Introduction: Gunapult

After all the fuss of the 3D printed gun, I thought; Why not laser cut one?

I spent an evening and a morning doodling, prototyping, and generally redefining the meaning of the word "gun" until I came up with this.

Gunapult, catapistol, pistol catapult... call it what you want, but it works.

Don’t have a laser cutter, but want to have a go at making this?

Upload the ‘Ponoko ready’ design files at the bottom of this step to the Ponoko website and they’ll handle the 3D laser printing stuff and send it out in the post. Just make sure you select 3.2mm thick, 24x12 sized sheet of birch plywood. It cost me about $27 plus shipping.

Step 1: Designing

Almost the first thing I decided was that the catapult would not be elastic, but geared.

I found pictured of rack-and-pinion gears online and drew over them in Inkscape, then edited the throwing arm onto the gear, and extended the straight rack into a slider and trigger.

Test-cutting in card, I discovered two things:

  • Small corrugated cardboard gears fail under any sort of load.
  • The grip was too small and angular.

I was happy with the redraw I did, so I already began adding some simple graphics to the gun, and a hole in the grip in case you want to add a lanyard or wrist strap.

I have added SVG, DXF and PDF versions of my design for you to use.

If you have used Ponoko to make your Gunapult, you’ll want to click here and jump to step 3 and start gluing yours.

Step 2: Cutting Extras

I arranged the parts of the catagun as snugly as possible, but there were still spaces. Not wanting to waste them, I added circles sized to be just right as ammunition.

Although the gun fills half my cutter's working space, it's a relatively quick job, since there is no engraving, just cuts.

The pieces cut out at speed 20, power 65%, the decoration was done at 20/20%. To make sure the graphics stayed in focus, I set things so that the graphics cut first, before anything shifted when pieces came free.

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If you are using Ponoko-cut pieces, the pieces of plywood come with a protective paper backing stuck to it. Do not peel the backing off the middle-layers that make the butt and front of the Gunapult. Peling them from the trigger and the arm means they have just enough clearance to move freely.

Step 3: Oh, No, the Dowel Is Too Big - a Mini Instructable

Although I designed the Gunapult to use 6mm dowel, come the time to build it, I found I only had 8mm dowel in "stock".

Not a problem - I cut a short length of the dowel, fitted it into the chuck of my drill, and spun it against a file clamped in my vice.

Once it was down to the right diameter, a quick cut to length and we're good to carry on...

Step 4: Gluing

Being wooden, the whole thing is held together with ordinary PVA glue.

I glued the middle layer to one side first, pegging it in place, and then made a worrying discovery: there was a little too much space for the slider, which meant it dropped down from the throwing arm and the gears jammed too easily.

After a few seconds frustration at myself for forgetting that card and plywood lose different amounts of material when they cut, I realised that I could easily fix it with shims. Not shown in the photos, I cut two wafer-thin strips of plywood to make up the space and lift the slider up to the throwing arm. (If you are using Ponoko-cut pieces, you do not need to add shims!)

If you re using your own-cut pieces, don't forget to sand down the slider and arm a little before fitting in place.

I dropped the slider into place and glued on the second side, being very careful not to get any glue on the slider, or in the space for it to slide.

I pegged it again while it dried, then moved on to the pivot for the throwing arm.

Step 5: Pivot

The holes cut in the sides and the throwing arm are 6mm in diameter, purely because I had some 6mm dowel in stock.

Since the plywood is 3mm per layer, I needed a 9mm piece of dowel for the pivot.

At this point, I realised that there was some serious rain between me and the hand saw in my shed, so I cheated - I set the laser cutter to cut out a rectangle 9mm wide and cut a neat chunk out of the dowel.

Make sure the slider trigger is forward before you drop the throwing arm into place, then slide the dowel through.

The dowel needs a small amount of glue to hold it in place, but you need to be careful not to use too much, or you'll glue the throwing arm in place.

Step 6: Firing

Firing the gunapult is easy - just drop a disc into the lowered arm, then pull the trigger.

In the video, you can see the disc peeking out of the top of the gunapult, but it disappears rather quickly when I pull the trigger.

Comments

author
GarethC made it! (author)2014-10-09

Only recently acquired a laser cutter and wanted something fun to run through it that would take up the entire cutting area (for testing). The gunapult is a great little project, fun and will keep my cat (and me) entertained with flying things for hours!

Thank you very much for posting this! :-)

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Kiteman (author)GarethC2014-10-09

That's awesome, thanks for posting.

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GarethC (author)Kiteman2014-10-09

not as awesome as designing something like this and making it available for others to cut and play with! Little things like this make the world a much better place - thank you!

I posted this on my blog, pointing folks at your Etsy store:

http://blog.holozip.co.uk/post/99566991346/gunapult

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Kiteman (author)GarethC2014-10-10

Cool, thank you!

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Dreamchronic made it! (author)2015-02-02

We have a few kids in our family, so i made it for them. Had to make some changes because they're not strong enough to fire it with just a finger so it works like a shotgun (shotgun'o'trebuchet??:D).And Instead of gears i used a cord, after all it's made just from a cardboard. Thanks Kiteman! .)

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Kiteman (author)Dreamchronic2015-02-02

Wow, that's cool - you made so many modifications, you ought to write your own instructable!

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Victor Does (author)2014-10-15

Two great things in one! rubber gun and a catapult! Great work! :)

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shizy25 (author)2014-10-12

That's really cool!

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Kiteman (author)shizy252014-10-13

Thank you!

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nightninja87 (author)2014-10-10

awesome design i was wondering if there be a way to make something like this but as a rubber band gun

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Kiteman (author)nightninja872014-10-12

Have a look at JonnyBGood's KNEX version, that give you ideas.

