Get/Make a "Coilmaster"

This is "The New Modern Coilmaster" made by MoReCo (MOrris REgister COmpany), Inc. of Council Bluffs, Iowa.

If you want to wind your own coils, and many people did, you need to build one of these. They are really pretty simple as you can see and with a little ingenuity you can make one. The turns counter is driven off a worm gear. The spring in front is to maintain contact between the wire guide assy and the different shaped cams, moving it back and forth. The cam is mounted right behind the crank handle. Each Coilmaster is equipped with four 32 pitch gears, with 39, 40, 42, and 44 teeth. This would give it a spindle to cam ratio of approximately 0.9:1 to 1.1:1. It says enameled wire must first be treated to give it "grip" by passing it through a quick-drying solution, such as resin dissolved in alcohol or other similiar material. Had you guessing too, huh ? Extra cams were $0.75 and gears were $1.00.

A Homebrew "Coilmaster"

This is homebrew "Coilmaster" using "whatever is available" parts. It has a variable spindle to cam ratio from 0.9:1 to 2.1:1, various cams, various wire feed heads, wire spool holder, turns counter, etc......even comes with two allen wrenches. It is shown with a small plastic bobbin coil spool mounted. Additional cams are located on the wire spool holder shaft and also prevent the wire feed spool from coming too close. The wooden spools are mounted on the spindle for large inner diameter coils.

The whole thing is made from aluminum scrap. Since aluminum is soft (and easy to work), the wear points are strengthened with brass bushings from old potentiometers. Be sure to grease all the bearing surfaces or they will jam. All shafts are 1/4" (steel or aluminum) cut to size. The collars are made from old knob inserts after the plastic/bakelite is removed via an application of cold chisel. The cams are made from knobs with thick aluminum skirts (plastic/bakelite removed). Some required a little hammer tweaking to tighten the skirt. Since the cam is soft it rides on a small ball bearing (from an old PC disk drive) cam follower.

The drive "gear" is a knob with a groove cut into it. A small "O" ring is installed into the groove and contacts/drives the aluminum skirt of another knob. A short spring is located behind the skirted knob to insure pressure on the "O" ring. Ran into one problem on my coil winder. The "O" ring kept "walking" off the knob on the right angle drive. After a little study, I decided that the "O" ring footprint is not "zero", so the inside of the track is actually running at a different ratio than the outside of the track. This tends to cause an outward force on the "O" ring in the plane of the "O" ring drive shaft. If the centerline of the "O" ring drive shaft is below that of the driven plate shaft centerline, you also have the additional outward force due to the direction of rotation of the driven plate. The way I solved the problem is to equalize the forces by locating the "O" ring drive shaft centerline ABOVE the center line of the driven plate (for this size plate, "O" ring, etc it turns out that 3/32"-1/8" works best). No more problem, everything runs true at any ratio. This was the first Engineering Change to my coil winder .....the driving shaft bushings are now mounted in vertical slots.

The crank is yet another aluminum skirted knob. The mechanical counter was something from a swapmeet and lends itself to being worked with a beveled collar. I could have used a cam to work the counter, but the counter reset knob would have been difficult to get to. The wire feed is a small hobby shop brass tube run through a drilled knob insert with one set screw used to hold the tube in place and the other used to tighten it to the shaft. This tube easily feeds #24 AWG and smaller wire but a larger tube could be used and you can make several wire feed heads. Most coils I need will be #28 AWG or smaller. It has a bail made from a safety pin on the end. The wire is fed into the back of the tube and wire tension is controlled with your fingers. A small piece of shrink tubing was put on the end to further protect the wire. The wire feed head rests on an adjustable bar to control height (yet another knob with aluminum skirt). Fun project.

The additional holes in the braces are for better cooling and to decrease weight ...Hi, Hi.

......and we have the "Cheapo-Winder"

This is "The Old Cheap Econo-Winder" used by many, including myself. It offers the advantages of: no cams to change, no gears to change, 4x chuck to crank ratio, infinitely adjustable, full control, able to wind multiple strands (above photo shows three #38 AWG strands being fed onto a spool). You are the turns counter....multiply the drill crank turns by 4.3 (this drill gear ratio). Turn the crank with one hand, tension and feed the wire in a pattern with the other hand. If you can "pat your head with one hand and rub your belly with the other", you can wind coils by hand. I you can't ....see above.

