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Step 8Prepping the Arm
Before we attach the arm to the catapult, we need to drill quite a few holes in it.
Depending on whether you're using a non-metallic arm or a metallic arm, there are two different ways to go about this.
Metallic Arm:
Start by getting really long lengths of steel pipe. I think the total length of the steel arm that I made was 14', which had an 8' double-barrel base (2 pipes welded next to eachother) and a 6' top piece. Basically, just weld the pipes together, putting about 2 inch welds every 4 inches or so. When you're done, weld a U-bolt onto the arm about 68" from the bottom of the arm, and a large eye bolt right below it - the u-bolt will hold the surgical tubing in place and the eye bolt will be the winding catch. About a foot and a half up, weld another large eye bolt - this will be the firing pin catch.
At the very tippy top of the arm, welt a bolt bent at a 45 degree angle to the top. Make sure that the bolt is facing the opposite way that the u-bolt and eye bolts are facing (which should all be facing the same direction).
Non-metallic Arm (fiberglass)
You're going to need a drill press and a whole bunch of drill bits. Since you're drilling into fiberglass, you have to slowly step through all of the sizes of the bits, until you reach the final bit.
You'll need to make out two holes for the u-bolt about 68" from the base of the pole, a hole for the eye bolt (winding catch) a few inches below that, and a hole for the other eye bolt (firing pin catch) about a foot or so above that.
Both:
Place the arm in its holder and mark where the holes are on the arm. Drill out the arm and test out how it fits. It should be pretty snug, and not able to move very much. This is GOOD!
You should check all of your measurements and hole alignments before drilling by putting the arm in its holder. The u-bolt should line up with the cross-brace, the winding catch should line up close to the winding "spool", and the firing pin catch should line up with the firing pin (this is a must).
Depending on whether you're using a non-metallic arm or a metallic arm, there are two different ways to go about this.
Metallic Arm:
Start by getting really long lengths of steel pipe. I think the total length of the steel arm that I made was 14', which had an 8' double-barrel base (2 pipes welded next to eachother) and a 6' top piece. Basically, just weld the pipes together, putting about 2 inch welds every 4 inches or so. When you're done, weld a U-bolt onto the arm about 68" from the bottom of the arm, and a large eye bolt right below it - the u-bolt will hold the surgical tubing in place and the eye bolt will be the winding catch. About a foot and a half up, weld another large eye bolt - this will be the firing pin catch.
At the very tippy top of the arm, welt a bolt bent at a 45 degree angle to the top. Make sure that the bolt is facing the opposite way that the u-bolt and eye bolts are facing (which should all be facing the same direction).
Non-metallic Arm (fiberglass)
You're going to need a drill press and a whole bunch of drill bits. Since you're drilling into fiberglass, you have to slowly step through all of the sizes of the bits, until you reach the final bit.
You'll need to make out two holes for the u-bolt about 68" from the base of the pole, a hole for the eye bolt (winding catch) a few inches below that, and a hole for the other eye bolt (firing pin catch) about a foot or so above that.
Both:
Place the arm in its holder and mark where the holes are on the arm. Drill out the arm and test out how it fits. It should be pretty snug, and not able to move very much. This is GOOD!
You should check all of your measurements and hole alignments before drilling by putting the arm in its holder. The u-bolt should line up with the cross-brace, the winding catch should line up close to the winding "spool", and the firing pin catch should line up with the firing pin (this is a must).
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