disappointment

[simonbaker]

My first coil using "coil winder sandwich" and lacquer bath -- not so good. In spite of spraying the wood thoroughly with silicone "non-stick" spray, my coil, coated with varathane as it was wound, stuck to the wood form, and windings were separated as I removed the top wood piece. Some wood actually broke off and stuck to the coil wires. Maybe the varathane is much stickier than Spar Varnish or able to penetrate the silicone. Or maybe I need much thicker silicone coating.

I will try to rescue the coil by wrapping in tape, but I'm disappointed with my method. It also is very slow waiting for varathane to dry, so can't make lots of coils in a hurry.

I think I chose too high a gap for the coil height - the coil thickness is too thin, not square enough cross-section.

I would like to find a way to wind directly onto a light form that can be incorporated into the coil head, similar to the video showing Tesoro making coils. I may try again my "foam core form" that almost worked:

http://www.geotech1.com/forums/showp...&postcount=129

The problem was the heavy wires forced the layers open. With lighter wire and using the new top disk on my coil winder "sandwich", maybe I can be more successful with it. However, it is not a professional looking coil and not the ultimate technique.

I would like to try some thin plastic channel, bent in a "D" shape, to wind the coils on. Then move the plastic channel into a normal vacuum formed shell or resin molded form. I don't know where to find such plastic channel.

There is some thin aluminum channel at the hardware store that would make an interesting experiment. The aluminum would act as a shield -- but maybe too much metal near the coil, it is much thicker than foil. The aluminum channel would be difficult to bend and require cuts at the bend points probably. Just a wacky idea.

Anyway, I'll try to perfect my "glue while winding" technique with more non-stick spray.

-SB

[dfbowers]

My first coil using "coil winder sandwich" and lacquer bath -- not so good. In spite of spraying the wood thoroughly with silicone "non-stick" spray, my coil, coated with varathane as it was wound, stuck to the wood form, and windings were separated as I removed the top wood piece. Some wood actually broke off and stuck to the coil wires. Maybe the varathane is much stickier than Spar Varnish or able to penetrate the silicone. Or maybe I need much thicker silicone coating.

I will try to rescue the coil by wrapping in tape, but I'm disappointed with my method. It also is very slow waiting for varathane to dry, so can't make lots of coils in a hurry.

I think I chose to high a gap for the coil height - the coil thickness is too thin, not square enough cross-section.

I would like to find a way to wind directly onto a light form that can be incorporated into the coil head, similar to the video showing Tesoro making coils. I may try again my "foam core form" that almost worked:

http://www.geotech1.com/forums/showp...&postcount=129

The problem was the heavy wires forced the layers open. With lighter wire and using the new top disk on my coil winder "sandwich", maybe I can be more successful with it. However, it is not a professional looking coil and not the ultimate technique.

I would like to try some thin plastic channel, bent in a "D" shape, to wind the coils on. Then move the plastic channel into a normal vacuum formed shell or resin molded form. I don't know where to find such plastic channel.

There is some thin aluminum channel at the hardware store that would make an interesting experiment. The aluminum would act as a shield -- but maybe too much metal near the coil, it is much thicker than foil. The aluminum channel would be difficult to bend and require cuts at the bend points probably. Just a wacky idea.

Anyway, I'll try to perfect my "glue while winding" technique with more non-stick spray.

-SB

Holy cow! Mine have come apart relativey easy. Another idea is to cover youf plywood with wax. Nothing will stick to it then. I have used wax when I ran out of dry mold realease agent. I just got a block of beeswax and rubbed the wood really good.

My very first form I used, I covered everything with wax paper, I got a long knife and slowly peeled the wires away.


Just a few idea.

Don

[simonbaker]

Holy cow! Mine have come apart relativey easy. Another idea is to cover youf plywood with wax. Nothing will stick to it then. I have used wax when I ran out of dry mold realease agent. I just got a block of beeswax and rubbed the wood really good.

My very first form I used, I covered everything with wax paper, I got a long knife and slowly peeled the wires away.


Just a few idea.

Don

Thanks for ideas... I live and learn. A good wax job sounds like the right approach. Maybe work on my bikini line also (I didn't say that...).

I haven't yet pried the coil off the bottom wood and pegs -- trying to find my wife's plastic pan scraper, has nice sharp edge. (Why do I always end up using my wife's kitchen stuff more than my own tools? Is this normal? Yes, no... maybe?)

I'll keep trying...

-SB

[Tinkerer]

Your coil making is very interesting.
I worked many years with all sorts of resins, molds, fiberglass, wood laminates, glues, etc. so maybe I could give you some useful tips.

Porous materials, like wood, must be sealed first with wood sealer, thick paint, resin or such. Then apply several thin coats of floor wax, then apply the silicone anti-adherant.
For fiberglass boats, I used PVA, that is POLYVYNIL ALCOHOL. This is dissolved in alcohol and water soluble, so it can be washed off with water after de-molding.

