I was taught that a 'perfect chain' is a loop where the number of drive links is divisible by 4; that is the way you end up with a perfect L-R-L-R sequence (full comp chain). Otherwise, you will have an extra L, extra R, extra space, etc. Does not make a practical difference.
Many "standard" DL count loops have an uneven number of teeth.
Most Stihl loops in my area have an uneven tooth count.
It makes no notable difference in real world operation!
For example: A 3/8" 115DL full comp loop intended for a 36" bar with D009 mount features two right or left cutters in a row, and an extra space between them.
Doesn't seem to make any notable difference.
But we also know that if the cutters on one side (or the depth gauges on one side) are significantly different than the other side, the chain will pull to one side, and even cut in a curve.
But usually only if the entire left or right handed tooth row is completely off set.
A single or two teeth not matching the rest, even when in a row, will not make the chain cut crooked.
Skip-tooth chain has extra spaces: to reduce the number of teeth in the cut (reducing load on the saw), and, to help clear chips when cutting larger diameter wood. Some people also like filing fewer teeth!
Semi-skip chain always seemed to me like it was for people who could not make up their minds. But in another thread, someone suggested that keeping the R and L cutters as close pairs helps to keep the chain from wandering in the kerf, while the extra spaces provide the benefits of full-skip chain? Not sure if this is accurate, but an interesting idea.
To clarify, "Skip tooth" or full skip features the same amount of extra spaces between both left and right handed teeth - that would suggest optimal chip clearance capabilities.
It also suggests that the entire loop, both cutter sides, behave the same.
"Semi skip" or half skip features one extra space followed by no extra space at all!
That would suggest that one cutter has extra space for chip clearance while the next cutter following it does not?!
Meaning, one cutter side is getting plugged by chips possibly even lifted off the wood by them and creating additional drag?!
This 'Cowboy Skip' chain would just be an improvisation. I would not try to make one if I had a loop of full-skip chain available (except to try it!).
Philbert
If the "Semi skip" geometry is a proven working thing, then I don't see any opposing reason why a homemade "Sorta-skip" wouldn't be real world condition certified as well.
W.