How to Make Anything (Using Acrylic and Machine Screws)

Well maybe not anything, but what follows is an Instructable about how we at oomlout.com build everything we produce.

It is a technique we call Interlocking T-Bolt Construction. It consists of a T-cutout in one piece of acrylic (or any 3 mm stock) and a receptacle in another piece. These pieces can then be bolted together making a very secure 90 degree joint. A deceptively simple technique that has unlimited possibilities.

All that is required is an idea, some drawing software, and access to a laser cutter.

Lets get started.

(shameless plug)
to check out our delightfully fun open source products try visiting oomlout.com

a note on metric units
it should be noted that throughout we refer to 3mm thick acrylic. This is often sold as 1/8" acrylic and is not a big issue as the difference is less than 0.007".

Before we start a simple drawing programme is required. Something like Corel Draw, or Adobe Illustrator will work. But we recommend an open source equivalent, Inkscape.

To Get Inkscape:

• Goto Inkscape.org and download the appropriate version for your operating system.
• Install it.
• If you are new to Inkscape perhaps going through a tutorial or two before hand may also be helpful, but not required.

When designing anything its important to take into account the properties of your chosen production method. Here are a few things to keep in mind when designing with Interlocking T-Bolt.

Scale

• We think a good size window to consider using this method for ranges from about computer mouse on the small end to a loaf of bread on the larger. Of course other sizes are possible, but much larger you get into prohibitively expensive laser cutting costs, and much smaller you start having issues with bolt clearances.

Angles:

• This method thrives on 90 degree angles. If you would like lovely flowing curves or a bevy of acute or obtuse angles another method is advisable.

Corners:

• Acrylic is quite a hard plastic and as such sharp corners can lead to an object that feels quite rough and angular. To combat this we like to round all corners.

Strength:

• Here are a few rules of thumb we use when designing our products to keep them from being brittle. They have been arrived at through trial and error and are just guidelines.
• Minimum distance for a hole from the edge (5mm)
• Minimum holding run (ie. amount of acrylic to leave either side of a cutout (5mm)
• Bolt repeat distance. (ie. if you have a run longer than this an additional bolt should be added) (100mm)

There are only 2 shapes required.

The T-Cutout

• This is the piece the machine screw extends into, a nut catching in the large cutout portion.

The RCR Slot (Rectangle-Circle-Rectangle)

• The cutout the T-Cutout slots into.

To use, simply download the template attached to this step (03-TBOL-T-Slot Template.cdr for Corel Draw or 03-TBOL-T-Slot Template.svg for InkScape)

The Nuts & Bolts
Putting everything together is as simple as a single machine screw and matching nut. McMaster Carr is a great source for these.

• 3mm x 16mm machine screw #92005a126
• 3mm x 10mm machine screw #92005a120
• 3mm nuts #90695a033

Finally the layout.

To illustrate the process I'm going to use a simple little box I made to hold a little Nixie tube kit i have (pictured below).

Conceptulization:

• Moving from a 2 dimensional drawing to a 3d object is something that can take a while to get your head around. To experiment I recommend printing out the example below on paper and cutting it out with an exacto to get a feeling for how it all fits together.

The Process:

1. Import Template

• Import the template from the previous step which has the T-Cutout and RCR-Slot in it.

2. Draw the Base

• Draw the bottom of your object before positioning RCR-Slots. In appropriate places. Something that makes things much easier down the line is if you keep your object as symetrical as possible.

3. Draw the Sides

• Using loads of guidelines pulled down from the rulers position the T-Cutouts so they pair up with the RCR Slots.

4. Add Corner Cutouts

• You can see in the design below that half the height is removed from the end of each side. These are to allow the sides to nicely interlock.

5. Make the Cap

• Draw the cap. If your piece is symmetrical at this point the cap will have the same hole pattern as the base. Just add an appropriate cutout to it.

6. Laser Cutting

• This is something that only a couple of years ago would have been very difficult. However a bevy of cut on demand services are now available.

A Few Cutting Services:
Spikenzie Labs Mini Cuts - http://www.spikenzielabs.com/Store/Mini_Cuts.html - Montreal based and his prices include shipping (to USA or Canada) which is always a nice touch.
Ponoko - http://www.ponoko.com - A great group.
Big Blue Saw - http://www.bigbluesaw.com - Offers laser cutting as well as waterjetting more rugged materials. Which means any design can be rendered in 1/8" stainless steel if you so desire.

Complete:

• Well a bit of an over simplified process, but it is something that is best experimented with. If you have any pressing questions drop a comment below or send us an e-mail at info@oomlout.com

Sadly you can only build so much using just T-Cutouts and RCR-Slots. However one of the best things about laser cutting is if you have anything with mounting holes, and a pair of calipers, you can quickly draw up a mounting hole for it.

I've Compiled a file with the main cutouts we use in our products.

The Cutouts:

• RC Servo
• Mini RC Servo
• LED
• NEMA 23 Motor
• Skate Bearing
• MicroSwitch
• Arduino Diecimiela
• Pololu Servo Controller

(cutout templates available below)

... Endless.

I won't leave it at that. Attached are a few examples of things we have made at oomlout.com .

We'd love to see anything you make. If you make something leave us a comment below or send us an e-mail at info@oomlout.com. We'd love to share what you've done here.

Stuff Made By Others

Doug Eastman made a lovely little box for his still in development Arduino project. I think it looks great (photo below)