How to Cut an Arc into End Grain
I’m making a table leg with a small arc in the bottom (see attached). I thought I’d just cut the arc into the end of the wood with the edge of my 1 5/8″ Forstner bit, but when the edge of the bit turned into the end grain, bad things happened. I was able to make the cut with a scrap piece of wood pushed against the end of the board, but I don’t have enough scrap to cut the ends of all the legs (the wood was not planed to a standard thickness). My idea now is to cut 1/2 of the arc with a top bearing pattern bit spinning counterclockwise from near the top of the arc to the end of the board, then flip the board over and cut the other 1/2 of the arc with a bottom bearing pattern bit. Then I’d clean out the very top of the arc with a rasp or sandpaper. That idea sounds like a lot of trouble with many opportunities for a mistake. Is there any better way to make this cut?
Replies
Could you use a coping saw to remove the majority of the waste, followed by a half round file to refine the shape?
I've done it this way and it works well. Could use oscillating spindle sander or sandpaper on dowel as well to refine the shape.
If the scrap wood worked for you stick with it. Mill some more material as close as you can get and then use paper to shim it perfect.
If I was to choose an alternative I would gang cut them 2 at a time on the bandsaw. The ones that will be seen together would be taped together for the cut, followed by hand-tool cleanup.
Leaving the legs over-long would have let you use the forstner and then cut down the leg, but of course that ship has sailed.
Drill many small holes along the inside arc of the line and remove the waste with a coping saw. Then clean it up with a drum sander.
Making the arc with a fostner bit was a good idea, the best time to do it was when the legs were still part of the plank so you could drill between two legs and then cut in the middle of the circle or have 3/4 inch of extra length and cut to length after the hole is drilled. If that is no longer possible you could butt two legs, hold them together with a pipe clamp and drill in at the junction.
Since you have the legs made already, I'd be inclined to make a guide for the Forstner bit. Something like this.
You didn't give your measurements, but can you drill your hole through a piece of quarter inch MDF, cut half off at the table saw and square it with your leg, hog out most of the waste, and use the pattern with your bearing bit. The pattern would ensure all the legs are the same.
After you make a successful cut using the scrap piece clamped to the work piece, just reuse the scrap piece for the next work piece. The half hole is already there but it will still serve to keep the forstner bit from wandering.
Gulfstar's idea of putting two legs together is a good one.
Also, if you can do this with a drill press, clamping the work piece down to the table should allow the bit to cut properly without wandering.