Sunday, 26 December 2021
Tuesday, 14 December 2021
Friday, 26 November 2021
I've recently written a 2 part article in Hackspace Magazine about locksport and lockpicking, the first part (issue 48) covers the basics around lockpicking practice and essential stuff such as the golden rules, never pick a lock you don't own and never pick a lock you depend on. The second part (issue 49) looks at DIY lockpicking/locksport tools where we made some picks, tension tools and a practice board. Occasionally when I am writing this type of piece I have to edit out sections to meet the word count requirements of the article, in this instance I culled a section on how to re-pin a lock. I'm posting it here as it's a really useful skill that can mean you need fewer practice locks and can get multiple setups/pinnings per lock.
Re-pinning a lock is a useful skill that can enable you to create a new challenge out of an existing lock that you have got used to picking. Essentially you are removing the centre core of the lock and removing the pins and replacing them to make the lock a different challenge. A standard 5 or 6 pin tumbler lock has the core of the lock retained with a C clip in a machined groove and this can be removed with a pair of pliers. Once you have removed the clip, be careful to not pull out the lock core until you are ready as all the pins will fly out and potentially get lost. You can’t remove the core until the lock is in the unlocked state. If your lock currently has a key that fits you can insert the key and then unlock the lock, but only turn the key an eight of a turn. With the key turned rotate the whole lock assembly so that the key is now vertical such that if you removed (but don’t do this yet) the core the key pins would remain sat in the now vertical channels in the core. A plug follower is a dowel, or indeed a 3D print in our case, that matches the diameter of the lock core. These are quite commonly half an inch in diameter. The plug follower allows you to remove the lock core without releasing all the pins at once. Whilst removing the lock core hold the plug follower flush with the far end of the core and feed it in as you move the core out. If all has gone well you now have the lock core, with the key inserted, and all the key pins still in the holes and you have the lock body with the springs and driver pins still in each channel hole block by the plug follower. Cover the end of the lock or place it flush onto a table top and then slowly retract the plug follower from the other end. You should hear each driver pin and spring release and once the plug follower is out you can lift the lock body and find all the springs and driver pins safely on your work surface. Re-pinning the lock reverses this process. Note that if you swap the key pins to different locations, making a new challenge from the same lock, your key will no longer fit or operate this lock. You can, of course, pick the lock into an open position and re-pin it back to work with the key.
To re-pin the lock place the plug follower at the back of the lock and with a pair of tweezers carefully place a spring into the hole furthest into the lock, next grab your driver pin with the tweezers and place that pin over the spring and push it until it is slightly seated into the hole. Next push the plug follower into the side of the driver pin, you should be able to trap the driver pin, binding it on the hole edge and then use your tweezers to push the pin fully down into the hole, you can then slide the plug follower over that pin to secure it and move on to repeat the process for the next pin. Finally once all the driver pins are replaced you can place the core, containing the key pins, back into position, lock the lock by rotating the core and then re attach the retaining C clip.
Tuesday, 9 November 2021
Tuesday, 5 October 2021
Tuesday, 28 September 2021
Today's Tool Tuesday is a particular favourite set of tools as they often are my first port of call when beginning to design or build a rocket! I often need accurate measurements of internal tube diameters and the Telescopic Bore Gauges are an excellent approach.
Each gauge covers a range of internal diameters and features 2 sprung probe sections that can be pushed back into the centre body of the gauge somewhat. In the handle mechanism there is a spring pushed bar which when you tighten a knurled nut at the back of the handle will lock the 2 probes in their current position. To get an accurate result you push the probes into the desired internal bore and hold the gauge at a slight angle and lock the probes to finger tight. You then pull the probes so that they span flat across the bore to bring it to it's final measured size. You then remove the bore gauge and use an accurate device to measure across the jaws of the probes, a well calibrated micrometer is best but often a vernier caliper across the probes is sufficiently accurate for most needs.
Wednesday, 22 September 2021
|Photo Credit Peter Barrett|
I'd never built an "odd rock"! Odd rocks are a category of rocketry reserved for those who create rockets from odd materials or make odd objects fly. I've seen loads of examples from flying cars to an office fan but it's never been an area I've delved into. At the milder end of odd rocks there has been a long history of people making rockets using confectionery packaging and in particular Pringles tubes. Pringles tubes are a very worthy rocket building material but they have been done a lot and I wanted to do something different. The Dorito's STAX tubes are a pleasing rounded triangular shape and I thought it might be a worthy candidate for a build.
This build was very quick and dirty and everything was done in between work and other commitments and definitely took a back seat priority wise to other rocket projects. I started by drawing around the tube to get a rough sketch of the tube profile and took a picture of it on my phone. I dragged the image into inkscape and then hand traced to get a vector of the tube shape. The tubes aren't quite an equilateral triangle which adds a bit of faff! I laser cut some plywood centring rings into which I cut a hole to receive the motor mount tube. This was finished off with a PETG 3d printed motor retainer.
The fins are 3mm balsa laser cut to a shape that kind of looked a bit dorito-esque! I originally planned to put the fins through the wall but ended up just gluing them on. I reinforced the oversize fins with a layer of tissue paper and glue. Due to the shape of the tube this rocket is impossible to simulate using a package such as openrocket. As such I decided to go very large with the fins to try and definitely pull the centre of pressure rearward in the airframe. The nosecone offered some challenges and I didn't really have time to create an accurate fitting cone. As a first attempt I decided to model a shoulder-less nosecone which would overlap the top of the tube somewhat rather than trying to accurately model to the tube. Having my rough nosecone model in FreeCAD to 3d print I then created a stack of lasercut plywood triangles to create a shoulder piece that could be sanded to a decent fit inside the tube. The recovery bridle was some thin kevlar and I flew this using a proven hexagonal annular parachute I'd made some time ago. Finished with a bit of satin black spraypaint and a quick vinyl cut graphic, DSTAX was finished!
|Photo credit Peter Barrett|
Due to this not being sim'able, once together I decided to add around 18 grams of nose weight (some small flat lead panels epoxied into the nosecone bulkhead) and this seemed to make the airframe stable when performing the classis "swing test". The swing test is where you attach a string at the centre of gravity (with the airframe loaded with a motor etc) and then swing it in a circle, it should correct itself slightly into the wind and then remain stable, an old school approach that works well to give you some indication of the stability. The other consideration was the maximum lift off weight limit of the target motor, an estes D12-5, which is 283 grams. All up weight of the rocket came in under the maximum at 224g.
As you can see in the video the first light was successful albeit with a slightly late deploy of the recovery system. I think it's a little over stable by the way it turned into the breeze but it's certainly within acceptable limits. If I built another I would consider reducing the ridiculously large fin area somewhat!