Saturday, 13 September 2014

Cheats Parametric Design and Catapult download


Parametric Design is the generation of files from an initial series of variables. The pattern is described in terms of these variables and when the values are changed the whole design is adjusted. These variables can typically be used to store things like the material thickness and object size. Something like this tabbed box maker offers true parametric design but it's an extension that is written in python so you require some programming skills before you can write your own. For something like this mini catapult design where we only want to change one variable a full blown extension would be overkill so there is an easier way.

I spent a lot of time working on the variants of this catapult so forgive another post centred around it. When I scaled it down to half size a lot of the press fit joints no longer fitted together because the material was a little bit more than 3mm so I realised there was a quick and easy solution to changing thickness.

When the design consists of entirely laser cut parts you can cheat the parametric design process. When the catapult is scaled all the parts stay sized relative each other, so I created a version of the file where the material width is considered to be 1 unit. Any tab or slot that relates to the material width is 1 unit wide (in my case mm's). When I want to cut the item in a new material I take this base file and scale it by the material width. When I have 3mm ply I scale it up by 300% and I'll save that file and run with it, but if I get some thinner stock, say 2.9mm, I can go back to the base file and quickly scale it by 290%.


This trick only works for items where most of the parts are laser cut. It wouldn't work with something like my marble machines because the marbles are a fixed size and the holes to mount the motor need to have the right spacing, but it will work for some designs and it is a lot quicker than recreating the whole thing parametrically.

Here is the catapult file scaled and ready for conversion to your own material thickness if you would like to give it a try. I recommend something like 0.5mm nylon chord for the string to go with it, you can work out exactly the right length of the string by wrapping it around the notches in the edge of the board. (svg here)

Catapults, large and small can be bought from my shop
https://msraynsford.myshopify.com/products/catapult-kit