Nothing new here but I took a couple of pictures and thought some of the newbs here would benefit.
I wet sanded the box to exactly perfectly flush with the board for starters. Then a light 220 sanding around the box.
Some have fretted over laying wet glass over an open slot and having resin drip in. I used to fill the slot with gelatin and fell really cleaver, but lately I’ve just been laying 4 oz glass pre wetted and scrapped of excess resin. Pic’s below.
A light fill coat and some sanding and we are all good.
If I’m worried, I fill the slot with flour or bisquick as much as possible then lay a thin layer of wax over that. I save partially used birthday candles for this, but I’ve also used old wax scraped off boards I keep that in a tin cup.
I use this technique to cap proboxes, and I fill the screw holes after seating them down. I cut out the hole carefully with a razor knife then heat up a fin box key to get to them later.
Charlie, good point. I have that equipment and have mostly done it that way, lately. But I had a few of the old boxes and most ppl won’t spend the several hundred dollars it takes for the one pass bit, template and a large router. So, and since I took a few pictures, I thought some might like to see how easy it can be the old way.
I like to use Probox because of the cant inserts and the forward/backward adjustments. I have used FCS fusion recently prelam, but I haven’t tried prelam long center boxes. I found that many of the boards I do are not perfectly flat rocker wise where the box is, and I figure that you sand through the glass when you need to sand down the box.