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M6 Version of MakerBeam

8 Jan

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A small experiment in 3d printing something like “MakerBeam”, an aluminium extrusion based construction technique, itself derived from 80/20 extrusion (which, by the way, is silly expensive here in New Zealand).

I have lots of sizes of M6 hex head bolts so I scaled it up a bit to fit the heads of those bolts, rather than special headed bolts or special nuts. There’s an M6 thread down the hole in the centre.

render

The four diagonal slits in the design are an attempt to be tricky. They’re only 0.1mm wide so they should get melted together when printed. However, they trigger the slicer software to add a full set of perimeters around them, greatly strengthening the weakest point of the shape. Not sure how well it will work, but worth a try. I could achieve the same effect by fiddling with the slicer and defining extra volumes to print with higher infill or solid, but I’d rather define it in the model, not the slicer.

sliced makerbeam

In the slicer (I use “Slic3r”) preview window, you can see how diagonal slits have added a lot of extra strength.

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Cosplay Experiment (3D Print + Cloth Mache) Spiral Horn

7 Jan

steps of spiral horn

Papier mache (and the related “cloth mache”) techniques has some excellent features. It’s extremely cheap, and can make strong and light weight objects. However – at least when I do it – it can end up rather lumpy and irregular.

I love 3D printing, but making large structures with a normal printer gets expensive fast, and also takes a long time. The longest print I’ve done took 16 hours, but some people routinely print 50 to 100 hour prints. The shapes should be exactly what you planned (except when something goes wrong) but laying down all those layers takes time.

I’m not the first person to think of combining these two techniques. I got the idea from 3d-print-and-papier-mache¬†and I’m sure others have done it as well.

I was playing around with “vase mode” on my printer the other day. This is a special way of 3d printing where, rather than laying down a series of layers, the printer lays down molten filament in one continuous SPIRAL layer. The resulting object has to be hollow, with thin walls only one layer thick. However, since the extruder doesn’t stop and start but just keeps looping around while slowly rising, the results tend to be very smooth and are surprisingly strong for their weight. It’s also much faster as only the outside skin is being printed

horn render

I drew up this horn shape in Fusion 360. (For those interested, it’s a loft between two circles, with a coil edge as the guide rail).

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Here it is printing. It came out very nicely, with lovely smooth curves that felt very nice to the touch.

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My first attempt wasn’t so good. In vase mode, each line of filament must partially overlap the one below, since there’s no interior. If it moves too far horizontally from the previous layer, it ends up splodging in mid-air. I need to do some more experimenting to find the shallowest angles I can print.

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I cut some strips of cloth from the rag pile, and wrapped my 3d printed “horn”. I worked in a spiral pattern from the bottom, dipping the cloth in heavily diluted white pva glue (probably 50/50 water to glue). It took a couple of tries but was surprisingly easy.

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The very wet mix took a long time to dry. I left it sitting for a couple of days. Since the armature was 3d printed, I didn’t need to worry about it getting damaged or mouldy.

I need to do a bit of trimming and sculpting at the ends, where the cloth ended, but only minor stuff.

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Here it is on the turntable, ready for painting. My turntable is built from a car wheel bearing, with a cordless drill motor for rotation. Using spray paint, this gives me a much more even coating.

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This is after a very quick paint job. I just grabbed the first couple of cans that came to hand (which happened to be blue and gold). However, it does look a lot nicer than the plain white.

It looks, and is, pretty rough. I’m sure I’ll do more experimenting with this, though. One big advantage of this technique is that I can simply mirror image the model, and hence the 3d print. Compared to trying to make two parts look the same by hand, that should be a big improvement.

Storage for Boot (Trunk) of Toyota Caldina

7 Jan

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The boot of our family car is usually full of ‘stuff’. Jackets and blankets in case of a breakdown, tow rope, leather gloves, etc. These tend to get shoved to and fro to make room but flop around and spread out. This annoyed me more than usual the other day, when I had to clear everything out to get access to the floor.

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I didn’t take a photo of the mess in the boot, but this is the sort of junk that was in there, hurled over into the back seat.

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Looking at the boot, there’s an area just behind the back seat where things could be stored vertically if there was a suitable container.

I took some measurements and used Fusion 360 to work out the angles. I could have drawn up a cad diagram of the unit but it was just as easy to lay it out on paper.

boot storage

This is what I came up with. It’s a simple box with two partitions. One side is angled to match the slope of the back of the back seat. The other is dropped down a bit to make access easier. Cardboard was the material of choice for this. (The rendering above was done after the fact, while experimenting with Fusion 360’s new sheet metal workspace, which can also be used for cardboard boxes).

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I found a suitable chunk of cardboard from our huge collection in the shed and we marked out the main shape and cut it out. Folded up and held with clamps, it looked pretty reasonable, and fitted firmly into the space I’d planned.

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When I put it down on the floor, it was immediately inspected.

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The weak point will probably be the back (front as you look at it) wall. It’s already got two layers of cardboard over much of it, so I filled in the gap, then covered it with another complete layer. Probably overkill, but cardboard is cheap and light. We slathered it with pva glue and weighted the sandwich of layers down with exercise weights and wood.

