The next step on the primary coolers is to construct six gate valves - these control the flow of gas in and out of each of the three coolers - using these can slow the flow or cut it off completely to service the one cooler without shutting down the plant. To make these valves I need a bunch of plastic (.040) disks. Cutting these disks are a common problem in steel mill modeling. I have two different circle cutters that I have shown before - both are adequate for cutting diameters of 1.25" and up, but problems arise when you need smaller diameters. In my case I need 5/8" disks. John Glaab of the Steel Mill Modelers meet in a presentation suggested using Forstner bits - buy a cheap set and grind the center points out - load in your drill press and you should be able to make them in a good range of smaller sizes. Other folks use architectural circle templates and a good scriber to scribe and then break out the circle. I've tried both methods and had success but did have some clean up on the edges. I just started using a different method. For me it is easy, fast, and produces any sized small disk with nice sharp edges, but I am using a machine that most people don't possess and can't easily buy.
That machine is a very old watchmaker's lathe. It was originally my grandfathers and is actually still mounted to his watchmaker's workbench - a near perfect modeling bench - high, putting your face right at the model, filled with many small drawers for small parts and tools, excellent lighting, and even a pull out drawer just above waist level with a fabric bottom to catch dropped parts. This bench is one of three that I use to model at - I have my primary one, only because it has most of my tools scattered about and more importantly, faces the television; another large one that is great for my bigger models and is lower so I use that if I am working on say the top of the blast furnace,..etc.; and then the watchmakers bench. The lathe under discussion is powered by a small motor and a few leather belts. The speed of the motor is controlled by a foot pedal under the bench. There are literally hundreds of different accessories, chucks, and other attachments for this lathe, but I primarily use the three jaw chuck and a cutter on a table that can be precisely adjusted on the x/y axis using small hand cranks. The three jaw chuck is hand tightened as are most parts on the lathe.
The process for making the disks - first - draw a 1.25" or so disk on a piece of plastic using a circle template and pencil. Cut out the disk with a pair of scissors - it doesn't have to be perfect. Put this rough disk in the three jar chuck, hand tightening it. Step on the speed pedal and as the piece is turning, crank the cutter in on the one axis that you have already set it at, cutting the plastic. Cut almost all the way through, and then pop the piece out of the chuck and you will have a nice sharp disk. I can sit there watching tv, cranking out a piece every minute or so.
Obviously, it might be hard to come by a similar lathe, however, I'm sure a Sherline or other bench top modeling lathe would work, as would even a larger bench top metal lathe.
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