Another option for slotting primary supports for 1/4" tubing

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Scott Hanson by way of Terry Fritz <twftesla-at-qwest-dot-net> by way of Terry Fritz <teslalist-at-qwest-dot-net>" <huil888-at-surfside-dot-net>

Rather than drilling a series of holes in your primary supports and then 
slicing off part of the supports with a saw cut, there is a way to use a 
radial arm saw to simulate a milling machine and make very accurately 
located slots to accept the primary conductor. This works great for 1/4", 
3/8" or 1/2" diameter copper tubing primary conductors.

The only needed equipment is a standard 8" or 10" radial arm saw, an 
adjustable dado blade, a piece of threaded rod and matching nut, a few 
clamps, and the plastic material you will use to fabricate your primary 
supports.

For simplicity's sake, lets assume that you want to use four radial 
supports for your primary (most medium sized coils will look best with at 
least six supports), and you'll use 1/4" soft copper tubing as the primary 
conductor.

First cut your support strips to the same length and width, and clamp them 
together. Offset the ends stair-step style by the pitch of one complete 
primary turn, divided by the number of supports. Clamp the supports 
together using small C-clamps.

Now, install the dado blade on the saw spindle and adjust it to cut a slot 
that's nominally 1/4" wide. Use a piece of scrap material to set up and 
verify the depth of cut and width. For 1/4" tubing, a cut of 1/4" to 3/8" 
deep works well. Remember that your tubing will be bent into a spiral, and 
the effective width where it passes through the support will be slightly 
greater than 1/4". If you are using support material that's 1/4" thick, a 
slot just a tiny bit wider than 1/4" will hold the tubing perfectly. If you 
use 3/8z' or 1/2" thick material, the slot will have to be proportionally 
wider to accept the tubing without deforming it.

Now, get a piece of threaded rod two feet or so long. Lets assume that you 
use 1/4"-20 threaded rod. Clamp a 1/4"-20 machine nut at the edge of the 
saw table near the fence. Attach a knob or something similar to the 
outboard end of the rod so it can be easily turned, and add some kind of 
index mark so you can count the turns. Position your stack of primary 
supports on the saw table, and locate the stack exactly where you want your 
first slot to be. Now, thread the rod through the nut, and bring the 
inboard end of the rod into contact with the end of the stack of supports. 
Double-check everything, check that the saw blade will clear all the 
clamps, etc, get your fingers out of the way, and cut the first slot. Now, 
use the threaded rod as a leadscrew to push the stack of supports along the 
saw fence to the next position where you want a slot. If you used 1/4"-20 
threaded rod, there are 20 threads per inch. Each full turn of the rod will 
advance it .050". Ten full turns will advance it .5". If you want your 
primary turns to be spaced on .5" centers, turn the "leadscrew" 10 turns, 
make a cut, advance another ten turns, make the next cut, etc. until all 
the slots are cut.

It takes a long time to explain the setup, but in actuality it is a very 
simple process. Once everything is adjusted, a full set of supports can be 
"machined" in less than 5 minutes.

  This process will yield precisely notched supports that look just like 
they were made on a $100,000 CNC milling  machine. A similar setup can be 
made on a table saw, but I prefer to use a radial arm saw.

Regards,
Scott Hanson