Armed with my new cardboard template, I am embarking on an adventure in toe-up flap heels. I've never really been happy with the fit I get from this style , mostly because I've never figured out how to consistently judge where to start increasing for the gussets. But I think I've got the problem licked now!
Basic toe-up flap:
1. knit sock to gusset line on your template
2. start increasing for gussets, 2 sts every other row. The traditional gusset increases are on either side of the sole. I usually do:
R1: K1, KTBL, K to 2nd last st on sole, KTBL, K1
While you are doing this, continue the instep sts in pattern.
Alternate R1 and R2 until you reach the "flap line". For fingering-weight socks, I usually find I increase about 14 sts on each side for my own feet (ladies' medium). Don't sweat this too much - socks are elastic.
(design note: of course, there is no reason you need to stick with tradition and do the gussets at the sides. You can make the gusset appear in the center of your heel, or in the center of your instep. These lead to interesting design options.)
3. when you reach the flap line, stop increasing. At this point, you need to place three markers on your sole stitches: two that section off the increased "gusset stitches" at either side, and a third marker at the midpoint of the sole. The stitches between the gusset markers are going to become the flap, and you should have the same number of these as you do the instep side of the sock.
4. Now you are going to knit a little wedge on the flap stitches, to round out the back of the heel. This you do as follows:
R1: K to center marker, K4, wrap and turn (or do whatever hole-hiding technique is your current fave)
R2: P to 4 beyond center marker, wrap and turn
R3: K to 8 beyond center marker, dealing with that wrap (or whatever) as you knit over it, wrap and turn.
R4: P to 8 beyond center marker, dealing with the wrap you encounter, wrap and turn.
R5: K to 12 beyond center marker, dealing with wrap, wrap and turn.
R6: P to 12 beyond center marker, deal with wrap, wrap and turn.
You've now added a little triangle 6 rows high (which works out to about 1/2" with fingering weight yarn) to the back of the sock. If you're knitting with sport or DK yarn, you'll have to adjust this because 6 rows will probably be too much, and make the sock too long. So do fewer short-rows. When you slip the template into the sock, the sock should be roughly 1/4" short of the end of the template. This is so that the sock will be snug!
5. Now you are ready to actually "turn the heel", by eating up the gusset stitches on either side as you knit back and forth:
R1: K to 1 before left hand gusset marker (the 3rd marker after the RH gusset and center marker) - remove the center marker as you knit over it, you're done with it. SSK, removing the gusset marker during this maneuver. Turn. (note: DO NOT WRAP or bother with hiding holes). And don't bother putting the marker back. You won't need it.
R2: sl 1 pw wyif, P to 1 before right hand gusset marker (the only marker left...), P2tog while removing this marker during the maneuver. Turn. (again: do not wrap or anything. Just turn.)
R3: sl 1 kw wyib, knit to 1 st before gap, SSK the next two stitches (bridge the gap) and turn.
R4: sl 1 pw wyif, purl to 1 st before gap, P2tog the next two stitches (bridge the gap) and turn.
Repeat R3 and R4 until you've made all the gusset sts disappear.
(design note: this is a flap with no reinforcement sts. You can easily to a slip-stitch pattern like "eye of partridge" or similar as you knit back and forth during its construction. I find slipped st patterns to be easiest to do over an ODD number of sts, so I'll add a stitch before I start, if that's needed)
Done-o-rama! You're ready to continue knitting the leg of the sock.
I like this construction - no picking up stitches, no holes, and pretty easy to execute. There is no "wrapping and turning", other than that little wedge at the end of the foot, which you could probably remove without too much ill effect (although you'd likely be better off extending the flap line by another few rows). If you have a super-high instep to contend with, either move the gusset line forward, or (easier) increase faster - like every row - to give yourself more gusset stitches at "flap time".