08-02-2015, 01:11 PM
I've built a lot of motorcycle exhaust systems in stainless. One task is rolling cones. I use a tool called a slip roll for this, and can usually get the ends of the cone to butt up when I'm done, but it takes some hand-skill to use: a flat cone has a long radius end and a short radius end (which, when rolled, correspond to the major diameter and the minor diameter). You have to manually cause the short end to slip (hence the name slip roll) so that the rollers are always aligned with the axis of the cone. It's the same reason a car needs a differential to turn.
A sincere question is this: does the ammo guide need to operate in a wet environment? If so, stainless is appropriate, if not, you're using a material which is known to be a drag to work with. Mild steel is significantly more agreeable to bend than stainless. And, 316 is tougher than 304.
One working solution to your sheet metal working problem is to build the cone in 2 equal parts - this will allow you to get your bending tools into the cone shape. TIG them together after the half-cones are formed.
Before I had my slip roll, I used to roll cones with a rubber mallet and a stiff bar in the bench vise. I would draw the axial lines on the blank, align them to the stiff bar, and hammer "off-dolly" to bend the parts. This would result in a slightly faceted cone. Then I'd use a flat-faced body hammer to plannish the parts into a more round shape.
Stainless has a lot of "spring back" and any bending form with a radius needs to be smaller than the desired radius to take spring back into account.
A sincere question is this: does the ammo guide need to operate in a wet environment? If so, stainless is appropriate, if not, you're using a material which is known to be a drag to work with. Mild steel is significantly more agreeable to bend than stainless. And, 316 is tougher than 304.
One working solution to your sheet metal working problem is to build the cone in 2 equal parts - this will allow you to get your bending tools into the cone shape. TIG them together after the half-cones are formed.
Before I had my slip roll, I used to roll cones with a rubber mallet and a stiff bar in the bench vise. I would draw the axial lines on the blank, align them to the stiff bar, and hammer "off-dolly" to bend the parts. This would result in a slightly faceted cone. Then I'd use a flat-faced body hammer to plannish the parts into a more round shape.
Stainless has a lot of "spring back" and any bending form with a radius needs to be smaller than the desired radius to take spring back into account.