Toys

Our son has reached The Age of Exploration. At last, he can pull himself upright and toddle along on his hind paws - so long as a support of some kind remains within reach. To give him some walking practice and a little independence, I sketched out a pushing/walking toy, then started digging through our wood-pile. Soon, odds and ends had been sawed and screwed into something closely resembling the sketch below (the height for the bars chosen to be just around our son's shoulders, low enough to be pushable, too high to fall over). One point to note: sanding off all edges and any rough surfaces will save grief later. With even a very cheap random orbital sander, this does not take long.

Version 1: Sled with upright handle

Full of anticipating, I presented the result of my labours to my son, who got the idea of the toy straight away, and set off at high speed, cackling with glee... and seconds later, rammed it a cupboard dead-on. No damage done, but also, no possibility of turning. The next problem was that he stood inside the sled, and tried to pull it over his own toes.

Version 2: platform to stand on, double-ended

I decided to solve the turning/reversing problem by making the pusher double-ended, duplicating the existing upright handle, and solved the standing-in-the-middle problem with a plywood platform. As I finished screwing this on, it occurred to me that I should have used bolts to secure the uprights to the base - then it would be very easy to take the whole thing apart into flat pieces for storage or transport.

The modifications were well received by my tiny test pilot: he used an upright to pull himself to his feet, then clambered grinning onto the platform, and tugged mightily at a handle, doing his best to rock the whole contraption. Which gave Dad an idea.

Version 3: build-in rocking function!

The final (so far) modification required some fairy delicate wood shaping: I made a long shallow curve from a single piece of wood, sawing, chiseling, sanding, then split it lengthwise into two identical pieces, which I glued with ordinary wood glue (do not risk snagging a screw head on your partner's tiles/carpet!) carefully to the existing runners, then clamped and allowed to set overnight.

Next morning, a very proud Dad presented his soon with the push-me-pull-you version. Son discovered that the new version made a very pleasing racket as it rocked on the kitchen tiles, and Dad was relieved to find that he hadn't overdone the rocking motion (no danger of head-over-heels).

This has been my first real foray into toy-making, at least as an adult; my son has got a lot of fun and exercise from a very simple toy, and I just as much, from the pleasure of making, of giving, and of seeing his fun.

Dads, Mums, Aunties and Uncles: to your sheds! Go build!

Making a new rudder, part 2

This post is part of a series on making a fibreglass rudder with a foam core:
Designing a rudder, part 1
Designing a rudder, part 2
Making a rudder, part 1

Calculations done, foam cut into neat rudder-sized rectangles, I had no alternative but to start shaping the foam. I did it like this...

Step 1: mark the depth of foam to be removed. I did this by setting a circular saw to the calculated depth for a given point in the profile, then running it the length of the rudder. I kept the trenches very close together at the leading edge of the foil - the first few tracks were only 2mm apart (the saw blade width), then, as the slope of the foil changed more slowly 4mm, 5mm, 10mm. On the rear half of the foil, whose slope is almost straight, the gaps increased to 20mm, then 40mm. With all the tracks cut, I sprayed blue paint into the cuts, making sure to get good coverage on the bottoms of the tracks.

Step 2: remove the bulk of the foam. I tried chisels: bad idea. What worked really well was to take a wood saw, hold it sideways and cut along the foil at a shallow angle, keeping a millimetre or two above the bottom of the trenches. In about 40 minutes I was able to remove most of the excess foam, leaving behind a nice flat surface.

Saws make short work of Corecell

Step 3: the saw was followed by a wood plane, which cut to within 1-0.5mm of the trench bottoms - but not lower, because the plane did not cut the foam as smoothly as wood, tending to leave the surface a little rough.

Step 4: I next used a surform to remove the last of the excess foam, leaving the surface of the foil flush with the trench bottoms.

Step 5: To get a really smooth finish, I followed up the surform with a random orbital sander.


With the two halves shaped and (I hoped) pretty symmetrical, I mixed up 250mm of epoxy, then stirred in enough colloidal silica (amazingly fine white powder) to make a paste with a honey-like consistency. A squeegee was perfect for getting an even spread on the flat side of the starboard foil half. Interesting to note: although the foam looks like a sponge, it certainly doesn't act like it - it doesn't the epoxy in, but leaves it on the surface - where I need it .

Rudder core halves clamped together; polythene drapes keep epoxy off the worktop

With an even spread of epoxy covering the starboard half, I dropped the port half into position, and applied my entire collection of clamps. You never have enough clamps. And that was it for the day: all going well, by tomorrow morning, the two halves will be one - permanently.

