Another approach for wire stability

Today we'll tackle the problem of coil stability in a new way.

Here is a new 10' section of schedule 40 4" Cantex, ready for cleaning. Scotch-Brite and windshield washer fluid are used to remove small surface nicks and dirt.

The two black plastic brackets holding the tube are called base spacers in Cantex-speak, part number
5355969, and are not very expensive. They come in very handy if you do any work with 4" material.

After cleaning, a protractor is attached to the bell end of the tube.

We'll make hash marks every 60 degrees, for a total of six on the circumference.

The protractor is fastened to the other end of the tube, and six more hash marks are drawn. Now we
have two end points for the next step, snapping a chalk line.

Next, we uses blue painter's tape to make a 1/2 inch channel.

Half of the tape is shown here. We remove the chalk line before putting on the second tape border.

With both tape lines in place, we're ready to apply the wire stabilizer. This is a very thin coating of DAP
Dynaflex 230 caulking compound, purchased from the Home Depot. Please read the instructions on the container. This stuff sticks to PVC and is useful over a wide temperature range. You may want to make a practice run first. Try putting down a bead about 1/10 of an inch in diameter.Then use a latex glove or wrap your index finger in plastic wrap and smooth out the caulk manually. The goal is to make a small adhesive pad for the coiled wire. Give the Dynaflex 5 minutes to set up before removing the tape.

The thin caulk line presents a low profile on the tube. Next, we wind the coil.

Another approach to coil stability.

The brake on the wire spool hub is set to hand tight plus three quarters of a complete turn. This yields a very high wire tension on the coil feed wire. The results are a uniform wind and no shift of wire on the form.

It doesn't get better than this. The whole 10 foot tube shows this consistency !
Here is another lathe shot:

This is a picture of the wire spool stand and the tube, at the half way point in construction.

 
And here is the finished antenna;

I fired this coil up on the low end of forty meters and was pleasantly surprised. I found three resonance points on the tuning capacitor on my MFJ antenna turner, and each time I changed frequency slightly on my transceiver, I had to reset the MFJ unit.
The next step will be a twenty footer !!! Must wait for the return of warmer weather.
A quick note to the coil builder. Stay with the Cantex conduit. I had occasion to try to use brand x PVC electrical conduit for a test trial and ran into serious problems;
1. Check for rigidity. The "x" 10 foot section took a bend on the way home in the back of my car. Not good.
2. Try drilling holes for tap positions. I drilled six holes; two were difficult and four went through the material like butter. Not good.
3. Here's the show stopper. The bell end was not sized correctly. It seized on my sheave mandrel and was an absolute nightmare to remove. Really not good.
In fairness to the conduit industry, I must point out that their product(s) are not designed for my applications.

A new vertical antenna.

Today a new 10 footer went up, wound with 1/16 inch aluminum wire. The 5356 alloy winds consistently, as shown below. Winding time was approximately 4 hours. If you try this assembly technique, please remember to use loose-fitting gloves and safety glasses !

The finished vertical antenna has continuous coil of 1025 feet of wire !

A New Approach to Winding Aluminum Wire October 8th, 2015, rejected October 11, 2015

The tried-and-tested techniques used with stainless steel wire do not work with 5356 aluminum 1/16" wire.

The wire kinks and changes position on the coil form after it exits the guiding tool. Any small amount of slack is immediately translated into random wire movement. Back to the drawing board.

We'll start by eliminating the wire bending tool on the feeder stand. Tension on the wire is set by the spring-loaded brake in the wire spool spindle. So far so good. However, the black ABS glue pads that worked well for stainless steel have no effect on the soft aluminum. Time for a new approach.

 Here is a test piece with an end-to-end chalk line. This line is the guide for a new tool, the router.

Before routing, we need a tool guide to keep the router from wandering on the tube. Cantex makes a coupler, p/n 6141632, that's just right for riding the tube surface. Here the coupler is cut in half and the inside stop is ground off. The shell is fastened to the router base plate, and we're ready for action.


The router is set up with a 1/2 inch straight bit, and is set for a 7/64 inch deep cut. The theory is that the hard edges made by the router channel will slightly deform the aluminum and hold the coils in place.

The rice-like crumbs from the process fly everywhere ! Keep that ShopVac handy.

Four cuts are made on the tube, each at 90 degree intervals. Next, we roll !


Sunday, 10/11/15; The tensile strength of the wire is such that the grooves proved worthless.
On to plan C.

Setting up the new 24 inch sheave...Slower surface travel speed and increased torque will yield high-quality coils with uniform spacing between the turns.

The tried-and-true drive assembly is placed in the worktable base.

The support rack idler wheels are centered over the drive pulley and pulled away from the table edge to accommodate the new sheave and flange unit.

The new head stock resting in place and waiting for a new 72" drive belt. C-clamps, a rubber mallet, and shim stock make the project gel in minutes.

Remember to clean thoroughly the bell end of the new tube section. Dirt and other corruption make the joint between the tube and the flange connector difficult to assemble and take apart. One go-around with a 10' section of tube and you'll realize immediately why 4 inch is as large as it gets for this project. 

