Saturday, August 30, 2014

Digging in the Dirt

The XR311 is painted up (not by me) and looks pretty good -- especially for the cheapest material Shapeways will print:

Unfortunately I can't offer that model for sale or download. But I did put the tires up for anyone to print, and re-organized my Shapeways store a little.

Went into TechShop today and tried out the billet of 7075 alloy I bought. Different stuff -- it was almost like first day on the lathe again. The main alloying element in 7075 is zinc, followed by magnesium. It is a high strength alloy -- comparable to steel in some of the tempers -- first developed for the Mitsubishi A6M "Zero" warplane. Corrosion resistance is worse than average, and machinability is considered only average. My experience with the stuff is that it made tough, springy chips that refused to break and were difficult to free. It looked very shiny when being cut, but left an obvious series of tool ridges even at extremely low feed rates. It also pushed up in cutting, leaving ridges at the ends of cuts.

So it was a good experience, but isn't going to wean me from the 2011 -- which is so machinable it is described as a "free machining" alloy. The primary alloying element in 2011 is copper, and it goes back even further than 7075; the 2000 series was known as Duralumin in 1904, when Alfred Wilm developed it at Dürener Metallwerke Aktien Gesellschaft. It is also an age-hardening alloy; left to itself, an object machined out of 2011 will slowly gain in strength until it reaches full temper.

What I was really hoping for was improved scratch resistance, but so no. The next alloy I'd like to mess around with, though, is 6061; practically pure aluminum (less than 1% of magnesium and silicon, plus a varying bit of iron, copper, zinc, chromium...) It is probably the most common general-use alloy out there, although one of its major strengths for general use is the high weldability.

What I'd really like is anodizing. But I'm going to have to live with powder coating (there's a class on Monday...if only I had sixty bucks to spare!)

Oh, yes. The machining. I managed only two finished grenades today. Outstanding orders as of this morning are six of the ones without springs, and one with a spring (which takes about twice as long to make). So about another hundred bucks coming in as the payments trickle in on this last batch. That will help.

Notice the snap lecture above? I've been doing that a lot. I set out to write a Tomb Raider/SG1 fanfic because I thought it would be fun. As of chapter 5 and about 20,000 words, I've settled down into a routine; spend a day or two looking up fun obscure facts, then condense them down into one or two pithy paragraphs.

Some scenes go faster, some take more. For a mere paragraph or two with Lara walking along a busy street in Cairo, I had to look up a huge volume of things, including colors and fare schedules of the rather complicated cab system, typical cat-calls (and a brief review of gender issues in modern Egypt), the filmography of two actresses and a little bit about the family of Alexander the Great, typical dress, the details on a nice outfit for her (no -- the shorts and turquoise top are not street wear!) and of course lots of maps and place names.

I'm overdoing it, of course. But its fun to have practically every scene an info-dump of the colorful and the obscure, and the readers seem to like it too...I have forty or fifty people following me already, waiting for new chapters.

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