Introduction: Designing for Ponoko Laser Cutting With SketchUp and Inkscape (a Study in Cubes)
This Instructable will discuss the practicalities of the designs presented in SketchUp, Inkscape, and Ponoko Laser Cutting. You will be shown successes and failures (there's no point in making my mistakes - I can make enough for everyone).
I like to call this approach the "novice with a shotgun" research methodology. If you put enough pellets in your cartridge (lots of small designs) and stand close enough to your target (start with simple cubes) then you are bound to hit something. Hopefully you wont self harm in the process (see step 5).
My previous instructable dealt with the software side of creating Ponoko laser cut creations. The main tool being the open source SVG Plugin for Google Sketchup. This plugin exports to SVG, and Inkscape can then import the file. Changes can be made in 2D within Inkscape, and the result can be laser cut by Ponoko.
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Step 1: Unboxing
To make this an Instructable, and less of a postmortem, each step will feature instructions derived from my learning experience (you learn as I do).
Instruction 1a: Learn from my mistakes (and hopefully my successes).
Remember to peruse the previous Instructable if you haven't already, this one builds upon the designs already presented.
I was genuinely surprised that shipping was so fast (seeing as wooden materials can be delayed in customs). The package arrived in what appeared to be a recycled cardboard. Nice! Be green people... be green...
I ripped the package open as was greeted with the sight below... oh*...
After peeling back the protective and sticky layers that hold the parts in place - everything looked much prettier. I felt a moment of pride in my designs (and then I was brought back to Earth).
Instruction 1b: Don't judge a delivery on its packaging - It'll look pretty once everything is peeled away. Remain calm.
Step 2: 2D Design: FAIL! (and Then Save)
My first mistake was to not triple check my Inkscape design and make sure that all cuts actually joined.
Luckily a rotary tool and engraving bit was able to save the day. Engraving bits eat though acrylic and have a fine point for fiddly work. I was able to cut out the piece, and with a bit of filing, fit it into place. Not pretty, but effective enough for a proof of concept: see the pictures below.
Instruction 2: Triple check your 2D layout! If you can't be bothered: invest in power tools and a file.
Step 3: Interlocking Tooth Design
There were two aspects that I wanted to experiment with: the first being the material, and the second being the tooth fitting process.
The first picture shows the pieces cut from 6mm Eurolite ply wood. You may notice that each of the teeth bow outwards slightly on one side. This is to allow for the laser cutting kerf and create a tighter fit (also shown in picture 2, an Inkscape design).
Picture 3 shows the fitted ply wood pieces constructed into a cube. Picture 4 shows the same design in 6mm black acrylic. Picture 5 compares 3mm green acrylic.
If you don't allow for fitting and cut straight from the SketchUp design you end up with a functional cube, but as picture 6 shows, the pieces come apart very easily (not a problem if you are going to use glue).
Instruction 3a: If using interlocking teeth, allow for fitting in 2D or buy some glue.
As the video below shows, putting the pieces together can be quite tricky (6mm Eurolite ply wood is shown).
Instruction 3b: If required, label your pieces for faster assembly (or to account for personal stupidity).
Once the cube is constructed, you can see that it holds its form quite well. The fitting needs to be tweaked a little as the pieces do feel a little loose even though it is meant to be taken apart.
The next video shows the same fitted design used with 6mm black acrylic with the same effect.
Instruction 3c: The interlocking teeth design can be used with both wooden and acrylic materials for similar results (although ply wood is sooo much prettier).
In terms of aesthetics it is really up to the individual to choose the right material. I am partial to the ply wood as is gives a range of tones in the grain and also in the cut ends. I like the thin acrylic because it refracts light, but I'm not a fan of the black acrylic because it hides the joins and is flat; however, it could be quite effective if using etching to outline borders and add graphics.
Instruction 3d: Consider the joins, tones, light, and etching when choosing a material (i.e. what will look prettiest).
The cost difference between a fitted cube design ($4.95USD*) and unaltered cube design ($3.30USD*) is $1.67USD* (*pricing on 1st August 2008 for "making" costs using 6mm Eurolite ply wood). This difference is because the number of cut lines can be reduced with an unaltered design (pieces share common edges see picture 7). In terms of time, it is quicker to produce an unaltered design, but manually intensive to glue together. A fitted design takes longer to perfect in Inkscape, but takes the hassle out of construction (my preference).
Instruction 3e: Take into account the cost in terms of design time, construction time, and sundries like glue, as well as the laser cutting cost. The same design on different materials will also affect the laser cutting cost.
Before moving to the next design take a moment to inspect picture 8, the original SketchUp design. It shows that the SketchUp-to-Inkscape-to-Ponoko pipe line is working!
Step 4: Double Layered Slot Design
The internal parts of the cube don't need to be completely solid, and we can cut other parts from them (in this case to make up the flush faces). Picture 1 shows the cube assembled in 6mm Eurolite ply wood - notice the hexagonal and triangle pieces - they have been cut from the internal pieces that you don't see. The same design is shown in 3mm green acrylic in pictures 2 and 3 (pieces and partial construction).
Instruction 4a: Plan your 2D layout to reuse a maximum amount of material. Be green people... be green...
