finally good winding

[simonbaker]

pics continued

pics continued...

Final texture is reproduction of dfbowers textured plastic shell.

[dfbowers]

pics continued...

Final texture is reproduction of dfbowers textured plastic shell.

Simon,


If nothing else I really have to give you an A for effort on that one! It does make an interesting looking coil. What is the volume of your coil? I can usually get a rough idea by filling the shells with water from a graduated cup.

Also, how long did the resin take to harden and how stiff is it? I'm looking for cheaper alternatives.

Thanks
Don

[Tinkerer]

Adding micro balloons to the resin reduces the weight.
Adding clean sand reduces the amount of resin but adds to the weight.

Tinkerer

[simonbaker]

Adding micro balloons to the resin reduces the weight.
Adding clean sand reduces the amount of resin but adds to the weight.

Tinkerer

I'm very interested in "micro balloons". Where get them, how much cost?

Regards,

-SB

[simonbaker]

Simon,


If nothing else I really have to give you an A for effort on that one! It does make an interesting looking coil. What is the volume of your coil? I can usually get a rough idea by filling the shells with water from a graduated cup.

Also, how long did the resin take to harden and how stiff is it? I'm looking for cheaper alternatives.

Thanks
Don

Hi Don:

Thanks for the A! I need it. (Or was that for pain in the A...)

My mold was cast from your (dfbowers) shell (exterior), but I probably poured a little deeper by building up the edges with clay. Also, my mold sagged and probably made everything a little wider. I tried to prop it with clay to prevent that. I think I poured at least 8 oz of resin into it.

Your coil weighs about 425 grams, mine about 475 grams. Some stuff still needs to be trimmed off mine. I could probably lighten it by drilling or carving to around 425 to 450 grams, but not worth the trouble at this time.

The resin is quite hard, almost brittle. Depending on how much hardener you use, surfaces exposed to air can end up slightly tacky. Acrylic spray is recommended to finish off with.

Your vacuum-formed shells are the way to go if you can do it of course. Many advantages:

1. Looks nice
2. You don't need to prepare mold.
3. Don't need several pourings of liquid.
4. Don't need to hassle with removal from mold, especially cable.
5. Don't need to worry about coils getting too near edge of mold.
6. Shell is lighter material.
7. Shell is probably more durable/pliable material, especially for pole attachment.
8. More choice of potting material.
9. More ability to put in micro balloons as Tinkerer suggested.
10. Easier to support and position cable and coils.

I think the resin mold-only idea still has merit for hobbiests who don't care about looks and if done a little differently. I'd skip the latex mold and just fashion a mold out of clay on wax paper, put a little resin in, then the coils, then more resin. The pole flanges are the hard part, haven't figured that out yet.

----------------------
Re: resin as potting

I used "casting resin" which may be a little more expensive than garden variety hardware store resin for fiberglass projects. But probably either would do for potting your shells.

I don't like resin because of the fumes. They are really powerful. I was starting to think fondly about your epoxy! I wouldn't recommend hovering over resin while nulling your coils indoors, unless you're in the mood and have run out of other hallucinogens.

Also, resin may set a little faster than you like -- depending on catalyst amount, between 30 to 90 minutes I think. It gels in 5 to 10 minutes. I like the speed myself.

Otherwise, I think it would work nicely as potting. And I'd seriously look into adding Tinkerer's micro balloons, seems like an excellent idea if not too expensive. Or experiment with frothing bubbles into it.

One question I'd have would be adhesion to the shell -- would there be chance of separation? Hopefully the shell can be shaped to grab it so no worries there.

I still feel there is a simpler, easier way out there for me to make coils. I'll keep looking, experimenting. Of course performance is the key endpoint. This last coil may be a dog, not sure why. Perhaps the tight shielding? Or wrong inductance proportions? Huge null signal made it hard to discern the exact nulling point characteristics.

-SB

[Tinkerer]

http://www.fiberglasssupply.com/Prod...s/fillers.html

check out the site above for micro balloons and other supply. I am sure there are similar shops in Australia.

Also check out "mold release agents", "molding supplies" etc.

Some of these places also sell graphite powder for adding it to the resins. This works great for shielding.

I can give you a recipe for the graphite mix.

Tinkerer

[simonbaker]

http://www.fiberglasssupply.com/Prod...s/fillers.html

check out the site above for micro balloons and other supply. I am sure there are similar shops in Australia.

Also check out "mold release agents", "molding supplies" etc.

Some of these places also sell graphite powder for adding it to the resins. This works great for shielding.

I can give you a recipe for the graphite mix.

Tinkerer

Good source, thanks.

Yes, interested in your recipe. I have some graphite. Have you measured resistance after hardens?

Regards,

-SB

[Tinkerer]

To make a graphite shield coating it takes a binder, graphite and if possible some colloidal silica.

The graphite is the conductor.
The silica helps in making a fluid past that does not run. It is a thixothropic.
Many kinds of resin are suitable, but the actual amount or percentage of the final dry coat needs to be found by trial an error.

If there is not enough binder (resin), the dry coat will flake, crumble and shed. Too much binder reduces the conductivity.

It is very important to use the proper solvent for the resin. Consult the resin manufacturer.

