Need help reading blue prints for wood horns.

[djn]

Hi All. I just bought a wood lathe and want to build a pair of 1Khz Yuichi horns. On the blue print there is a center line that is ticed off at some increment but I can't figure out what the increment means.

See the pic below. The increment starts at 4 and ends at 16. I've been reading blue prints for years and have never seen where a segment is not marked for length.

[DougL]

The Tic marks are the width of the horn from the center in MM.
Note the 6 mm from the throat is 12.5 mm (total 1 inch diameter)

At to 10 mm from the throat, the radius is 31mm
At 14 mm from the throat, its 75 mm radius ( about 6 inches diameter)

[djn]

Yep, I get that Doug, but I don't think that the station marks on the CL is mm.

[DougL]

I see what you mean. Could they be Centimeters?
Clearly the 4 to 6 in the throat is labeled "20" on the outside of the horn.
So the throat depth is 20 mm, the center-line starts at 0, which is the zero point for the 170 mm radius.

[jinkslynx]

Looks like the distance from one increment to the next in cm.

[dumptruck]

I thought I'd have a go at doing this drawing to scale, and it doesn't seem to work out at all? The 104mm line doesn't reach the outer radius if those are supposed to be cm up the middle. (edit: whoops, made a mistake, fixed, but same problem still)

[dumptruck]

The width lines make don't make a smooth curve either. I guess I don't get it.

[djn]

Your drawing sure does help DT. I think the numbers are markers not measures. So if I start at the crosshairs and count my 10cm for each station marker, it seems to get close to working out. I agree though, that the drawing is not right.

I can whip one up out of plywood and measure it.....sound wise.

[GM]

Originally Posted by djn

Yep, I get that Doug, but I don't think that the station marks on the CL is mm.

Hmm, the distance from the focal point to the beginning of the flare is 34 mm and is [3] segments long, so seems it's 34/3 = 11.3333 mm between segments, but in the metric world this begs the question: 'why'?

GM

[dumptruck]

Originally Posted by GM

Hmm, the distance from the focal point to the beginning of the flare is 34 mm and is [3] segments long, so seems it's 34/3 = 11.3333 mm between segments, but in the metric world this begs the question: 'why'?

Heh, well, I've still got this drawing open and that's easy to do... It doesn't seem to work out any less odd. I'm not sure where you're getting 3 segments for that, though, as no '0' mark is definite. Meanwhile, the 20mm deep section is clearly two segments, bringing it back to 1cm per segment.