Wedding Bands

Here is the project I have been working on for a while.  It's the reason I needed 4th axis support in the first place.  These are the wedding bands for Kirstin and I.  They are made from Titanium.  The profile of the band itself was cut on the mill, and then the knot work and constellation art was engraved into the surface.  The final step is to polish out the surfaces, first using sandpaper, and then progressing to various grades of lapping paste (silicon carbide grain mixed with oil) applied with a hard felt buff.
These pictures show the knot work common to both rings, and we put the constellation for each others birth months on the part closest to the hand.  These still need one final level of polish, and they will be complete.

Finished Amulet

Kirstin mixed a little paint to add an older weathered and worn look, and a piece of oven bake modeling clay was used to form the "gem" in the center.  Clear drying craft glue adds a bit of shine.

Amulet Construction

To make the amulet shown below in CAD drawings I first start with a piece of 360 brass stock.  It is held to the plate below with a layer of paper and wax based adhesive.  This can be applied or removed with just over 200 degrees fahrenheit, easily supplied by a hot plate.  This has the advantage of not having to be pried off like double stick tape.  It allows you to cut all sides of the part free without additional clamping.

The first program cuts the outside of the amulet profile and the center pocket for the gem.  This cut is made with a square end mill.

The second program roughs out the 3 dimensional contours of the part.  I use a 1/8" diameter ball end mill.  It leaves a minimum of .007" of an inch everywhere on the part to allow for a finish cut.  This cut took approximately 20 minutes to make, and removed the bulk of the material.  Although the cut is shiny, the detail does not match the model very closely.

The finish cut is made with a 3/64" ball end mill.  The tool moves in a spiral from center to outside. Each  arm of the spiral is .0015" apart.  It moves up and down at the same time to form the contours of the part.  This cut takes much longer to make (~2hrs) but produces the fine finish seen here.  The part and plate it was resting on were returned to the hot plate and separated.  

Setup And Testing

In order to make sure that everything lines up, the first thing that has to be done is to make the axis of rotation of the rotary table parallel to the table travel.  Once that is done, I chucked a piece of machinable wax in the 4 jaw.  

By cutting 4 faces at 90 degrees I can measure to the center of rotation, and set the center of the system to the center of the rotary table.  In this picture I am starting to "turn" down some of the excess wax to make a cylinder.  The wax is entirely recyclable, it can be remelted and re-poured at a little over 200F.  It doesn't wear tools either making it perfect for testing out unproven complicated programs.  

In this video I have "turned" the cylinder down further and I am engraving a pattern on the outside.  It's a very simple knot work pattern.  The final project may evolve this style a bit.  Again Alibre is a bit different than other software I am used to.  I need to work with the rotary axis post/setup to get the output that I want.  Currently I don't have things working so rotary feed is output correctly.  Everything is correct, but I had to trick the system into moving this fast.

Here is a close up of the result.

Blam-o!

With a minor issue or two, everything went together rather well.  I still have to align things a bit more carefully and make the tailstock mount and belt guard.  The 4 jaw chuck will allow the gripping of round or non round stock, a rectangular bar of delrin is shown here.  Wiring is complete and the rotary turns well.