Long Ears

In the morning, there was a small brown scrap on our lawn where none had been before. Turning over, as I thought, the corpse of a headless bat, I was startled by squeaks of fear or rage. The mouse-sized animal had curled its wings in tight around its body, and tucked its head into its chest; even its ears had curled up, looking something like a ram's horns. The face was relatively pretty, as bats go, without the weird pressed-up nose that some species have; the massive ears are the feature you'll remember, though.

Brown long-eared bat

According to the excellent "Exploring Irish Mammals", Plecotus auritus, described by Linaeus in 1758, is found across most of Europe north of the Pyreness, and also in the far east, in regions within Russia, China, and Japan. This bat likes to "foliage glean", plucking its prey from leaves or even the ground as it flys.

~

My tiny specimen was soaked in dew, and motionless - this last must be what saved it from our cat, who loves to chase, but tires of prey which can no longer flee. I tucked my patient away for the day in an empty toolbox, with a few crumbs of cat food for sustenance.

~

After sunset, I took my patient for a walk, to a wooded and cat-free place. Out of the toolbox, the ears inflated and the head looked up; then, the tiny creatures crawled from my gloved hand onto the rough bark of a large tree, hooking on tight with claws on the leading edge of the wing, while black and hand-like hind paws sought purchase.

Making a new rudder, part 1

Following on from the previous posts on the design of rudder foils, our hero now begins the tricky fabrication stage.

As discussed previously, my new rudder will have a fibreglass skin (6 layers) wrapped around a foam core. Not just any old foam - Corecell, a light, stiff material that is absorbs little resin (or water) and will contain any damage to a very localised area. It won't rot, delaminate or crack, and the sheet I bought from the helpful folk at MID has a density of just 60kg / cubic metre.

I've never used this material before, so wasn't sure how easy it would be to work with. First, I trimmed the lengths I needed for the rudder itself from the original 4ft by 8ft x 25mm sheet using a jig saw. No problems, and surprisingly little dust - most of the material from the kerf seemed to stick together, hinting at one potential difficultly: since this foam is a very good insulator, heat from cutting tools disspates slowly - so cutting at higher speeds can cause melting.

Next, I used an off-cut to practice my foam-shaping skills (never shaped foam before, didn't want to start by destroying my proto-rudder). First, I clamped a straight-edged piece of wood atop the foam as a cutting guide (straightness verified against a handy glass window - float glass is very flat). Then, I set the cutting depth on my hand-held circular saw and cut a series of trenches in the foam, the depths calculated from my spreadsheet describing the NACA 0012 foil I want to make.


Next, I sprayed the yellow foam with blue paint, making certain it penetrated to the bottom of the trenches.
Once the blue paint was on, it was now "safe" to start cutting away excess foam; I tried a random orbital sander, but, especially at high revs, discs clogged too quickly. Tried a sharp penknife: not too useful. A block plane worked reasonably well, and a rasp/file came in very handy for tidying up small irregularities. The paint worked a treat - you can see below how the blue lines allow me to be sure I've not removed too much material.


Shaping the leading edge of the foil was quite easy; shaping the trailing edge - much more material to remove, but accuracy is less crucial - turned out to be more difficult. I actually tried chiseling, which worked up to a point, but was slow and difficult. Not sure about the best way to do this yet - I hope to try an angle grinder soon to slice the bulk off, then follow that with plane, disc sander and rasp for the final finish.

Conclusions so far: Corecell is very easy to cut. Shaping it is much easier than shaping wood, but the same techniques won't work.

This post is part of a series on making a fibreglass rudder with a foam core:
Designing a rudder, part 1
Designing a rudder, part 2
Making a rudder, part 1

Astronavigation / Celestial Navigation, Part 2

Last night, a (briefly) clear sky gave me a chance to try a key element of practical celestial navigation. Following the example of Marvin Creamer and countless forgotten sailors of the pre-sextant era, I attempted to measure the altitude of some celestial bodies using no instruments whatsoever (partly because, aside from my telescope, I haven't made or bought any yet).

Why no instruments? Obviously, this decreases the accuracy of the observations that you can make; not so obviously, it is still possible to be accurate enough to make measurements that are accurate enough to be useful. Marvin Creamer made fairly accurate landfalls all around the world using this method, generally maintaining his latitude to within half a degree of the intended value , and any experienced navigation venturing deep into desert or out of sight of land before the coming of "modern" instruments like the sextant almost certainly relied on such techniques. So, it is possible, but is it useful?

Well, sometimes; today, people like myself who like to use the "road" less travelled have the benefit of tools like GPS (I recommend the excellent, cheap, tough Garmin Etrex); however, the very nature of independent travel in remote places means that equipment may well be lost, broken, or simply out-of-charge. By learning how to navigate without any instruments which aren't permanent (I hope!) parts of my body, I'll be able to travel with a permanent built-in backup for the GPS and the compass (you'ld be surprised how many sailors run into GPS trouble). Apart from hypothetical equipment failures, navigation is a subject that I enjoy for its own sake; there is something deeply magical about looking up into the night sky, knowing the stars by ancient names from foreign tongues, and, simply by looking, to find yourself.

