SELECTING & SPLITTING BAMBOO FOR RODMAKING
by Ron Grantham
(adapted from the method developed by John Bokstrom)

SELECTING BAMBOO:
Each culm of bamboo is unique. In a bundle of 20 culms, you may have 20 with different node spacing. If you randomly select one and follow the common practice of utilizing the upper portion of the 12-foot culm for tip strips, and the lower portion for butts, the nodes will probably not fall in the best locations with regard to the tip and ferrules. However, if you select a culm with node spacing that matches the splitting length of your rod (see Splitting Guide, below), you will end up with a maximum of node-free strips. When you find one that is suitable, cut out and discard the node between the butt and tip pieces, discard the off-cut below the butt piece, and the off-cut above the tip piece. The larger cutoff piece may be on the top or bottom of the culm. If the ideal culm is not available, keeping nodes away from the tip deserves priority.

SPLITTING GUIDE  -- 6" for staggering, 1" leeway each end.
These splitting widths are suggestions only and with experience can likely be reduced.

	BUTT STRIPS			TIP STRIPS
Rod length	Splitting length	Planing length	Splitting width	Splitting length	Planing length	Splitting width
7' 0"	49.5"	43.5"	.235"	50.5"	44.5"	.160"
7' 3"	51"	45"	.240"	52"	46"	.165"
7' 6"	52.5"	46.5"	.245"	53.5"	47.5"	.170"
7' 9"	54"	48"	.250"	55"	49"	.175"
8' 0"	55.5"	49.5"	.257"	56.5"	50.5"	.178"
8' 3"	57"	51"	.263"	58"	52"	.181"
8' 6"	58.5"	52.5"	.269"	59.5"	53.5"	.184"
8' 9"	60"	54"	.275"	61"	55"	.187"
9' 0"	61.5"	55.5"	.280"	62.5"	56.5"	.190"

Splitting width is the half diameter at the thick end of strip + 15% + allowance for charring of nodes and leeway. (To convert the height of an equilateral triangle to the length of its side the precise factor is 15.5% but 15% is close enough and can more easily be calculated.)
Allowances that are too great mean fewer strips and excessive work in straightening and planing, but until you have split a culm or two this way it is wise to leave the strips slightly larger. - J. Bokstrom

SPLITTING BAMBOO:

Draw the usual spiral lines around the lower ends of both the butt and tip sections so the strips can be arranged back into their original order.

Set your dividers or callipers to the splitting width for four single strips, using butt splitting widths for the butt section, and tip splitting widths for the tip section. Beginning at the major split, step off the widths around the culm. Then, using a pen or pencil, mark each four-strip-width on the end of the culm. On an ideal culm there would be an exact multiple of four, but that isn't likely so some portion of four may be left over, or you can readjust the dividers and start over to achieve an even number.

Filing the nodes before splitting is optional.

The splitting tool is an ordinary kitchen paring knife with a rounded tip for safety. The thin blade keeps the split travel to a minimum ensuring maximum control over the work.

In your workbench vise, grip the paring knife leaving about one inch of the blade exposed. Against the sharp edge of the knife blade, align the mark between the two groups of four that come nearest to halving the culm, and sharply rap the far end to start the split. Push the culm to split it into two pieces, then clean out the inside of the node dams. All splitting is done with the knife in the vise allowing you to use the strong muscles of your legs, back and arms.

For an eight-foot rod, the individual tip splitting width used is .178". The marks shown on the end of the culm represent groups of four strips, each .178" wide, or .712" for each group.

Splitting into groups. At these early stages, the split should follow the grain.

Split each section into single groups of four.

Using the vise jaws as a guide, split each group of four into double-wide strips.

Splitting doubles into singles. If the split runs off to either side, put pressure on the opposite side (the wide side) to bring the split back towards the centre.

The result: 34 strips from this culm.

STRAIGHTENING THE NODES:

After splitting the bamboo, the nodes are filed smooth and the strips are soaked in water for twenty-four hours or more. Very large pieces such as butt strips for double-handed rods may need soaking for several days. The application of heat softens the cells and allows the bamboo to be manipulated.

Using a common hot air gun, heat the node area and approximately two inches on both sides of the node, rotating the strip for even application of heat. Continue heating until the node section is softened and can be easily bent by hand.

The area on both sides of the node, and the node itself, are bent in their opposite directions until the curves are overcorrected. Straighten all four sides while the bamboo is still hot, then clamp the strip in a vise with the enamel side against a flat, smooth surface until cool.

The nodes are not pressed flat. They are clamped in the vise under just enough pressure to hold them straight. The rubber back surface allows for variations in thickness while keeping the enamel flat against the smooth opposite surface.

Working on two strips at a time allows time for one strip to cool in the vise while the other is being heated and straightened.

Web site created and managed by Ron Grantham. Updated 01/06/2010.