Pipe Measuring Project

A forum to discuss the arcane art of making uilleann pipes, reeds, and set maintenance.

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Richard Evans
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Re: Pipe Measuring Project

Post by Richard Evans » Sun Mar 03, 2013 3:41 pm

I've been looking at the B chanter bore data, beginning to think about making a set of reamers. How to best deal with the oval vs. round probe measurements? Looks to me like one practical method would be to use the round data but be prepared to ream a little deeper when finalising the bore. Another method would be to take the mean of the two insertion depths for each diameter. David Quinn on his CDROM demonstrates a method involving adding 75% of the difference in insertion depth to the round bore (minimum) depth but I don't understand the reasoning on that one.

Any thoughts Bill? David?

Thanks
Richard

billh
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Re: Pipe Measuring Project

Post by billh » Mon Mar 04, 2013 4:49 pm

Richard Evans wrote:How to best deal with the oval vs. round probe measurements? Looks to me like one practical method would be to use the round data but be prepared to ream a little deeper when finalising the bore. Another method would be to take the mean of the two insertion depths for each diameter. David Quinn on his CDROM demonstrates a method involving adding 75% of the difference in insertion depth to the round bore (minimum) depth but I don't understand the reasoning on that one.
I don't think there's a single "right" answer to that. If you want to reproduce the way a chanter behaves now, then you want to produce equal cross-sectional area. If for a moment you assume you are able to produce a round bore (probably not strictly true!), then the diameter of the reamer at each depth should be in between the minimum and maximum diameters at each depth. The mathematically correct answer is SQRT(A*B), where A and B are major and minor diameters of the ellipse. Just picking midway between will do for our purposes. If you want to make a refinement and assume that your actual bore will be 'instantly oval' due to the flexing of timber away from your reamer, then it may be that you want to make your reamer a wee bit oversize - I'll leave it to David to comment as to whether that was his thinking. In any case, if your result yields a bore that lies halfway between the round probe and oval probe results, you are probably close to the acoustic behavior of the 'current, actual' bore.

When a bore shrinks it also become oval. If you assume on the other hand that some of the ovality of a bore is due to shrinkage, then of course the 'target' diameter will be larger even than the 'major axis' of the ellipse, i.e. the 'original' bore was, formerly, everywhere larger than it is now. If you want to try and reproduce the maker's intention, or the instrument's original condition, you will probably end up pursuing this line of reasoning. However it's a very slippery slope and I don't have any faith that we know enough to reliably make these sorts of extrapolations. As far as I know it's not possible to fully separate out the two causes of ovality, i.e. differential shrinkage versus different elasticity...one of which would have been present in the original instrument, as it left the maker's hands, and the other would not. In reality both factors are probably in play.

Bill

Richard Evans
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Joined: Tue Feb 23, 2010 3:21 pm
Real Name: Richard Evans
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Re: Pipe Measuring Project

Post by Richard Evans » Tue Mar 05, 2013 3:37 am

Thanks Bill. Looks like I need to get in touch with one of my friends who makes pipes, but who can also manipulate spreadsheets, which I can't!

Cheers
Richard

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