A quick make, 3d printing threads.

I've had this piece of plastic tube for ages, I use it to protect my small model rocket launch rail rods that need to be kept straight and protected from bends. It has had numerous bits of gaffa tape over each end which had slowly turned it into a sticky mess. I've been trying to get to grips with 3d printing threaded items, it's been a challenge until I realised I was expecting to much by applying machining tolerances to the 3d prints. Once I started under sizing the internal threads by around 0.25mm on the radius I started having some success. So now my rod protecting pipe has a nice end-cap one end and a screw lid on the other and I've learnt some new stuff on the journey!

Hackspace Magazine! Keeping track of my articles.

It's been a privilege to write for the Raspberry Pi foundations Hackspace Magazine since October 2018 and I have been meaning to create a post about various articles I have written but never got around to it. So I thought I might create this post with links to all the issues I have article in and a little description of the articles and keep adding to it as (hopefully) the articles keep getting commissioned and published!

Issue 12, Where it all began! I had a "design your own rocket" tutorial in here using the amazing opensource Openrocket design and simulation package.

Issue 14,  An article on Manual Milling machines and beginning machining.

Issue 15, An article on Lathes and their use and a review of a Neke Laser Engraver.

Issue 16, An article on Making a multi headed screwdriver using the lathe and mill and a review of the Eleksmaker Eleksdraw pen plotter.

Issue 17,  Part one of a two part introduction to laying out PCB's for professional fabrication with Kicad.

Issue 18, Big issue for me this one! I had the feature article on Space, featuring lots of maker/amateur satellites, a focus on Libre Space Foundation and a tutorial on setting up a SatNOGS ground station. Also had a tutorial on making a "Slim Jim" antenna and also the second part of the Kicad two part tutorial.

Issue 19, Tutorial on Marking out and Centre punching accurately for metalwork and I also wrote the space of the month article on the fabulous Prishtina Hackspace.

Issue 20, Tutorial on Drilling and Tapping threads.

Issue 21, Tutorial on making a Stud Clamp Tool.

Issue 22, Let's Learn LoRa a tutorial on the ttn uno, the things network and a cayenne dashboard.

Issue 23, Tutorial on using Inkscape and SVG2Shenzhen plugin to create artistic PCB in KiCad. A write up of International Rocketry Week 2019 in Scotland.

Issue 24  Tutorial on making an antenna and optimizing it using a budget N1202sa analyzer, an article on the Arbor press tool, its uses and modifications. Finally, I did a small write up of the magnificent Wuthering Bytes Festival day.

Issue 25 Tutorial on FreeCAD and making CAM tool paths for CNC routers. A review of the RC2014 micro a DIY kit to build a cool Z80 based retro computer and I wrote Space of The Month which featured Hackerspace.gr the amazing hackspace in Athens and home of the Libre Space Foundation. 

Issue 26 Tutorial on CNC routing building on and using the CAM toolpaths we made in last month's issue in FreeCAD.

Issue 27 Tutorial on Nuts and Bolts and threaded fasteners, includes how to identify mystery threads, and related issues like counter sinking, counterboring and spot facing. There's also a review of an arc ignitor kit as a direct from shenzhen article.

Issue 28 Tutorial on Boring using the lathe and boring tools and the milling machine and boring head. Also a review of the Pokitmeter a portable bluetooth DSO, Multimeter and data logger.

Issue 29 Tutorial on Dividing and Indexing Hackspace style, a review of the Pimoroni Fan Shim and a review of the Kitronic Move Mini mk2 robot kit.

Issue 30 Tutorial on getting started with radios on the Micro Bits and a review of a portable workbench by Kennedy tools.

Issue 31 Tutorial on CMOS noise making/Lunetta's, making multiple voltage controlled oscillators with a CD40106. Also a tutorial on making Bench Blocks, useful for holding and working on cylindrical objects in the tool room.

Issue 32 Tutorial on "MTV" A Modular Tracked Vehicle robotics platform I designed around a cheap tracked robot chassis blogpost about this article here. Also a tutorial on making and testing small fibreglass components using 3d printed moulds.

Issue 33 A tutorial on linking an off the shelf RC system to an Arduino and a 2 page review on some Moore and Wright dial calipers. 

Issue 34 A review of a Tenma benchtop power supply and short tutorial on using DC -DC variable power supply modules, including those with constant current supply capabilities. 

Issue 35 A tutorial on building and using DTMF tones as robot control, featuring a bluetooth headset hack! Also a review of  Mitch Electronics through hole soldering kit. 

Issue 36  A story on my boat building adventure! Building a plywood boat. A tutorial on functional 3d printing, jigs, tools and workholders and finally a review of the Warco Formit sheet metal shear, roller, and press. 

