Logical Engine function casing

This is, I think, the final design for the function casing for the Logical Engine. I took 1/2" acrylic sheet and fed it to the ShopBot, making a series of sections, each of which can be lifted entirely up and out of the casing if they need to be repaired. An additional guide screws on the outside which further aligns the rods.

This idea was sparked by a member of the DIY Book Scanner forum, Charles Morrill.

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IMG 0255Closeup of the alignment system.

The horizontal slots were easy to make with the ShopBot, but those slots would allow the rods to shift horizontally. The outside guides simultaneously restrict their horizontal movement and precisely vertically position each horizontal segment to be one inch apart (plus or minus a few mils).

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The rods still need to be significantly straight. I found that the steel has a simple bow to it that can be corrected by applying a force to bow the steel in the other direction. They don't appear to be randomly twisted or bent, so hopefully I wouldn't have to go the route of destressing with heat.

Acrylic casing for Logical Engine modules

I haven't written in a while, and that's because the attempts of the past weeks had nothing but problems. I moved from the Trotec laser cutter to the ShopBot to see if I could cut out parts from acrylic. Wood just wasn't good enough. So in learning the software and the machine, I ended up with parts that weren't designed right, parts missing features, bits that broke. Finally I managed to use the right bit (Onsrud has a great selection of bits that work very well with ShopBots) with the right file, and ended up with a full module casing made out of 3/8" acrylic.

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I had some acrylic left over, so I cut a 10-position Geneva mechanism:

 

Shopbot geneva

 

The coming weeks will be devoted to preparing for MakerFaire in NYC. I'll be dressing up the Geneva mechanism, and ShopBotting a few more mechanisms such as a ratchet counter and maybe some simple rod logic, and putting them all together in a sort of Victorian Cabinet of Curiosities. They'll all run continuously using a motor.

Wooden casing for Logical Engine bit slice

Behold, two sides for the casing of a bit slice, cut using the Trotec laser cutter into 1/2" plywood. I wonder if wood is strong enough? If so, I could save a lot of money, since acrylic is much more expensive than wood. And wood can be stained to look 19th century :)

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The slots are for metal support rods which hold the bit rods in place. If a bit rod needs to be adjusted, the support rods can be slid out, and the bit rods can be removed.

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The support rods will be held in place with sheet metal strips bolted on through the holes. Maybe even brass sheet metal. Decorated etched brass sheet metal strips.

Each pair of sides takes 1h45m to cut.

Some interesting tips I learned while making (and failing to make) several of these: apparently when the laser cuts through wood, it generates a lot of carbon particles. Running the gas constantly helps blow the carbon particles out of the cut, but if the laser doesn't cut all the way through, a second pass doesn't do much. The problem with a partial cut is that the carbon particles tend to stay stuck in the cut even with the gas on. During the second pass, all the laser is doing is heating up the carbonized wood rather than cutting through the rest of the thickness. Therefore, it's important to turn the laser speed down to make a full cut in one pass. Keeping the speed of the laser high and making several passes doesn't work on wood. I had to use a speed of 0.2 (approximately, but not exactly, 0.2 inches per second).

Considering that each side is about 15 inches long, and considering all those cutouts, you can see why it takes so long to cut.

Also, for some reason, the Trotec 500 has a problem with speed settings between 1.0 and 2.0 (not inclusive). Some fine programmer apparently felt that these speeds should also result in the laser power being turned down. So avoid those speeds.

If the ShopBot at NextFab had a drill attachment, I could probably cut this out on the ShopBot a lot faster. I should ask if they can get the drill attachment. The problem is that the standard spindle on the ShopBot rotates too fast for drilling, and cannot be slowed down to drilling speeds.