This technique is called drive and mesh lace, release stitch or summer fair isle by Passap, and drop stitch lace in some of the pattern books. Drive lace typically has lines of patterning where loops are formed between rows of all knit stitches. The main fabric, usually stockinette, is knitted and produced by either bed. Selected needles knit pattern stitches on the other bed for one or more rows, then are dropped from those needles, unraveling back to their starting point, creating the larger, open stitches.
The fabric may be created both as a hand technique or using automated patterning. In sources that show loops being formed on the ribber, stitches are released by uncoupling the ribber carriages and moving the it across the knitting and then back to its original spot, thus dropping the stitches. In studio machines the P carriage may be used to drop stitches, see previous posts on modifying one for use on Brother KM.
The tension setting on the patterning bed affects the loop size and its tension is frequently one to three numbers looser than the all knit bed tension. In Brother machines the ribber knits at a tighter gauge than main bed, so take that into consideration and adjust it when knitting all knit rows on every needle on the ribber, where the tension may need to be loosened one or more numbers than when knitting same yarn in stocking stitch on the main bed. Matching tensions numbers on both beds may provide enough of a difference in stitch size for loop formation. The difference in gauge between the beds also merits calculating adjustments when knitting in circular or U format.
Releasing stitches may happen after every pattern row, after groups of pattern rows (such as bubbles or check patterns), or even at times when knitting is completed. With groups of pattern rows I have had better results with more frequent stitch release. Two types of mesh can be created. “Stockinette” mesh has an equal number of rows on both beds. The result is enlarged “stocking” stitches along with narrower, single bed ones on any one row. Half Milano mesh has a horizontal ridge on the purl side with 2 rows knit on the all knit fabric bed, to every one row on the patterning bed. One of the rows has the patterning bed slip every needle, with the ribber only knitting, the second row forms the combination size stitches as discussed previously. In patterning in Brother KMs this would need to have such rows added to the programmed design. The fabric is a bit more “stable”. Passap offers multiple techniques for dropping stitches, often referred to as summer fair isle and using 2 colors per row. Different looks are achieved by changing built in technique number, as well as when using a stitch ditcher on every row knit, as opposed to using “empty” passes of locks to drop the stitches.
Previous posts on topic: http://alessandrina.com/2012/09/24/working-out-the-kinks-in-my-drop-stitch-lace-saga/
knitting patterns with no blank knit rows between loop formation http://alessandrina.com/2015/06/16/geometric-shapes-in-drop-stitch-lace-2-brother-km/
anther related fabric: http://alessandrina.com/2017/10/18/revisiting-knit-bubbles-brother-km/
using ribber cast on comb for an open cast on single (either) bed http://alessandrina.com/2017/02/14/ribber-cast-on-comb-open-stitch-single-bed-cast-on/
Working with positive and negative space variations: the repeat is suitable for any machine, my sample is executed on Brother KM. Since alternate, all blank rows have no needle selection, before knitting that row (ribber only will knit), dropping stitches knit on the main bed on the previous row will not alter pattern
using any method you prefer, set up knitting so all stitches are on the ribber. If you prefer to set up complete repeats prior to watching, “air knitting” prior to ribber set up or using position option on the main bed if that is available, will help achieve that set knit carriage to KC II (used when patterning does not occur on every needle across needle bed), both part buttons pushed in for free pass to opposite side of km, no knitting occurs but first row of pattern knitting is selected. Ribber is set to N<–> throughoutas the carriages now move to opposite side, selected needles on the main bed pick up loops, non selected needles stay empty. Ribber knits every stitch using a ribber cast on comb, stitch “dumper”, or other tool, move needles holding stitches forward to drop loops, and return empty needles to work position (B)as carriages move to opposite side, needles are selected for next row of knit stitches to be knit on main bed carriages now move to opposite side, loops are picked up on selected needles all needles are now not selected, above stitches/ loops are dropped, needles are returned to B position before the next carriages’ passcarriages move to opposite side, selecting pattern needlescarriages move to opposite side, picking up loops
before carriages move again, drop stitches formed. Watch loops after they are dropped, if tugging on knit is not enough to pull them out of way of needles returning to patterning, take a tool or something like a credit card. Slide it from one side to the other between the beds, thus keeping loops clear away from main bed
In summary; assuming one is starting on right side of machine COR
step 1. <-carriages select needles that will form loops
step 2. ->carriages knit picking up loops
step 3. drop loops just formed, returning all empty needles to B position
step 4+ repeat 1-3 for entire length of piece
My sample was knit in a slightly fuzzy wool. Smooth, thinner yarns result in longer stitches whose patterns get read more easily. Because wool has “memory” the vertical edges tend to roll to purl side, and return to rolling even after heavy pressing and steaming. There are a couple of spots where no long stitch was created due to markings on mylar not being dark enough.
Other things to consider: this fabric widens when blocked, so cast on, bind off, and beginning and ending edges need to accommodate that. This particular design creates a fairly balanced fabric. In many drop stitch fabrics, it is recommended that edges contain stitches dropped in pattern in order to maintain vertical length at edges. To achieve that, first and last needles on both sides should be on the main bed. That said, having an all knit border (stitches knitting only on ribber, no dropped stitches) may work well in your pattern, or pull edges in too tightly when compared to the all over motif released repeats. Testing on your swatch can be achieved easily by simply taking some needles on the main bed out of work on one side, thus creating the “all knit border”. The latter can happen by accident if not all needles are returned to B position properly after dropping stitches.