Issue 37 The cover feature on Robots which looks at land based robot rovers, chassis choices, sensor and power ups etc. Also Part 1 of a mini series on FreeCAD for beginners.

Issue 38 Part two of the FreeCAD mini series where we use some more advanced sketching and part design tools to make a bird feeder and a Direct from Shenzhen review of a mini compressor.

Issue 39 Part 3 of the FreeCAD series, in this part we look at parametric design in FreeCAD and make an automatic lidded box generator amongst other things. Also in this issue I wrote a Direct from Shenzhen review on a cheap hot air reflow station. 

Issue 40 Part 4 of the FreeCAD series where we look at making more curvy shapes using lofting and other path tools. Also a review of the Pinecil, the $35 opensource risc v soldering iron. 

Issue 41  Part 5 of the FreeCAD series, in this one we work through using the technical drawing add on workbench. 

Issue 42 Part 6 of the FreeCAD series on using the Laser Cut Interlocking addon workbench which has heaps of tools for working on tabbed designs. Part 1 of a mini series building and using the budget CNC 3018 pro CNC router. 

Issue 43 Part 7 of the FreeCAD series on working with assemblies on the A2plus workbench. Part 2 of the CNC 3018 pro series where we look at cutting a variety of materials in 2D using krabzCAM for creating toolpaths. Knots In SPAAAAACE! Feature, looking at the art of NASA grade cable lacing as seen on the perseverance rover and finally a Direct From Shenzhen on a cheap tachometer addon for lathes/mills/drills etc. 

Issue 44 Part 8 of the FreeCAD series looking at making multiples of objects or geometry using a range of tools across numerous workbenches, with introduction to the Draft workbench in particular. Part 3 of the CNC 3018 pro series where we look at creating 3D toolpaths and also cut a range of more advanced materials. Direct from Shenzhen on a very cheap Bluetooth amp module and a review of the Kitronik Picorobotics board which allows control of up to 4 motors, 8 servos and 2 stepper motors with a Raspberry Pi Pico. 

Issue 45 Part 9 of the FreeCAD series looking at curved surfaces and projecting geometry onto or into curved surfaces. Part 4 of the CNC3018 pro series where I share some modifications and add ons to make the machine easier to use. 

Issue 46 Part 10 of the FreeCAD series, using the curves workbench, creating a "maker ring" using a mapped sketch and creating a complex geometry of 4 curves to form a aeroplane cockpit canopy. Also a review of the Miniware MHP30 mini hotplate for small reflow soldering. 

Issue 47 Part 11 of the FreeCAD series, using the KiCADstepUp workbench to create a custom 3D component for use in KiCAD but also importing the entire KiCAD 3D render of a board into FreeCAD for use in assemblies and designs. Also in this issue is the final part of the CNC 3018 pro series where we look at PCB milling with FlatCAM. Finally I wrote the Direct from Shenzhen article which features a huge CNC Diode laser rig I bought for very little money.  

Issue 48 Part 12 of the FreeCAD series looking atworking with the Mesh workbench tools to both dreate and edit meshes, really useful for modifying downloaded objects where only an STL is available. First part of a two parter on Lockpicking and Locksport. Finally I reviewed a Sunnko 709a battery spot welder as a direct from Shenzhen article. 

Issue 49 Part 13 of the FreeCAD series looking at advanced sketching concepts including importing images and setting a drawing plane to sketch over them. Part two of the two part look at Lockpicking and Locksport, in this part we look at making DIY locksport tools and equipment. Two reviews this month, one for the Jumper T Lite RC controller which runs the brilliant opentx firmware and also a review of a cheap and hackable bluetooth enabled thermal printer. 

Issue 50 Part 14 of the FreeCAD series looking at the Sheet Metal workbench which enables folded designs to be created simply in a variety of materials. 

Issue 51 Part 15 of the FreeCAD series looking at the Dodo workbench that enables complex frames or pipework systems to be made from simple sketches and objects. Also a review of some of the Troika construction pen range, excellent maker stationery. 

Issue 52 The final part 16 of the FreeCAD series, we look at customising the UI, simple animations of parts and blast through some areas you might want to dive into on your own! Also a "How I built a Solar Generator" project and finally I reviewed the Pimoroni PGA2040 tiny RP2040 based board in a PGA format.

Issue 53 A folded metal robot tank shell tutorial using the sheet metal workbench in FreeCAD and then using a variety of techniques to cut and fold the panels. Also a review of the Prusa Mini + 3D printer. 

Issue 54 Tutorial on Getting Going with Gears, basic gear ratio theory plus how to create gears in inkscape and FreeCAD. Also 2 review of pimoroni products, the Badger, a RP2040 based eink display badge with a funky OS called badgerOS (can also be programmed directly like any rp2040 device) and I also reviewed the 3 wheel Trilobot robot. 