A few winding hints/ideas/observations

Factors Affecting Coil Q ...some experiments

EXPERIMENT #1 ....Skin Effect

Four coils were wound by hand. Coil Q will increase if the turn-to-turn capacitance is reduced. This can be accomplished by using a "basket weave" pattern. The "basket weave" coils have roughly 1-2 spool length traverses of the wire per revolution of the spool (coil Q will be even higher on fixed pattern wound coils made using a coil winder). Q can also be increased by using multi strands of smaller gauge wire due to increased surface area (skin effect) at frequencies below about 3Mhz. It's a substantial improvement in Q to use two strands of #39 AWG vs one strand of #36 AWG, or better yet .....six strands of #42 AWG vs one strand of #36 AWG. All three of those examples have the same current handling capability. Many small, higher quality, IF transformers are wound with two strands of smaller gauge wire. Larger, high quality IF transformers are wound with Litz wire, dipped, etc.

All coils were trimmed to 2.0 mH with no slug, and 3.0 mH with a slug. Q Data is "unloaded Q" as measured on a Boonton 260-A.

At 200Khz, all coils trimmed to 2mH, no tuning slug

At 170Khz, all coils trimmed to 2mH, no tuning slug

At 150Khz, all coils adjusted to 3mH with the tuning slug

EXPERIMENT #2 ....Coil Form Dielectrics

Other factors which effect coil Q are the coil form material and the adhesive used to hold the windings. Any coil form which can absorb moisture, like the old cardboard oatmeal boxes and toilet paper tubes used for crystal sets, is a problem unless the cardboard is treated with varnish, shellac, etc ....but it's cheap.

Some have suggested using old plastic pill bottles which is OK if they are sturdy so the coil turns don't move. Recently some testing has shown that coils wound on those amber pill bottles have just has high a "Q" as those wound on the Amphenol 5-pin forms. Some PVC is the same way. What does affect "Q" is the material you use to coat the windings (materials to be tested later ...beeswax, refined paraffin, varnish, laquer, other "glues"). Here is an example of coils wound (adjacent turns) with #28 AWG magnet wire:

"Q" at 6 Mhz with all coils measuring 20.5uH
ReferenceNote 1Note 2Note 3note 4
1-1/4" Amphenol 5-pin175 -- 175 --
1-1/4" amber pill bottle180 -- 177172
1-1/2" amber pill bottle161147 -- --
1-1/4" untreated cardboard152130 -- --
1-1/4" PVC173 -- 175 --


  1. Plain wiring, no adhesives, no tape to hold windings
  2. Use a light coat of clear fingernail polish to hold windings (strips across windings didn't work), Q reading 15-20 points lower when first applied, above readings are after 48 hours.
  3. Use Elmer's Stix-All silicone to hold windings (4 strips across coil windings)
  4. Use Scotch black electrical tape to hold coil windings (1-1/2 turn)

EXPERIMENT #3 ...Turn Spacing

The highest Q coil for a given inductance is "air wound" with space between the turns (less turn-to-turn capacitance), the next is space winding on a good coil form (ceramic, phenolic, etc). Space winding on a coil form by winding string or another wire along with the coil wire and removing the "spacer" later is good. Ceramic and some phenolic coil forms came with wire groves to space the turns. You do have the problem of having to stabilize the separated turns with Q-Dope, paraffin, Duco cement, etc.

Here is some data on two coils:

At 3.4MHz ..... coil "A" Q=107, coil "B" Q=175

Granted, these are unloaded Q measurements on a Boonton 260-A and loaded Q will be less, however the improvement will be carried over and the "trend" is there.

What does this mean for the signal (loaded Q will be less dramatic):

EXPERIMENT #4 ....Coil Dope

"E6000" Craft Glue was used on a coil with a Q of "175" ...absolutely no change in Q as you put the material on, as it dries, or 24 hrs later, even for a very heavy application of glue. I believe it's some kind of silicone based product .....waterproof, clear, and remains flexible. My wife didn't even tell me she had some "really good coil dope" material in her crafts pile.

"CG Clear Ice" fingernail polish was used on a coil with a Q of "107" and the Q dropped to "97".