One of my hobbies is building radios from scratch. I construct them in bread board style fashion. So far my "home brew" radios have all been of regenerative type that require few custom made coils that have 50 turns or less.
My next project is a Super Heterodyne receiver with custom built 400 KHz IF (Intermediate Frequency) transformers. Each IF transformer will require two 620 turn helical coils wound on a cardboard form. This project will require two IF transformer plus a LO (Local Oscillator) coil for a total of five helical coils. As you can see, a Helical Coil Winder Jig will come in handy for this project.
Below is a picture of the finished Helical Coil Winder Jig in action:
Step1: Main Body Construction
I started with a miniature crate I purchased from a local craft store. Woodworking is not one of my strong skills so I always try to start with a finished wood product then modify it for my needs.
I then cut the crate down to size using a jigsaw. The smaller piece to the right in the picture below will be used as the body of my Helical Coil Winder Jig. The rest of the crate will be broken down into its discrete pieces and used in this project.
The end piece from the unused part of the crate was nailed in place to form a small box 4 1/2 x 5 x 6 Inch in size. The nail holes were filled in with wood putty. The wood putty will be sanded down in a later step.
3/8 Inch holes were drilled for the main shaft using a drill press. The holes were drilled approximately 7/8 Inch from the top and centered horizontally.
The surface of the crate was rough. I used an orbital sander with fine grit sandpaper to smooth all surfaces and to remove excess wood putty.
Step2: Main Axle Construction
The main axle is made from a 3/8 Diameter 24 Inch Aluminum Rod. I drilled/tapped a hole on one end. A 10-32 x 4 Inch long screw will serve as the crank handle.
The 10-32 x 4 Inch screw is threaded into the aluminum rod until the head is almost flush with the rod. I then secure it in place with a lock washer and 10-32 nut.
I use a vise to bend the screw 90 degrees in order to form the crank handle. The bend starts about 1 1/4 Inch away from the 10-32 nut.
A 7/8 Inch Diameter dowel is cut down to 1 1/2 Inch and a hole is drilled down the center. This will serve as the crank handle. The hole down the center has to be just big enough to allow the dowel to move freely on the screw without binding.
Step3: Coil Arms Added
Two 10 inch x 1 1/2 arms were made from scrap pieces of the miniature crate then nailed to the base of the main body, flush with the bottom. These arms will hold the copper wire spool.
Here is a picture with both arms nailed in place.
Once again, wood putty was used to cover the countersunk nail heads.
Step4: Counter Added
My Helical Coil Winder Jig will incorporate an electronic counter, in order to keep track of the number of turns of wire, on the coil form. I created a small 2 Inch x 1 1/2 Inch arm to hold the counter. It is nailed to the side of the main body with it pointing up at a 35 Degree angle. Again, wood putty was applied to hide the countersunk nail holes.
The base of the electronic counter was temporarily mounted for fitment. Two small brass screws will hold it in place.
Here is what the electronic counter will look like when it is finally mounted. The counter runs on a watch battery and does not require external power.
The green and yellow wires coming out of the back of the electronic counter are soldered to the printed circuit board inside. Each wire is soldered to a point on the printed circuit board so that I can emulate the count button being press externally.
The green and yellow wires are soldered to a reed switch that will be triggered by a magnet.
The fragile reed switch is encased in heat shrink tubing for protection.
The magnet will be attached to the axle with the reed switch nearby so that the count on the electronic counter is incremented with each turn.
Step5: Coil Holder Construction
I needed a way to hold a variety of different size tubes on the axle during the coil winding process. I established that a cone shape would work best to hold the tubes centered on the axle. Once again a trip to our local crafts store yielded these small bird houses with 3 Inch diameter conical roofs.
A few swift hits of hammer removed the bottom part of the bird houses, leaving only the conical roofs. The rope hanging loops on top were cut off.
3/8 Inch diameter holes were drilled through the centers so that they could be threaded on the axle.
I reinforced the base of each cones with a generous amount of wood glue.
