Illusionist's Heart Locket Pt. 7

This weekend was our graduation, and with everyone's family in town I took my girlfriend's sister to the machine shop to teach her some machining. She helped make part of the locket I'm making for my girlfriend. We had to cut shallow flat bottomed holes in the barrels for the pictures to go in. Because the barrels have a semicircular geometry, they could not be mounted on the table using a regular vise or any of that hardware. So we made a custom fixture to hold the barrel for the hole cutting operation.

We used a 1/2" ballmill to cut a groove in a square piece of aluminum so that the 1/2" barrel would fit snug in the groove. We then superglued the barrel in the groove and clamped the whole thing in the vise to drill the hole .050" deep with a 3/8" flat end mill. We then heated it up with a propane torch to release the superglue bond and used some acetone to get rid of any residue. Superglue is a very easy way to fix parts that would otherwise require the manufacture of a complex fixture or jig. I don't know if I would trust it for precision machine work though.

We also made some spare parts for our robot on the lasercutter, as we are taking it to ConEdison on Tuesday to present to them and we want to make sure it works! 

Illusionist's Heart Locket Pt. 6

Today I made another piece for the Illusionist's Heart Locket. Now that classes are over I have free time to work on personal projects, which is a relaxing way to end the school year. The purpose of this piece is to punch the pictures that will go into the locket at the correct size. A regular hole punch can't be used as it is much too small. Instead I made a custom hole punch to get the correct size photo.

The Die

The die is a block of 6061 aluminum with a hole drilled and reamed to .376" and a slot cut with a slitting saw at a 15 degree angle. The angle allows the punch to cut through the paper gradually rather than all at once, reducing the force required by the user. 

The Punch

The punch is a cylindrical piece of tool steel turned to .375" on one side and .50" on the other. The .375" side cuts the photo, while the other side is larger to stop the punch from going all the way through and also for the user to grip. Now that I know this works, I can harden the steel. The sharp edge from turning is already starting to degrade even though I've only been cutting paper...

Illusionist's Locket Pt. 5

Quick update or my locket project. The pin is complete, and to spec. I decided to try using a corner rounding tool to give the locket more refined appearance. They are notoriously difficult to setup in the CNC machine, so I did a test run on a plastic part and on 2 aluminum parts to make sure I got it right before machining into my expensive copper. I also tested the drilling operations on the barrel hole. I originally made this feature with a ballnose mill on the CNC, but the finish was very poor and I would have to ream it anyway to improve the finish. So I decided I might as well drill and ream it from the get-go. 

To do this, I simply clamped two pieces together in the vice, using a parallel bar over the top of the vice to keep the faces normal to the axis of the mill spindle. Then I used an edge finder to locate the hole locations and drilled, reamed and countersunk the holes. 

After confirming all of these things could be done, I decided I was ready to begin making the final product from my copper plate. The feeds and speeds for copper are very slow, and it took almost 2 hours just to make these four little parts. The quality of two of the parts was acceptable, however the other two had gouges in them from the .25" end mill. I think that it was caused by two of the parts being mirrors of the other. For some reason, when coming around the parts the other way, the end mill got sucked into the part, causing those gouges. I may need to remake two of those parts. 

Illusionist's Locket Pt. 4

I did some work on the locket today. The first thing I did was I marked the sides of the magnets with a sharpie so I could distinguish between the N and S poles. To do this, I just stacked them all up and sharpie-d the tops one by one. 

The next thing I did was I heat treated a pin I turned from O1 tool steel. I used the furnace to gradually heat it to 1450F and let it soak for 15min. I then quenched it in oil. The subsequent hardness test shows a hardness of almost C59 Rockwell. It started out as B96. The spec sheet says it can be hardened up to C64, but I am satisfied with C59. This just means I don't have to temper it back down again. Next I'm going to turn down the diameter a bit more with a tungsten-carbide tool and finish it with a grindstone on the lathe. I would use a cylindrical grinding method, but we don't really have that capability at the shop. 

Experimenting With Copper Patinas

When debating what material to make the locket out of, I learned of an interesting technique used by metal artists/jewelers to give their work pieces interesting colors. By heating the work, you are speeding up the chemical corrosion of the surface of the copper. You can also submerge the work in chemical solutions to achieve the desired reaction. Using a torch requires less overhead, so I'm going to see if I can get this to work. 

