually refocused or is the lens a fixed focus? What I’m trying to say is that the overhead lens has a sort of fish eye view of the entire bed and based on the thickness you enter the S/W digitally corrects to give the best real world rectangular image possible. But I’m still not sure that focusing is involved. I guess I’ll have to play with a small pattern directly below the overhead camera and change the material height to see if it actually changes focus.

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It definitely has a mechanical focus ring, since support told me to turn it when it was too blurry to recognize PG QR codes when I got the device initially. Made a huge difference. Not sure if it has autofocus within a small range, and it was outside the DOF, or it is simply digital correction.