Re: [PSUBS-MAILIST] ASME PVHO

Hugh,

Good point on the difficulty in measuring exterior diameter on a large cylinder such as a hull. That has to be done at the exposed ends before an end cap is in place. As you pointed out, what can be measured on the exterior is the variation in diameter.

Once the baseline measurements are established on the bare-bones cylinder, I expect the challenge is going to be in controlling distortion introduced by major cuts and welds such as the hatch installation. That's one more reason I'm going to be very picky about who welds on my hull.

Dan, you know who I'm going to be calling for advice once I get to that point. I'd love to see posts about what others have encountered during hull fabrication or what they encounter in the future. This is one more reason for keeping good logs throughout the design/build process.

Thanks,

Jim

In a message dated 11/3/2010 12:46:25 P.M. Central Daylight Time, hc.fulton@gmail.com writes:

3 point measuring is generally accepted in Engineering as the most accurate way of measuring roundness on shafts and bores so rollers would be a great indicator as discussed, I think by Jim, earlier in the thread.

2 sets of rollers would also give straightness a good indication over the length. Jim’s method of using the rollers with top and bottom indicator would be good but difficult to get true diameter. However true diameter is almost irrelevant as differences in diameter are the crucial indicator.

1% is the allowable which on 48” diameter is almost ½ an inch(0.48”). If you are within ½ the diameter of an opening then you can add 2% of the inside diameter of that opening. So next to a 24 inch hatch you are allowed almost an inch (0.96”) difference between maximum and minimum diameter.

To be honest that makes me nervous that much but welding of hatches and windows pulls it out of shape somewhat. I have just had mine measured as the hull is now finished and the maximum was 14mm. that was allowable as it was next to a window and a hatch. I am going to try and press it out a wee bit if possible. My template chord was almost 9 inches in length and the deviation was 1/8 inch. My hull was really complicated and looks like swiss cheese with holes all over the place. Hugh