I designed designed this vest for my oldest son, who was away at college, and I was anxious to see how it fit. My middle son was a good sport in trying it on so I could check dimensions while in progress.
That summer we took a family trip to Mackinac Island. When my oldest son played the piano in the Geranium Room at the Grand Hotel, he chose to wear the vest.

I love how the v-neck finessing turned out. Before starting the V-neck split, I added two sts tucked behind to serve as the new Selvedge stitches so they would be discreet after picking up the sts for the neck band.
In the cable and rib pattern of the body, I increased the central k4 column to be a k5 and the central knit st continued as the middle knit stitch in the neck ribbing.

I worked up numbers for a 42” chest which would fit my two oldest sons and a 38” chest which would fit my youngest son. I’ve done much deliberations on depth of V-neck or armholes for a men’s or a women’s garment or how wide you might want the shoulders. How to transition ribbing or cable into the v-neck— I had a k5 center column so the center stitch will be maintained as the apex in the single Ribbed neck band and wanted the k2 to continue on either side of the v-neck so I increased one stitch on either side of the center stitch when I divided for the v-neck. The increased stitches will be hidden as the selvedge stitch when I pick up and knit the neck band. Shaping shoulders and back of neck and adjusting the placement of cable crossings to fit with the armhole and v-neck decreases. I even chose a k,p,k/k,p,k cable to tie in with the k1, p1 ribbing.

Raw (unblocked) Gauge: (single rib) 18 sts &19 rows per 2”
Two 20 row repeats = 5” in Cable rib pattern w US 6;
8 rows per inch.
88 sts = 9.5” in Cable rib pattern w US 6 = 9.26 spi

Blocked gauge: (back panel)160 sts / 22.86” = 7 spi
(Front panel) 148 sts / 21.14” = 7 spi
Blocked gauge: (back panel) 5 repeats= 100 rows
100 rows / 14.29” = 7 rows per in.
14.29” + 2.5” rib = 16.8” before armhole.
Block to 21” across, 15.7” btn ribbing to armhole, armhole 10.4”, V-neck: 10”

Armhole decreases per side: Dec 28 public viewed sts each armhole 28x7spi= 4” width of armhole.
Armhole count before binding off and cable dec and selvedge sts: 24+6st Cable + 2selvedge sts = 32 sts
V-neck width: 7”~ 50sts
V-neck depth 8.5” before ribbing. Rows 10-20 + 3full rep.; 70 rows.
V-neck dec a st 2 sts in from neck edge every RS Row 22 times, then EORS 4 times for total of 26 dec each side of v-neck.
Armhole Depth 4 rep = 10”
Shoulder width: 4.5” (33 sts before ribbing is added on needle for 3-needle Bindoff after 2 sts were dec over each cable on last row before 3-needle bindoff. 38 sts on each shoulder before cable decreases.
50 sts marked off for back off neck. After 2 sts dec at each cable, there will be 46 sts to be bound off at back of neck.
V-neck starts on Row2-20+ 2 rep+ rows 1-10. 19+40+10=69 rows each side of V and 46 bound off sts at back of neck. Pick up 10 sts/ 2” or 5/6 and 6/7. Pick up 1:1 at horizontal edge at back of neck.
Armhole is 71 rows after the bind offs at the base.
71x 4/5= 56x2= 112 sts+ 20 at base of armhole= 132 (need to p/u even number at armholes to follow single rib)
v-neck is 69 rows x 4/5= 54X2+46= 154sts picked up (need an odd number for held center mitered stitch to be a knit and follow single rib.)

Armhole Depth= 1/2 x (upperarm meas + 5”ease)
Armhole Depth = 1/2 x (13 + 5) = 9”
Start V-neck 1.5” after starting armhole (beg armhole bind-off on Row 10, worked rows 11-20 & row1, beg v-neck dec on Row 2= 1.5” from beg of armhole.)
6 row shoulder shaping + 7.5 v-neck depth before short rows + 1” single rib ~ 7” depth of neck opening.
https://knitmuch.com/which-measurements-matter-in-designi...

