Forums/Tutorials/Laser Cutting Tutorials & Tips

Laser-cut project box tutorial

Rich Decibels
posted this on August 09, 2011 22:14

Lately I've been learning about laser-cutting my own project boxes for the electronic gear I build.

The process took me a little while to get my head around, but now that I know what I'm doing, I'm hooked. The finished product looks great and works great.

For about the same price as I would pay for a generic plastic box from an electronics retailer, I can get my own enclosure made with every hole cut out perfectly and all the labelling included.

I use the tab-in-slot method as described in this popular Instructable [http://tinyurl.com/3me672n ]. This is required reading for anyone making laser-cut enclosures, in my opinion.

I thought I'd document my process of designing a case for a new project, as a real-world example of how to use this tab-in-slot method. I'm using 3mm frosted black acrylic and M3x10mm machine screws. The project I'm working on is called the Rich Decibels Dirt Filter.

1. Circuit schematic design (Eagle)
The Dirt Filter is a really simple circuit based on the output section of Ray Wilson's exquisite 'Weird Sound Generator' [http://tinyurl.com/58e46q ]. Here's the schematic I've used. (I'm using Eagle [http://www.cadsoftusa.com/downloads/ ] because it is free and good.)

image1_large.jpg

2. Circuit layout design (Eagle)
Once the schematic is tested and confirmed, it's time to figure out the best way to layout the parts. Laying out circuits is both a science and an art, it's all about balancing priorities. In this instance, my priority is to make the smallest possible finished product, so I've crammed all the parts into a tiny area. Here's my finalised layout.

image2_large.jpg

3. Arrange other components in 3D (Sketchup)
The circuit is squeezed over on the left. Immediately next to that is space for a 9V battery holder, and input and output jacks. Along the top of the board are the 4 potentiometers used to control the filter parameters.

To get to this stage I had to use a combination of Eagle and SketchUp, to help visualise all these components in 3D. Here's a quick render:

image3_large.jpg

All these parts are models of the electronic components I can purchase locally at Jaycar. I have modeled them fairly accurately (usually +/- 0.2mm) and I make them available (after they've been verified) in the Google 3D Warehouse [http://tinyurl.com/3c2aqtr ]. (The white rectangle represents the footprint of the actual circuitry).

4. Model suitable enclosure (Sketchup)
With the parts laid out in a logical location, it's time to build the box around them. This is a straightforward process of making a few rectangles and Push/Pulling them out to 3mm thickness (to match the 3mm acrylic I'm using).

Deciding on what size to make the case is a bit of a balancing act. My first priority is to make all the pieces fit within a Ponoko P1 sheet (181 x 181mm). I also want to make sure that there's room for the electronics. For strength, I try to keep slots and holes at least 5mm back from the edge of any piece so that also has to be factored into the dimensioning process.

image4.jpg

5. Add slots, tabs, dog-bones, kerf allowance
Now that the design is pretty well finalised, it's time to add the tabs and slots for construction. The details of this process are in the Instructable linked earlier, but here's an example of how I interpreted those instructions:

i) Lay out all the pieces in the same plane

image5_large.jpg

ii) Add tabs and slots at appropriate intervals

image6_large.jpg

iii) Add kerf allowance and dog-bone corners

image7_large.jpg

I use a figure 0.1mm for kerf [http://tinyurl.com/4xdqu4x ] which in my experience has proven to be snug, without being so snug it cracks things out. I checked the finished product with callipers and found the slots measure 10.05mm on average and the tabs measure 9.94mm on average so that's good enough for me.

I dog-bone all internal corners using the free Bezier Spline plugin [registration required: http://tinyurl.com/3d9bhxo ]. I arbitrarily chose a radius of 0.2mm which looks good to me. This is an optional step for a low-stress design like this, but is good practice anyway. Acrylic loves to crack on square corners.

6. Export to Inkscape (Flight of Ideas .svg plugin)
Next I export everything to Inkscape with the Flight of Ideas .svg plugin [http://tinyurl.com/4yfthjo ]. I start by making a copy of one face of each of the pieces. Then I arrange them so they fit neatly within a 181x181mm bounding box. I 'explode' everything so there are no groups and then export the whole thing, bounding box included, using the svg plugin.

image8_large.jpg

Finally, I take the svg file and copy the contents into a P1 template [http://tinyurl.com/3lsgr86 ]. At this point I also add the engraving details and then it's off to the Personal Factory to get cut! (I've attached my .svg file if you want to check the finer points.)

7. Finished!
Here's the finished product:

image9_large.jpg

image10_large.jpg

image11_large.jpg

image12_large.jpg

I hope this is of some help to you. I know I've glossed over a few details so feel free to ask me to elaborate on any of the finer points.

 

Comments

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Eric Hall

Thanks for sharing! The pointer to the tab-in-slot method was key. I just recevied my first Ponoko design this week, which was layered lasercut acrylic for a microcontroller. I'll use this approach for the next rev of that design, which will give me what I need for knob and switch mounting points. 

August 12, 2011 10:38
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Alvaro Aguilar

Hey thanks for the cool tutorial! You have inspired me, and even though I never used sketchup before, I tried it out for my first laser-cut project... 

I have something exactly like what you got on Sketchup (all the faces lying on a bounding box that is 181mmX181mm... However, when I export it to SVG, the strokes on some of my faces come out as red while others come out as blue... 

Do I have to change this manually inside of inkspace? 

Thanks

August 18, 2011 14:10
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Rich Decibels

Hi Alvaro, I believe that is a setting in the Flight of Ideas SVG plugin. There are different colouring options for lines depending on whether they are intersecting faces or defining face edges. I set all lines to blue in the plugin.

Hope this helps.

August 18, 2011 14:13
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Alvaro Aguilar

Thanks for the quick reply! Yeah I tried that but I figured those lines could be useful for other stuff... In the end, I chagned the colors in Inkspace and I am now about ready to order it! Hopefully it all goes well and fits together when it finally gets here (I've NEVER done this before, so there is a large room for error)... 

 

Anyway, thanks for the help!

August 18, 2011 14:32
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David Kavanagh

The problem I've had with Sketch-up is that it won't do true circles, they are polygons. A local laser cutter doesn't like that. Does InkScape have a way to clean those up (i.e. replace the polygons with true circles)? I like Sketch-up now that I've learned it.

August 22, 2011 07:19
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Josh Judkins
Ponoko

Hi David - I'm not aware of a way to easily turn polygons into true circles in Inkscape myself, but it's possible someone in the community will have a trick to do it.

Polygon-circles should cut just fine though - we have them come through all the time, generally from files created in CAD programs and imported into Inkscapde/Illustrator for final formatting.

August 22, 2011 07:46
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Eric Kort

Rich, great post.  Looking at the laser kerf data linked in your post, it seems that the approximate laser kerf for this project would be 0.2mm, with half of this presumably being "inside the line" and half "outside the line".  The tabs would then be about 9.9mm (10.1-0.2),  and the slots would be about 10.2mm (10.0+0.2).  That would be about 0.3mm of "play" between the tab and slot.  Looking at the images, it appears that could be about right.  Would you say you have about 0.3mm difference of size between tab and slot on average?

(I also note from the docs that the tolerances on the width of acrylic stock is +/- 10%.  Given that the fit of the tab relies on the width of the acrylic stock, 0.3mm seems like a decent bet to ensure the pieces actually go together).

December 05, 2011 12:34