The main problem with flame patination is creating/speeding up unwanted chemical reactions that may produce visual effects that interfere with the one you want. I'm still doing research to try and understand exactly what the red patina is, and how it's different than the black flaky firescale, which, as I understand, is also a type of oxidation reaction. 

I tried making a traditional boric acid flux. Typically, the powdered boric acid crystals are dissolved in denatured alcohol or methanol to form a saturated solution. The work is then coated in this solution, and when the alcohol evaporates/burns off, a thin layer of boric acid crystals remains on the surface of the work. I didn't realize that boric acid was different than borax, and so the flux wasn't very effective, and heating the borax turned it into a weak brittle glass. Boric acid can be easily made from borax simply by reacting it with hydrochloric acid, so I may try that tomorrow. 

Even without using the proper flux, I was able to get some decent purple-ish red colors. I will buff them tomorrow and see how they look, and try the flux as well. Then I'll need to figure out the best way to clear-coat them to protect the patina. 

Illusionist's Locket Pt. 3

I machined the first parts of a prototype today. I used a 3/8" ball-mill to get the central channel for the barrel pivot to rest in. I'm trying to see if there is a better way to do this, as the ballmill leaves a circular edge when I'd rather have a flat face. Also, slight errors in the depth of the ballmill correspond to the channel for the barrel not being cylindrical. There are still many improvements to be made!

Illusionist's Locket Pt. 2

Today I was able to reverse engineer the mechanism that switches the photos in the locket depending on the configuration. The key is having a two-part barrel that the halves pivot about. The two parts of the barrel are not attached, allowing them to separate when the locket is opened. Each half of the barrel is fixed to one of the movable heart pieces, allowing the other heart pieces to rotate around them, and allowing the barrel halves to slide over each other. 

The next step is to incorporate this mechanism into my existing design. I will probably need a few more magnets to hold the locket closed. I will also modify some of the geometry of the barrels and the barrel slots so they are machinable. 

Illusionist's Locket

This is a present I plan on making for my girlfriend for Valentine's Day. It is a metal heart made of two halves that are connected with a dowel pin and magnets. When the two halves are arranged in the heart configuration, the magnets attract each other and so the configuration is stable. When you twist the halves apart, the halves take the form of an oval. With the magnets' positions switched, the halves repel each other, allowing the user to separate the halves and gain access to the secret pockets inside each half. The secret pockets can be used to small rings, a small note, etc.

I've also decided to take advantage of the fact that our initials form a palindrome. If our initials are engraved a certain way on the two halves, on one side of the heart configuration the letters read "MD" (her initials) and on the other side the initials read "DM" (my initials). When rotated to the oval configuration, both sides are the same but are upside down relative to each other. So it reads "DM" or "MD" depending on how you look at it. I like to think of it as being symbolic of our partnership together.

Manufacturing should be relatively simple. The two halves can be CNC'd out of bar stock. I made the angle on each half 45 deg so that any standard shop gauge block could be used to mount the middle face parallel to the table of the mill for drilling the holes and milling the slot. I plan to use a 1/8" steel dowel pin for the center pivot shaft which can be turned on the lathe. Adhesive backed neodymium magnets will be used for retention. If I decide to do the engraving I will need to make some sort of fixture or jig for a flip milling operation on the reverse side of each half of the heart. Hopefully I can make a simple jig with some locating pins mounted on the mill table.

Note: This design is inspired by an Instructable I remembered seeing a while back. The author of the Instructable credits the design to a scene from the movie "The Illusionist". As you can see, the locket in the movie has 2 additional hinges that allow the locket to swing open in both the oval and heart configuration. The "illusion" is that when you open the locket in one configuration, one person's image appears. But when you open the locket in the other configuration, the other person's image appears. And the baffling thing is, it's hard to understand how twisting the locket from the heart to the oval configuration doesn't rip the picture in half. This is a *greatly* simplified version where there really is no illusion. I will use this design as a starting point and hopefully be able to design a locket that has the full functionality as seen in the movie.