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- Jun 24, 2010
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Most of Trimble math and calculations are beyond my ability to understand them but I am unsure if a slight deviation in dowel size is a problem as long as the mandrel diameter and the offset are adjusted accordingly. With the small dowel as calculated it is difficult to get a pin sized to the correct diameter. For instance in his 1" bore example the dowel is .150. 5/32 is .156 and is a standard rod size. Would using the oversized dowel be a problem as long as the mandrel and offset are adjusted accordingly? A 1 1/8 bore would give a dowel of .16875. Would a 5/32 diameter be too much variation?
The answer to your question is found by looking at how any T/B and D/B coordinates land relative to the plot. The only math is dividing two numbers. It might fall within the recommended guidance range, or it may push/exceed one or more of the boundaries. I happen to know that several commercial & operational rings land around the periphery of the 4 constraint curves, which I suppose is good news. To what degree, or how well they run, or reliability of measured dimensions is different discussion. But if you have to make rings from scratch & you accept the Trimble methodology, why not follow the recipe? Aim for the bullseye or consciously target an area that makes sense to your engine and/or skills?
To your second point (IMHO) if someone can produce the other 99% of a typical model engine up to and including the last but critically important bits: a finicky, thin section cast iron ring, a matching piston, both to +/- 0.0005" & appropriate finish, I just don't see how turning a 1" long straight dowel shaft to within 0.001" is a significant or time consuming challenge by comparison. The dowel seems easy by comparison. What is achieved by swapping in a different sized nominal 32nds stock at hand & making mandrel / spacing adjustments on the fly? This is just my own view but I accept there are many ways to get the job done.