Bowhunting Tip: Boost Your Accuracy With This D.I.Y Spine Tester

Illustration by Steve Sanford

Spine, the degree to which an arrow will flex, is not uniform, and the best archers use this to their advantage. By finding the stiff side and fletching your arrows consistently in relation to it--usually with the cock feather on the stiff side--you'll get more uniform arrow flight, especially at longer ranges. Although it sounds complicated, building an inexpensive spine tester and checking your arrows is not. For about $25 in specialty parts, and some spare hardware you can probably find in your garage, you can build a spine tester in less than an hour.

Materials
- One 30-inch 1x10 board
- 1-inch Travel Machinist's Dial Indicator ($14; harborfreight.com)
- 2 lb. scuba weight ($10; ­lead​weights​online.com)
- Two 4-inch corner brackets
- Two 1-inch corner brackets
- One No. 10 screw hook
- One 3⁄4-inch machine screw and hex nut
- Eight wood screws

Illustration by Steve Sanford

Directions
1. Cut and Mount

Cut your board down to 28 inches. The remaining 2-inch piece of scrap will function as your dial mount; secure it vertically to the board using wood screws, backset widthwise about 11⁄2 inches from the centerline.

2. Dial In
Secure the two 1-inch corner brackets 11⁄2 inches from the top of your dial mount. With the 3⁄4-inch machine screw and nut, attach the dial to the brackets.

3. Arrow Support
With a drill, widen the top hole on your 4-inch corner brackets with a 3⁄8-inch bit to hold your arrow. (Go wider if you shoot fat shafts.) Secure the corner brackets to the ends of your board, tweaking the exact spot to ensure that (a) the arrow lines up under the dial gauge and (b) your arrow supports are 28 inches apart--the Archery Manufacturing Organization (AMO) test standard.

4. Weight it down
Drill a pilot hole in the center of your 2-pound scuba weight, then attach your No. 10 screw hook. The AMO standard calls for a 1.94-pound or 880-gram weight, but if you're not calculating exact stiffness, 2 pounds is close enough. If you're a stickler like me, you can punch a few small holes in the weight with the drill to be more precise.

5. Test it
To test an arrow's spine, raise the spring-loaded pin of your dial gauge, then place your arrow in the supports. Lower the pin so it's making good contact. Hang your weight in the center of the arrow. Simply spin your arrow slowly while reading the gauge to identify the stiffest side, and start fletching.