Intro to Laser Cutting Course, September 2013

As part of my role as DoES Liverpool’s technician, I get to give introductions to new users to get them started with using DoES’s laser cutter. However, because it’s only an introduction I only get to spend an hour or so going over the basics when I’d like to spend longer and help them on their project in more detail.

So, to get around this, I’ll be running an introductory laser cutting course in Liverpool to help more people get started with using this technique for cutting their own designs. It’s a course for everyone; laser cutting is a very accessible process, and if you can use a computer, draw out a design and press the start button on the laser, then you can use a laser cutter.

Eventbrite - Introduction to Laser Cutting

21st September 2013

Would you like to get started with using a laser cutter?

Do you want to be able to produce your own designs and cut them on a laser cutter?

Then this course can help. You can book online now at defproc.eventbrite.co.uk for just £69.55 including materials. The minimum number of tickets sold for this course to go ahead is 1. If there’s an attendee, this course will run.

Starting from the basics of laser cutting and operating a hobby laser cutter, this course will take you through preparing designs for cutting or engraving to making your own items.

  • How a laser cutter works.
  • Cutting, line engraving and fill engraving,
  • Using Inkscape to produce cut-files
  • Material choice
  • 2D to 3D, joining and jointing techniques.
  • Concentrated help and support for protyping and refining your own designs

This course is much more in depth than the normal introduction I give to new users of DoES Liverpool’s laser cutter, so at the end of the day you should be proficient enough to come in and use a hobby laser cutter by your self.

Reading Strain Gauge Scales with Arduino

One of the smaller projects that I took to Maker Faire last month was a strain gauge reading circuit for Arduino. While the Arduino in the demo setup was actually redundant (the voltage input from the scales was output to a 5V dial gauge directly) there was also a circuit diagram setup to show how to use an instrumentation amplifier to boost the voltage output from the strain gauges in a set of supermarket weighing scales to a value great enough that the Arduino could read it as an analogue input.

One of the reasons I took this to Maker Faire UK was because I couldn’t find a guide to connecting strain gauges to Arduino that said “here’s the amplifier that you need, here’s how to connect it and here’s how to take readings”.

INA125P to Arduino
Breadboard layout for INA125P to Arduino

As I don’t have lots of experiences with OpAmp circuits I took the INA125P instrumentation amplifier, the same one as used in the Arduino Wifi body scale from Open Electronics. This is a 3 OpAmp amplifier as a single chip that gives high gain and low noise output that is designed to be used with measuring equiptment such as strain gauges. While you can roll-your-own instrumentation amplifier, using a complete circuit-on-a-chip simplified development while also giving a nice bonus of the on-board voltage regulator. Continue reading Reading Strain Gauge Scales with Arduino

Perceptive Radio Build Pics

I’m sure you’ve seen the write up from Mudlark and the blog post from BBC R&D about their new Perceptive Radio that localises content and adjusts playback characteristics depending on listener interaction. I was approached by MCQN Ltd as the electronics part of the radio was nearing completion and asked if I could help with creating an enclosure that would portray the project well as a radio-type device.

While I am expecting to get the clearance to open-source the case design the same way that the electronics and code has been, in the meantime I can show you some of detail that went into the case build and some of the laser cut parts that place the components.

The case internals
Showing off the case internals
showing the mountings under the fascia
The fascia hides the component mountings
Complete Case
Complete Case

If you want to see how the perceptive radio works, the radio play is available online at futurebroadcasts.com

Maker Faire UK 2013

This coming weekend, Maker Faire UK is at the Centre for Life in Newcastle. I’ll be exhibiting as part of the DoES Liverpool stall this year.

While I initially started going to DoES Liverpool, it was to get some hands-on experience with running a laser cutter, which would improve the work I was doing with the Atomic Duck. Since the start of this year, I’ve been working as the technician for the co-working, workshop and makerspace.

Along with helping users get started with the laser cutter and the 3D printer in the workshop, I’ve also been able to do some really interesting smaller projects too and I’m looking forward to showing some of those off at Maker Faire this year.

Included on the stand from me will be:

And new for Maker Faire:

  • A £6 Arduino-shield-compatible board based on the shrimping.it project (a £3 barebones arduino clone-on-a-breadboard).
  • The Doodlebot-Pro, a more permanent version of the pens+cup+tape+vibrating motor robot. This version has a laser cut chassis with 120 degree finger joints and integrated elastic clips so it can be assembled and disassembled in seconds.
  • An animated, 90 LED wordclock that is driven from 10 digital pins on the Arduino using Charlieplexing. Also there will be a demo circuit showing the charlieplexing schematic and the persistence of vision effect.
  • Arduino scales built using an instrumentation amplifier to get readings directly from the strain gauges in a commercial kitchen scales.

So What’s a Practical Laser-Cut Clip Size?

I’ve previously shown for laser-cut elastic-clips for comb joints what the equations are for calculating maximum bending stress and operating force, using the distance that the clip has to deflect in use as the starting point. I also explained how a tapering clip profile was preferable to a straight one. This time I’m going to share an example of a practical clip geometry that I’ve been using regularly to hold small parts together in 3mm acrylic.

