One of the things we're keen to stick to is repeat-ability (the other is, of course, a shoestring budget). So instead of expensive (and as a few people have pointed out, extremely accurate, precision-made) pulleys and belts, we're going all out with laser-cut acrylic and little, cheap stepper motors.
The previous platform we built was nice and sturdy, but during it's construction we came across a little problem. It's not a major problem, and can surely be remedied easily by anyone with the proper tools and a bit of time and effort, but it does stand in the way of repeat-ability. Basically, getting the two runners exactly parallel is a little bit difficult.
If the runners are not exactly equi-distant, along their entire length, the platform "binds" as it reaches the end of its travel in both directions. This isn't really a major project if the length of travel is kept to about half the total length of the bed (in fact, this is about the maximum we're expecting our bed to travel) but there's just something about the fact that it's so easy to mess this part up that we're not happy with.
So we're going with a much easier (and some would say, slightly shonky) design:
It's a single runner with the platform bolted along the centre-line. The single runner can be mounted onto a scrap of wood (exactly what we used here!) and it's not really important how square this mounting is (we mounted it along a centre-line along the wood for neatness, but it's not critical).
The only bit that's really important is getting the gantry mounts on the sides square with the runner.
BUT - having mounted the runner onto the board, the runner is fixed nice and securely. Using a set-square the gantry mount can be placed and fitted from the same side of the board. In our previous design, having to bolt everything together meant lifting the whole assembly up, and this is where things slipped out of alignment.
With this design, it's quite easy to get the runner and gantry at 90 degrees.
With the two gantry supports fitted, the top/cross piece just clips into place.
In theory, everything should be nice and square. Next we need to fit the stepper motors and actually get something moving to see if this design actually works ;-)
One thing that isn't immediately obvious from these photos is just how teeny tiny this little machine is. It's almost comical. In fact, a few BuildBrighton regulars have decided that it's not only comical but unusable - and have already started a book on how long before this design is abandoned and v3.0 started. We'll show 'em....
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