The plastic channel is a good idea. Aluminium will not work.

If you use the PP spacer shown below, to make a molding channel, the spacer will provide the distance between the coil and the shield.
This material is often used instead of cardboard. It is made of Polypropylene which is a good dielectric.

The next picture is my coil jig. The acrylic disk turns on a center axle and is coated with wax and PVA, so that the epoxy resin does not stick on it.

Tinkerer

[simonbaker]

Your coil making is very interesting.
I worked many years with all sorts of resins, molds, fiberglass, wood laminates, glues, etc. so maybe I could give you some useful tips.

Porous materials, like wood, must be sealed first with wood sealer, thick paint, resin or such. Then apply several thin coats of floor wax, then apply the silicone anti-adherant.
For fiberglass boats, I used PVA, that is POLYVYNIL ALCOHOL. This is dissolved in alcohol and water soluble, so it can be washed off with water after de-molding.

The plastic channel is a good idea. Aluminium will not work.

If you use the PP spacer shown below, to make a molding channel, the spacer will provide the distance between the coil and the shield.
This material is often used instead of cardboard. It is made of Polypropylene which is a good dielectric.

The next picture is my coil jig. The acrylic disk turns on a center axle and is coated with wax and PVA, so that the epoxy resin does not stick on it.

Tinkerer

Thanks for sharing your experience -- I was naive about making non-sticky wood.

I love these contraptions; it's like Faraday himself is walking amongst us...or someone's planning time travel....

Looks like you are making a concentric coil there?

If you use the PP spacer shown below, to make a molding channel, the spacer will provide the distance between the coil and the shield.

Do you feel there should be a space between the coil and the shield? Why so?

-SB

[nabiul]

Try using a polyethylene cutting board for the base, stuff is so slippery that even epoxy will come off of it in time, and I've used epoxy to glue anodized aluminium to blued steel!

Cutting boards are cheap enough too, I got 4 small board like this at canadian tire for like $5.

[dfbowers]

Try using a polyethylene cutting board for the base, stuff is so slippery that even epoxy will come off of it in time, and I've used epoxy to glue anodized aluminium to blued steel!

Cutting boards are cheap enough too, I got 4 small board like this at canadian tire for like $5.

I wonder if anyone has access to pics on how commercial coils are wound. (come on Carl.. throw us a bone). I always had a vision of a two piece machined spool that spits in half after the wire is wound. Or.. winding the coil DIRECTLY inside the coil shell.

[simonbaker]

Try using a polyethylene cutting board for the base, stuff is so slippery that even epoxy will come off of it in time, and I've used epoxy to glue anodized aluminium to blued steel!

Cutting boards are cheap enough too, I got 4 small board like this at canadian tire for like $5.

It's worth a look. Maybe a little thin to put pegs in, but I'm sure there is a way. I start thinking about it...

-SB

[simonbaker]

I wonder if anyone has access to pics on how commercial coils are wound. (come on Carl.. throw us a bone). I always had a vision of a two piece machined spool that spits in half after the wire is wound. Or.. winding the coil DIRECTLY inside the coil shell.

There was a video link on this forum showing a worker at the Tesoro factory making a coil (concentric I think). It was funny how quick she wound it, slapped a dab of glue here and there, bada bing, out the door!

She wound it on a form that was inserted in the coil head I recall.

Can't find it now though.

-SB

[Tinkerer]

Thanks for sharing your experience -- I was naive about making non-sticky wood.

I love these contraptions; it's like Faraday himself is walking amongst us...or someone's planning time travel....

Looks like you are making a concentric coil there?



Do you feel there should be a space between the coil and the shield? Why so?

-SB

The coils shown are a concentric combination of a TX coil with 450mm diameter and a RX coil of 225mm for the TEM TX method.

The spacer helps a lot for reducing the coil to shield capacitance, very useful for PI coils. I apply the graphite composition shield outside of the spacer with very good results.

Tinkerer

[Merc]

Garrett coil making

Here is the video of Garrett coil manufacturing.


http://www.youtube.com/watch?v=izZBq5r5DEs

[mikebg]

HOT IMPREGNATED COILS

SB, Here is a technology used by the (R)EMI group to produce hot impregnated with epoxy resin coils. The form is wooden because it is warmed to tempetarure about 100 degrees Celsius. Rotating of the form is by hand in a simple device as a crank. Instead crank can be used hand drill.
Before winding is smeared with silicone cream all surfaces that will touch the wire. After the winding, current is placed over the coil until it is heated to about 110 degrees Celsius. Then a little epoxy glue is dripped out (in the gaps between the plates), which is immediately absorbed between hot turns and quickly hardens. For the removal of the coil loosen the screws and plates pivot.

[simonbaker]

Here is the video of Garrett coil manufacturing.


http://www.youtube.com/watch?v=izZBq5r5DEs

That's it! Garrett, not Tesoro.

