Captain America Sling Shot

Materials....

1. Mountain bike rigid fork

2. BMX handlebar grip

3. Sling Shot tubular replacement bands and 4 small zip-ties

4. Cowhide leather

5. Snap buttons (with hammer assembly tools)

6. Metal Hole Plug

7. Plugs (corks or dowels)

8. Captain America Pins

9. 1/2" steel balls

Tools...

1. Hacksaw or metal bandsaw

2. Assorted metal files

3. Black spray paint and paint remover (optional)

3. Synthetic steel wool (Scotch-Brite)

4. Sanding pads/paper

5. Simple Green and Acetone (or equivalent)

5. Vise

6. Rivet gun

7. Black silicone or gap-filling glue

8. Five-minute epoxy

9. Rotary tool with ball grinder

10. Contact cement

The bike fork is one that I had saved as it had been damaged. I had hung onto it for years thinking one day I might be able to use it (or parts of it) for a project. This one happens to be a Chromoly steel alloy rigid mountain bike fork made by SALSA. Since this project is going to be a gift for my grown nephew...the size of this fork is about right. For a younger person with smaller hands, consider sourcing a smaller fork especially one that has a smaller diameter steering tube.

Btw, this one already had the paint removed because I had attempted a weld it but botched the job enough that I determined that it was no longer safe to use for biking.

Determine the length of the handle. My measurement for the handle was determined by me holding it and marking the steering tube at the base of my gripped hand. I had read that shallower sling shot arms are preferred so I used blue painters tape to create the lines where it will be cut. I happen to have a metal band saw so I use that for my cuts. This can be done with other cutting tools including an angle grinder with a ferrous metal cutting blade or even a hacksaw.

After the cuts have been made, I secured the piece vertically into my bench vise using soft-jaws (the yellowish-orange polyurethane pieces) to prevent marring of the surface. Using half-round files, I cleaned up the inner parts of the tubing. A flat file was used to clean up the outer edges.

From there I marked (using blue painters tape) where the grooves will be made to help embed the sling shot tubing (which is intended to keep the tubing from creeping up or down along the arms of the sling-shot). The Chromoly tubing wall is not very thick so I was careful to file in a groove that did not effect the structural integrity of the steel (ie, don't file through the wall or too deep).

After creating a groove that wrapped the circumference of the tubes, either a 180 or 220 grit sanding pad can be used (rolled up to fit inside the ends of the tubing and rotated back and forth) to soften the filed edges.

Be patient and thorough with the above steps so you don't have to revisit any of these steps later.

Before deciding that this project was going to be a Captain America themed piece, I was going to just paint it black... so some of the following steps represent that approach and are optional.

Using a degreaser (like Simple Green), a Scotch-Brite pad helps strip off any unwanted surface grime. Rinse with water and dry afterwards.

A uniform dulled matte surface was achieved after stripping almost all of the black paint off with the Scotch-Brite pad and some paint stripper. One may be content with the raw steel finish after the initial clean. In this case, the black paint helped dull the sheen and finish of the steel (which can help resemble the appearance of the battle-worn Titanium shield of Captain America). I did not buff it after this step.

When the steel finish is achieved to your liking, use a couple coats of a clear spray (in this case, I used a matte lacquer) it to prevent the raw Chromoly from oxidation, etc.

I found a pair of blue BMX bike grips for the handle. The grip was a little longer than the handle length of the sling-shot (the steering tube section), so I carefully cut the grip down to size using a utility knife (before installing it).

Since the steering tube diameter is -- in this case -- larger than a BMX bike handle bar diameter, it required a bit of extra effort to get the grip over the end of the steering tube. With some help from something to act as a lubricant (in this case I had some silicone sealant nearby) the installation process went as planned (though a bit straining). It may help to hold the sling-shot arms in a vise (using the soft-jaws).

This particular handle bar grip is open ended (meaning, it will have the end of the steel tubing visible), so a metal end cap is used to finish off the bottom (and will serve an additional purpose later revealed in this Instructable). These caps are designed to snap in place. Find one that has the same (or nearly the same diameter size as the tubing it is intended for a solid fit). This particular end-cap was found in those small and random parts drawers at my local hardware store (see the last photo if you are not familiar with those).

This next part of the build process required some extra patience as the pins required some delicate handling for the parts to be secured into place. It just so happened that I found some shield pins that were nearly the exact internal diameter of the steel sling shot arm tubes... which was great (although, it meant that I had to figure out a less-than-straightforward solution to secure them and have them be centered). So, I wanted to find a an object made from a material or texture that of something that could be reliably glued or bonded. I rummaged around in my garage until I found a satisfactory solution (which in this case was some plastic JABIRU Bottle Top Stems that I cut free from their platform bases). Keep in mind, a wood dowel or even a large cork could have done the job to create the platform for which the pin was adhered to. I was closing in on a birthday deadline so I was required to be resourceful. In any case, I used silicone to bond the plugs to the inside of the steel tubes and to the pins. Silicone, albeit messy, is forgiving it that it allows for it to be moved around and is a good gap-filling bonding agent. In addition to the silicone bond created, there was a small mechanical bond from the pin as well...because I left the pin-back on and pushed it into the base it was being supported by. After both sides had the pins in place and centered, I let the silicone cure overnight.

Also, not shown in the photo, I used blue painters tape to wrap around the outside top steel tube near where the pin was glued. I also recommend wearing disposable gloves when handling the black silicone.

