I have a bit of free time on my hands and I was toying with the idea of trying to build a low D whistle. I found a whopping oneweb site and was wondering if any one had any tips they would like to share with me before i begin this little experiment.
My new found love is PVC. For me, it’s been easier to work with and has a very “flutey” sound. I make the mouthpiece part of the whistle differently than the directions you found. I stole the design from my Silkstone whistles and I think it’s much easier and you kill two birds. You create the window and the airway channel. Here’s some pictures of one I did in copper to illustrate… Most importantly, don’t get discouraged. Play around with different dimensions and have fun!
Tom
In making that copper low D make sure you do not make the window too large. I would make it too small rather than too large. If you are careful you can make a very nice low D.
Ron
it’s the shape that’s more important than the size. If you make the window too small on a lower keyed whistle you won’t be able to get the Lowest Two tones to sound. If you make it too big you might have problems with the upper register. The copper low D’s I made had rather large windows and worked just fine. They just had a little trouble in the upper register, I had to blow harder or it would skip down into the lower register. But at least the lower register played.
that actually looks pretty cool, i think i might have to try that. 
thanks for the help.