Issue 55 A tutorial on cheap and fun DIY Hydraulics and Pneumatics using syringes and aquarium tubing. I also review the Kitronik Simply Servo's board. A great board for driving up to 8 servos from a Raspberry Pi Pico. 

Issue 56 A tutorial on my Swing Wing Rocket Glider project and a review of the Phyx Space Shuttle soldering kit.

Issue 57 NOTHING! Due to various non interesting reasons I had no articles in issue 57! You should still read it though... it's full of ace stuff!

Issue 58 Part 1 of a 2 part mini series on Vinyl Cutting/cutters and a review of the 3 coil crane folding scalpel. 

Issue 59 Part 2 of the 2 part mini series on Vinyl Cutting, looking at cutting and scoring card, cutting copper and aluminium tapes for circuits or engine gaskets and more! I also reviewed a tiny mechanical keyboard soldering kit, the Pockettype. 

Issue 60 In this issue I have a tutorial on building flatpack rockets, rockets built entirely from sheet materials which flew well and look great as I used an interesting sublimation print onto laminated balsa technique. I also have a piece on building a dive watch worth arounnd £250-500 using about £90 worth of components! Finally I reviewed the Gameboy camera wifi printer accessory which is great for digging out and getting creative with your vintage Gameboy camera!

Issue 61 In this issue I have a "How I Made" on my indoor hot air balloon experiments. I also wrote a review on the Engineer TS04 spanner set. 

Issue 63 A review of the Sunlu S1 filament dryer for 3D printing. 

Issue 64  How I made, An Air Cannon Rocket launcher. Using ABS plumbing pipes, a valve and some bits and bobs this launcher works really well blasting small rockets!

Issue 65 How I made, Supercapacitor powered free flight planes. Super fun, cheap and you can fly again and again and again with a couple of AA batteries as a charger for the supercapacitor. 

Issue 66 Advanced Paper Aeroplanes, including laminated planes as well as advanced folded designs. ALSO! KiCAD! Part one of a new series on using KiCAD 7 to design  PCB's, we'll be exploring lots in this series including different fabrication options and also using PCB assembly services amongst other subjects!

DIY Screw Switches for Rocketry

In high power rocketry its good practice to have some kind of keyed switch or remove before flight system that isolates the avionics from power. Important as often these systems are connected to small wells filled with explosives that are fired at points in the flight to split airframe sections and deploy recovery parachutes etc. Isolating the system (killing the power) enables the flyer to handle, carry and prepare other aspects of the rocket and only arm the system when necessary.

I've used small 3.5mm stereo jacks and sockets and when the stereo jack is removed 2 pins are connected under a spring steel load to which I have soldered a power cable. I have also experimented with rotary key switches. I have never flown key switches and recently read about some failures using rotary key switches and I've always wondered at what force/speed would it be possible that my clamping stereo jack socket might separate in flight and and kill power?

I then came across the idea of screw switches. A screw switch essentially is a system where a circuit only becomes connected when a screw is tightened. They are often made by hand by epoxying a nut onto a metal bar which is insulated and another metal piece added on top which will be connected when the screw/bolt is tightened. I wanted to try and make one that was accurately repeatable so I could make a multiples but also smaller, tougher and neater.

So I quickly decided on using double sided copper clad fr4 and a PEM nut press fitted to one side. I CNC routed the boards with a hole to receive the PEM nut and 2 holes for M2 mounting bolts. As the M2 mounting bolts would connect the 2 sides of the FR4 I routed a clearance area which generously clears the head of the M2. I fitted a PEM nut (press fit using a 1.5 ton arbour press) to the first prototype and continuity checked that the two sides of the board where still electrically isolated. To make the switching screw I have epoxied another PEM nut onto an M2 bolt and when fully tightened it connects the 2 sides of the board. On the other end of the M2 bolt I made a small punch mark to disrupt the last couple of threads on the bolt which means it cannot be fully unscrewed.

As the device is copper clad I routed the board to have a tab on one end  (at the top of the picture below) onto which power wires can be soldered either side. Therefore when the M2 bolt is fully tightened it connects the wires and allows current to flow.

It then just needs to be mounted in a position inside the rockets electronics bay where its possible to have a small hole in the airframe allowing a small screwdriver to be inserted to open and close the switch. As a mockup I made a small 29mm bulkhead and added a standoff to mount the switch too.
Finally one of the great benefits of a CNC is repeatability, I have now knocked up a few of these and they sit awaiting deployment in upcoming rocket builds.

EDIT!! So some people where asking questions and struggling to see how this worked so I've done a little video explanation and demo! 

DIY Rocketry Screw Switch from concretedog on Vimeo.