Weight with hardware is 22.2 lbs., and the new travel speed on the 4" work piece surface is 171 inches per minute.

The new travel speed is ideal for 1/16" 5356 aluminum wire. Removing one of the shims, shown stacked to the right of the pulley, allows the operator to rotate the sheave by hand during set up.

Before winding, we'll put on four adhesive strips. Here is the "before" shot.

And here is the "after" result, with the blue painter's tape removed.

General information, September 2015

The tube section shown above displays the first of four pinstripes made of black ABS glue, each at a 90 degree interval. The edges of the stripes hold the coil wire even on hot, sunny days. When the pipe is free-standing, it will bend slightly in the wind. The wire will move a finite distance on the coil form! The black adhesive will keep the wire secure.

Be sure to have lots of ventilation if you use this stuff !! Most hardware stores

sell Oatey ABS cement in several flavors. Be sure to get the black version.

The data sheet from Oatey is recommended reading;

http://www.oatey.com/doc/medium-black-abs-cement.pdf

Blue painter's tape defines the black channel. Allow the cement to harden for a day before winding wire on the form.

PVC electrical conduit is inexpensive and available everywhere. It's ideal for Tesla coil projects and RF coil forms.

A 10' piece of Cantex 4 inch schedule 40 electrical conduit, part number A52EA12, ready for coiling, is shown below. A plastic scouring pad and windshield washer fluid are used to clean the section prior to winding.

Electrical conduit is designed for above-ground and below ground service, and is stable over a wide temperature range. The Cantex formulation is consistent from lot to lot. The tube does not exhibit "chalking", or surface weathering.

References;

PVC Pipe Association;  http://uni-bell.org/

All kinds of useful data here.

Here are two sites that outline the dielectric properties of different plastics, including PVC.

http://www.pupman.com/listarchives/1998/April/msg00337.html

http://www.professionalplastics.com/professionalplastics/ElectricalPropertiesofPlastics.pdf

Cantex pipe data sources;

                                              

http://www.cantexinc.com

A thoroughly developed web site; easy to navigate and packed with information.

A copy of the Cantex catalog; http://www.cantexinc.com/resources/product-catalog

http://www.mars-electric.com

My local source for all things Cantex. The company has several stocking facilities in northeast Ohio.  Call 800 288 6277  for more information.

Here is an all-band vertical dipole antenna for my ham station. The stand is a discarded safety sign base, and brings new meaning to the term "portable". The wire is 309 stainless steel, .045" diameter.

Above, a re-wound single wind on the same 4" coil form as was used for the dipole.

The wire spacing is determined by the tool shown below.

Several readers have asked for more specifics on the winding guide. The tool shown above is a 3" piece of 1/4" Teflon(R) PTFE tubing with a 1/16" inside diameter. I buy this from McMaster-Carr in Ohio. The part number is 8547K22. It's sold by the foot and is not very expensive.

Two sets of cuts are made on the tubing with a razor blade. The first set is made for the tubing to conform to the coil form as it rotates under the operator's  hand.

I use 2 cuts, each at 30 degrees with respect to the tool end, on opposite sides of the tool. Configured this way, the tool rests on the coil form surface without twisting or turning.

The second set of cuts is made on the right and left sides of the tool. These determine the distance between the wire on the coil form and the wire exiting the tool, in other words, the coil spacing.

As shown above, I'm experimenting with a 1.5 times wire diameter spacing for a trade off between the amount of wire on the form and the capacitance between the turns. 

http://www.w8ji.com/loading_inductors.htm presents some interesting data on the subject.

http://www.kennethkuhn.com-students-crystal_radios-designing_inductors.pdf has compiled an insightful primer here.

http://www.g3ynh.info/zdocs/magnetics/appendix/self_res/gallery.html has a fascinating article on coil phenomena.

http://www.crystalradio.net/professorcoyle/professorcoylecyl.shtml has a calculator that every Coil Builder will find useful.

 As to the type and size of wire shown on theses pages, the best wire is the wire you can get your hands on at the right price.

Adhesive tape is wound on the Teflon(R) tool as a grip pad for the operator. Five or six layers of tape should be sufficient for the operator to hold the tool between the thumb and index finger of one hand without interfering with the winding process.

The Teflon(R) tool material has a very low wear rate. I've used the one you see on six 10' coils and have yet to see any appreciable wear.

Let's get into production. Always wear loose-fitting gloves and safety glasses.
The motor start switch is mounted just to the left of the wire spool. As the wire is wound on to the tube, the operator moves the wire transport with his/her feet.

Here is the prime mover for driving the headstock.  The wood pillars are not fixed in position; other pulley combinations can be plugged in to give different shaft speeds. Ideally the surface speed on the 4" shaft will be between 175 and 200 inches per minute.

  The two small blocks on the bottom allow space for the operator's fingers. Portability and flexibility are key to the construction process.
 
The small 1 1/2" pulley is fastened to the major 10" pulley with J-B Weld. Scrapped clothes washers and dryers are good sources for pulleys and drive belts of all sizes. In my experience, Maytag and Westinghouse are the brand names to look for.

  The motor is a Westinghouse single phase 115 volt workhorse with a 25' cable for the remote on/off switch.