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.

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.

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.

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...

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.

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.

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.