Back to practicalities. At this latitude, the July sky isn't really dark at 23:00, so there weren't very many bodies to measure - simple identification was tricky, because only the very brightest bodies were visible. Even worse, not being at sea, I didn't have a clear horizon either. Nevertheless, I extended an arm and spread thumb and forefinger as far apart as they would go; for the average person, the span between thumb and forefinger will cover about 15 degrees of sky. I levelled my arm at the invisible horizon, and began to measure.

Waving my arm around the summer sky, I measured the altitude of a rising moon (itself covering only 0.5 degrees of sky, a useful checking-fact) at about 10 degrees and the bright orange of Arcturus (Alpha Bootes) at about 38 degrees. I sighted Dubhe (part of the Plough Constellation) too, although I forget the number; then, checked the observed altitudes against what Mobile StarChart app on my phone said they should be. I got the moon nearly dead-on - its real altitude being about 10.5 degrees - and Arcturus turned out to be just over 40 degrees above the horizon. The error for Dubhe was higher, about 3 degrees.

For a first attempt, with no clear horizon, these measurements strike me as acceptable; if I had been using them to find my latitude, I would've had a pretty fair chance of finding my home country. Marvin Creamer did a lot better, though, so the next time I've got a clear horizon after dark, I'll give the procedure another try. In the meantime, I'm now wondering what simple instrument I might be able to construct to get those errors a little smaller. Ideally, these will be simple instruments, such as a lost sailor on a small boat might plausibly fabricate. Also, wouldn't it be nice to measure latitude and longitude?

Coming soon...

Designing a new rudder, part 2

By measuring photographs and doing a little maths, courtesy of the NACA 0012 formula, I was able to discover what size and shape my new rudder (transom-hung, constant foil cross section) should be. Next problem: what materials?

My old rudder was a single piece, almost certainly a tropical hardwood, dense and strong. Marine plywood was an obvious option, except that no local suppliers had real marine-grade plywood (non-marine grade, which I have used for cabin furniture, can have voids and gaps within interior laminates, hidden weaknesses which could be fatal in a load-bearing structure). My old rudder was a single piece of tropical hardwood, which I also tried to source: a local supplier had lots of beautiful teak and iroko, but no planks wide enough to make a rudder in a single piece - they simply aren't there to be had (they've all been made into rudders already?). It might be just as well: a solid piece of timber can be sundered by a single stress-grown crack, not such a problem with laminates.

Abandoning nature, I talked to the very helpful Liam Phelan of mid.ie, and began to investigate the possibility of a synthetic foam core (Corecell) wrapped in fibreglass. To get an accurate spec on which foam and how much glass, Liam suggested I talk to Martin Armstrong, chief technologist at Gurit, a firm which supplies composite materials to pretty much everybody who builds composite structures - submarines, wind farms, huge racing yachts, aircraft, etc. Martin is a busy guy, but he spent half an hour talking an amateur sailor and novice builder through the materials and techniques necessary to fabricate a composite rudder.

First, the core: A550 foam (Corecell) for the rudder core; a single 8ft x 4ft x 25mm sheet would suffice. I wasn't sure how easy this would be to shape, but Martin reassured me that it is far less dense than wood, while also having no grain; normal wood working tools would suffice, it could even be sanded into shape; a surf form might be handy. Only one problem to watch: being an excellent insulator, it is really bad at dissipating heat, so power tools should have fresh, sharp blades to minimize friction.

Layers making up my composite rudder

Then, the exterior, from which will come much of the strength; Martin specified six layers of glass cloth:

Layer 1: 290g 4-harness satin, laid at a 45 degree angle, and with a 100mm overlap both sides at the leading edge, and a similar tail at the trailing edge
Layer 2,3,4: uni-directional 500g fabric running top to bottom (no overlap)
Layer 5: 290g 4-harness satin, 45 degrees again
Layer 6: 290g 4-harness satin, 0 degrees

This post is part of a series on making a fibreglass rudder with a foam core:
Designing a rudder, part 1
Designing a rudder, part 2
Making a rudder, part 1

Car cleaning tip

One of our cars has a light-grey plastic trim in the interior all around the ceiling. Looks nice and bright, but not so easy to keep clean. Today, we found the solution: all the black grubbiness around areas that hands touch a lot (e.g. the sunroof controls) was removed instantly by the simple application of a popular brand of baby wipe. Looks good as new now. Excellent stuff.