Bow Drill – How many things could be ‘just not quite right?’ Blog 4 of 5

In this blog we are going to focus on the bearing block and bow of the bow drill set. If you have not read the previous three blogs that dealt with the ground & ember pan, hearth board and then the drill I suggest you have a quick read of those.

The bearing block ideally wants to be from a harder wood than the drill, however, a hazel baring block works well with a hazel drill if correctly carved with the use of a natural lubricant such as Galium aparine (Cleevers / Goose Grass / Sticky Weed) to reduce friction. Harder woods you might consider are the H’s – Hawthorn, Hornbeam and Holly, as well as Oak. Whilst it is possible to source dead standing wood, make and use the bearing block straight away

The trick to a good bearing block is in the carving. Over time the sharp, pencil point on the top of the drill will wear down and look more like the rounded base of the drill. You can bet that this will occur just when you’re getting close to an ember. If more of the bearing block is in contact with the tip of the drill, friction increases, making it harder work to continuing the bowing action.

Bearing Block Narrow hole image Bill Burden

The illustration above shows a hole in the bearing block carved, with the tip of a knife, so that the side walls are slightly less steep than the point on the top of the drill. When the drill is inserted, just the tip of the drill is in contact with the bearing block. Great! But, when the drill begins to round and wear down during the bowing process, more and more of the drill becomes in contact with the baring block. Over time the profile of the worn drill matches that of the hole and the two surfaces are in complete contact, maximising friction.

Baring Block Wide hole image Bill Burden

In the second illustration a much shallower side wall to the hole is carved. In the centre, deepest part a small steeper-sided hole is carved to seat the tip of the drill, so it doesn’t move about. In this scenario, as the tip of the drill wears down, less of the drill comes into contact with the bearing block, therefore less friction and bowing can continue more easily.

So, the things to consider:

  1. A harder, or the same, wood for the bearing block than the drill, NOT softer.
  2. Carve the hole to seat the drill in the bearing block too steep, risk of too much friction and harder bowing.
  3. Carve the hole to seat the drill in the bearing block too shallow, drill will not seat securely and move about.
  4. Carve a shallow hole with a small steeper-sided hole to seat the tip in the centre.
  5. Reduce friction by placing squashed, juicy vegetation between drill and bearing block e.g. Galium aparine.
  6. Block to fit comfortably in hand, not too small as to potentially break under pressure.
  7. Block not too long as to interfere with bowing (N.B. A longer bearing block is used in a Group Bow Drill where multiple people are involved in the process).

Bearing block alternatives:

  1. 2 limpet shells (2 to avoid heat transfer to hand, and if the bottom one breaks) hold with ok sign around the edge.
  2. bone with dimple cut out.
  3. stone with dimple in.

The bow is often quoted as needing to be the length from your sternum to the tip of your fingers. As a starting point that’s OK, but as you become more comfortable with getting an ember from your bow drill set you may find a different length more suitable. The whole purpose of the bow is to gain a mechanical advantage over the hand drill so the spinning of the drill in the hearth board can create more friction, fine powder and heat.

The amount of curve in the bow is not crucial, in fact I have seen many instructors use virtually a straight stick. The reason is the position of the drill in the bow string is to the outside (see below). As we have been trying to identify the factors that make the perfect bow drill set, the Woodland Ways instructors cut their bows green, string them to the desired curvature, and then leave to season for a year so that the bow dries and sets in that desired curve. The species of wood is not particularly important, Hazel is very often used simply because when sourcing the drills, a bow may show itself in the piece already cut for the drill. Ash is very good, and Sycamore often grows with a natural curved shape. Ideally choosing a stick with a fork at the end makes it easy to pop a loop of the bow string over. Create a notch for other end of bow with the string tensioned like the start of a taut tarp hitch, with x2 1/2 hitches tied the reverse of each other. See the Try-Stick curving project for bow notch

A green bow can be used, however, the extra weight can be more tiring and more cumbersome to controll and the flexibility may cause the bow string to varying in tension, which can be controlled by where the hand holds the bow – more in the next blog on the bow drill “stance”.

Drill on outside of string image Bill Burden

A few things to have in mind when selecting a bow:

  1. Not too long, more likely to touch the ground and potentially flick dirt on to the ember.
  2. Not too short, will not gain the mechanical advantage.
  3. Not dead, likely to be brittle and likely to snap under tension.
  4. Season bow in shape.

Lastly with respect to the bow, the bow string. Again to create your best chance of success, the string of choice is lawn mower pull cord. It is designed to take a lot of friction when pull starting an engine. The advantage over paracord is that it doesn’t stretch, paracord on the other hand is designed with approximately 15% stretch. Of course, if we were being authentic and sourcing all elements from nature, we would be looking to make our own natural cordage. Urtica dioica (Stinging Nettles) is the obvious one to go for in the UK due to its abundance and natural properties that allow it to tolerate a degree of friction. When making the cordage, you will need twice the length of the bow, and then some for tying off, so you can double over for the bow string. The cordage will need to be six-ply. Check out this blog on how to make your own nettle fire bow cordage.

Related posts