I don’t think I’ve posted a pic from this angle:

We’ve got roofs. Four of them. Two will be green roofs, for which we need to order over two thousand plants. The soil is only 100 mm deep, so it’s mostly tussock and succulents.

It’s surprising how quickly the house has gone a bunch of bits of wood, sticking up in the air, to a house. Putting the roofs on was a major transition, even if one of them is still made from tarps.

This is above the bedrooms:

In other project news, testing the third and final circuit board for the Fannies reveals that it works. Woohoo! Here’s a tiny, two batteries to five volts converter that kicks out 600 mA. Three Watts is pretty grunty for something this small:

I did discover a new potential failure mode. The heatsink, the shiny bit of aluminium in the pic above, is a little bit small, to fit into ludicrously tiny space. This is fine, coz the power supply is so efficient that not much heat needs to be sunk. Well, that is to say, the MAX1703 chip is very efficient (90%+) at the designed maximum load. However, when turned down, the efficiency drops as low as 50%, and the heat to be sunk goes up. Up lots. The Fannies have a ridiculous peak power, but most of the time, they’ll be turned down, so major heat production. Hmm… I don’t have the kit to test the variable load properly, and there’s no room for a bigger heatsink without changing a whole bunch of other stuff. Ah, hell, we’ll just try it and see if it explodes.

Scuffing PVC
And now, a question. I’ve some clear, flexible PVC tubing that I’m using as light guides. I want to scuff up the inside of the tube. I’ve yet to find a good way to do this.
It’s 5 mm inside diameter, to fit snuggly over the LEDs. I want the LED light to come out evenly along the length of a 100 mm piece of tube. Right now, it’s too shiny, and the light just bounces along and comes out the end. I want it out of the sides and scuffing up the surface works wonders. However, the surface is the inside of a 5 m tube, so too small to easily get sandpaper down there.

I’ve tried:

  • Acetone to dissolve the surface. Didn’t work, just made it tacky.
  • DEET, the insect repellent stuff which dissolves lots of plastics, that didn’t work either.
  • Filling the tube with sand and shaking it didn’t work, or didn’t make any impression after I duct-taped a sand-filled tube to the washing machine for a week.

Best I’ve come up with so far is fine sandpaper taped to a bamboo skewer. It’s just small enough to fit in, only falls apart every five minutes, and I can do a tube in about twenty minutes. I’ve got 39 more to do, hence I’m looking for a better option.

Option 1 – Ideal would be a solvent, but if acetone won’t touch it, then I’ll have to round up something really nasty, like tetrahydrofuran.
Option 2- Something abrasive that fits onto a thin rod better than sandpaper. Abrasive heat shrink does exist, but is mainly for handles. I don’t know if it’s abrasive enough or I get get some small enough.

Any suggestions?

18 thoughts on “Progress”

    1. Yeah, that was attempt three. Either my sand isn’t sharp enough, or I’m not shaking it right, or it’s just very erosion resistant. Dammit.

  1. I’m going to suggest a small ball of steel wool on a string being dragged backwards and forwards through the tube.

    It might work on the end of a stick like a big scrapy q-tip too.

        1. That is an awesome suggestion, which led me to this from NZ Brush. I think that will do the job quite nicely.

          I love that there is a company called NZ Brush.

          (I’m going to try the steel wool idea first though.)

    1. Bore brush for cleaning rifle barrels? Not steel, but brass . . . 5mm is approximately 20 caliber, so probably could fit a 22 bore brush down it, and they come threaded with rods, etc.


  2. You can get modelling files that are circular and less than 5mm thick. They are about 100-150 mm long – I used to use them for finishing figurines before painting them (when I was into that).

    … and the house is looking more impressive and house-like by the week!

  3. I’ve been trying to scuff the inside of PVC for quite a while and so far haven’t gotten anything good. The best thing I’ve come up with was to put a green 3M pot-scrubber sponge, the stuff with the imbedded glass that can scrub stainless steel, on something vaguely like a screwdriver, chucked the screwdriver in a drill, and run that through the inside a number of times whilst spinning, a la a gun cleaner. It’s done okay but it leaves mostly radial scratches rather than the random scratches I want. My next try will be to build something like a cylinder hone with 600 grit sandpaper on each of the hone faces. 600 grit double-sticky-taped to a dowel 0.5mm smaller than the ID of my PVC also did a pretty good job, but it again left mostly radial scratches. Both did manage to make the PVC opaque. I suspect I’m using it for the same reason you are: optical diffuser for extremely bright, near-point sources.

    1. Update – I’ve found a round file from the local model shop. It’s small enough to fit in there. Time to scratch up each tube is about five minutes, which is doable for forty tubes.

      It abrades only a small area at one time, so getting an even scratch pattern is tricky, but the tube will have an additional diffuser over the top of it, so I can live with that.

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