I’m looking for someone that totally understands the calculated results for the Purdy Rx calculator. I’ve gone in and entered by numbers which are similar to the example below. I understand paragraph (2) those numbers which again mine are similar to. I understand paragraph (3) that the distance should be measured from the tuner barrel face, not the tuner inner tube. Now comes paragraph (4) and a response to it paragraph (5). This is where the confusion sets in for me. I’m okay up to the “it appears sentence in that paragraph. Where does the 250 plus 0.3 x 250 come from? I understand the 250 number but where does the 0.3 come from? Now for paragraph (5), total confusion. So, when using the result numbers, you do the subtraction as he stated for the End Correction to get the right setting? Then suddenly the weight ring comes into place which was never discussed or I don’t believe used in the calculations. Again that 0.3 number.
I hope someone out there can help me understand this all.
This example is for a 24” barrel. Much as I have, I have, a 24.5”.
According to Purdy Rx, acoustic length needs to be 27” for 9th harmonic. I removed and cleaned the Harrell’s tuner but left the extension ring off that I have for it. I’ve never found any instructions online for the tuner. It appears to me to have range from 0 to 5 with 1/4 marks. The “barrel” has 25 clicks per revolution. I was originally thinking this was some sort of length scale but now I’m thinking it’s just a way to count clicks.
Since the optimum harmonic length of 27’ is longer than the physical length of the barrel and we desire the ability to fine tune the barrel, we install the Harrell’s tuner. Most of the online Purdy calculators already have the key dimensions for the Harrell’s tuner already entered and my measurements confirmed those default values. Using a 1.34” tuner diameter and a 0.62” inner tube diameter, the end correction reduces the optimum tuner length to 2.814”.
Here is my question. Is the tuner length measured from the inside face, which contacts the end of the barrel, to the edge of the inner tube or to the face of the tuner barrel? I’m guessing it’s to the face of the tuner barrel since that’s the distance that changes as the tuner barrel is turned in and out.
So, with the tuner barrel set at 2.5, which I’m assuming means 250 clicks out from zero, the distance from the inner face to the face of the outer barrel is about 2.56”. That’s still a little short of the 2.814” needed. If I adjust the tuner to 500 clicks, the length is now about 3.5”. So, it appears that the required length of 2.814” can be achieved somewhere around 325 clicks (250 plus 0.3 x 250). Is this the way the tuner works with the Purdy Rx? If so, then I don’t think the extension ring is necessary.
You are correct that the acoustic length for your 24" barrel is 27, but I think you may have forgotten to remove the End Correction to account for the tuners opening diameter. With the weight ring in place, the EC would be figured by multiplying the ring's opening (.92) by .3. This would be .276. Subtract this from the from the acoustic length, 27 - .276 = 26.724. To figure from the muzzle just subtract the original barrel length. 26.726 - 24 = 2.726.
I hope someone out there can help me understand this all.
This example is for a 24” barrel. Much as I have, I have, a 24.5”.
According to Purdy Rx, acoustic length needs to be 27” for 9th harmonic. I removed and cleaned the Harrell’s tuner but left the extension ring off that I have for it. I’ve never found any instructions online for the tuner. It appears to me to have range from 0 to 5 with 1/4 marks. The “barrel” has 25 clicks per revolution. I was originally thinking this was some sort of length scale but now I’m thinking it’s just a way to count clicks.
Since the optimum harmonic length of 27’ is longer than the physical length of the barrel and we desire the ability to fine tune the barrel, we install the Harrell’s tuner. Most of the online Purdy calculators already have the key dimensions for the Harrell’s tuner already entered and my measurements confirmed those default values. Using a 1.34” tuner diameter and a 0.62” inner tube diameter, the end correction reduces the optimum tuner length to 2.814”.
Here is my question. Is the tuner length measured from the inside face, which contacts the end of the barrel, to the edge of the inner tube or to the face of the tuner barrel? I’m guessing it’s to the face of the tuner barrel since that’s the distance that changes as the tuner barrel is turned in and out.
So, with the tuner barrel set at 2.5, which I’m assuming means 250 clicks out from zero, the distance from the inner face to the face of the outer barrel is about 2.56”. That’s still a little short of the 2.814” needed. If I adjust the tuner to 500 clicks, the length is now about 3.5”. So, it appears that the required length of 2.814” can be achieved somewhere around 325 clicks (250 plus 0.3 x 250). Is this the way the tuner works with the Purdy Rx? If so, then I don’t think the extension ring is necessary.
You are correct that the acoustic length for your 24" barrel is 27, but I think you may have forgotten to remove the End Correction to account for the tuners opening diameter. With the weight ring in place, the EC would be figured by multiplying the ring's opening (.92) by .3. This would be .276. Subtract this from the from the acoustic length, 27 - .276 = 26.724. To figure from the muzzle just subtract the original barrel length. 26.726 - 24 = 2.726.
