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Picture of Laser cut enclosure with living hinge lid
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This instructable shows how I made a laser cut box with a curved lid to house a wireless sensor node.  I made it at Techshop SF.  The node measures temperature and relays its measurements to a central logger so that I can plot graphs from the data.  The box needs a port for the antenna, good air flow for the sensor and it needed to be attractive so it can sit on a shelf unnoticed.

I did all my laser cutting at TechShop San Francisco.  It was my first attempt and 2 of the 3 boxes that I made worked out but one broke when I tried to bend the lid into place.  I tried 3mm MDF, aromatic cedar "laser wood" from www.laserbits.com and birch "laser wood" from the same.  The MDF cut and bent perfectly; the cedar burned quite a lot in the cutting (more on that later); the birch cut well but it was too thick to bend.

[Update] I've now improved the design (pictured) and it works perfectly with birch as well as the other woods.  See the final step for the updated design files.

Materials:
  • ~3mm laser ply or MDF.
  • 6 x 10mm M2 screws and nuts.
  • 1 x wireless sensor node (mine is my own design but a friend of mine has written up a very similar one, from which mine is derived)
  • 1 x laser cutter, I used a 60W Epilog Helix.
The design files and code are available in my github.
 
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Step 1: Designing the box

Picture of Designing the box
I had quite a good picture in my head of the shape I wanted the box to be.  I used Inkscape to create the design, working in "outline" mode so that I could set all the lines to be 0.001mm, as required by the laser cutter software.  

Here's how I built up the design (sorry for the lack of screenshots of the working):
  1. Set the file to be 24inches x 18inches, which is the bed size of the laser cutter I was working with.
  2. In File > properties add a 1mm grid.  (I prefer to work in metric 
  3. Draw a 6 cm square for the base.  I didn't worry about details like the screw slots at this stage.
  4. Draw half-circle for one side and extend down from the ends 1cm to give a flat portion; close the base.
  5. Calculate the required length for the top = PI * 3 + 2 cm = 11.5cm
  6. Create a rectangle of that length and 6cm tall.
  7. Using the grid snap, draw one copy of the living hinge pattern.
  8. Clone the pattern along the length of the lid.
  9. Using the path editing tool, refine the shapes, drawing in the pegs and T-slots for the screws.  I used a 1mm grid for 90% of the work.  For precise pieces like the T-slots, I selected nodes that needed to be "off grid" and manually entered the coordinates.
  10. Using the grid, draw in 2mm circles for the screw holes.  For the antenna hole, I used the snap toolbar to turn on snap to cusp and snap to centre and then let the centre of the circle snap tot he end of the line.  Then I used the path tool to edit the line to remove overlap.
  11. Finally, I added some rounder rectangles to the end piece for air holes and cloned the end piece.
Tips:
  • I was planning to cut different types of wood that have slightly different thicknesses and I didn't want to have to alter the design for each type so I made the pegs stick out past the end of the slots and curved the ends.  On a thinner material, they stick out a bit further but no matter.
  • I made made the pegs slightly wider than the holes (by 0.2mm) in the design to account for the kerf of the laser beam.

Step 2: The fun part: using the laser cutter

Picture of The fun part: using the laser cutter
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I used Inkscape to draw the design but TechShop uses CorelDraw to operate the laser cutter.  I found the only way I could get CorelDraw to read an Inkscape file was to export as DXF.  I exported as DXF using 1mm units and imported 1:1 using 1mm units in CorelDraw.  The design was automatically centred in the Corel document so I moved it to the top-left corner, which is the origin of the laser cutter.

I selected the whole design and confirmed the pen width was hairline, as required, then hit print.

Cutting MDF worked very well with close to the recommended starting settings.  However, I found that cutting the cedar ply was problematic.  The same settings that cut the MDF only went about 25% through the cedar.  Juggling settings, I ended up cutting the cedar 3-4 times before the cut went through.  This lead to a fuzzy cut with a lot of soot.  However, the widening of the cut made bending the piece a lot easier later on so if I go back with corrected settings I'll have to alter the design to widen the bending slots!

I cut the birch in one pass using the settings I'd worked out on the cedar but that made a very precise cut and the birch snapped when I tried to make the bend. (See the update in step 7 for my improved design that works well with birch.)

Step 3: Assembling the box sides

Follow the instructions in the images to assemble the sides of the box.

Step 4: Install the lid

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  • Feed the antenna through the hole in the lid.
  • Carefully bend the lid down symmetrically to avoid snapping the small pegs on the sides.
  • Hold the lid tightly in place while you install the remaining nuts and screws.

Step 5: Finished

Picture of Finished
Here's the completed article.

Step 6: What might go wrong

Picture of What might go wrong
Here's what happened to the birch ply lid with my original design when I tried to make the bend.  back to the drawing board!  (See step 7 for my improved design.)

Step 7: [Update] Improved design

Picture of [Update] Improved design
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Since only 2 of 3 of my first batch of boxes survived the bending process, I made a few different modifications to the design and cut them over the weekend.  One of the alternate designs worked much better.  The lid was very flexible, and I could even bend it round in a circle!

