The safest and most economical way to professionally install center fins in your board. The Aluminum Bushing Base Plate screws to the router and allows you to take multiple shallow passes instead of one deep pass like other router jigs. Much safer an no router bit jumping when you hit the stringer (scary!).
We recommend plunging the router bit vertically into the foam starting on the right side of the jig to prevent the router from jumping. Do not rotate the router down into the foam or stringer like other dangerous fin install systems! Take incremental passes at 1/4", 1/2", 3/4", and 1" pocket depth to keep it easy and safe.
10 Steps to installing a longboard surfboard centerfin box:
How to install a longboard center fin box with the Greenlight plunge router and center fin install template jig.
We've designed this finbox router system to be the safest way to install fin boxes by using a plunge routing method and plastic jig template.
Step 1. Position router jig and tape down firmly
Step 2. Place Greenlight Router Base Plate Bushing on RIGHT LOWER CORNER of jig (when the spinning router bit touches the board it will want to move sideways to the right, this won't happen if you start in the right corner position - safety first!)
Step 3. Turn on router and slowly plunge into the foam. Note: For stringerless blanks or High Density Stringers you can plunge full 1" depth (with 1" depth stop collar included). For wood stringers we recommend plunging only 1/4" increments at a time for less stress and increased safety. You can also plunge the full 1" depth and skim cut the stringer with multiple passes to "shave" the wood away.
Step 4. Check the depth and size of the routed pocket is correct before removing the jig from the board.
Step 5. Cut a strip of fiberglass approximately 3" wide x 10" long for reinforcing the center finbox
Step 6. Tape off the area around the pocket to keep resin off the fiberglass for less sanding
Step 7. Mix 3 oz of resin and pour about 2 ounces into the routed pocket.
Step 8. Lay the fiberglass strip over the pocket and push the finbox down so the resin squeezes up. Top off the sides on the box with resin and pop any air bubbles. Make sure there are no air pockets around the perimeter of the fin box.
Step 9. Tape a dummy fin or piece of 3/8" wood to the board to keep the fin box perpendicular and put a downward force on the box to ensure it doesn't float up on the resin.
Step 10. When the resin cures sand the top of the fin box to the rocker curve of the surfboard and remove tape. You can remove any tape residue with WD-40 or acetone and scrape with a razor blade.
Best way you recommend if you wanted to install a smaller box say 7.5 box instead?
The center fin install kit comes with a jig spacer to cut an 8.5" fin box pocket as well as a 10.5" pocket. For a 7.5" fin box you can make a 3" spacer from wood, plastic or foam to reudce the length of the channel.
can i use this jig with other router brands?
The longboard centerfin install kit is also compatible with the Makita RT0701C trim router
At what step in the board build do you router out the fin box? Before or after laminating?
The centerfin pocket is routed and the finbox is installed after the sealcoat/hotcoat. The finbox plastic is sanded flush with the board when sanding the sealcoat. More info in our Surfboard Building Guide
Do you recommend installing the centerfin box before or after laminating?
We recommend installing the centerfin box after hotcoating and sand it flush with the bottom of the board while sanding the hotcoat.
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