[simonbaker]

SB, Here is a technology used by the (R)EMI group to produce hot impregnated with epoxy resin coils. The form is wooden because it is warmed to tempetarure about 100 degrees Celsius. Rotating of the form is by hand in a simple device as a crank. Instead crank can be used hand drill.
Before winding is smeared with silicone cream all surfaces that will touch the wire. After the winding, current is placed over the coil until it is heated to about 110 degrees Celsius. Then a little epoxy glue is dripped out (in the gaps between the plates), which is immediately absorbed between hot turns and quickly hardens. For the removal of the coil loosen the screws and plates pivot.

Interesting, food for thought. It's all about knowing your materials well, it seems.

-SB

[simonbaker]

better, but not great

There is no giving up in metal detectors, so I decided to kick it up a notch and try to make the wood of my coil winder really slippery so Varathane would not stick.

dfbowers suggested beeswax, so I called the hardware store. The guy I talked to said they had something similar, but that he knew that woodworkers use car wax to protect areas of wood from glue. So off to the local car parts store to get car wax. Most of the products didn't seem right, too liquid, and the guy there suggested surfboard wax. Dude! why not? So I drive to the local surf shop -- I find it boarded up, they had recently shut down and moved. Dude! What's a dude to do?

I had used up my day's quota of running around and so, deflated, returned home. Not to be defeated entirely, and out of inspired desperation, I commandeered a particularly ugly tea candle we had received as a gift, probably recycled, and pressed it into service as a lubricant, energetically scrubbing the surface of my winder disks and wooden pegs with candle wax, trying not to waken my wife who slept while I worked feverishly into the wee hours of the night (wee if you subtract them from 12). I noticed too late the cheese grater effect as I went over the holes, and deposited no small amount of wax shavings on the rug.

Waxed to the max, I excitedly hooked up my winder, threaded the wire through my little lacquer bath (consisting of a film can attached to the base with a screw hook whose double duty was to guide the wire under the Varathane lacquer), and began to wind with the enthusiasm of a sausage maker.

After about 20 turns I noticed that in my impassioned frenzy I had neglected to insert two of the pegs in my form.

As I tried to cope with feelings of dark self reproach, I thought I heard a raven tapping at my window. I sat, torn between the impulse to say "FTSIGTB" (f** this s** I'm going to bed) and "WTGGTTTGG" (when the going gets tough, the tough get going).

Glumly contemplating unwrapping 20 turns of sticky toxic wire, I drew a breath and launched into the salvage operation, first obtaining an empty vitamin bottle to wrap the gooey wire around, and second declining to put on rubber gloves because, hey, they were in another room.

Because of the difference in diameters, it seemed an interminable number of coils on the pill bottle before I undid my work. My hands were a crusted mess of Varathane, god knows what coursed through my veins and DNA.

Without further ado, I inserted the missing pegs (rewaxing them for good measure), threaded the wire from the pill bottle into the bath for a recoating, and resumed winding. I worried that the tension was not uniform, since the wire spilled easily off the end of the bottle. After about 20 winds, I was back to the original coil of wire, and, cranking in high gear, I made short work of laying down about 100 turns.

I scraped the insulation off the wire and checked inductance, added a few turns, and stopped the process when the inductance read about 6 mH. I knew from experience it rises about .3 to .4 mH as the lacquer dries. I was trying to duplicate the coils that dfbowers sent me, which ended up at about 6.4 and 6.8 mH.

--------------------
Next Morning

I was so excited to see the results the next morning that I shaved, had breakfast, read the paper, checked my email, paid some bills, and rushed to check the coil.

--------------------------------
The Good, The Bad, and The Ugly

Well, some improvement, but still some problems. I found by twisting the pegs, any sticking can be released without affecting the coil. But the coil did still stick to one area of the lower platter, and maybe to the top because it required force to remove it (hammer claws).

I am feeling that Varathane is really sticky stuff, it sticks to anything, including wax. A lot of wax ended up stuck to the coil, making a very not pretty looking coil. And one corner of the coil stuck sufficiently to the wood to cause separation of the windings.

The coil has a nicer thickness because I narrowed the space between platters, making an almost square cross section. I notice though that the D shape needs some improvement, maybe move a peg or two.

I probably need to throw out my plywood platters, they are maybe too rough to get a smooth coating of wax or silicone, and replace with something better, like smoother wood or cutting board, etc. Maybe I can put a layer of something on them (hey, what about Teflon?).

Anyway, still struggling, but that's what this is all about.

I still would like a faster way, like the Garrett factory, to make coils. I'm thinking of a winder design using cross-angled pegs where I can put in foil first, wind the coil on the foil, either lacquered or apply glue later, and then wrap the foil as I remove the coil.

For now, I'll see what I can do with a couple of coils that look like they just got out of bed.

-SB