Knitting with 2 carriages

Recently there has been a lot of press about a particular personality using 2 carriages in her knitting. This is not a new idea. Some points to ponder: if color changing is required there many ways to deal with it, beginning with doing it manually and devising a yarn holder of sorts to slip into space where the needle retainer bar sits. Then there are color changers, an absolute necessity in double bed work for DBJ. Not all machine models have changers that will work on both beds, Brother happens to be one that does not. Though Passap Autocolor will change colors automatically, the Brother single bed one is operated by one’s fingers pushing buttons, is a bit fussy, and it is really good not to hit an empty holder and go across with “no yarn”, since the object is usually not to have knitting fall off and onto floor.
Extra KH carriages are a bigger expense than color changers. Many production knitters have backups for their machine models. It is obviously best if both carriages are the same model year. Sometimes sequential model ones may be used, and all that may be required is a sinker plate adjustment, other times the carriages are incompatible with the new knitting beds though changes may appear to be small ones to the eye.
Unless I specify otherwise, my comments usually pertain to Brother KMs.
Aside from the fact that punchcard models have no power source, the pattern rotation is also different and that needs to be taken into consideration when punching holes in the card. Electronic machines advance a design row for each carriage pass on each side. Punchcard models do not.
In knitting stripes, the second carriage may house a thinner or thicker yarn, same yarn at a different tension, or hold the alternate color for frequent color changes.  It may also be used with different cam settings than the other ie one for fair isle, the other for weaving or tuck, etc.
If combining stitch types a clear understanding of how punchcard holes and mylar or computer interface “squares” relate to needle selection and fabric formation is helpful and boils down to planning selection for needles one actually wants knitting. Patterning sequences must happen so each carriage makes an even number of passes, and returns home to its “side” for “automatic” use. Lace extension rails must be used and the alternate carriage is off the needle bed to avoid belt breakage.

The image below is a lo-tech “color changer” marketed decades ago. Old credit cards can be used for a DIY version.

Doilies: Lace meets hold and goes round

There is an excellent online resource for the Bond Machine. Techniques are applicable to other KM models for those who enjoy hand techniques. The round lace tablecloth series provides a number of “doily” charts. Here is a working graph for a Brother electronic 910 “inspired” by them. The stitch width total which forms the radius of the circle reflects the 60 max width on the mylar. Slip setting in both cam buttons is used on the KH for automatic shaping: end needle selection is canceled. It is critical that carriages be off the machine and on the lace extension rails while the alternate carriage is in use as they both engage the timing belt, and the latter can be broken if pulled in opposing directions at the same time. If drawing on the back of mylar, the image below may be drawn as is, and number 1 pattern case “A” reverse lever to up position. Repeat design principles are shared in creating edgings, ruffles, and more.

One of the critical differences when using 2 carriages to select patterns, is that with the electronics on machines such as the 910 each carriage pass advances the design repeat one row. With Brother punchcards, the first pass of the second carriage does not as it makes its first “trip” from the opposite side. Back in 02 exchanges with a fellow member of an Australian Yahoo Group, OzMKers, led to her final edit of the punchcard repeat resulting in the following (half actual card is shown).