The main change that I made was to reduce the width of the zig-zags in the living hinge.  Before it was around 3.5mm, which was the width of the boards.  My new design uses 2mm for the width and reduces the number of central supports to 1 in order to give maximum bend.

I've attached my final Inkscape SVG file to this step. 

gmendez3 made it!7 months ago

Excelent design, I cutted out and it bended perfectly!! I use Inkscape too for all my laser cut designs, sometimes is anoying because almost all the laser cutter in Mexico work with dwg/autocad files, and in the conversion I loose sometimes the dimensions! Thanks a lot!

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putyn1 year ago

Hello great project, but i have one question im interested in building something using living hinge, but im not really sure how to calculate the spacing or the length of the cut lines. Can you give me more details on how you calculated them or its trial and error ?

fasaxc (author)  putyn1 year ago
It was trial and error. I think I shared the plans on the ible though so you can start with that. I think the bands were about the same width as the material was thick. The top of the boxes is very flexible, you can bend it much tighter than the box requires.
streetart1 year ago
This is good! But i can't download the file.
jhall303 years ago
I've found that I can save Inkscape files as PDFs (on the Mac), or export PDFs from Illustrator, and then "print" them from Acrobat Reader (on a PC, of course, as Epilog's driver doesn't support Mac OS). Inkscape (and Draw Plus) rasterizes when printing, so it is only useful for raster engraving on Epilog laser cutters.

Regardless of TechShop SF's use of CorelDraw, you don't need to use it. Printing from Acrobat Reader works just fine, as the Epilog driver mimics a printer driver, and can be used from any program (it must print a vector image to cut).

I did have problems importing some file formats to CorelDraw, as it appears you have found. Since I primarily work on a Mac, I am happiest just using PDFs for the actual cutting. The same trick works with Inkscape on Windows.

Beautiful work, by the way, and great instruct able. Now I want to find some reason to make one of these (or I could just make something pretty).
fasaxc (author)  jhall303 years ago
Thanks for the tip. Just to be sure I understand, you are saying that the Inkscape->PDF->Acrobat reader->Print to Epilog path does not rasterize vector lines, so it should work for both vector and raster engraving? (But if you just print from Inkscape then it rasterizes before printing so that's no good.)
jhall30 fasaxc2 years ago
Correct. Printing directly from InkScape rasterizes the image, while exporting to a PDF file does not. Acrobat Reader will then send the properly vector image when printing.
tytower3 years ago
This is a novel way but not very structurally sound.
saw kerfs on the underside 2/3rds the way through 1/2 inch apart would look better and finish better plus some epoxy glue added later upside down to the kerfs would make it strong enough to stand on
fasaxc (author)  tytower3 years ago
I quite like the aesthetic of the living inge. It's more than strong enough for my purposes. The plywood is only 3mm thick and the whole box would fit on your palm; I don't think cutting a "traditional" kerf bend, as you describe, at that scale would be easy.
Rob3113 years ago
do you have an instructable about the wireless network?
fasaxc (author)  Rob3113 years ago
Not yet. It's on my todo list. It's largely based on the one described by a friend at http://mchr3k-arduino.blogspot.com/ (search for Wireless sensor node, I think it starts in Jan 2012).
laserline3 years ago
FWIW: I cut quite a bit of 3mm ply. I find poplar bends far more readily than birch.
Kewl project!
fasaxc (author)  laserline3 years ago
I've updated the design with narrower zigzags. Now it works perfectly with all the wood that I've tried.
fasaxc (author)  laserline3 years ago
Thanks for the tip. I think I have some poplar ply as well (looks just like the beech).
sabu.dawdy3 years ago
this is a very lovely instructable . this will look awesome in form of jewelry box =)
fasaxc (author)  sabu.dawdy3 years ago
Thanks. I'll upload the design files to my github soon so people can base their own designs on them.
you are welcome :)
Informative and stylish, love it.
fasaxc (author)  The Cartographer3 years ago
Thanks.
jo_mo3 years ago
Well done. Got to make one too. In my experience using any plywoods can be a problem with these type of "bendy" cuts. I'm open to any suggestions.

Keep on with Inkscape. It's the future!
fasaxc (author)  jo_mo3 years ago
Yep, it was definitely hit and miss. Need to get my hands on some thin sheets of real wood.
Lorddrake3 years ago
did you try steaming the top cover to make it more plyable before attempting to bend it?
fasaxc (author)  Lorddrake3 years ago
No, I haven't tried steam bending. I'd be a bit worried that this sort of ply (veneered MDF) might delaminate or swell if I exposed it to water. Any thoughts?
veneered MDF will more than likely delaminate if you try to steam it.

I thought this was made from one of the solid woods you listed at the begining ( that will teach me to skim and comment lol)
fasaxc (author)  Lorddrake3 years ago
Unfortunately not, I'd like to work with thin planks of wood instead but I'm not sure where to go to buy such things. I bought my "laser wood" from laserbits.com.
lyaxovvv3 years ago
cool
fasaxc (author)  lyaxovvv3 years ago
Thanks!