While the clip is useful as a component of other parts, it’s helpful to see how it is used to make something practical, so I’ve also made a clip-together box that can be completely made from laser cut acrylic, with no other parts or tools needed. Both the clip geometry and the box are available on thingiverse for you to download, use and remix.

As a measure of how robust the clips that hold the box together are, we’re now also producing some Raspberry Pi cases using a derivative of the box design above. Manufactured in Liverpool, in the UK, we have some of the first batch available to buy in the shop now. (More on the Clip-R-Pi cases next time)

4 laser-cut, clipped-together, Rasspberry Pi cases
Clip-R-Pi, laser-cut clipped-together Raspberry Pi cases
Continue reading So What’s a Practical Laser-Cut Clip Size?

Laser-Cut Elastic-Clipped Comb-Joints

Comb-Jointed Box in Clear Acrylic
Comb-Jointed Box in Clear Acrylic. By Pete Prodoehl. Licenced under Creative Commons BY-NC-SA

During a makerday, I saw a someone struggling to put together a Raspberry Pi box that they’d laser cut, and were trying to hold together:

  • two pieces of acrylic to make the joint,
  • and the Raspberry Pi board,
  • and a nut into a slot,
  • while also attempting to screw in a bolt,
  • and not drop everything.

So I started thinking about if it would be possible to extend the work I have been doing on making flexible areas in acrylic to make a clip mechanism that could be laser cut to make self-fixing comb-jointed parts.

A comb joint (also called a finger joint) is a carpentry joint that has come to the attention of makers with the increasing accessibility of laser cutting. The finger joint can be used to make boxes from laser cut sheet materials (there are a couple of automated tools available including BoxMaker and Box-o-Tron). It is relatively easy to implement and the fitting of the crenelations gives much better alignment of the joining parts than butting together the edges of the adjoining sheets (this is a butt joint). Because “complexity is included” with laser cutting, the cutting effort needed for a comb-jointed box is not much more than for a straight-edged butt-jointed box.

However, to stay as one piece, the comb joints must either be friction fitted together or glued. For both these methods, the mechanical strength of the joint is limited by the relatively small area of the mating surfaces. To give the joint greater strength, one set of combs can be closed, so it is mechanically supported in 2 directions (which then makes it a mortice-and-tenon joint), and if a captive T-slotted nut and bolt is also included (this effectively “closes” the other set of combs — making a bolted mortice-and-tenon joint) the joint is well supported against movement in all directions planar to the component plates. Variations on the t-slot and nut exist, such as the using delrin clips, and while they are very robust, they all require hardware in addition to the laser cut acrylic.


If you’re interested in seeing more possibilities for laser cut joints, MSRaynsford has shown a good selection of posibilities.


Flexible plastic clips are a staple of contemporary product design, just look at your phone; there’s almost certainly a version of a moulded plastic clip that hold the parts of the case together. If you’ve got an older/non-smart phone, then it’s quite possible that you also have moulded button for the back panel with a living (elactically deforming) hinge in. Having already demonstrated that it is possible to make acrylic flexible with a lattice cut living hinge, I investigated how to cut acrylic into an elastic clip that could be used to secure a comb joint.

Elastic Clip Geometry

I’ve been calling this an elastic clip because of it’s structural properties. To operate successfully, the material must only be operating in the elastic-region of it’s stress/strain capabilities. Under elastic deformation, once any force is removed, the material will return to it’s original shape. If the yield stress of the material is exceeded, it enters plastic deformation where there will be a permanent change in the shape of the structure after all force has been removed; because the applied force was great enough to start permanently re-aligning the molecules that make up the material. For a brittle material, such as acrylic, the difference between the yield stress and ultimate stress (the absolute maximum it can sustain before it breaks) is very small, so for a clip to stand repeated use, the maximum stress in operation needs to stay well away from the ultimate stress of the material.

Any kind of integrated clip is going to take the form of a cantilevered beam, where the operation of the clip bends the beam along its length, until the clip is “open”. Having a back stop will limit the size of the maximum deformation of the clip, and therefore the maximum stress it will experience, so the limit of motion gives a starting point for calculating maximum operating stress.

Constant depth cantelevered clip
Constant depth cantelevered clip
Continue reading Laser-Cut Elastic-Clipped Comb-Joints

Second Lattice Hinge Samples

As part of my first week as the new Technician-in-Residence at DoES Liverpool I’ve found time to photograph the acrylic test samples.

From the earlier posts, this second set of samples is sized to have the minimum possible bend radius for single laser cut to create the torsional links, and has three torsional stress levels; each with a different amount of robustness.

