Re: Lobsterscope....
PLASMA CUTTER???!!! What for? 22ga sheet metal and a pair of
hand snips will do the cutting. When they made lobster scopes for
limelight spots in the 19th century, I guarantee there were no plasma cutters to make the discs! Believe me you have all the tools you need.
Just a question, why are you trying to make a lobersterscope? Class project, historical investigation,
etc.
etc.??
One of the biggest problems is creating your cut-out disc in an exact mirror
image pattern so it is evenly balanced and doesn't try to wobble, shake and tear itself apart.
Lay out your
pattern in any
cad program, this will let you create an evenly balanced
layout. Spray adhesive the full scale
pattern to the sheet metal and proceed to cut. If you use
hand snips, drill, hole saw
etc to open up the center of the openings and make a series of cuts to within about 3/8" of the finish
line, then snip to the corners and then make the final cuts. Note
hand snips come in left and right
hand styles with the blades over lapped in the opposite direction and they make curved cuts
in one direction better than the other, you should have a pair of each.
A couple of quick metal cutting bits of info.
Armour Archive -- Essays: Sheetmetal Cutting Tools by Sasha
How to Cut Sheet Metal | eHow.com
Other ways to cut sheet metal is with a Scroll Saw, sabre/
jig saw and band saws, using the appropriate metal cutting blades of course. Scroll saws and sabre saws can cut inside holes, a band saw can cut only out side holes or you have to make a cut through the
edge to the inner cutout and patch the cut later. with thin sheet metal the best way to make the cut is with a blade that has the finest tooth available and then adhere the sheet metal to a piece of 1/4"
masonite or other very smooth wood or hard board. Best way to adhere is with wax. Plain old ordinary wax. Heat the wax to a liquid and pour a very thin layer on the wood
lay the metal over it and then using a heat gun or
plug in a
fresnel and aim it at the metal from about 3' away, soften the wax and now the two are adhered. The
point of the wood is to prevent the saw blade from grabbing and ripping or tearing the thin metal during the cutting process. The
point of the wax is when the cutting is done, a little hot water bath or a heat gun UN-GLUES the wood and metal cleanly with no residue and you don't risk bending the thin metal while peeling it up. Note: drill your center hole for the axle rod while it is still attached.
Next, balance the disc. put it on a rod you can chuck into a drill and spin very slowly. check for wobble and
play. The heavy side will tend to
swing a little wider than the light side. Use a
grease pencil and as the disc wobbles, bring the pencil up until it just touches the
edge of the disc.
Mark the start and stop
point of the pencil
mark. Now drill an 1/8" hole near the
edge of the disc on the center
point between start/stop points, or alternatively put a 1" strip of
gaff tape on the light side directly opposite the pencil marks. Work in small increments until the disc can spin without wobble.
A couple versions of a scroll saw are:
Delta 40-690 20-Inch Variable Speed Scroll Saw
Rockwell RK7315 16" Scroll Saw, 16" Scroll Saw
Buying Guide: Scroll Saws
There are so many ways of connecting your disc to a drive motor, so many suitable AC and DC motors available, I can't begin to describe them all. You'll have to do a
bit of design and engineering yourself. Some small motors have a shaft with a threaded hole in the end and you can attach the disc directly to the motor. You can use very small V belts and pulleys, lots of choices.
Now, Note most of the directions will also work with wood except for the
hand snips. If you use a wood product I strongly suggest 1/8" or 1/4" hardboard (
masonite) rather than wood or plywood. The composite material is more uniform in weight from
point to
point and will be far easier to balance and sanding down the
edge is a balancing option. For
hand cranking, think belt drive. You'll need some small pillow blocks to support the drive shaft for the disc and the same for the shaft attached to the crank handle. Small belts and pulleys look at McMaster, Grainger, Tractor Supply and of course the big box stores. I would try to shoot for about 4:1 ratio with your pulleys, i.e. one turn of the crank makes about 4 turns of the disc. So a 1" pulley on the disc would be a 4" pulley on the crank handle.
Good luck!! Hope this helps a
bit.