I flipped it the next morning, and glued the angled face. The partitions were added with more pva and some tricky clamping. I added a rim of clear tape just for looks

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This is what it looks like in place for a test fit. I mucked up the measurements slightly and had to cut a notch for the handle which releases the sunshade fitting. A lot easier to change in cardboard than something harder.

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And this is what it looks like full of stuff. It absorbs a heap of bits and pieces and still leaves most of the boot clear.

 

Avoiding electrocution while testing 240v circuits

3 Jan

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I needed to measure the output voltages on a bunch of unmarked transformers I’d accumulated. (No, I’m not a hoarder. I can stop any time I want to. Perhaps.)

I’ve done this before, with just a bunch of alligator clips, a mains cord, and a multi-meter. It’s very simple, but it’s *dangerous*. Reaching over live 240v wires to take measurements isn’t a good idea. Worse is that a bunch of wires in mid-air have a tendency to move around, generally shorting something wires together.

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I recently made up a number of little test boards to hold test circuits in place without having to worry about wires getting loose. Here, for example, is a test with an arduino (on a solderless breadboard), an L298 motor driver, and a worm geared motor. The boards are 85mm long, with two rows of M4 holes 10mm apart. The rows are 75mm apart. They’re mounted to a laser cut piece of 6mm mdf, with two long rows of M4 tapped holes. (MDF taps quite well with a tap in a cordless drill).

I really don’t know, yet, whether these ‘boards mounted on boards’ are a good idea or not. However, they’re cheap and worth trying. In particular, they hold wires securely for testing which was exactly what I wanted for testing my transformers.

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Here’s a test victim hooked up to a test setup. I grabbed a spare chunk of 12mm MDF (I didn’t even bother cutting it square). I marked a grid of cross marks at 10mm x 25mm spacing using the laser cutter, then drilled and tapped just the few holes I wanted to hold things down. Chocolate blocks, hot melt glued down, gave me a secure but adjustable fixing for wires.

Note that I used a female EAN mains plug rather than a standard power cord to supply power. I physically unplugged it every time I changed the circuit, which I probably wouldn’t have done if it was a plug into a wall socket.

This particular transformer made me glad I’d gone to the trouble, as it was very easy to power it off when I plugged it in and it started to hiss and smoke. Looks like I picked up a 110V primary transformer somewhere along the line and it *really* didn’t like running on 240V.

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Even when I ended up using crocodile clips, they were much more secure when clipped into the immobile terminal blocks.
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A quick test of a crude opto-coupled triac circuit felt a lot safer when wired up like this as well. I wouldn’t trust a solderless breadboard at 240V.

Compact ATX power supply to lab supply conversion

7 Oct

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I wanted a simple 12V + 5V supply of power available on my (already very crowded) desk. There were already two other supplies in the room (one of them a fancy fully ajustable lab supply), but they were … metres away. I wanted something right beside the keyboard for powering Arduino experiments, etc.

I took a standard PC power supply, cut off the plugs that go to the motherboard, and wired a small (100mm x 75mm x 30mm) box onto the end. The actual supply is tucked a few feet away.
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This is my original 12V/5V conversion. It’s ugly but it’s been in use for nearly 20 years. At the time I didn’t know what types of (cheap) connector would be most useful. I fitted a push to open, release to clamp fitting off a stereo, a ‘chocolate block’ screw terminal block, some RCA phono connectors, and a solder tab that alligator clips attach to easily. In actual fact, I’ve found the RCA connectors the most useful. They’re quick, easily salvaged from old electronics, and I haven’t melted any yet, even running 5+ amps through them for hot wire cutters.
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Here’s another compact conversion – just a simple terminal block with GND, +3.3V, +5V, +12V, and GND again.

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And another one where I unsoldered everything except three of the 12V lines and three of the ground lines, plaited for convenience.

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Here’s the victim – a bog standard supply. I’ve cut off the mother board plugs and removed the zip ties. Note the messy tangle of wires.

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I used the laser cutter to make up a couple of “cable combs” to tidy up the tangle of wires. I split the wires into two sets, as they were different lengths.

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Here you can see a comb in use, taking a tangle of 12 wires and keeping them nicely parallel as I zip tied them. A side effect was that the resulting cable was much straighter, without the curves that were in the original wires.

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This is the unit that will sit on my desk. A simple laser cut tabbed box (yay for Inkscape and the Tabbed Box Extension). There’s a chunk of angle iron (20x20x3) glued in for weight, and beefy resistor to put a load on the 5V rail. (I believe most modern supplies no longer require this). Two rows of RCA connectors – 3.3V, 5V, 12V. Since I long ago standardised on red for 5V and yellow for 12V (same as the power supply wires), I don’t need to label them. There’s a socket (black) for the 5V standby which stays on when the supply is turned off, a switch which turns on the supply, a power led, and another press connector stolen from a stereo. (They come red and black, I painted one tab yellow).

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As I mentioned, some of the wires were shorter, so I decided to add in another box with just 5V and 12V and some salvaged connectors. This box was made with thicker 6mm mdf to give it some weight. The black objects were 3d printed covers to disguise the salvaged state of the connectors.

