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Written by Austin

Category: Hardware hacking

Published: 26 November 2022

Hits: 32

Sort of what it sounds like: a Christmas Tree, but also a T-Rex. And naturally it's eating elves.

Source files: T. Rex Easy Print and Glue

Read more: Tree Rex

Details

Written by Austin

Category: Hardware hacking

Published: 15 September 2022

Hits: 114

For the uninitiated: 3D printers use 3D CAD files for their source data (sort of). Laser cutters are strictly 2D, and AFAICT there aren't any awesome modeling programs designed for making 3D stuff on a 2D matchine.

Fortunately, OnShape (free online CAD -- highly recommend) has a tool to make a "laser joint." This is maybe what it sounds like -- for two intersecting parts (like, slabs of wood) this will cut "fingers" so they can be glued together later. It's quick-n-dirty joinery in two dimensions.

So here's how to make an OK box:

1. Make a variable for your material thickness. For cheapie hobby plywood, 3mm. 1/4" works well too, but is a little heavy for a small box.
2. model the thing to its final shape: for a simple tea box, make a rectangle the size of the outer dimensions (so "interior + 2x thickness"), hollow it out and all that. if you want a lid, make a lid. Same basic rules. These are solid 3D parts.
3. Model the slabs from the faces: this is DEAD SIMPLE: in OnShape, extrude the outer faces by thickness. If you're doing it right, these slabs will all intersect.
4. Use OnShape's "laser joint" tool on the parts which will be glued. It can make single joints, or has a pretty good "automatic" mode which can do an entire glued-up part. For a box lid this might be 5 slabs all jointed and glued up. Twist the knobs, there's some good stuff in there. For the example tea box there are two laserjoint features -- one for the base, one for the lid
5. For each of the "slabs" (10 total): select the outer face of the slab an "export DXF".
6. Import those 10 DXFs into your favorite laser software (LightBurn) and go nuts. Feel free to put some pirates or creative text on there.

This works shockingly well, considering how easy it is. Boxes don't have to be cubes -- LJ doesn't require it. Just be sure you extend the parts if you're making weird joints, to keep enough wood in the joint. You also don't have to make a box; check out my snappy switch stand!

Details

Written by Austin

Category: Hardware hacking

Published: 25 August 2022

Hits: 152

• caterham
• seven

• what do you want to learn?
• risk management
• cost (budget), time (to build), scope / complexity: the iron triangle

General principles which can guide any project, can also be applied to tomfoolery like "making a car." Like if you're bored or something.

What do you want to learn?

Cars are complex and this might be a long, frustrating project. Figure out what parts you want to figure out, and what parts you'd rather just have ready-made. Some project options might be (say) "build an engine and put it in a mostly-working car," some might be "take a mostly-working car and build new frame around the guts," etc. Knowing where you want to directly contribute can help narrow the search for your next project.

For me: I wanted to learn the end-to-end assembly, but not new construction techniques. No welding, but start from 'scratch.'

Risk Management

There are a lot of potential risks with undertaking a biggish project:

• you're sending maybe a lot of cash to someone who might be hard to go strangle (figuratively)
• the thing-you're-making is probably rare, therefore hard to just... "test drive"
• what if you screw it up? Nobody wants to spend time and money failing
• what if the backing for your project... dries up? these things take time, companies come and go.

References go a long way here. Being able to find a working version can help get past the 'test drive' problem, and can provide some sense of stability for the supporting community. Having a community of people who have done this before can help ensure your support for the inevitable "why doesn't tab A fit into slot B" kinda issues.

Ditto, history can often -- but not always -- help assuage concerns of a company becoming insolvent along the way. Unfortunately this is probably a huge risk. Lotus keeps getting bought & sold, for instance. Westfield up and vanished. OTOH Factory Five have been around for a while and may stay. Exomotive supplies relatively little direct parts (or support) and may not really be required post-shipment.

For me: the 7 community is pretty well-supported, if you look hard enough. Density is relatively low, like 1 example per region, but they're out there.

Iron triangle: cost, time, scope.

In project management there's the concept of a triad of conflicting axes: cost, time, and scope are often selected. These tend to directly interact with each other: constrain time, and you may have to flex cost or scope. Specifically, you can do things faster in exchange for money (higher cost) or less things-to-do (reduced scope). Or, "more scope will increase time or money (or both)."

In "project car" space:

• cost is m-o-n-e-y. Less money almost certainly means more complexity or longer time... and you can buy lower complexity and faster delivery.
• time is calendar time, in two forms: time-to-acquire-stuff and time-to-build-stuff. Some projects can show up quickly (project car -> new car), some can take months or worse (kit from UK + JP + CN -> boxes in driveway). Assembly time can also play a role: some projects might be months or years of assembly, some maybe weeks. In exchange for potentially higher cost or complexity.
• scope is complexity. "Rebuilding a 30-year-old engine" might be fairly complex. "Designing an electric powertrain" might be very very complex. "Assembling a kit from reasonably well-understood parts" might be ... less complex. In exchange for longer delivery time and higher cost, of course.

I ended up with ~12-16 mos of shipping (partly because COVID / supply chain) and ~2 mos of construction. We're not talking about the cash, but a benefit of "this is a 2-year project" is that much more time saving up...