Lookie what I finally swatched for!
That's right, it's my dad's custom-designed DNA vest. I think the DNA isn't really obvious, but that might not be a bad thing. Subtle isn't a bad thing on clothes for my dad.
Anyway, I armed myself with this huge swatch (knit mock in the round with strands in the back, AND washed AND blocked!), a generic V-neck vest pattern, and Knitting Workshop by Zimmerman, and set to work.
My swatch measures 18.5 stitches per 4 inches on stockinette. The DNA panel, knit over 20 stitches, is 3.5 inches wide.
I want the chest to measure 43 inches around (my mom measured my dad's favorite vest, and that's what she got). If I were knitting in stockinette, then, I would cast on (43/4)*18.5 = 198.9 stitches, or 200 stitches for the same of ease. (I am planning on working this in the round up to the armholes, then back and forth to shape the armholes and neck.)
There is the DNA panel, which will be front and center and framed by a four-stitch cable on either side. It pulls in alot more than stockingette -- I get 20 st/3.5 inches = 5.7 stitches per inch in the DNA pattern, and 18.5 st/4 inches = 4.6 stitches per inch in stockinette. That means that my vest will pull in quite a bit in the center, so casting on 200 will not be enough.
So. The chest is 43"/2 - 21.5". Of that, approximately 7 inches will be taken up by the cable panel. (This I figured because on either side of the DNA panel I will have k2, p, 4 stitches of cable, p1, k2, p1, return to stockinette. That's 11 stitches per side, or 22 stitches total, in cabling, which, I'm assuming, will pull in almost as much as the 20 stitches of the DNA panel. So 7 inches total.)
Those 7 cabled inches will comprise 42 stitches (22 for side cables, 20 for DNA). That leaves me with 21.5-7 = 14.5 inches to be worked in stockinette.
(14.5"/4)*18.5 = 68 stitches of stockinette for the chest.
68+42 = 110 stitches for the front. The back, however, will not have the cable pattern, and so will need only (21.5/4)*18.5 = 100 stitches. That's 210 stitches total, which is not divisible by 4, so I dropped two stitches to make it 208.
So, I have cast on 208 stitches and am working the ribbing on size 7 needles. Once that measures about 3 inches, I will switch to size 8s, place all kinds of markers, and go to work.
Erm. I think I just confused myself with the math. Am I doing this right? I guess we'll find out. Once I get about halfway up the back, I'll try it on The Husband for fit. He's not too much bigger than Dad, so I'll be able to gauge it from there and frog if need be.
Also, before shaping the armholes, I'm going to lay that sucker flat and see where the side-most stitches are. If they leave 100 stitches for the back and 108 for the front, as I predicted, great, but if not, I'll be able to adjust that before I start working the armholes. Yay for knitting in the round!
UPDATE: Since pre-publishing this post, I decided I didn't like the side cable pattern, and changed it to k2, p2, cable 4, p2, k2, p2, giving me 14 inches. I had the body of the vest all cast on, so I was working with those 108 stitches for the front. That meant that the sides of the front became 30 stitches instead of 33. That goes against my math a bit, but we'll see how it works out. The ribbing around the cables will give me some leeway in terms of size, I think.