OK, I will take a shot at this!
Straight is a relative term when it comes to describing antler. However you can get it fairly straight if that is what you desire. The first time I tried this I did not have great success. I did not get it hot enough or clamp it fast enough or hard enough and quite possibly I did not leave it clamped long enough!
I think I used vinegar, but it was a limited amount, just a couple of tablespoons in a pot of water. When you boil it in water it does not have to be an extremely hard boil once it begins to boil. Just enough to keep the heat and steam there and
do not let it boil dry!
I do not recommend that you to do this in the house.
The Misses won't like the smell you have introduced into her house. Boil for 45 minutes to an hour and this is where
you will need gloves because you want to go straight from the hot water to the press. Have your boards you are going to use to clamp with already in position and the clamp or vice set and ready to go.
I used my vise and the
"break, bust or bleed" method to clamp. In other words all the pressure you can put on the antler. When it went to straight I never stopped until I could put no more presssure on a small Sears vice. Look at it this way the piece is no good the way it is bowed and straight is what you are trying to achieve, so put the pressure to it!
The piece will only straighten as much as the boards will allow it too. It will
embed into the wood some and the shape will also dictate the amount of straightness you obtain. Here is the other key do not be in a hurry to remove it from the clamp. I gave it 48 hrs. Now I am not sure it takes that long but it didn't hurt it either. It has to have time to take as set and dry out again completely.
This knife was made from a piece of antler that was straightened. It is a primitive folder and it had to be straight enough to allow for the the body to swing in and out. It was the outer time of a whitetail antler and had approx. 3" curve in it, or more when I first started with it! I don't have a straight down shot of the knife but you can get the idea of how much curve I took out of this piece.
(click thumbnail for larger image)
A word of caution I have not tried this with a really thick or heavy piece of antler so I am unsure of what the result would be! However I would think it will work but, the steam/boil time may need to be increased and the amount of pressure needed may be even more! This piece I used for this knife was approx 3/4" thick average and at its widest 1 1/4", if you look closely you can see where I cut the other side of the fork off on the bottom of the knife.