Instructions worked out for 38” size:(for Dan)

Back piece:
Using the smaller needles (US4), Long Tail CastOn in Pattern 142 sts.
Sweater will be seamed and plan for the single rib to continue over seamed edge without interrupting the pattern:
CastOn/Row 1 (RS): K2, ^p1, k1; rep from ^ to the end.
Row2 (WS): ^P1, k1; rep from ^ until 2 sts rem, p2.
Rep Rows 1 & 2 until ribbing is 1.5”. End on RS.

LTCO purl: hold yarn as sling shot.
Bring tip over yarn to outside index strand and pick it up from bottom up. Take tip down between index and thumb pairs, pick up inside thumb strand from bottom up, and draw it through the loop formed from index. Drop loop from index and snug the cast on purl stitch.
https://youtu.be/z1iHlK_RfOg

Switch to larger needles (US6)
Row 1 (WS): P2, k2, p4, k2, p2, ^k2, p1, k1, p2, k1, p1, k2, p2, k2, p4, k2, p2; rep from ^ to end.
Row 2 & 10 (RS): RS): ^K2, p2, k4, p2, k2, p2, k1, (k,p,k)/(k,p,k) Cable Left, p2; rep from ^ until 12 sts rem. Work k2, p2, k4, p2, k2.
Row 3 and all odd numbered rows (WS): Work Row 1.
Row 4 and all even rows except Row 10 (RS): ^K2, p2, k4, p2, k2, p2, k1, p1, k2, p1, k1, p2; rep from ^ until 12 sts rem. Work k2, p2, k4, p2, k2.

2nd Instructions worked out for a 42” size:(for Jack and Scot)

Yarn: 3 light. Skill Intermediate
Size Men’s Large 45”
Including 5” ease
Length: 26.5”
Gauge. In Cable Rib Pattern, 28 sts & 28 rows = 4”/10 cm. To save time, take time to check gauge.

Back: with smaller needles (US4) CastOn 162 sts (this includes 2 shelved get sts) 23”
Single Rib: Row 1 (WS): P1, k1; rep from to last 2 sts, p2.
Row 2 (RS): k2, p1, k1; rep from to end.
Repeat Rows 1 and 2 until piece measures 2.5” ending on RS Row. (Ribbing is 23 rows —note # rows to help w seaming)

Switch to US6 needles.
Maintain one knit stitch at each end for selvedge and, beginning on WS Row, maintain a selvedge stitch at each end, work 7 multiples of Chart, then work another 6 stitch cable. Work the 20-row chart for 5 repeats plus 9 rows of chart until piece measures 16.5” from cast on. Ending on a WS before a cable crossing. Mark every 10 rows so you can match row counts between front and back pieces to help later with seaming.
Row 1 (WS): P2, k1, p2, k1 p1, ^ k2, p2, k2, p4, k2, p2, k2, p1, k1, p2, k1, p1; rep from ^. p1, k1, p2, k1, k2.
Row 2&10 (RS): K1, ^(k,p,k)/(k,p,k) Left Cable, p2, k2, p2, k4, p2, k2, p2; rep from ^. Work (k,p,k)/(k,p,k) Left Cable, k1.

Rep Rows 1-22 until piece measures 16.5” ending on WS. Decrease 2 sts over cable at last crossing before beginning armhole. For this size, Begin bind off for armholes on cable crossing Row 10 of the 6th rep from ribbing.

