Spark....not trying to be a pain in the butt, but it does matter....I'm not clever enough to demonatrate....mayhaps someone can?
Hi Rich
It really does not cut a warp in the wood. I have done this on every plane I have built for the past 30 years, NO Warps.
example Flaps, mine are 3/8 inch tapered to 1/8 inch
I take a 3/8 inch rod and put it at the lead edge or hinge line, this stops any cutting of the flap at that end.
the trail edge gets a 1/4 inch rod, I sand this side with rough paper and it will cut an even taper of 1/8 inch on one side of the flap.
I then turn the flap over, and put a 1/8 inch rod at the trailing edge which is now 1/4 inch thick, I sand this side and it cuts a 1/8 inch taper into the flap.
This is now a flap that has a 1/8 inch taper cut evenly in both sides, they come out straight with ZERO warps cut into them.
100s of people use this rod trick and have no problems, The only ones I have seen have problems are not following directions.
Now if your using a curved trailing edge, you can get in trouble, you have to bend the trail edge rod to the same curve as the flap.
You can also get in to problems if you push down hard on the sanding block...example, your sanding on your card table, when you push down hard it warps the table, since the flap is laying on the table it will warp too.
So you just need to be careful.
Randy