Okay, i’ve had a dig through the archives looking for a (better) way to shape concaves into the bottom and here’s what I have found (so far)
Plane the stringer to the max depth of the concave depression over the desired length, taper subsequent passes in the desired oval and blend with sanding materials.
Use the surform and hand plane to basically do the same.
Bend a piece of plywood to the shape desired and afix sandpaper, forward and backward motion along the stringer til desired depression is made.Similar, create a wooden “jig” to afix sandpaper.
Now, what are you guys doing and what works well?
Personally I have been toying with planing the stringer but I am not happy with the blending of the tapers to make a nice smooth and even depression. On my current work I have pre-depressed the stringer prior to glue-up so it wont interfere with sanding the surrounding foam and I am partial to making a bent jig. Obviously for double concaves a slightly different approach will be needed and as I hope to make this current board concave-to-double-to-V I have much learning to do…
C’mon guys, speak up and share your concave secrets!!
I don’t think there’s one best way to do concaves. I don’t use templates… others swear by them. I don’t use jigs… others wouldn’t do it any other way.
I sketch the placement and outlines of my concaves with a pencil and rough them out with a surform, then use a series of sanding pads to smooth them out. The only “trick” for me is keep eyeballing them with a straight edge… I use a 3 ft level. I’ll admit a lot of this is done by feel and eye, keeping even pressure on your tools, and feeling the shape as you work, both through the tool and with your bare hand and naked eye. Kind of like squaring up the outline… you’re feeling the dips and bumps through the tool as you run it up and down the length of the board. You’ve gotta feel those concaves developing as you go, making subtle changes in your strokes to get what you’re after, and using the level and mini tape measure to check your work.
I use the Planer first, then sureform then Sandpaper, only I cheat by using masking tape at the sanding stage to get a clean outline where it transitions from flat. I then blend in with 120 grit later
I would love to see a video of one of the masters doing a tear drop nose concave, and also some single to double tail concaves. I have not seen Jim Phillips video - does he show it? JC’s Shaping 101 is just that - 101. After a couple of boards you realize how much more there is to learn.
My method is similar to others posted here. I don’t care much for teardrops and prefer a subtle blended concave. So I mark the outside edge(rail) with a pencil. I use the same tool I use to mark rail bands when shaping. I usually come in about two inches from the rail. I hand plane the stringer down to the depth that I want the concave. Like others I use a level or straight edge to check my depth and the over-all flow of the blend. To cut the concave I have used my Hitachi(for deeper concaves) a small surform or a sanding block. Once I have got it down to the desirded depth I blend it with a sanding block and finish it off with screen and a foam pad.
On one of the videos there (and you have to go a page or back in the archives) you get a glimpse of Malcolm kind of whittling out the concaves of a Bonzer 3 (I’m assuming, given the age of the video) with a surform. It was a curious technique.
By the way. I forgot to mention that for double-barreled concave in the tail, I use a “Louisville Slugger” baseball bat wrapped in sandpaper. Wood bats are hard to find these days, but I have found them at garage sales. They have a nicer “barrel” than their aliumnum counterparts. PS --A “cricket bat” won’t do.
I use a curved sanding block made out of balsa with 50 grit paper glued to it. Very light and controllable. It works for both the concave in the middle of the board (after hand planing the stringer) and for the double concave in the tail. It takes a lighter touch for the middle concave.
It also helps immensely to have lighting on only one side of the board to check the eveness of the concaves.
Lillibel03 - I saw that clip a while before I started my five fin recently, and had it in the back of my mind. I watched it again just now and realize I did it pretty much exactly how he did. And I thought he had used a curved cheese grater surform but it looks like he did it with a flat one, which was all I had. That little scraping motion he makes perpendicular to the stringer line is key - it’s only on screen for a couple of seconds. A cool thing in that film is the board being glassed in 1974 - extreme bonzer concave, looks to be 3/4 of an inch deep.
I’ve had the opportunity to watch an experienced shaper put in a single to double using a grinder with 8 inch soft sanding pad and 80 grit. He’d worked at a factory here in town and also at rusty and was very impressive to watch. Fast and precise. I believe he said this was the method used by Bill Johnson, if I’m not mistaken, and by Dave Endress at pride, I think.
He sketched his concave and made just a few smooth, sort of rocking passes and used the rounded edge of the pad. It was done perfectly. Very cool!
The Jim Phillips video is very helpful, I highly recomend watching it… If you are used to the 101 style of shaping it will throw you for a loop, but it’s great because it really makes you think about the process as a whole and not just blowing thru it.
I used a small wire brush to rouph in the concaves, then a small scrub brush to clean that , then sand paper and screen over a rounded foam block, worked fine but slow, no stringer to deal with.