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The printed covers did make things look tidier. However, they were a BAD IDEA. It took way more effort than they were worth, and the one fault I found when I tested the system was in one of those covered connectors – now potted with hot glue and no longer accessible.

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I rebuilt the “secondary” box with a new design. I made another 100x75x30 tabbed box in 6mm mdf, but this time with a cutout area and four 3mm holes. I tapped the holes, M4, with a tap in a cordless drill. A 3mm mounting plate goes over the top, this time with proper panel connectors, and screws down. This was much better than the first attempt, and I’ll use the technique again.

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Here’s the result. It all took more time than I’d expected, particularly the actual soldering of the wires. With so many wires fitting in a small space, I had to do some messy joins. Lots of incentive for me to get on top of laser cut/etched printed circuit boards.

However, I’ve got a useful tool that may get me doing more Arduino/robotics projects. I also learned a lot about using Inkscape, and found some techniques for making enclosures that I will definitely use again.

Cardboard Sword Coffin

22 May

00 sword coffin

My daughter asked me to pack some of her belongings, including some swords. Before I packed the fancy Japanese ones, I thought I would practice by making a protective box for a (cheap) wooden one.

01 sword

The sword – a bit over a metre (40″) long , 250mm (10″) wide.

02 base outline

I drew lines onto a cardboard box, forming a six sided shape. Out from the ‘coffin’ shaped hexagon, I drew parallel lines 50mm, then 10mm (for a fold), and another 50mm.

03 base cut out

Cutting around the outside makes the shape more obvious.

04 base cut and bent

Then scoring all the fold lines and cutting out tabs.

06 pizza wheel

This is my favourite tool for putting folds into corrugated cardboard. It’s a pizza wheel from a $2 shop, but I ran the edge against a grinder for a moment to take the cutting edge off it. Pressing down on that 1mm edge will crush most cardboard quite easily – even the triple thickness stuff. I found it tends to run off the line rather easily unless I prescore the line with a knife.

05 side glued and clamped

Here I’ve folded over a side, glued it (cheap white PVA glue) and clamped it to a piece of wood to keep it straight. Keeping it vertical (i.e. perpendicular to the base) was a problem. I used a bungee cord to put tension on it but I should really have grabbed a right angle brace of some kind.

07 clamping other side

And then gluing and clamping the other sides. You can see the first long side glued up here, looking quite solid.

08 base folded and glued

Gluing sides with PVA glue is a slow process, with time to watch about 1/2 an episode of NCIS before the glue has set enough to remove the clamps.

09 test of sword in base

A quick test to make sure the sword actually fits inside. Did I mention that this was the second box I made?

10 marking lid shape

I found another chunk of cardboard box and drew around the coffin to mark out a lid.

11 pattern of lid

The pattern of the lid is much simpler, as the sides are only one thickness of cardboard, not two folded over. Equally, it’s nowhere near as strong.

12 lid cut and bent

The lid cut out and folded. Unfortunately, since I used a chunk of cardboard from a shipping carton, there was a large slot going most of the way through it. Hence the offcut waiting to be glued in to strengthen it.

13 gluing support for lid

Gluing the support piece onto the lid. I was working in the living room so some flour and a bag of potatoes got drafted as gluing weights. They worked well.

14 lid partially glued

Again, working around the sides to glue the lid. As with the base, I was able to leave sizable tabs to glue to, for four of the joints. However the joints in the sides are at a very shallow angle which means the tabs left over are quite small. I had to add small strips of cardboard to make the joints solid enough.

15c sword with supports

I folded and glued a couple of support brackets out of cardboard, cutting notches to hold the handle and blade. The handle notch had to be cut reasonably accurately. The one for the blade was easier. I just cut it oversize then slid it up the (tapered) blade until it fit nicely, then glued it in place.

15b support bracket closeup

A closeup of one of the support brackets.

16 closed coffin

Result, one closed coffin which should protect the sword quite nicely. Rather a lot of work when I could have just wrapped it in bubble wrap, but a good chance to try out some different techniques.

Secure Destruction

29 Mar

I was tidying up and found some old tape backups from years ago:

Secure 1

I couldn’t just throw them out as they might have had clients’ data on them (unlikely but quite possible). Hence the blurring of the photo for security reasons – nothing to do with bad photography!

Remove two screws and you have a small set of parts:

Secure 2

Now unwind the tape off the spools and collect it into a “scrunch”.

Secure 3 - scrunch

Chop through the scrunch with a pair of scissors – four or five cuts turns it into about 100 short lengths of tape.

Secure 4 - chopped

To show how small some of the pieces end up, here’s a closeup.

Secure 5 - small pieces

And as a side benefit, the little tape reels just cry out “use me in a Science Fiction themed prop”. They are about 20mm across.

Secure 6 - reels

Of course, there were a bunch of CDs as well. They met an 8mm drill bit in the drill press.

Secure 7 - cds

A technique which actually works quite well with the larger Zip (100MB) and Jaz (1GB) disks.

Secure 8 - jaz & zip

None of this would stop the CIA from recovering (most of) the information, but your average “go through your rubbish and see what I can find” chappie would have a lot more trouble.