Front View	Rear View	Left Side View	Right Side View

Technical Details

I made my Double Helical Spool fin 2022.

My Double Helical Spool is 272 mm. tall, 60 mm. wide, 51 mm. thick, and weighs 950 g.

I used 2” (50 mm.) 6061-T6 round stock to make this spool, and made a simple frame from 9.5 mm. 1018 rod. I milled a 11 mm. wide, 5.5 mm. deep, 13 mm. pitch helical rope groove in each spool. The top helix is right-handed and the bottom left-handed. I drilled and threaded the spool for the rods. The top spool threads into both rods, while the short rod also threads into the bottom spool. Recalling the problems that I had with the North Texas Speleological Society Double Spool, I spaced the spools far enough apart to allow rigging PMI Pit rope. The jam and acorn nuts secure the rods and act as horns to back up holding the rope in place.

I stamped the spool with my logo.

Comments

After assembling the double spool, I realized that I should have stopped the helices at one full turn and shortened the spools accordingly. Alternately, keeping the same spool length and moving them outward would allow an extra quarter-turn on the lower spool groove, facilitating right-hand braking for extra friction.

The double spool weighs too much for routine use. As with any device, performance depends on the rope in use. I found that it may require some hand feeding when I use it on PMI Pit Rope and is fully controllable but is slightly fast for my taste on 9 mm. BlueWater II.