For an epoxy base coating use:

One part resin/hardener mix
10 parts graphite powder
9 parts epoxy solvent (xilene or toluene or a mix thereof or just what is called epoxy paint thinner.
1 part of fumed or colloidal silicone.

Mix the resin/hardener well, then add a very little solvent and mix well again. Then add the graphite and silica. mix very well, then add the rest of the solvent.

This paint will only harden as the solvent evaporates. CAREFUL these solvents are toxic. Work outdoors.

Add a drain wire in the coating. The drain wire is best a very thinly stranded # 28 wire,or thereabouts. Hold the drain wire in place with a few narrow strips of tape and add rnough thickness of coating to embed the drain wire.

Solder the other end of the drain wire to the cable shield that is grounded on the box or PCB.

The thickness of the coating regulates the conductivity. Several coats can be applied, but if desired, the coating can be made quite paste like by adding more graphite.

After drying you can measure the conductivity between the drain wire and the coating, by measuring with the Ohm meter at different distances.

You can apply a very thin coat overall and add a second thicker coat in a pattern to obtain the most excellent results.

Tinkerer

[lunamay]

hi simon your coil looks nice..how about weight and air distance did You test it yet?

best regards

[simonbaker]

To make a graphite shield coating it takes a binder, graphite and if possible some colloidal silica.

The graphite is the conductor.
The silica helps in making a fluid past that does not run. It is a thixothropic.
Many kinds of resin are suitable, but the actual amount or percentage of the final dry coat needs to be found by trial an error.

If there is not enough binder (resin), the dry coat will flake, crumble and shed. Too much binder reduces the conductivity.

It is very important to use the proper solvent for the resin. Consult the resin manufacturer.

For an epoxy base coating use:

One part resin/hardener mix
10 parts graphite powder
9 parts epoxy solvent (xilene or toluene or a mix thereof or just what is called epoxy paint thinner.
1 part of fumed or colloidal silicone.

Mix the resin/hardener well, then add a very little solvent and mix well again. Then add the graphite and silica. mix very well, then add the rest of the solvent.

This paint will only harden as the solvent evaporates. CAREFUL these solvents are toxic. Work outdoors.

Add a drain wire in the coating. The drain wire is best a very thinly stranded # 28 wire,or thereabouts. Hold the drain wire in place with a few narrow strips of tape and add rnough thickness of coating to embed the drain wire.

Solder the other end of the drain wire to the cable shield that is grounded on the box or PCB.

The thickness of the coating regulates the conductivity. Several coats can be applied, but if desired, the coating can be made quite paste like by adding more graphite.

After drying you can measure the conductivity between the drain wire and the coating, by measuring with the Ohm meter at different distances.

You can apply a very thin coat overall and add a second thicker coat in a pattern to obtain the most excellent results.

Tinkerer

Thanks Tinkerer! Do you think we can use that mix as potting and kill two birds with one stone?

-SB

[simonbaker]

hi simon your coil looks nice..how about weight and air distance did You test it yet?

best regards

It is a little heavier than the coil dfbowers made, but not too bad. About 12% heavier. 475 grams.

Because I didn't get the inductances quite right, I'll need to tune it with capacitor C6 I think. So I don't expect as good air distance with dfbowers PCB compared to his coil.

I will need to take it to the mountains to test air distance. The noise in my house makes it impossible to get more than 10 to 15 cm with any MD.

I think maybe putting the shield so tight to the coil makes it difficult to null - I get a very large null signal. However, I do not yet believe that is necessarily a problem as long as the null signal is due to capacitive coupling.

I was not patient enough to get everything perfect this time. But at least I made a finished coil. If I can clean the silicone off it I'll paint it.

I did find the pole "flanges" came out a little closer together than dfbowers coil, so I had to put a thinner washer on his pole to make it fit. But it will attach. Next time I would add a support spacer on my mold.

It was not too bad to drill holes in the resin. Sort of like drilling plexiglass.

Cheers,

-SB

[Tinkerer]

Definitely not!!!!!

The mix contains solvent. This solvent needs to totally evaporate. Only relative thin coats will let the solvent evaporate.

Tinkerer

[simonbaker]

Definitely not!!!!!

The mix contains solvent. This solvent needs to totally evaporate. Only relative thin coats will let the solvent evaporate.

Tinkerer

Ok, good for a "paint-on" shield then. That's useful.

Regards,

-SB

[lunamay]

simon could you explain to me how to tune coil using ferrite rod? how big should it be and how use it to tune a coil right

best regards

[simonbaker]

simon could you explain to me how to tune coil using ferrite rod? how big should it be and how use it to tune a coil right

best regards

Hi lunamay:

I am not an expert at the ground balance and still have many questions.

I believe the accepted procedure is to turn the DISC and GB pots to minimum.

Then wave a ferrite rod across the coil, maybe 10 cm from coil, making a beep (it may not be a very clear beep).

Slowly turn the GB pot until the beep breaks up, or disappears.

However, I find if I turn the GB pot too far, my air distance for Euro gets much smaller. So I like to check with a Euro and reduce the GB pot if necessary to make sure I have a pretty good air distance with Euro.

Still waiting for pictures of your TGSL and workshop -- show us what you have -- or I'll send Peroon after you...

-SB