Armhole shaping: The actual side measured equally from center of back and front pieces falls in the exact middle of the 6-stitch cable so adjust the armhole shaping so it centers about the cable. The first BO is a total of 14 +selvedge sts between the front and back pieces. You will dec 2 sts over the cable at the same time that you BO, so there will be 4 sts to be bound off at the cable plus another 5 sts on either side of cable for the total of 14sts plus the selvedge stitches. Then BO 4 sts at the beginning of the next two rows.
Next RS Row: K2, ssk, work in established pattern to last 4 sts, K2tog, k2.
Next WS Row: P2, work across in est pat to last 2 sts, p2.
Rep dec rows 4 (7 for 48” chest) more times for a total of 5 dec on each side. Dec selvedge+19 sts each side of back armhole
Total 124 (incl selvedge)sts rem: 38+48+38.
Cont in est pat until armhole measures 9.5” and back measures 25.5”. End on RS Row. (Work rows 10-20, then 3 full rep, work rows 1&2, beg 8row shoulder shaping on WS Row 3 so that, after the three short rows of 8 sts, the neck bind off occurs at cable crossing on Row 10 of Chart to vertically balance the cables in the center of the back and front pieces and the short rows allow the three needle Bindoff at the shoulders to occur between cable crossings.)
https://youtu.be/EvKMDdnhY2M Time 2:28.
Three-needle Bindoff will bind off 34 sts at each shoulder.
Shoulder shaping:
(selvedge st, 13sts, 11 sts, 13sts, neck 48 sts, 13sts, 11 sts, 13sts, selvedge st. The 13 sts hides the turning sts in the purl ditch.
Short Row 1(WS): Work across in pat to last 14sts. Turn.
(RS): Make German Short Row Double St and work across in pat to last 14 sts. Turn.
(WS): Make DS and work across in pat to last 25 sts. Turn.
(RS): Make DS and work across in Pattern to last 25 sts.
(WS): Work across neck and right shoulder sts, working DS as you come to them. Turn.
(RS): Work across entire back, decreasing 2 sts at each shoulder cable and work the DS as you come to them. Turn.
(WS): Work left shoulder and the center 48 neck stitches. Turn. Make cable dec on Row preceding Bindoff gave flatter smoother, transition edge for ribbing pick up. Dec 2 sts on cable in back of neck. Cross knit st over purl st on public side and slant in same direction of cable by bringing yarn to front and purl 2 tog through back loop pointing needle tip left to right through purl then knit st
(RS): Bind-off neck stitches on Row 10 as you dec 2 sts over each cable at the back of the neck.
Bind off all sts knitwise instead of binding off in Pattern to make it easier to pick up sts for ribbing.
Shoulders have 34 sts each (after the cable decreases) for the three-needle bind-off.

Shoulder shaping for three needle bind off:
https://youtu.be/ZoxS5_wE3xQ

Plan three needle bind off between cable crossings
https://pattylyons.com/2015/09/tuesday-tip-bind-off-in-ca...

Shaping V-neck https://knitmuch.com/colorburst-looks-best-with-a-steeked...

V-neck dec in pattern
https://youtu.be/gVdVCj8Stzg

Front. With smaller needles (US4) CO 150 sts and set up and work single ribbing as for Back, ending on a WS. Incr 1 on this last WS Row to form a center stitch for v-neck. 151 sts. Switch to larger needles (US 6).
RS Row: k1, p2, k2, p2, k4, p2, k2, p2, beg Row 1 of Chart pat for 2 multiples.
On center 23 sts: k1, p1, k2, p1, k1, p2, k2, p2, k5, p2, k2, p2. Resume following Chart Pat for 3 multiples, k1.
Cont est pat until piece measures 16.5”.
Front armhole shaping:
RS Row: BO selvedge st and next 5 sts, work est pat to end. Turn.
WS Row: BO selvedge st and next 5 sts, work est pat. Turn.
Beg of next 2 rows. BO 4 sts at beg next 2 rows. Turn.
RS Row: k2, ssk, work across in est pat until 4 sts rem, K2tog, k2. Turn.
WS Row: P2, work across in est pat until 2 sts rem, p2.
Rep dec rows 3 more times on every RS Row for a total of 4 dec on each side. Results in one column of purl bet the 3 edge sts and the cable.
At same time, when piece measures 1.5” from start of armhole, beg V-neck shaping. (Row 2 at beg of 7th rep)
Place a stitch marker through the center stitch of the front panel which is the center of the k5. A Lifted Increase will be worked on either side of the center stitch to form a selvedge edge which will be tucked away after the stitches are picked up and knit for the Ribbed band. This allows the two columns of knit sts on either side of the center st to continue up either side of the v-neck.
Work across until 4 sts before the center stitch, k2tog, k2, M1. Hold center sts on stitch marker.
Add new ball of yarn on work on right shoulder sts. After the held center stitch, M1, k2, ssk. Cont working in est pat dec 1 st two sts in at each neck edge on each RS Row for 21 dec, then dec every other RS Row for 4 more neck decreases for a total of 25 dec on each side on center st. Cont working back and forth in est pat until piece measures 26.5”, ending on RS Row 2 of chart. Beg German Short Row shoulder shaping on WS Row 3. (sts rem + held center stitch.)