In addition to the slot joins, compression is also used to hold pieces in place - namely the hexagonal and triangular pieces; the frame around them hold the pieces in place. As picture 4 shows, the hexagonal pieces has been altered in Inkscape to bow the ends which come into contact with the triangular pieces; hence the compression.
When using compression, I found that the approach works much better with wooden materials rather than acrylic. See what happens in the video below when I squeeze the acrylic cube. Also see picture 5 for a close up of the same 6mm black acrylic cube.
Instruction 4b: Compression fitting techniques should only be used with compressible materials - such as ply wood - duh!
Unaltered slots in this design produced the following result in 3mm green acrylic. (See picture 6 for an altered/fitted slot in Inkscape)
As you can see above, the slots for the frame are passable, but not allowing for the fitting of the hexagonal pieces was a mistake, and the smaller pieces simply fell out of the cube. As you can see, the cube is also too easy to pull apart.
Instruction 4c: Fit your slot joins and pieces relying on compression in 2D (or buy some more glue).
The final video shows a combination that actually works. Ply wood + fitted slots + fitted compression pieces = pretty cube. I love the sound as everything clicks into place.
Again, aesthetics are an individual issue, but my preference is for ply wood once again. The slotted joins form great patterns, but I'm not thrilled with the gaps that the bowed hexagon creates. The black acrylic really highlights gaps between pieces and pieces that are not flush.
From a cost point of view, the difference between the unaltered ($6.70 USD*) and fitted design ($8.07 USD*) is $1.37*; on the whole more expensive than the the previous interlocking teeth design, because there are double the cuts (*pricing on 1st August 2008 for "making" costs using 6mm Eurolite ply wood). The reason that there is a difference between the fitted and unaltered design is that there are eight curved cuts in the design (the hexagon). Both the fitted and unaltered designs have the same common edges that can be shared.
To illustrate how SketchUp visualisation compares to the final laser cut product, compare the following video (taken from the previous Instructable) to the video above.
The design pipeline works again...
Step 5: Screw-Together Design
I used 2M screws that were 12mm long so that they would embed half their length and fasten/ratchet against the face with the pilot holes. I found that using a 1.5mm drill bit I could screw into the ply wood and the hold was rock solid.
The video below shows the process sped up a little. I used a rotary tool, but I also experimented with a cordless drill and found them both suitable for the job.
Construction is fast, and 100 stainless steel miniature screws will only set you back $5-$10 depending on the exact specifications.
Constructing an acrylic cube proved to be quite difficult. I attempted construction in the same way as the ply wood cube, but the tapping was hit and miss.
Without a drill press it is quite easy to elongate and misshape a hole in acrylic, and tapping a misshapen hole provides very little hold. The other problem is that the acrylic is heavier and slides around more then ply wood (a jig instead of tape would have been better to hold the pieces together). I've drilled and tapped a variety of materials with hand tools, but never as small as 2M screws (which was my undoing). Picture 4 shows a snapped drill bit and a snapped tapping tool.
Instruction 5a: Evaluate the tools required for construction, and whether common or specialist tools are needed. Material choice can make a big difference.
I decided to try again with the acrylic cube (I had laser cut a spare), and this time just drill a 1.5mm hole and try fastening without tapping. To do this you need quite a bit of force, and if using miniature screws you need a fine tapered screwdriver. For the cheese head screws I was using, my multi-tool was perfect - sort of (see picture 5).
Instruction 5b: Thou shalt not self harm.
I did finally get the acrylic cube together (see picture 6), but I wouldn't describe it as successful (gaps and faces not quite square to each other). I wouldn't go down this road again without a jig and drill press.
In terms of cost, laser cutting for this design was the cheapest of all ($1.57 USD* using square holes, or $1.90 USD* using round holes). Cost per screw is 5-10 cents; 24 screws per cube is a little bit of overkill. (*pricing on 1st August 2008 for "making" costs using 6mm Eurolite ply wood).
Instruction 5c: Curves take more time to cut (and thus cost more) - don't use curves where they wont be seen (like when they are covered by the head of a screw).
Construction time with ply wood was negligible, just a few minutes to drill all the holes, and then a few more minutes to fasten the screws. Acrylic took forever. The actual design was very quick and no fitting was required in Inkscape because everything was joined with screws.
Aesthetically, I think that ply wood and metallic screws could be used to make some steampunk inspired creations. I don't think that acrylic is worth the effort with this design unless there was an underlying need for the material (e.g. moisture resistance).
To end on a good note, compare the original SketchUp design (picture 7) with the ply wood cube.
The SketchUp->Inkscape->Ponoko pipeline works once again.
Step 6: Conclusion
Having presented three different designs, different approaches, and different materials for making cubes, it is time to show practical application of this learning process.
The following pictures show a combination of the different joins used in the cubes. Also notice that as a side-effect of exporting from Sketchup, curves are actually approximated with lines. It is hardly noticeable to the eye, but it reduces cutting costs significantly.
What are the pictures showing? Well it's not quite finished (there are still pieces to be added) - but to give you a clue, the hole on top is a sound hole.
Instruction 6: Visit my blog - Flights of Ideas
O.K. That last instruction is optional.
Have fun designing your own creations - and remember to visit the previous Instructable for more information, and the SVG plugin website for all of the cube examples used in this Instructable.