Since the handle (steering tube) on the bike fork is hollow, I thought it would be useful to add a cover over the opening so it could be filled with ammo. A leather snap-enclosure seemed to be a fitting solution for this. I had some black cow-hide leather that was nice and thick (roughly 3/16" thick) so I made a paper pattern of the shape I wanted and test-fitted it for size on the top of the handle opening. After some modifications (compensating for the thickness of the leather) I proceeded to transfer the shape to the leather by tracing it onto its raw (rough) side. Unfortunately, I was so involved with getting this done that I had not photographed some of these steps. The leather shape was cut by making a series of individual cuts using an Exacto knife.

With a rotary hole punch (or a hole cutter) I created an approximate 1/8" hole where the rivet would attach it to the to the top of the handle (the location of this hole is all determined during the test-fitting). To attach the snap cap and socket to the leather, place the cap into the smooth side of the two-sided aluminum holder (anvil)...seen in the first photo. The cap is seen on the left side of the 7th image. Lay down the leather (raw side up through the barrel of the cap). Load the socket last. Using the hammer and the snap setting punch the barrel of the eye-let will spread apart to mechanically attach itself to the other piece. This step is almost pointless to describe (especially since no photos were captured) when there are many videos that walk through the steps... like the one seen here.

I used a washer to decrease the size of the existing hole in the fork by placing it on the inside of the steering tube. This allowed the smaller rivet I had to grasp firmly against the steering tube (without popping through the hole). The same method (with a smaller washer) was used to rivet the other side of the snap (the stud) to the opposite side of the steering tube. I did need to modify the rivet head by filing it smaller so it would fit within the diameter of the stud. Lastly, the hole in the stud of the snap had to be made larger to accept the rivet pin... this was achieved by using a countersink drill bit (a regular drill bit ought to work, too) and a pair of pliers to hold the stud in place while drilling it through against a sacrificial piece of wood. To prevent the washer from moving around during the rivet attachment process, one can tack (temporarily secure) the washer in place with an appropriate adhesive. The rivet mandrel end goes into the rivet gun and will automatically be cut off after a few squeezes of the gun handle.

To finish off the the leather cover, a belt sander or a file can be used to remove the pin assembly from the back of a pewter C.A. Shield pin. Barge's contact cement was used to adhere it to the top of the leather (apply this cement to both surfaces and allow to dry -- 15 mins or so -- before attaching the two surfaces together). Remember to only apply the cement to the area of the leather that this pin will cover.

The exposed rivet head (used to attach the leather strap) was somewhat unfinished looking so I found a Captain America Head Ata-Boy enamel pin to attach over the rivet head. Using a grinding ball on a rotary tool, I slowly (to avoid generating too much heat), ground a concave depression into the back of the pin so it will rest as flush as possible against the rivet head. I do not recommend grinding down the rivet as it is an integral part of the fastening assembly. Five-minute epoxy was used to glue the concave area to the rivet head and black silicone for the small spaces above and below it...to attach it to the leather. By using two different types of glues (one solid and one flexible) I felt the pin would be more secure to bumps and knocks. I did leave the pin in tact to also push into the leather... although I did need to file down the length of the pin as it was longer than the thickness of the cowhide. With quick-setting epoxy, one can just hold it (or use a appropriately sized spring clamp) until it sets up. The silicone will set up a bit later but the pin will stay put until it does.

Now on to installing the sling-shot tubing.....

So I sourced red sling-shot replacement bands sold as a four-pack by doing some browser searching. I thought it would be nice to include some extras as part of the gift in the event there is an untimely malfunction. In this set of steps, I recommend having an extra set of hands to help. Although this is somewhat straight forward it will make it easier...as long as the person helping you knows what they are supposed to do. I chose to use miniature (~4 inches in length) red zip-ties as the fasteners for the tubing. First make a loop with the zip-tie (until you hear with the audible click of it engaging). Run the end of red tubing through the loop of the zip-tie then along the inside of the arms then around to the outside of the chromoly arm (at the filed groove) and back through the loop of the zip-tie. Important: keep the tubing aligned during these steps to ensure there aren't any kins or twists... this will help with the final outcome. Btw, the Ata-Boy C.A. head pin will be on the opposite side of the leather projectile cradle (see photo). With tension on the tube end and the tube (where they come together) pull them away from the arm. This will allow the person tightening the zip-ties to have it be a snug fit around the chromoly arm. It's okay if there is some space between the chromoly tubing and where the zip-tie is because it will come back to fit after the tension is released by the person pulling the tubing away. Once the first zip-tie is in place, pull it the red tubing out again (at the location of the first zip-ties) to secure a second zip-tie in front (closest to the Chromoly arm) of the one that was just fastened... by doing so, in the above order, a tighter fit will be made. Here is a video that pretty much does the same thing but without the use of zip-ties.

Once the zip-ties are tight, cut off the excess....

I found a soft C.A. lunch box, a tote bag, and stickers to embellish the gift presentation with the theme. The black leather ammo container (seen in the lunch box) was also found online... coincidentally, the snap cap had a star embossed in to it so I had to color it with some careful blue and white paint-pen work.

Also, found some hard clay ammo that bio-degrades and explodes on contact to include for some target practice. Most of them were transferred to clear plastic tubes -- found online -- for easy transport. These are in the white gift box along with the extra replacement red tubes and miniature zip-ties.

Fortunately, everything fit into the tote bag... and it was a fun and challenging project that was well-received.