Step6: Protect the Wood
The main body of the Helical Coil Winder Jig was treated to two coats of Minwax Water-Based Semi-Gloss Polyurethane. I use semi-gloss because it is better at hiding imperfections than gloss. Water-based Polyurethane is much easier to cleanup and does not smell as bad as oil-based. Once dry, I lightly sand the pieces with fine grit sandpaper in between coats.
The conical coil holders are also treated to two coats of Polyurethane.
Even the hand crafted wooden knob received two coats of Polyurethane!
Once dry, all the holes in the main body where reamed out with a drill to remove residual Polyurethane that dripped in them during the coating process.
Step7: Final Assembly
A circular magnet was attached with Super Glue to one of the Drill Stop Collars. The magnet was attached opposite of the set screw.
I expanded the center hole in three 1 1/4 inch fender washers to 3/8 diameter so that I could slide them on the axle.
The Drill Stop Collar with the magnet attached was first threaded on the axle and cinched down about an inch from the crank handle. Next, a fender washer was threaded onto the axle. The axle was then threaded through the first hole in the main body.
Then another fender washer was threaded on the axle followed by a spring, fender washer, and another Drill Stop Collar. Finally, the axle was threaded through the other hole in the main body.
The the spring was compressed, then the second Drill Stop Collar to be threaded on the axle was cinched down. This assembly will keep tension on the axle and prevent it from moving backwards when you remove your hand from the crank.
The electronic counter was then attached to the main body. I used hot glue to keep the reed switch in close proximity to the circular magnet attached to the Drill Stop Collar. In addition, the hot glue was used to secure the wiring to the side of the main body.
Time to test the electronic counter, first I press the small silver button to set the counter to zero. Then I rotated the crank four times to made sure the counter reflected the correct number of turns.
Two more 1 1/4 fender had their center holes expanded to 3/8 diameter so that they would slide on the axle. I then mounted them to the base of each conical coil holder with two wood screws.
Automotive hose clamps will hold the conical coil holders in place on the axle.
A second 3/8 Diameter 24 Inch Aluminum Rod is threaded through the two coil arms. This rod will be stationary and hold the copper wire spool. The rod is held in place by two decorative hinges I had left over from another project. Two brass screws hold the hinge to the coil arm. I drilled a hole through the other part of the hinge then through the aluminum rod. A 1 Inch 4-40 screw holds the rod securely to the hinge.
The rod was also secured to the other coil arm in the same fashion.
Step8: Coil Winder in Action!
The conical coil holders can be used in various ways to hold a coil form. Below is the coil form configuration I use when only one side of the coil form is open. I did have to drill a 3/8 hole in the center of closed end in order to thread it onto the axle.
I use the conical coil holders in the following fashion when the coil form is open on both ends.
Typically, I drill two small holes then thread the copper wire through the holes at the starting end.
Before I start winding the coil, I click on the small silver reset button to zero the counter.
When winding the coil, I pinch the copper wire between my thumb and index finger to keep tension on it. You may want to wear gloves as this could cause a blister to form on your finger and thumb tips.
As you start winding the coil you may notice small gaps in the windings. While keeping tension on the copper wire, use your other hand to push the windings together to remove the gaps.
When I get to the proper amount of turns, I place a piece of masking tape on the end to secure the copper wire. Failure to do so will cause your coil to loose tension and unwind. I then use a bead of E6000 clear adhesive to keep the copper wire in place. I typically run beads of E6000 clear adhesive at 0, 90, 180, and 270 degree positions of the tube.
Finally, I use my Mega328 Component Tester to check the Inductance of my newly wound coil. The Inductance should be close to coils with the same number of windings on the same diameter coil form.
You should consider building my Home Brew Helical Coil Winder Jig if you find the need for creating numerous homemade coils for your electronic hobby projects.
Who Writes This Blog?
John is an IT professional from Cleveland, OH who enjoys amateur radio, ham radio, metal detecting,
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