Hello all! I’ve been trying to make an 8-hole PVC flute, but I can’t seem to find the right dimensions. I’ve tried using the Flutomat calculator, but I can’t seem to make a good flute from using it (for the 8 hole). They all seem to be very weak compared to my 6-hole flutes. I’ve also tried just starting with the flute tuned to a C, and then making a hole that looks like it’s in about the right place, from pictures, for the C#, and then another for the D (yes, I tuned it “correctly”). Again, it’s weak. I’ve also looked around to find measurements, and, of course, no such luck there either. Someone told me that the holes need to be big (naturally), but they seem to keep ending up too small. 
So, if anyone has an 8-hole D flute, also known as having a C foot, whether conical, or cylindrical bore, could you please take a quick measurement of how far down the tube the bottom two holes are, in reference to the embouchure hole, and post it here? Or if you just have a realistic suggestion, that would be appreciated too. Thanks!
That Doug feller has made a couple of 'em…
https://sites.google.com/site/dougsflutes/makingasimpleirishflute
Yeah, but sadly he only goes into 6 hole…
so it’s only 3/4ths?
the last hole doesn’t make much difference
let’s make it 7/8ths 
There is a flutomat calculator for 8-hole flutes. The link to it is at the top of the 6-hole calculator. Try using 7/16" vent holes. There should be no problem making a good playing flute from the numbers given by the flutomat calculator.
Ah ha! I figured out the problem. The absolute bottom note (with both vents closed) should be a C. The Flutomat has it almost a B, but the second note (one vent open) tuned to a C#! 
So, once I changed the Hertz to the right number, all was well. Now I have a perfectly nice and powerful flute! 