"axolotl" wrote in message
...
My daughter has an interest in presenting illusions on stage. (She was a
costumer's assistant for the Teller/Posner production of Macbeth and
enjoyed the blood and illusions) One of the common illusions is having a
coin disappear by capturing it with a magnet. I want to make a coin with a
large enough hollow for a supermagnet disc. Has anyone a procedure they
can walk me through?
I have a lathe, mill, and the usual accessories.

Kevin Gallimore

Hi Kevin.
Don't make the mistake of facing the coin down all the way across the face.
Instead of that, face a hollow which stops before the rim of the coin, if
possible coincident with a ridge or line of denticles. This will make
concealing the join very much easier.
The large half (with the hollow) can be turned easily in a three-jaw chuck,
using a turned timber spacer to keep the coin normal to the axis of the
lathe.
The second piece, the small plug, is a little trickier as it must be turned
accurately to the correct diameter - to wedge fit into the recess you have
turned in the other half. I usually do this by wedging the coin bewteen two
hardwood centres turned to slightly smaller than the desired final diameter.
(Actually, it doesn't matter if they are too big, you simply turn them down
along with the plug.) The coin is held in place by (over)-tightening the
tailstock screw.
To reduce the plug to the desired thickness, turn down a hardwood mandrel,
supported in the three-jaw. Face the mandrel and bore a 1/4" hole right
through it. Turn an accurate recess in the hardwood face to match the plug,
then wedge the plug into it.
Face the plug until the dia is OK. (Use your feed graduations to determine
this.)
Remove the plug by pushing a pencil through the 1/4" hole. (Betch'a glad you
didn't forget that hole, yes?)
The plug can now be inserted in the recess in the face of the other half,
and if you've done it well the join will be utterly invisible. (Bonus: No
seam around the rim.)
Warning: You won't be able to get it apart, so go easy when trial fitting.
No glue will be necessary if you fit them accurately.

This is how two-headed coins are made. It's up to you to organise the
recess for the magnet.

This awfully complex-sounding method is actually not that difficult, and it
results in an excellent deception.

(So they tell me :-) )

--
Jeff R.
(who never defaces the Queen's currency)