The finished center finder.

Center Finder

When it’s time to stake out some middle ground.

I was trying to find the exact center of the root rib on an Aquila XL so I could replace the tiny 1/4" rods with a decent 1/2" carbon joiner. Trying to get the measurement just right with just a rule, wasn’t that easy. I had a Robart center finder that has really helped me find centerlines for hinges and such. The only problem is that it is too small for a lot of my needs.

Photos 1 and 2: Left: The Robart Hinge Point Drill Jig which I simply refer to as their center finder because that’s what it actually does. Right: Clearly, not big enough to meet my needs.

Soooo…I made a quick and simple center marking gauge large enough to fit the thicker ribs on many of my planes.

Materials

• (2) 1/4 inch by 3/8 inch by 3 inch block (you can vary the sizes however you want)
• (1) 5/8 inch by 3 inch block (the longer this block the thicker the thing you want to find the center of can be)
• (2) Machine screws ( I used 8–32 stainless because that’s what I have handy)
• (2) Nuts
• (2) ‘O’ rings (optional)
• (1) Scribe insert (optional)

Photos 3 and 4: The basic parts, and the assembled center finder.

• Cut out the blanks and mark for the holes.
• Drill the appropriate end holes in the three blocks. I counter sunk for the screw heads, but it is not necessary.
• Assemble the unit (I chose to use knurled nuts and “O” rings to make it work like I wanted).

Photos 5 and 6: This is the trick to finding the exact center.

• This is a critical step to get the exact center. Take and push the blocks together and scribe a line on the main block. Flip the outer bocks the other direction and scribe again. This gives you an “X” right in the center of the block.

Photos 7 and 8: The finished center finder both with the marking pin on the left and, alternatively, a pencil on the right.

• Drill the center hole. I chose to use a center scribe insert, since I had several in my tool chest, but you can drill a small hole for a pin or a larger one for a pencil.

Thanks for reading. Please let me know what you think or if you have any questions, feel free to write a response below.

©2021 Tom Broeski

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