Shoulder Shaping. On back piece, mark center 48 sts as neck sts.
Row1 (WS Row 3 on Cable Chart): Work across to last 14sts. Turn.
Row2 (RS): Make double stitch and work across until 14 sts rem. Turn.
Row 3 (WS): Make double stitch and work across until 25 sts rem. Turn.
Row 4 (RS): Make double stitch and work across until 25 sts rem. Turn.
Row 5 (WS): Make double stitch, work across neck, and left shoulder sts to very end of row working the double sts as you come to them. Turn.
Row 6 (RS): Work across left shoulder, the center neck sts, and the right shoulder to the end of row working the right shoulder’s double sts as you come to them and dec 2 sts at the cables outside the center neck sts. Turn.
Row 7 (WS): On front piece, work across one shoulder. End and hold sts for three-needle Bind-off.
On back piece, work across right shoulder sts and the center 48 neck sts. Turn.
Row 8 (RS): Bind off as you work cable crossing on Row 10 of the Cable Rib chart and dec 2 sts at each cable.

Join shoulders w three needle bind off, holding the RS facing each other and dec 2 sts at each cable.

Block pieces to flatten selvedge sts. Seam up the sides using mattress st.

Pick up for Ribbing https://knitmuch.com/designing-those-just-right-finishing...

Neckband
With smaller needle (US4), pick up even number of stitches (including held center stitch: 44 along horizontal edge along back, 56 sts along left side of v-neck, center st, and 57 sts along right side of v-neck gives even total of 158sts to maintain single rib with the held center stitch being a knit stitch. Adjust pickup ratio so the Ribbed band will be relaxed at the bind-off edge and slightly stretched at the selvedge edge so it will lay flat. (Picked up Alternating ratios of 5 sts per 6 rows and 4 sts per 5 rows) Work ribbing until 1 st before center st. Work CDD by slipping next 2 sts tog knitwise, k1, pass the 2 slipped sts over. Cont working single rib and CDD for 9 rounds. BO in pat.

Armband
With smaller needle pick up even number of sts in 1:1 ratio at BO edges and 5sts : 6 rows along sides and top. Total142 sts Work single rib for 1”. After 9 rows, bind off in pattern.

On neck band start pick up at back of right shoulder, picked up 48 sts, 56 sts, slip help center st, and 57 sts on right side of V-neck to get even number for single rib.

Swatched the sewn Bind off which does mirror Long Tail CastOn but it is very stretchy and tends to flare so did not use the sewn bind off on this garment. I did traditional bind off in pattern.
Cheryl: https://youtu.be/KbSRKcNa3FU
Jenn: https://youtu.be/rgQH69gZe4I

Weave in ends. Block.

6 Stitch Cable:slip 3 sts to cn and hold in front, (k1, p1) k1 from left needle, then (k1, p1) k1 from cn
Work cable crossing on RS Rows 1 & 9 on 20 row rep.

First test Sweater: CO total 308
Arm bind-off 14 base, then BO 4 each side, then dec7 each side for total of 36 sts bound-off. Base BO over p3,k2,p2, then over k4, dec ends
V-neck m1R&L each side of center st on same row of dec.
Dec 15 every RS, then dec 7 EORS for total of 22 sts each side of V-neck. Cable, p2,k2,p2,k3, neck opening.
Width of V before rib 5.75” and 4.75” either side
Width of shoulder band: 3.675” in photo.
Bottom hem 2.5”.
Start arm hole: Five 20 rep plus rows 1-10
Start V-neck after 6 full rep plus 1-2 rows. (1.5” from armholes)
Armhole decreases per side 36 sts/ 9.26 = 3.89”
V-neck width: 8” ~ 52 sts
V-neck depth 8”; 3 rep x 2.75”
Armhole Depth 9.6” ; 3.5 rep x 2.75”
In Pat:26sts+24 dec
22sts+ 14 dec

Favorite fitting sweater (medium) sweater:
Width 42”
Length 25”
Depth of V-neck 5” depth measured from top rob band to top of 1” rib band at center of V.
Arm hole 9.5” depth.
Finished back neck opening width 6.25”
7” width shoulder band meas edge of arm and neck ribs.

Son projects he wants 2”positive ease (actual chest 40”)
Width 21”
Length 26”
Start armhole at 16.5” from cast-on
Armhole depth 9.5”
Start V-neck at 18” from cast-on
V-neck depth 8”-1”rib result in finished opening7” depth