GPI sort and batch-tracking table

What you’ll do #

Weigh all 28 raw shafts, calculate GPI for each, and use the batch-tracking table below to identify your keeper group. By the end you will have: a completed table for all 28 shafts, a chosen GPI center value, and a subset of shafts marked KEEP that fall within ±1 GPI of that center.

Setup #

You need:

• Your 28 raw 11/32-inch Port Orford cedar shafts (from the supplier bundle)
• A grain scale — a reloading scale with 0.1 grain resolution works well; a digital kitchen scale may not have enough resolution
• A ruler or tape measure in inches
• A pencil and the tracking table below, or a notebook set up with the same columns

Power on the scale, zero it, and let it stabilize for two minutes before you start.

Starter scaffold #

Step 1 — Prepare the scale.

Place each shaft on the scale pan one at a time. Record the weight to the nearest 0.1 grain. If the shaft rocks or overhangs, support the ends evenly.

[TODO: Record the tare / zero weight shown on your scale before each measurement.
       If your scale does not auto-tare, describe how you confirmed a clean zero.]

Step 2 — Measure shaft length.

Measure each shaft from one end to the other (tip to tip, parallel to the shaft axis) in inches, to the nearest 1/16 inch. Convert to decimal (e.g., 30 3/8" = 30.375").

[TODO: Write down the measuring method you used — ruler laid alongside shaft,
       or tape measure with one end held at the shaft tip. Consistency matters
       more than perfection.]

Step 3 — Calculate GPI for each shaft.

Use the formula: GPI = weight (grains) ÷ length (inches)

Round to one decimal place (e.g., 274.5 gr ÷ 30.5 in = 9.0 GPI).

[TODO: Fill in all 28 rows of the batch-tracking table below.]

Batch-tracking table — copy this into your notebook or print it out:

Straightness column: leave blank for now — you fill this in during the next exercise (straighten + taper sequence). Write PASS or FAIL after the straightening step.

Taper date columns: fill in the date you made each taper cut. Leaving them blank is your signal that the shaft is not yet tapered.

Status column: write KEEP, CULL-WEIGHT, or CULL-STRAIGHT as each shaft clears (or fails) its gate.

Step 4 — Choose your GPI center value.

[TODO: Sort your GPI values from lowest to highest. Identify the cluster
       where the most shafts land. Write down your chosen center GPI value
       and your ±1 GPI window (e.g., "center = 10.5 GPI, keep range = 9.5–11.5").
       How many shafts are inside that window?]

Step 5 — Mark culls.

[TODO: For any shaft outside your GPI window, write CULL-WEIGHT in the Status
       column. Count how many culls you have. Is it within the expected 5–15%
       reject rate (1–4 shafts from a bundle of 28)? If you have more than 4,
       consider widening your tolerance to ±1.5 GPI and note the reason.]

Verification #

You’ve completed this exercise correctly when:

1. All 28 rows in the batch-tracking table have Weight, Length, and GPI filled in.
2. You have a written center GPI value and ±1 GPI window.
3. Shafts outside the window are marked CULL-WEIGHT in the Status column.
4. You have at least 24 shafts marked KEEP (or are within 1–2 shafts of 24 after considering a slightly wider tolerance).

If you ended up with fewer than 22 KEEPs, check your GPI arithmetic on any outliers — a transcription error in weight or length can throw off the calculation. If the math checks out and you still have a high cull rate, make a note in your tracking table and proceed — you’ll need to order replacement shafts before Module 3.