Month: May 2010

Back to casting

So back to casting again, now the mini degasser’s working (and working well at that!).

Success in casting the hemispheres in water-clear styrene!
Last night I carefully trimmed the silicone moulds back to make the walls very thin, so they were drawn in with the surface tension as the styrene shrinks. This meant no streaks anymore, and there doesn’t seem to be any noticeable distortion of the shape.

The biggest problem us then actually getting the styrene out of the tin, especially in small amounts. It’s provided in a paint-tin, so unless you’re using the whole lot in one, you need a way to extract small amounts, and a plastic mixing cup is too big to fit in. So today I quickly brazed together mini ladle out of the stainless lid from a cocktail shaker and a long bolt with a couple of nuts for grip.
I’m keeping it in a glass jar, since I only have one sort of styrene to use, and apparently it’s not hygroscopic like the PU resins are. So this’ll keep it from needing repeated cleaning.

Colour mixing
Tonight I finally got a really rich chocolate colour for the only remaining casting order from before Confuzzled. “What would a melted KitKat look like?” was a good visual guide.

10pts Green, 4pts Red, 1pt Black

The resin claws and footpads are setting overnight. As tomorrow is MCM Expo and I don’t know what time I’ll get home, casting will probably resume on sunday.

T-shirts
I’ve been making enquiries into new variations on the standard UKFur design shirts. I’ll be getting a few “4XL” in in the unisex. Technically they’re still 3XL, but of a shirt type where it corresponds to a 54/56″ chest rather than a 50/52″.

Also been gaining interest in getting some shirts in fitted ladies sizes. Currently looking at getting some in standard black.. but also pink. And other colours too, of course!

http://www.promotional-store.com/%28ec5bicj0gpbrwr45b3qfzt45%29/product.aspx?sqs=5lBamEO6TJFdo0YhKUaoMLQ1W5R4IEWzphCPIqTnTSY%253d

Oddly enough, this one is a heavier weight of cotton than the one I was previously looking at, but much more affordable, and should put the ladies shirts at £12 in whatever colour.

As the next LondonFurs meet is only a week away, I’ll likely make the next order after that (as I may need the extra cash I’ll hopefully earn there, to make this increasingly large order).

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

Scavengers amazement

I just want to say, I’m always amazed by the things people throw away these days.
If the adjustable bed I found a few weeks back that’d only had the cable pulled out (contained some ok motors, a lot of angle iron, two 250Watt linear actuators and proof of my disgust of commercial medical equipment design), today I found a 19″ TFT monitor, a proper powered photo-scanner and a PC base unit with a dual-CPU mainboard (admittedly full of twigs, but it’s been dry recently and it was under a tree).

I asked the householder first, and they said the monitor still worked when it went out. After a day of safety drying time and checking inside the housing for debris, I’ll give it a go.

How old will I be when someone just chucks out their old household Replicator or robot servant because they can’t be bothered to feed it into the recycler?

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

Some experimental pretty things

I recently took a £20 commission from a dear friend to make a basic modification to a set of driving goggles. She wanted them “steampunked” and I had a lovely bit of filigree from a 1920/30s wall clock. I’m sad to see it go, but it did seem to be the perfect use for it. So on with making some Winged Messenger goggles.
The first thing I had to do was cut out the middle of the “sun flare”, as it had an odd number of points.

I then filed and put it on the sanding disk to get the burrs off and round the edges. The natural tarnish looks good and authentic, so there didn’t seem need to polish it.
The brass is also thicker than I remembered, so it didn’t seem like it would need extra reinforcement, and I just drilled out the existing holes to put in some rivets.
Standard rivets? Yes. But the frame on the goggles is silver, so the aluminium rivets fade in very well. Okay they’re not real metal (aluminised plastic frames), but the mix is pretty good and it drilled nicely. Too nicely. It was hard to stop the drill pulling through and through the padding.

Still, basically turned out nice. :)

Will be dropping it to them at Expo at the weekend rather than posting it as the timing’s not right for postage (will be refunding the postage, of course).

I’ve also just tried styrene water-clear resin for the first time, and have learnt a few things.

  1. It’s cheap.
  2. It STINKS. The whole workshop. Even after airing it for several days.
  3. 6% shrinkage is a problem when casting eyes, unless you’re costuming as something from a Rob Zombie music video.

