ID students: Now that the semester's in full swing, you're hopefully covered in blue foam dust from executing projects in the shop. And while all of you are learning to use existing tools, eventually you'll run into a problem they can't solve, and you'll have to design and build your own tools. This can be something as simple as a jig or moderate hack that makes an existing tool easier to use for your application.
Here's an excellent example of this. Let's say that you need to cut vinyl tubing for a prototype. Sure, you can hack into it with any number of bladed tools from the shop's tool room, but you need perfect cuts, both across the tube and lengthwise.
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That's when you'd give it some thought, scrounge around for some cheap materials, and come up with something like this:
This was done by Pocket83, and he's provided a free template of the first cutter here.