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JonnyBGood (author)2014-10-08

Nice! I should make a K'nex one. =P

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Kiteman (author)JonnyBGood2014-10-08

Go for it - post pictures when you do.

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JonnyBGood (author)Kiteman2014-10-09

K'nex are very good for elastics, not so good at rack and pinion setups. I enjoyed this project a lot, its very amusing to use. Behold my doomsday gun of destruction!! And then a catapult comes out the top XD. Deffinitly a super villain weapon we have here.

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Kiteman (author)JonnyBGood2014-10-09

That's cool - are you writing it up?

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JonnyBGood (author)Kiteman2014-10-09

I may have too. Its just so amusing! I'll have to clean it up a little because I didn't have much time to make it as ergonomic as I wanted it.

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JonnyBGood (author)Kiteman2014-10-08

With pleasure, I'll probably get around to doing so this weekend. It'll be fun mess around with.

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nassau (author)2014-10-08

looks cool.

cant make it though :( My family doesn't have wood.

I know I can get at lowe's though or something.

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Kiteman (author)nassau2014-10-08

*cough*hint*cough*

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dwhite0 (author)2014-10-07

Have you looked at the pdf pattern file you made for us to download?

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Kiteman (author)dwhite02014-10-07

Fixed!

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abdullahsadiq7 (author)Kiteman2014-10-08

I was talking about that :P

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Kiteman (author)abdullahsadiq72014-10-08

:-p

;-)

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arnav chachra (author)2014-10-08

why there is nothing in PDF file except circle???

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Kiteman (author)arnav chachra2014-10-08

Zoom out a little - the circles are ammunition, fitted in between the parts of the actual Gunapult.

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ruisantos10 (author)2014-10-07

Very cool toy!! Also it was good to know you are a Scout too! I left them some years ago, but have been active since I was very, veery little. It's THE school of life ;)

Keep up the good work!

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Kiteman (author)ruisantos102014-10-07

Thank you!

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abdullahsadiq7 (author)2014-10-07

It looks very good but why does the PDF file not come complete for me ?

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Kiteman (author)abdullahsadiq72014-10-07

If you mean in step , I don't know.

If you mean the PDF for the whole project, you need to be a Pro member to do that.

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AndyGadget (author)2014-10-05

The video was a surprise; I was expecting a rubber-band type gun and then the catapult arm shoots out the top - Brilliant!

(And undetectable by airport security. Is that a Daily Mail reporter peering over your fence? Black helicopters on your shed roof? #;¬)

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Kiteman (author)AndyGadget2014-10-05

Nothing elastic anywhere, although I am thinking of redrawing the gears because they seem to bind or jam slightly as I put the arm back (are there any particular changes you might make to the gears [size, angle, number etc]?).

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AndyGadget (author)Kiteman2014-10-05

I'm no expert on gearing; you've no doubt done the research so know about as much as me. However I'm wondering about the trigger breaking when overenthusiastic users try to get maximum range. It looks a bit of a weak point. Finger blisters would be the other issue but a bit of padding would sort that. For the sticking, have you tried a bit of furniture polish?

author
Kiteman (author)AndyGadget2014-10-05

The gear teeth are the weak point there, they're only a couple of millimetres across.

Regarding blisters, I'd be more inclined to smooth the trigger (filing and sanding) than pad it, but that's my personal taste.

Thanks for the polish tip.

author
spark master (author)Kiteman2014-10-07

soak the gear ends in crazy glue to make them harder then sand them, and of course lube them, to make it smoother (perhaps). I have used the crazy glue thing on wood after my kid told me to try it. silly enough and safe enough for mot kids....not all or course ...

nice though.

cheers!!!

author
AndyGadget (author)Kiteman2014-10-05

One way to reduce the strain on your gears at the start and get a faster arm at the finish would be to have a spiral gear and ramped rack, so the ratio is lower at the start than the pull than at the finish. I doubt if it's practical here but may be worth bearing in mind. (Would that work? - I can't see why it wouldn't.)

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AndyGadget (author)AndyGadget2014-10-05

Like THIS (but not so extreme), only having one gear and the rack ramp matching the gear radius.

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Kiteman (author)AndyGadget2014-10-05

Oh, I see.

That could be interesting to try on a larger model.

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AndyGadget (author)Kiteman2014-10-05

Just looking at your photos again, and it looks like you've got aninvolute tooth profile on the pinion and a simple triangular one on the rack. May make a slight difference . . . may not.

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Kiteman (author)AndyGadget2014-10-05

The profiles are just copied from the image I found.

Leaving the gunapult with a gaggle of teenagers for an hour or so seemed to ease everything.

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M.C. Langer (author)2014-10-07

great job, Kiteman!

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Kiteman (author)M.C. Langer2014-10-07

Thank you!

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FernandoH (author)2014-10-07

Awesome! Great job.

Catapult!

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Kiteman (author)FernandoH2014-10-07

Thank you - slightly different scale, though...

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nerfrocketeer (author)2014-10-04

Awesome build, Kiteman! I plan to make one!

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Kiteman (author)nerfrocketeer2014-10-05

Don't forget to post pictures!

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nerfrocketeer (author)Kiteman2014-10-06

Ok, but I might take a slightly different approach to building! ;)

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Kiteman (author)nerfrocketeer2014-10-07

I'm looking forward to it.

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tkleinauskas (author)2014-10-06

Cool idea!

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Kiteman (author)tkleinauskas2014-10-06

Thank you!

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Antzy Carmasaic (author)2014-10-06

Time for a duel with gunapult and shotfun...

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Bio: The answer is "lasers", now, what was the question? If you need help, feel free to contact me. Project previews on Tumblr & Twitter: @KitemanX
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