  • 36MPa — While this is a low enough stress for normal, gentle handling and can bend to 90 degrees; this is likely to break if mistreated, and does not bend much beyond 90 degrees before breaking.
  • 20MPa — Better than the 36MPa sample, this one can easily bend to 90 degrees, but may break if the sample is bent as far as 180 degrees, especially if the sample is cool.
  • 10MPa — More robust again, this can bend comfortably to touch both ends of the sample together, but is noticably less stiff than the 20MPa sample.

The minimum internal bend radius for 3mm panels with square cross-section links so the inner links do not bind was shown to be 44mm, so the test samples includes a 44mm radius corner.

The samples have 3 different sized hinges, where the torsional link length varies to affect the maximum stress that those links experience in a 90 degree bend (the design specification). The different lengths also affect the stiffness of the hinge too, so the longest (28mm) sample is much more flexible, and allows the hinge to twist slightly when handled as well as bend, though the lower stress give a much more robust hinge that can deal with rougher handling without breaking. By comparison, the stiffest hinge (8mm links) may break if moved too quickly or at too low a temperature; though it may be suitable for permanent or pre-assembled structures and the reduced length may be an advantage for use in shallow structures.

Laser Cut Christmas Trees

I had half an hour at the end of the day at the DoES Liverpool makerspace the other day, so I had time to cut out christmas tree decoration from card and mdf that comes out of the cutter fully finished.

The cut files are available for you below, or on Thingiverse, to cut your own from some A4 card and 3mm board — I used mdf, but plywood and acrylic would work too. If you are demoing laser cutting around christmas time or you want to cut some decorations, these trees dont take too long, and don’t need anything besides assembly after they come out of the cutter.

Laser Cut Christmas Tree Decoration
Laser Cut Christmas Tree Decoration

I’d seen a similar idea for a card pull-out decoration on Thingiverse, but as I had some problems downloading the files, I had spent some time beforehand drawing up a similar concentric extending design and cutting it by hand to check it worked as expected.
Continue reading Laser Cut Christmas Trees

Lattice Hinged Booklets

A Set of Hinged Covers
A Set of Hinged Covers

I’m pleased to have created a first product using the lattice hinges: a laser engraved, hand printed A5 sketchbook for Red-Violet Made.

They use a pair of lattice hinges gives a double fold that operates like a normal hard back book, with a flat spine instead of curved like other booklets. Using such a small radius corner with the lattice hinges means only having a small number of torsional links, so there must be more clearance than a single laser cut between each link so the hinge doesn’t bind at maximum bending deflection.

To lower the stiffness of the hinge and make it soft enough to open and close, this booklet uses long, thin torsional links. However, the increased link gap with the lower stiffness links means the hinge needs to be supported on the inside to stop any extension and perform normally.

The inner liner is screen-printed by hand, as well as a pocket on each side that holds the card cover of the sketchbook. The sketchbook inside is held by the pocket, so it can be replaced to refill the wooden cover. A ribbon on each side can be used to tie the book closed, though the softness of the hinge means it will stay closed without it.

The front covers are engraved by laser with original hand-drawn artwork from Jennifer Fenner (under the studio name Red-Violet Made) that are scanned and resized to cover the whole area. Using laser etching gives a consistent depth of etch and allows very fine detail in the wood, while also picking up some of the grain detail and a fine striated pattern where material is removed, caused by the repeated close scanning of the laser beam.

This first run of booklets were presented for sale at the Bluecoat Artist’s Book Fair. Of the seven manufactured, only three remain unsold, and we’ve been asked to present the remainder for sale in our online shop — with only a short time before the last posting dates for Christmas!

More detail of the manufacturing procedure is shown below. Continue reading Lattice Hinged Booklets

Lattice Hinge Design — Choosing Torsional Stress

The first set of lattice hinge tests I generated were a little fragile, with the maximum stress in the torsional links set to be 60MPa (the yield stress of the acrylic) it’s not very surprising that, with acrylic being a very brittle material (where the ultimate/breaking stress is very close to the yield stress) that the samples were very easy to break.

For a 90 degree bend in a 3mm thick sheet of acrylic with 3mm wide links, 23 torsional links are needed if the laser kerf is 0.2mm. This will form a bend with a 44mm internal radius. The minimum length of link (rounded up to the nearest mm for simplicity) is dependant on maximum allowed torsional stress:

14mm long, 23 Link Hinge around 44mm Radius
14mm long, 23 Link Hinge around 44mm Radius
  • For \( \tau_{allowed} = 36 \)MPa, \( l = 8 \)mm;
  • For \( \tau_{allowed} = 20 \)MPa, \( l = 14 \)mm;
  • For \( \tau_{allowed} = 10 \)MPa, \( l = 28 \)mm.

To test this, I’ve produced a cut file for the hinges with the three sizes of link. Included is a arc of 44mm radius to act as a guide for the calculated internal radius of each lattice hinge bend.

The SVG file is linked below if you’d like to cut your own. Or if you’d like these samples but you don’t have access to a laser cutter at the moment, or you normally send away for samples, Lattice Hinge Test 2 is also available to purchase from Ponoko. Continue reading Lattice Hinge Design — Choosing Torsional Stress