Accuracy question


#1

Quick question. I know there’s been discussion of a ~1/4" variance in placement of a cut vs. how it appears on the camera. Correct?

My question is, what about multiple cuts? Say, I open a design, print it, put another piece in the same place, then print it again. I’m assuming that’s pretty precise, if it’s just following the same G-code each time.

In other words, can I expect the first cut to be up to 1/4" off from where it appears on the camera, but all subsequent cuts to be in precisely the same place?


#2

Yes, this works extremely well. You’re talking about using a jig, which is very accurate.

The first cut accounts for the discrepancy of the camera eye. Anything else you place into the hole created by the cut lines up perfectly. :slightly_smiling_face:


#3

That’s exactly where I was going. Thanks!


#4

Big caveat on that, though: the UI lacks any facilities for precision placement or repeatability (well ok, it has one, see below). So when it says “golly gee, something went wrong” and kicks you back to the home screen, you may have to start over with your design shoved into the upper left corner.

There’s one workaround where you make your SVG file the exact size of the bed and it will always load at 0, 0, although I can’t find the post… too much noise on this forum generated by people like me. But if you do that then you have to do your alignment by positioning the material in the right place.

I’m hoping that hopper item for just being able to type in numeric values for position and size will be done soon.


#5

Hi Jules,
Okay but how on earth did you print that grain of rice? Last time i checked the grains are smaller than the accuracy of the machine? :grinning:


#6

Zoomed way in. 500% (using Chrome) :grin:

I’ve always had better accuracy on the initial camera image than the secondary shot. (Basically I ignore that second one entirely.)

Every once in a while it can get a bit out of whack when they are working on it, but mostly I get pretty spot-on placement under the lens.

A lot of the alignment issues are coming and going right now. It’s going to be a different story in a few months.


#7

Ah okay right under the camera… I really think they are going to have problems around the outer edge each lens has its own distortion level and the only way to get the software to adjust would be to create a test pattern and compensate based on what the camera sees. Thanks for the information


#8

I’m already trying to work out how to plot the variation so I can get precise cuts the first time. Maybe put graph paper down on the bed and run several jobs where I pew through various intersections?

But then I figure somebody at :glowforge: has already cracked a computer vision book or six and will get there before I do. :slight_smile:


#9

Yes.

(My apologies to the many folks who have seen me post this link like a million times.)


#10

Yes. If exactly placed, should hit the exact same spot.
Just so you know, Glowforge does not use G-code.


#11

If you start out with an art board in your design program of 20" wide by 12 " high, the design will go in the exact same spot every time in relation to the full bed of the Glowforge. If your art board is any other size, it ends up in other places.


#12

My only problem with this approach (btw, ALL my inkscape designs are done on a 20" wide x 12" high storyboard), is that I can’t seem to place my material in the exact place needed.

The best that I’ve been able to do is to make sure the material is masked and then run the fastest and lightest score that I can to make sure that the design will land where I want it to, before doing anything that needs that level of precision.


#13

I have marked my lower left cuttable corner with blue tape (so I can replace it every time they make an improvement in the cut height increases) on the border of the bed. Technically not precisely able to repeat placement since the bed can move in the divots but when I use a target score I almost never need to move it in the GFUI more than one or two clicks in either direction.

If if were my permanent unit, I’d have a carpenter square cut out and attached to the black bed border with double-sided sticky tape so I could really lock it in vs matching a corner to the tape.


#14

Ah! Good to know. Probably hadn’t thought about the mechanism since late 2015 when we were all just guessing. :slight_smile:


#15

Do you have to draw a box around it or is just having the artboard size correct enough to trigger the magic?

Asking because in my limited playing around so far, the size of the document seems to be irrelevant and once I export an SVG and load it into the Glowforge app, it doesn’t show up as any kind of a box or boundary, it just uses the extents of the actual drawing. Maybe I’m doing it wrong.


#17

My plan is to use a 20x12 template for everything in Illustrator, and adjust for cuttable surface using margins. Then, as it adapts, I’ll just change the template.

The fun part will be when I start slicing larger designs into 11" or so at a time and try to link them together seamlessly. (Again, if :glowforge: doesn’t get to it first. :slight_smile: )


#18

Yeah, that makes sense. I’ll try the 20x12 trick when I get home.

I’ve made a few things where for example I know I have a 4" square object to engrave my design on, so I set the artboard to 4x4 in Illustrator and I can ensure it fits and the size and placement are good. If I want to bring that into GF and use the bounding box to align it with my material, I need to explicitly draw the box.

Nothing wrong with that, it was just non-obvious enough to me that I kept forgetting to do it.


#19

No, the artboard is enough as @jrnelson suggests. I use the front door to register larger sheets of cardboard and then cut out a place in the cardboard as a jig to repeat or even do one offs. It’s a little setup.

Using one of the corners for registration isn’t too bad. Try it out with some cardboard and get a feel for where the designs end up.


#20

But doesn’t that change depending on the height of the material in the bed?


#22

I usually call it the garage door. I hope we can settle on a name for this. Front access panel, front drop down panel, not really a doggie door, that’s the pass through slot. Well, at least a flatwork can get through. the two corners where it shuts against the case are pretty reliable registrations slots for a jig.