Faking Bone

Making a Fake Bone Part For a Crystal Chamber Cover

A word on methods:

This is only one method for making a fake bone-like part.  Most people don't have access to a lathe.  It is a convenient tool, but is not a necessity for working up an excellent part.

Making the part:

Above is a picture of my first practice piece (3/4 inch PVC pipe) compared to the actual diameter pipe needed, which is 1 1/4 inches in diameter.  The bigger pipe has been cut much longer than I need for the actual part because it will be chucked up in a lathe for facing, boring out, and turning.  Facing is cutting the end square in regards to the table of the lathe.  Boring out is increasing the inner diameter (I.D.) of the pipe in this case - essentially, it's drilling a larger hole in a part.  Turning is the process of decreasing the outside diameter (O.D.) of the pipe in this case - essentially, this process makes the diameter of the piece smaller.

First, though, the PVC pipe has to be chucked up in the lathe.

Here, I've chucked up the piece in the lathe.  The trick is to try and center the piece so that I remove the least amount of material to do the job.  In most cases, I'd worry about the strength of the part.  Since this is a part that really doesn't get any load or stress, I can be fairly sloppy with it, but it's good practice to always do the best job possible.  That will keep me in practice for when it matters to center the piece precisely.

In the picture above, I've completed the job of facing the piece.  In the next set of pictures, I'm boring out the pipe so that it will fit an MHS part for the lightsaber I'm making.

The tool here is a boring bar.  I've spent many hours tending a lathe during a boring out procedure.  There's a reason it's called "boring," because it is.  I think I've told every joke I know about boring 2-3 times over.

After boring the pipe round on the inside, the MHS part won't even fit it's threads into the pipe.  I should note here that raw pipe (like you buy from Home Depot) is never perfectly round on the inside.  It's good practice to never trust that bought stock is round and check it before you work it.

Now, I've bored the pipe out so that the threads go in, but the part can't slip into the pipe.  At this point, I'm moving the tool to cut 1/1000 of an inch (.001 inches) which will remove a total of 2/1000 of an inch off the diameter.  As I get closer to the size of the part, I start cutting less by moving to half that amount (approximately 1/2000 of an inch).

Here's a picture of the boring process starting.  PVC cuts pretty good, though not as good as other plastics I've worked with in the past.

After a few passes, the MHS emitter fits in the pipe with just a little force.  I'm not working to a specific tolerance (or wiggle room), but the emitter barely wiggles as I slip it into the pipe.

Now that I finished boring the part out, I start turning the pipe down.  This performs two vital tasks for making a fake bone part.  First, it shaves off the shiny and painted outside of the PVC pipe (if you've seen PVC in stores, you know what it looks like).  Second, thinning the pipe (which is what turning will do in this case) will allow it to become more translucent.

Above, the two pictures show two different kinds of turning.  The top picture shows 3 bands that are somewhat raised from the rest of the surface.  That makes this a rough cut, removing a large amount of material without making the piece look nice.  The bottom picture is a finish cut, leaving the surface turned to a very uniform surface.  Because PVC is a plastic ceramic amalgam (I'd call it an alloy if it was metal, but I don't know the proper word when referring to plastics), the surface is matte.

Here, I've found the really nice feature of this new lathe (the last lathe I used burned up in an unfortunate house fire).  It has an auto-feed for the compound rest (where the tool is fixed to the lathe).  This is the very first time I've had an extremely clean cut-off of a piece I've worked on: it felt like magic.  As you can see, I caught the part with my finger as it was cut off.  DO NOT DO THIS.  Every material is sharp after being worked on the lathe (or, at the least, I assume it to be) and this is a very good way to lose a finger or something equally hideous.  I did this very carefully, but I'd never ever do something like this if I were working with metal parts.

Here, I've cut fissures in the PVC to simulate aged bone cracking as it dries.  I've seen this in scrimshaw (bone carvings), especially in carvings on teeth.

Using a combination of paints and PVC cleaner, I've yellowed the piece but dulled the fissures.  This is not the best combination, in my opinion.  My favorite routine is to cut the fissures, paint with black spray paint (wipe it off while still wet with paint thinner), apply a brown paint (again, wipe most away), and apply a yellow paint (wiping most away).  Between paint coats, I can remove dried paint with clear PVC cleaner solution, however doing so dulls previous layers of paint.  Below is the outcome with a final re-application of black paint.

Now, before I go on, I have to admit to a mistake.  When I measured the length of the fake bone part, I didn't have all the parts necessary to measure.  That is, I couldn't put the lightsaber together and see the complete picture.  I, therefore, took the measurement of the part I was covering (1.5 inches) and made my part exactly 1.55 inches in length.  When the final part came in, I found my mistake.  The crystal chamber piece is 1.5 inches in length but, with the Trim Rings I'm using to fence in the "bone" part, the length of the fake bone part should have been 1.35 inches in length.  Lesson re-learned - ALWAYS have all the parts together before making measurements.

Translucence of PVC

When I first noticed how translucent PVC became as I thinned it, I began to see how interesting this would make the crystal chamber cover.  Here's a picture:

The red light is a red LED in a small key chain pocket knife.  (The blue gloves are for me while I do other shop things.)  The PVC part is one I put threads in while experimenting on the lathe.

This translucence gave me an insane idea.  If I'm very good/lucky, I will post my next blog on the result of my insanity.  Until next time, MWHAHAHAHAHA!