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Hello: I agree. Bygraves could be build. However, there are some cumbersome questions, the most obvious being, How to generate a drum-shaped scales with the required accuracy and resolution. Remember, we will have to maintain sub-millimeter acc/res over many turns, with "many" meaning perhaps 20 to 50. This should be possible, but is still not easy. If someone could generate the mechanical construction and quality assurance methods for this challenge we could talk about manufacturing more seriously. Her are my ideas: Personally, I am thinking of an ink-jet head printing on a turning drum where the printing is synchronised with a digital encoder on the drum' s axis. The process control could be handled by one of the relatively simple contollers on the market. Another approach would be to replace the ink-jet printing with an engraving system. With the first  I personally have experience, with the second none whatsoever. However, more problems lurk. What are the limits for excentricity of the drums when in use? How about friction? How to stabilize the thing when under the influence of temparature changes, humidity, sun's UV, spray salt water, etc, etc. So, you can see that the conceptual simplicity of the Byraves is offset by many practical obstacles. Compare this, for instance, with the Ageton method (H.O. 211)! Only 12 pages of a table, a sheet of paper and a pencil is virtually all you need to get a generally higher res/acc than with a practical Bygrave. Yes, you will also need the skill and concentration to exercise the HO 211 calculations under virtually any condition at sea - particularly when you are a submarine commander at war. Well, I guess, in this case a Bygrave, well designed under a government contract, does make sense! --- On Fri, 7/3/09, Greg Rudzinski <gregrudzinski@yahoo.com> wrote: From: Greg Rudzinski <gregrudzinski@yahoo.com> Subject: [NavList 8924] Re: Manufacture new Bygraves? To: "NavList" <NavList@fer3.com> Date: Friday, July 3, 2009, 9:40 AM There must be a combination of PVC tubing that fits on itself snugly. If the white PVC were engraved with black and red scale markings as a regular plastic slide rule is then I think you would have something. On Jul 3, 12:18 am, <engin...@clear.net.nz> wrote: > A few years ago, when I and a couple of friends wanted each to own a gear hobbing machine, we cooperated. One made the casting patterns and saw them through the local foundry, another did the heavy machining and I did the small parts like feedscrews and their nuts. It occurs to me that several handy people could combine their skills to produce replica Bygraves slide rules. There will surely be someone who knows where to access tubing in which each size nests snuggly in the next largest size, someone else will know how to produce hard-wearing replica scales, another may be prepared to turn the bobbins at each end and I would volunteer to do small bits of metalwork. The results do not have to make profits, though a little would be nice. Since there seem to be very few surviving Bygraves calculators, one could at least have the satisfaction of owning a replica. The starting point of course would have to be accurate, dimensioned drawings of an original, preferably following the metric system, so the manufacturing consortium would not have to be confined to the USA. > > Any offers/takers?