I made a wall clock at the Fablab, and here's the story, in all it's glory, with all my mistakes, so you can learn from them :)
The clock dial
I got the idea for the dial a year ago. I explained it to my girlfriend, and she drew it by hand on a random piece of paper - she's really good at drawing, and I'm awful at drawing by hand :)
And then the drawing collected dust, in a pile of random pieces of paper on my desktop for a year. I think it might still be there. In the meantime I learned a bit about Blender - a free 3D drawing and animation tool (https://www.blender.org/features/). Two weeks ago my brain decides to remind me that there was this idea once about a wall clock. Luckily, as you can see above, I took a picture of the drawing last year, so I didn't have to go through the pile of papers on my desktop. Instead I searched my Google Photo library for "drawing" and the AI found it immediately - quite amazing. So I loaded the drawing into blender and started modeling the clock dial, using the drawing as a background.
In blender I also made a twelve sided polygon - each "corner" of the polygon corresponds to where the twelve numbers on a wall dial should be. On the drawing the twelve leaves aren't placed accurately, but in Blender I could easily drag the leaves and trunks I had modelled, so the leaves were placed correctly above the corners of the polygon.
I then converted the mesh to a path and exported it using a plugin that can export the path to SVG for use in Inkscape http://blenderartists.org/forum/showthread.php?282824-SVG-output-script.
In Inkscape I used the tweak tool to tweak the path - some of the leaves and trunks needed a little tweaking. Beware that the tweak tool modifies the entire path, and not just the part that you are actually tweaking. This can make arcs on the path less rounded unless you set the fidelity of the tweak tool real high - in my case it had to be set to 100 which is the highest it goes, and that takes a lot of compute power, so be patient when editing a complex path with the tweak tool.
Finally I drew a pattern on all the big leaves, and converted the line of the paths so they would work with the laser cutter (setting the line width to 0.02 mm). For the leave pattern I went with vector engraving instead of raster engraving, as explained to me by Liisa: ""vector engraving" - you prepare the "engraving" file like you would for cutting (line thickness 0,02 mm) - but instead of cutting through we will make the machine only score the surface following the vector lines. It's much faster and gives a different result than "raster engraving"."
To do this I needed to save the leave pattern and the dial path separately, into two identically sized pdf's, and "print" the two files on the laser cutter, one after the other. In the save dialog for pdf's in Inkscape, you can choose "export area is drawing" or "export area is document" - choose the latter one, making sure the document properties are the same for the two files. I only had one file, and just deleted the pattern, saved, undid the delete, deleted the path and saved - thus making sure the document was the exact same size. Actually what I did first was choosing "export area is drawing", and that was wrong - when I "printed" the two files the leave pattern was a bit off relative to the cut path - as long as I'll learn I'll make mistakes (it's a Beastie Boys rewrite of the original quote from their song "This is just a test" https://youtu.be/RLZOXw6RUqE?t=1m14s :) ). Even though it came out wrong It still looked good, and the pattern being a bit off, actually made it look like the leaves was bending a bit - an unexpected cool sideeffect. So I ended up making two wall clocks and gave one away as a gift :)
Why didn't I just use Inkscape all the way, using "trace bitmap" to get a path from the drawing or drew the path directly in Inkscape? I've tried using "trace bitmap" a lot of times before, with other drawings, and for me it only works with really simple paths. A drawing like the one of the wall clock, would create a really complex path, and editing the path afterwards would be hard. Moving the location of the leaves is also much easier for me to do in Blender than in Inkscape.
If you have some insights on how to do this in Inkscape, please share them in the comments below. As for drawing directly in Inkscape, I actually find it a lot easier to model in Blender.
I bought it here https://www.elextra.dk/main.aspx?page=article&artno=H17970, because then I could get it immediately. You can get them cheaper on the interwebs, and in lot's of different flavors at ebay. You can even buy high torq ones if you have heavy/large clock hands.
The Clock Hands
I didn't go with laser cutting for the hands - I think they will be too heavy for the clockwork I bought if I made them with the same material, and there's also less than 3mm to fit them on (height). Maybe I could get 3mm thick wood or plastic plates, but then I also wanted the hands to be rounded on the top surface, and finally I wanted to try the 3D printers (ok - it was probably mostly me wanting to try the 3D printers :) ).
I used my Blender model for the dial and "cut" of a trunk with a leave to make the hands. They are in a different layer in the blender file. I first made some long way to large hands, and doing that, I discovered that the center of mass of the hands, has to be where the hole is (the hole that fits onto the clockwork) - if it isn't, the hands will all to easily slide of the clockwork even if it fits nicely. So I remade the clock hands.
I had to reprint many many times because of the following errors:
Often the plastic suddenly lost the grip on the glass plate and bended up and caught the plastic comming out of the nozzle and thus completely ruined the printing pattern (I did apply glue on the plate before printing, I also calibrated the printer)
The plastic feeder was stuck because it had grinded into the plastic in stead of pulling it through
The plastic wouldn't be all the wya out at the nozzle before printing started and thus no plastic was comming out (ghost printing).
I prevailed and got my clock hands in the end. I have previously modelled lot's of different things and used Shapeways (http://www.shapeways.com/shops/artificial) to get them printed, and it has worked really well, although it is a little bit expensive. Now that I've tried the Ultimakers at the Fablab, I must say Shapeways is worth the money - they of course have far more advanced printers there, so it would be unfair to compare directly with the Ultimakers. But with all the hassle I experienced, I wouldn't recommend printing models with small details unless you are prepared to use a lot of time on printing and finishing afterwards (polishing etc.). If you need a plastic thingy for some mechanical thing where the shape isn't "organic" but pretty straight forward, like gears or boxes with holes for a screw, etc. I think the Ultimakers can be exellent. They worked quite well for the clock hands, when the printing finaly came through, allthough details of the leaves was lost (I printed with the "normal" setting), and I had to grind the holes a bit before they would fit on the clockwork. I also printed a hand for "seconds", but to fit on the clockwork it had to have a tiny hollow cylinder 2 mm in outer diamater, 1 mm in inner diameter, and that was impossible to print with the normal setting, the Ultimaker just made a blop of plastic. I didn't try with ulti quality, as I was/am impatient :)
Thanks to the people of Fablab helping me out, it has been fun, and I'm already working on my next project - printing as I'm typing this actually :)