Okay, I am having a big mental lapse with the math part of this, as far as figuring out the diameter of wire/drill bit I need to use. I have a flat, rectangular piece of perforated photoetch for a 1/72nd gun barrel. The piece measures 1/8" W x 5/8" L . I have read a couple posts that the easiest way to create a gun barrel is to roll the PE around a piece of wire or drill bit. How do I figure the diameter of the wire needed to roll around to turn that flat piece of metal into a cylinder? Haven’t touched that kind of math in years and, quite frankly, I’m stumped!
Perhaps find a drill bit that matches a plastic 1/72 barrel, or roll the PE around the 1/72 barrel?
As to the math, a circle’s circumference equals pi times the diameter (or 2 pi times the radius), and pi is 3.14159265358979323846264338327950288419716939937510… (22/7ths or 355/113ths work well as approximations). HOWEVER in this case it matters not one whit!!! Here’s why:
When one rolls PE, one does NOT start with the finished diameter. Start “large”, pressing say a 1/8" (if that’s the length of the side you’re trying to roll up) drill shank against the part resting a semi-soft base (got any medium stiff leather?), and work down.
Think of it as being like rolling dough. Do you flatten a pie crust at one go? No, you work at in in stages, and in this case, totally ignoring any math, you stop when the 2 edges meet.
BTW, a 1/8" (0.125") circumference circle has a diameter under 1/25" (less than 0.04"). If I did my sums correctly the original (real world) barrel would be roughly 2-7/8" in diameter; does that sound right to you?
Thanks for the tip … and the math calculations! I should have thought of that myself, really. Just a case of severe brain lock.
If I’m not mistaken, the .50 Cal tapers down to approximately 1 1/2 to 1 3/4 inches at the end of the barrel where the flash suppressor would be. That is just going off memory from when I actually fired one … years ago, though! I will have to do a little research on that one.
Thanks, again, for the tip. I will give it a shot this weekend and see how it goes.
Tom
Others are handling the size thing, but be sure to anneal the brass before trying to roll it. The brass usually comes in a “hard” condition. Light a little candle and run brass over the frame until it glows a dull red. Then let it cool. It will roll and bend much easier.
Thanks, Don, for the reminder! Completely forgot about that step… Just read up on that one. My understanding is that I just have to heat it to a dull red color and then let it air cool. Now the gun barrels aren’t looking all that intimidating and the best part is that I somehow ended up with two frets of PE so at least I have a couple to practice on if I don’t get it right!
After the PE is annealed, what Don described, take a drill bit or rod that is smaller than the final diameter. Place the PE on a flat surface that has a little give to it like a sanding stick. Roll the rod over the PE back and forth and it will start to curl around the rod. With a little pressure you can sometimes almost get it into a tube all the way. Now use a bit the final size and roll it until it’s tight and the edges meet. You end up with a perfect cylinder.
I have to ask you, why not use brass tubing?? You can chuck the part in the good old DREMEL (make sure your piece of tubing is longer than what you need) And using the lowest speed (the re-chargeable has a slower low speed)You can use fine emery cloth or good files and file the taper (if it has one ) into the brass tube If the part is done right when you roll score it with an X-acto knofe (like a tubing cutter) you will have your gun barrels.I created 1/200 gun barrels for the KRONPRINZ by using this method in three successive sizes and VIOLA stepped ,tapered main battery barrels!!! tankerbuilder
I guess the only question I would have regarding that method would be if there are micro bits small enough to drill the holes in it to represent the cooling jacket? I like the ingenuity of it, though … just not sure it would work for machine gun barrels. Definitely something I am going to keep in mind for future ship builds!
Yes, the spring-back is important. Calculating the amount of spring-back is almost impossible, so you do not really need to use the math. You need to use a form considerably smaller than the final diameter, but how much smaller is very hard to figure. Best to start with a form just a little smaller, then go to smaller-yet diameters to close the gap. A set of small drills gives you lots of steps to try.