The latter is actually an interesting effect, though likely to be hard to reproduce exactly. The pulling away from the mould due to shrinkage during gelling has left river-delta style patterns down the sides, with a clear centre underneath.
It may be avoidable by using a double-fill to take up the slack (but that may increase optical distortion), or a very thin mould that will pull in with the shrinkage due to surface tension (but may distort the shape).
The urethanes are more expensive, but looking more reliable. Will be making a comparison set tomorrow. The cure time is much shorter on PU’s compared to styrenes (3-5min vs 15-20). Gives much less time for proper degassing. May be doable degassing in-mould in a small fast chamber.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

New MkIII benchtop degasser

So I’ve finally managed to get some bits together and assemble the new smaller degasser.

I used the fire extinguisher from the MkI degasser, which I cut shorter. Sadly it’d been out in the rain, as well as having been used for degassing previously.
Even sanding it heavily obviously didn’t remove all the traces. I used a nice zinc primer on the inside which seemed to take, but once I went over it with white enamel it refused to bond where the resins had previously splashed.
Next time I’ll fork out for some Hammerite. I’m not even sure this enamel will survive cleaning any spatter off the inside later.

Found that Poundland is doing rather large tubes of two-part epoxy! Handy stuff to have around. Especially for £6 cheaper than Araldite. It does reek of fish before it sets though.
The 99p Shop nearby provided a cheap frying pan which got cut up into the lid surround. Fitted so tightly there was no need for a retaining pipe-clip strap.

I brazed a load spreader to the UTA manifold, and glued it on. The nossle holder of the extinguishers base perfectly holds the up-to-air filter so it’s a ready-made support. Without it I’d be worried about the lever-handled ball-valve dislodged the manifold after only a few uses.

Made a proper handle from some curved extruded aluminium and some bolts. Again, glued onto 10mm polycarbonate cut to size. I’m unsure if it’ll need internal lighting yet. The white inside reflects a lot of ambient light and it’s not as deep. Will see.

So I now have a nice small degasser for using on the workbench! Both controls are nice easy to use lever-handled ball valves. I should be able to leave the pump running to the catchpot and simply switch the two valves for fast control.
It should make the degassing of the resins prior to pouring them far simpler. And if one is sealed under a static vacuum, the other chamber can be used under pumped vacuum.

One thing to note is that it looks messy because the Poundland 131 epoxy is thinner and slower-setting than Araldite. But if it works, it works, and it seems just as strong when set.

As another improvement to the system I also mounted up the MkII chamber, pump and catchpot to a plank of wood. It reduces the footprint a bit but mostly stops them from moving around in use and flexing the pipes which can result in leaks or manifolds breaking.

Will try to get a short demo video up on youtube.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

Buster: Car and batteries examination

So here’s the lil fella I picked up for £3..

This little mock quad-bike is pretty lightweight. There’s some metal framework for the axles, but the rest is all a moulded plastic body. I’d be worried about it taking the weight of extra parts if it wasn’t designed to cart around reasonably large children.
The rear drive wheels are pretty worn, and all are the cheap hollow plastic variety.
They’re a lot wider and with less grip than the ones on the original Buster’s frame as best I can judge from the few photos. I’ll keep it in mind as it may have issues with drive and steering.

The rear wheels have separate drive motors, driven together on a static axle. Cheapest design, but running the motors together should be fine.

Controls are pretty simple. Two sealed 6v lead-acid batteries, a two-button toggle for forward and reverse, another for fast and slow (seems to switch the batteries from serial to parallel connection, so 6v to 12v) and a foot pedal switch to make it go.
The controls on the handlebars are purely for show. There’s nothing in them beside a horn powered by a separate set of AA batteries.

I should be able to strip off a few odds and ends, but as it’s a monocoque they’ll be a limit. And since I’m running out of space here, my Buster will need to be able to be stored outside.
I suspect the control electronics may be a bit smaller, even using as close to 1970s parts as I can. Maybe if I upturn a plastic bin on them that’ll be sufficient rainproof housing.

I was quite excited to find it used two 6v batteries, as that’s what Buster was designed to run on. However when I measured them they only read 2.27v each.
Lead-acid batteries are also not meant to be concave.

My charger wouldn’t read it as needing the charge. Rather wish the charger gave out more information on battery status. Charging complete has the same indication as being unable to charge.

As a last-ditch effort I pried the sealed cover off one of the batteries and found three rubber caps. On pulling one off there was a characteristic sucking noise. All the cells were under vacuum. So I suspect the car may have been left out in hot sun for a long time, and literally boiled the batteries dry. So when they cooled the covers were sucked on.
With nothing to loose I grabbed a bottle of demin water and proceeded to refill the cells with a syringe through the tiny vent holes.

Sadly, that didn’t work. Even after a few days for the plates to re-wet, the readings didn’t change at all. Due to construction there’s no way of getting electrolyte back out again to check the gravity. At this point though it’ll just be simpler to spend the £20 buying a new set of more powerful batts.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]