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May 23, 2019, 07:34 PM
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Preparing data for laser cutting

I've downloaded QTee and the Jetfire 20 plans from outerzone and would like to cut some of the parts using a laser cutter.

I believe my friend's machine is a GlowForge. He looked at the plans and said we should use Inkscape.

The QTee - I want to scale, so I can't buy a kit. The actual plan is very "noisy". Tons of very useful and necessary comments all over the place.

The Jetfire - there is a laser cut kit available but I've wanted to do a laser cut project for at least ten years, so, I'd like to try it out. If it doesn't work out, I'll buy the kit but at least I'll learn somethings along the way.

Anyway, for the QTee, I was thinking of importing the PDF into Inkscape, scaling it and then on a new layer, capturing the outlines of the items. Then scaling it. Then, I will modify the spar openings in the ribs, etc. to use standard size wood. Does this sound like a reasonable approach?

The Jetfire would be similar but without the scaling. Since the wing is a symmetrical airfoil, I'm tempted to put in holes so that I can use rods to assemble it.

It seems very advantageous to do tab and slot for the formers, for the bottom / top planking and the fuselage or at least some alignment features to make assembly easier and the model true. I would greatly appreciate tips on this i.e. how much to oversize the slot, what to watch out for, etc.

Thanks in advance.
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May 24, 2019, 11:07 AM
Team of ONE....or...Team Me
DeadTom's Avatar
Your approach seems to be a logical way of tackling this issue.
I had an original Q-Tee back in the day with a three channel radio from HobbyShack.

Good luck and keep us posted on your progress
May 24, 2019, 10:26 PM
If it flies, I can crash it.
rocketsled666's Avatar
If you want stuff to fit together seamlessly, you're going to need to remember to compensate for the GF's kerf. The laser beam has thickness. The cut will follow the centerline of the vector. So if the vector describes the outside perimeter of a former, for instance, the final part will be slightly undersized (by 1/2 the beam width).

The final artwork has to be vectors. The GF won't cut bitmaps data, it thinks it's a picture and it will only engrave (lower power surface etch).

A handy trick I have stolen from what you often see in kits, I add a small amount of text to the component to identify it. After you cut everything and it gets jumbled up, having the parts marked makes a huge difference. However, it does extend the amount of time it takes to complete the job.

The best format for the GF is SVG. But the GF doesn't handle text objects, they have to be converted to outlines.

I own a GF.

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May 24, 2019, 11:21 PM
Registered User
Thread OP
Thank you for the great insights!

How much is the kerf? Are we talking 0.1mm? 0.5mm? or?
May 25, 2019, 01:16 AM
If it flies, I can crash it.
rocketsled666's Avatar
I knew you'd ask, and I don't remember. But if your friend has one, he'll know where to go to find the info. But I pretty much ignore it. Sometimes I end up with a looser fit than I want, but a little gap-filling glue fixes the problem. There have been a few non-RC related things I've done where it mattered and I think I made a few test cuts and measured them with a caliper and adjusted based on that rather than depend on a number from Glowforge.
May 25, 2019, 05:51 AM
Registered User
Some pdfs can be already vector, just need cleaned up. In that case you just import/break them in your software of choice (mine would be coreldraw, yours may be inkscape or AI).

As for marking, use old cad plotter friendly ISO fonts on lower power. They are very quick to draw out due to not being outlines, just centerlines without any fills. (i come from CAD background and always used them for marking things on pen plotters, instead of using proper filled ttf fonts).

For filling i use superglue with bicarb soda+sawdust trick. Sawdust for wooden bits, just ca+bicarb for plastic.

For fit test cut two interlocking squares out of the material you will use for final product BEFORE you cut final product. Check fit and adjust accordingly.

Also, focus beam to the middle of the material, not the surface, that way you avoid tapered fit on one side.
Last edited by BaronPork; May 25, 2019 at 06:02 AM.
May 25, 2019, 09:38 PM
Neophyte hacker
portablevcb's Avatar
The Jetfire plan I downloaded is a picture saved in pdf format. That means you have to trace the lines and, IMHO, Inkscape is your best bet.

Now you get to trace all the parts you want cut. Just use the drawing tools to make the part outlines. I would not account for kerf unless you are going to measure the notches carefully when tracing (unless you take a lot of time to do it, you cannot trace to an accuracy of .005").

Once the parts are traced you make the number of copies you need (eg, six of the ribs) and then layout how you want them cut on the sheet of balsa (4x36 or 4x24). Consult your laser cutter for preferences with cut files.

Since you are going to change parts to make them tab and slot then think about wood sizes and the variance in wood thicknesses that you buy.


PS Inkscape does have a 'trace' function, but, it will trace every line on the drawing, including cross hatching, centerlines, etc. It is more time consuming to clean that up than to trace it by hand.

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