Thick or Thin? A Tale of Two Spindles (Bow Drill)

How thick should your bow drill spindle be? Thinner spindles concentrate the heat, and thicker spindles generate more of it, but that’s just one of many factors to consider…

I was poking around a beautiful riverbed this morning with my eye out for friction fire materials when I came across a very interesting piece of cottonwood root. I have heard that this is a very soft and excellent material for friction fire, but every time tried cutting a chunk from a downed tree, it was even harder than the wood.

This piece felt completely different and was extremely soft and very lightweight. I usually see it recommended for hand drill, and I broke off a dead willow intending to spin up an ember that way, but my hands were still healing from a previous failed attempt, so I opted to try bow drilling with a hand drill sized spindle.

Unfortunately, this caused several problems. Because the hearth material was so soft, the concentrated pressure of the thinner spindle made it so that anything but the lightest amount of pressure would grind out course material instead of creating heat and fine dust.

The solution to this is usually extra speed, but with a bow drill, that combined with a smaller gearing on a thin spindle also results in stronger horizontal forces being transferred into the hearth. I had repeated issues with it failing under the pressure, which would send the spindle and dust pile flying.

After three attempts with the thin spindle, I recognized the issue and scrounged up a new thicker spindle from one of the debris piles. I’m not sure of the species on this one, but I suspect that it was willow as well.

This thicker spindle was just what was needed and the extra width slowed its decent into the hearth allowed me to drill for longer to create more heat.
It is possible that the thinner spindle would have worked as a hand drill, as the lateral forces aren’t nearly as violent when drilling by hand, but I think this ended up being a good accidental illustration of a key principle.

The ideal spindle diameter depends on the materials that you are working with. Softer materials may require thicker spindles and a lighter touch, while harder materials often call for more pressure, which can be achieved with a thinner spindle, and more force on the bearing block.

Friction fire success is often about finding the sweet spots in materials, set dimensions, speed and pressure. A set that is not cooperating sometimes just needs another attempt to dry things out, but sometimes examining the variables above and making a change is the best course of action.

The tinder bundle was a collection of loose river debris that appeared to be a mix of roots, bark, and sand. This fine fibrous material made an excellent bundle that ignited on its own before I was ready for it. I didn’t intend for it to keep burning after I tossed it in the water, so I chucked a rock at it and got lucky. Had I missed I would have ran it down and made sure it was out, but this was still a pretty bone-headed move on my part.

Hearth: Black Cottonwood Root (Populus trichocarpa)
Spindles: Willow (unknown Salix) & Mystery Driftwood Branch
Tinder Bundle: River Debris

Knife: Ontario RAT 1 AUS 8

Music: Fredji – Endless Nights
https://www.youtube.com/watch?v=KePN7-dF_lw

Questions, comments, and suggestions are always welcome and appreciated.