Sunday, November 29, 2009

Saturday's temperature reached 40degC, so decided not to coat the mast in epoxy in the heat. Instead, we visited to hardware store to buy some 2x4 pine so make some sawhorses, and I spent the afternoon knocking them up ....and of course, hydrating. :)
Like Bob who is also building a GIS in Sacramento CA, I too decided to build Chris Baylor's solid looking horses. These are without doubt the most solid sawhorses you'll ever come across. Check out his free sawhorse plans here:

Here's how they turned out. After taking this pic, I slapped on a coat of linseed oil.

Today's temperature was a decidedly cooler 33degC, still hot, but I decided to get the mast epoxy coated anyway. I'm using the West System 105 epoxy with the 206 slow hardener. This provides plenty of working time, even in this heat. The big problem was that a VERY strong, warm and gusty wind whipped up and soon the dust from South Australia was blowing in :(
Oh well, too late, I'd already started the first of 3 "wet-on-wet" coats of epoxy. Wet-on-wet is a technique that saves a lot of labour. Once the epoxy goes stiff and tacky, you roll on the next coat, and then you repeat it. This is a really good method and one that the Goat's designer, Michael Storer, advocates. 3 Hours later, the dust, insects and leaves sticking to the mast had to be seen to be believed! Never mind, the Bosch random orbit sander, took care of that :)

About 3 hours after rolling on the last coat, the epoxy was quite hard. This is the stage when sanding epoxy is much easier rather than waiting for a full cure, and it doesn't cause a fine dust that floats in the air. I like to use No Fill sand paper, because it doesn't clog. In fact, the epoxy in this state actually cleans the paper and it stays sharp.

Just some quick pointers on sandpaper:
  • The most expensive sandpaper is the cheapest in the long run! Believe me, don't baulk at the price of the expensive stuff, it really is good and will save you money because it lasts 4-5 times longer and you'll need to buy far less of it.
  • I've found the "No Fill" stuff, made in Australia to be the best available by far.
  • They have a teflon-like coating that helps prevent clogging.
  • The good brands produce a much better swirl free finish too. This is for three main reasons:
  1. The grit particles are more uniform in size, are harder material and are sharper.
  2. The grit particles have a stronger bond to the paper substrate and don't dislodge. If you are getting a lot of swirls appearing on your timber (frustrating!), this is because the grit particles are dislodging and being rolled around between the paper and your timber, producing those hard-to-remove swirls.
  3. The grit particles are actually wider at the bottom (the side bonded to the paper), and have a sharper point that does the cutting.
OK, that's a very brief tip about sandpaper.

My mast is now nice and smooth and awaits a few coats of UV resistant marine spar varnish.
This pic shows the mast suspended by two screws through a couple of timber scraps clamped in the jaws of these terribly cheap (and very crap) work benches. (These things are rubbish, and only good for this sort of use. A sticker on them says they will support 300kg, but I think that's very optimistic)

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