This is why a custom string builder will NEVER EVER install a center serving, with the bowstring on a bow.
Just not enough tension, to prevent the bowstring bundle from TWISTING while installing the end servings, while installing the center servings.
Just 6 lbs of serving tool drag force,
needs about 300 lbs of tension on a bowstring stretcher, to be tight enough for stretching power,
to prevent just only 6 lbs of serving tool draw force.
If your serving tool drag force is 7 lbs, then you need 360 lbs of stretching tension to prevent the bowstring from twisting, while you are spinning the serving tool. 70 lb bow might have at most, 210 lbs of tension.
Take the bowstring off the bow.
Use a draw board to provide stretching tension. Boat winch is SUPER handy for stretching purposes.
Use an adjustable chain link in each bowstring end loop. Anchor one end of the bowstring.
Attach boat winch from draw board to the other end of the bowstring.
I use a spring scale (no batteries required, and SUPER reliable, dead accurate). Stretch to 300+ lbs of tension.
Great time to rub in some string wax, and scrape off the excess wax, using a loop of serving thread. Wrap around once and pull on the tag ends. This also evens out the tension in each and every strand.
Peep rotation is UN-equal tension in the strands.
Slide in a short length of bowstring material, or serving thread
in between the two colors (pull out the peep, before stretching).
So, while spinning the serving tool, with bowstring at 300+ lbs of tension,
keep your eye on the FLAG of serving thread. The serving thread should not be wagging at you much.
If the serving thread FLAG is spinning around and around, DROP/LOWER the serving tool tension (drag)
and INcREASE the stretching tension up to 350 lbs.
Helps to also CLAMP the bowstring, to the left and to the right of the area you are serving.
Clamp the string lightly, and these clamps PLUS the 350+ of stretching tension
will make it impossible for the bowstring bundle, to rotate while you are spinning the serving tool.
THIS is the secret to a ZERO peep rotation bowstring.