Intro: Intergalactic War Bullet Keychain
So this project is the result of when an intern is put in charge of testing CNC lathes, put a bunch of other dangerous tools next to him, and gets bored during work hours.... Please don't fire me.
Anyways, this project was an experimental test I was doing, attempting to color heat treat stainless steel by zapping it with a TIG welder. I knew things wouldn't go as planned, but the premise was there, and I was ultimately curious as to what the results would be.
Surprisingly, the actual result was more appealing to me than what I originally had in mind, so I decided to press out a few in the CNC and make keychain out of them for gifts!
DISCLAIMER: Please don't try this without proper precautionary measures. Lets just say a TIG welder grounding itself through your arm isn't the best feeling in the world.
Step 1: Make Z Part
I started off by modeling it on Autodesk's Inventor, then did the CAM toolpathing on Inventor HSM. Since I would be making a few of these, I decided to use the Haas ST10Y Turning Center to press them out. I used a 1" diameter stainless steel rod stock.
In case anyone is curious about the feeds/ speeds I use for turning stainless, I dialed in at 300SFM at .01 in/rev for roughing passes, and 450SFM at .003 in/rev for the fishing pass. Cut depths were .04~.02 inches for roughing passes and .004" for the finishing pass. A lot of the reference for speeds and feeds can be found online, and its a matter of playing around with it to dial it right in.
If you're curious about CNC/CAM, check this instructable out here , made by Pier 9's very own Dan. I learned everything from Dan who has been a fantastic mentor for me, and this foundation allowed me to explore more in depth about CNC machining on my own.
If you have any question particularly regarding turning operations on CNCs, message me!
Step 2: Post CNC Prep Steps
After pressing a few off the CNC, I noticed that the parting tool left a little at the rear end. This can be remedied by doing another parting operation at lower RPMs, but sometimes the manual lathe is the best thing for quick dirty setups. I threw the bullets into the chuck and did a light facing pass to get a smooth finish on the rear.
This is a very important step since we will need to drill a hole in the rear later, and the nub would make the drill bit walk.
Step 3: TIG Zapping
Okay, TIG Zapping is in no way an official term... I just had no better way to express it. I used a TIG welder because a MIG would naturally cause spool to feed material while welding, and I wanted to avoid the setup.
SAFETY THIRD!!! And by that I mean safety first. Remember to have all the proper safety equipment: Welding Mask, Gloves, Long Sleeves, etc. etc.
So the setup I have for the TIG welder was using 1/16" tip, set at 200A DC. The other settings I didn't mess with since I wasn't necessarily looking for a good weld joint or anything. There's no reason to fixture down the bullet since no other material will be pushing on it, and you'll want to turn it around as you zap it.
With the tip of the welder around 1/4" above the bullet, feed it power slowly until you see the arc jump the gap. Once this happens, steadily move the welder in some pattern, while intermittently stopping to twist the bullet around. CAUTION: The bullet will be very hot as this process goes on, so handle it with pliers.
After you feel like you evenly bombarded the bullet with ions, it should look something something like the picture. You will notice scorch marks, craters, and some pretty cool discoloration on the surfaces.
Make sure to give the bullet adequate time to cool in air, or cool it in some oil or water before you proceed.
Step 4: Drill and Tap
I decided to drill and tap a hole on the flat side to insert a small bolt into there. The bolt will have the chain and the key ring welded to it. I used a 1/4-20 bolt, which required a #7 drill bit. Always remember when drilling: Spot drill first. This works as a guiding hole for you regular drill bit, which has a higher chance of deflecting and walking off mark.
Stainless can prove to be a little tough to tap, so remember to use tapping/cutting fluid, and ease into it.
Step 5: I Screwd Up, But Trust.
So... I screwd up a little here. I seemed to have lost my pictures of the finishing and chain welding steps. However, I shall just write brief comments on how to approach the task.
Once the 1/4-20 has been threaded, I salvaged a key ring/chain from an old key chain I found lying around and welded it onto a 1/4-20, 1/2" long socket head bolt. The welding settings I used were the same as the TIG zapping, but at 180A with the shield gas post-flow setting on. You want to be very careful and quick with this step, since the chain has a tendency to melt rather quickly in respect with the bolt. Once you get a tack weld on, feed some filler material at small increments, until you feel the joint is adequately filled.
Next, we want to throw or now-decrepit-looking bullet back on the lathe and sand it while it spins. You'll have to flip it around to get both sides. I did a wet sanding process, with 300 grit to start, and 1000 grit to finish. You want to be cautious with the lower grit count, since we don't want to be completely removing all the scorch marks. Do it just enough to start seeing a rough shine, then proceed to the 1000.
After that's done, you can screw on the bolt, and have your own little awesome keychain!