Polargraph Drawing Machine

Step 15 Assemble the gondola

The gondola is the pen holder.  There's a few alternative designs out there for them, including this 3D printable one that seems to do the business nicely.  My design is much heavier, and has a hollow centre so that the pen can always be in the exact point where the cords converge.  In practice, I'm unclear about how much difference this makes, but it makes me feel good.

I made the first one from corrugated cardboard, and a blank CD, stuck to some ball bearings (see the last picture on this step). Later I graduated onto some fancy-dan laser cut parts (available through ponoko), but the principle is the same.  I've attached the design in an EPS on a ponoko P1 sized board.

The parts just slide together, and then onto a length of brass pipe (see parts list).  The laser cut parts have nodes in them that will need a little filing to get them on. Just be careful because the acrylic is pretty brittle.  It should all push-fit together, but if it gets too loose, a few dabs of glue will keep it together.  I usually make these as a stack, and put a bead of glue around the tube before pushing on the very top-most acrylic ring.  This glued ring lets me handle it a bit more confidently when it's hanging.  It makes just as much sense to glue the big stabiliser instead.

The sequence is, from bottom to top:

1. Big stabiliser
2. Empty bearing
3. Spacer ring
4. Bearing with straight cord hanger arm
5. Spacer ring
6. Bearing with offset cord hanger arm
7. Spacer ring (this is the one I glue)
8. And a plywood ring as a decorative touch

Comments

[sleepybrett]

It might be nice if you had a photograph or a diagram that shows which parts go where on the gondola. From photograph #1 it seems like it the order is:
* plate
* empty bearing
* bearing with 'short arm facing up'
* acrylic spacer x 2
* bearing with 'long arm facing down'
* acrylic spacer
* wooden cap

Is this correct? If so I'm having a problem with non flat hanging on a vertical surface. Suggestions?

[Euphy]

Hi Brett, sorry it wasn't clear, you've got it right except there's a spacer between the empty bearing and the bearing with the short arm, and only one spacer where you've got a double.

The wooden cap is purely decorative. I usually glue the last spacer on the top so I've got something reliable to push against when I'm handling it.

I guess it is hanging tilted so that the pen is pointed downwards, and only the top-edge of the stabiliser is against the surface? I would fix this by installing the pen, and sticking some more blu-tack on the end of the pen until it balances. Alternatively, you could move the cord hangers onto the next bearing down - so the empty bearing was the top-most one. This will have the effect of moving the gondola away from the surface (which is why I haven't done it), but you might be ok.

Cheers!