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Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Nice tutorial
Some things i have found out while doing my coils:
Epoxies are different. These days i prefer epoxies that are designed for coating such as Gurit SP 320. General purpose epoxies that are meant for laminating or as adhesive are much thicker. SP 320 is very viscous compared to these general purpose epoxies and does not need vacuum degassing or tedious bubble hunting after it has been applied.
Mixing pot size vs pot life is a thing, guys at composite shops call this as surface area vs volume ratio. You want it to be as large as possible to prevent thermal runaway. Initial coat should be very light, leaving tops of the wires exposed. This way there wont be nearly as many bubbles when the air escapes from behind the windings. Heating the initial coat may make bubble problem even worse as the air trapped behind windings expand from heat.
You can never get it truly perfect, but you can certainly mess with it too much. I have had random bugs stuck on my coils every now and then. For spreading i used cheap disposable foam brushes that i didnt bother to clean after use. And tiny wooden stick to pop any bubbles.
Overall its hard to imagine why people still use polyurethane for tesla coils, epoxy is so much nicer and doesnt smell nearly as toxic :)
Registered Member #1732
Joined: Thu Oct 02 2008, 02:34PM
Location: Huntsville, AL
Posts: 112
Thanks for the additional tips.
Kizmo wrote ...
You can never get it truly perfect, but you can certainly mess with it too much. I have had random bugs stuck on my coils every now and then. For spreading i used cheap disposable foam brushes that i didnt bother to clean after use. And tiny wooden stick to pop any bubbles.
Overall its hard to imagine why people still use polyurethane for tesla coils, epoxy is so much nicer and doesnt smell nearly as toxic :)
So my experience with foam brushes (and it only applies to the kind of epoxy you can get from a hardware store) is that the put bubbles into the finish. I suppose if you're using a much thinner epoxy then this wouldn't be a problem.
I also wonder why people still use poly to coat their coils. I only coated one coil years ago with poly, and then I went to epoxy.
Registered Member #55219
Joined: Tue Jun 09 2015, 11:21PM
Location:
Posts: 80
Have you guys tried using a Casting Resin or is Epoxy the preferred product?
I have not used this on a coil, but have used it quite a bit, and used to work for this company as well as a fabricator(many moons ago). Clear-Lite Resin I would think application would be almost the same, if not quite a bit easier.. Add catalyst mix and pour. It's virtually indestructible as well, where epoxy would be more shatter prone on impact.
I'm getting ready to build my 2nd coil, 6" x 18" #28awg, and have been thinking about what to use, My head keeps thinking about this, but I'm fairly new to TC's so was wondering what you thought. ?
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Phillip Slawinski wrote ...
Thanks for the additional tips.
Kizmo wrote ...
You can never get it truly perfect, but you can certainly mess with it too much. I have had random bugs stuck on my coils every now and then. For spreading i used cheap disposable foam brushes that i didnt bother to clean after use. And tiny wooden stick to pop any bubbles.
Overall its hard to imagine why people still use polyurethane for tesla coils, epoxy is so much nicer and doesnt smell nearly as toxic :)
So my experience with foam brushes (and it only applies to the kind of epoxy you can get from a hardware store) is that the put bubbles into the finish. I suppose if you're using a much thinner epoxy then this wouldn't be a problem.
I also wonder why people still use poly to coat their coils. I only coated one coil years ago with poly, and then I went to epoxy.
Are there any issues with polyurethane?
I used it because the sort I used is moisture curing, which means any moisture is absorbed when it dries which i thought would be a good advantage to the coil.
Epoxy takes longer to dry, but is harder and i guess that could offer more protection to the coil?
Registered Member #1732
Joined: Thu Oct 02 2008, 02:34PM
Location: Huntsville, AL
Posts: 112
I've never used any of the casting resin, but I think it might be worth a try.
Issues with polyurethane? I don't know how it stacks up head to head against epoxy for equal coating thicknesses. I do know that the epoxy is quite a bit easier to get a thick coat with, which is one of the primary reasons why I use it. In three coats I was able to build up about 0.0625 inches of epoxy on the form in the video. I've had coils in the past that flashed over end to end with no signs of visible damage, but maybe some could say the same for poly...?
I'm not sure about the epoxy taking longer to cure. Curing time really depends on temperature with the epoxy, and the warmer it is, the faster it will cure. I find that typical curing time is in the range of 4-8hrs.
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Thing i like about epoxy is the wide range of hardeners. It takes out the guess work and worthless waiting. For example for the SP320 I prefer is available with different hardeners from 30 minutes to 10 hours. And thickness is big thing, when i coated my large space wound secondary i dumped nearly 1kg of epoxy on it in one shot. It would have taken ridiculously many coats of polyurethane to get same thickness.
No several coats, no hours of waiting, no sanding, nothing. Just dump, spread, and done.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Phillip Slawinski wrote ...
I've never used any of the casting resin, but I think it might be worth a try.
Issues with polyurethane? I don't know how it stacks up head to head against epoxy for equal coating thicknesses. I do know that the epoxy is quite a bit easier to get a thick coat with, which is one of the primary reasons why I use it. In three coats I was able to build up about 0.0625 inches of epoxy on the form in the video. I've had coils in the past that flashed over end to end with no signs of visible damage, but maybe some could say the same for poly...?
I'm not sure about the epoxy taking longer to cure. Curing time really depends on temperature with the epoxy, and the warmer it is, the faster it will cure. I find that typical curing time is in the range of 4-8hrs.
The polyurethane I was using was designed for use on wooden floors. It gives a real thick coat on the first coat, and would have almost been enough, giving it one more coat and its given it a really good build!
The brand i used was uroxsys moisture curing polyurethane, but thats a New Zealand brand, you might be able to find a similar product no doubt, but you want to look for a good quality one designed for floors. This stuff was touch dry in 20mins to less than an hour.
Registered Member #2899
Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255
nzoomed wrote ...
Phillip Slawinski wrote ...
I've never used any of the casting resin, but I think it might be worth a try.
Issues with polyurethane? I don't know how it stacks up head to head against epoxy for equal coating thicknesses. I do know that the epoxy is quite a bit easier to get a thick coat with, which is one of the primary reasons why I use it. In three coats I was able to build up about 0.0625 inches of epoxy on the form in the video. I've had coils in the past that flashed over end to end with no signs of visible damage, but maybe some could say the same for poly...?
I'm not sure about the epoxy taking longer to cure. Curing time really depends on temperature with the epoxy, and the warmer it is, the faster it will cure. I find that typical curing time is in the range of 4-8hrs.
The polyurethane I was using was designed for use on wooden floors. It gives a real thick coat on the first coat, and would have almost been enough, giving it one more coat and its given it a really good build!
The brand i used was uroxsys moisture curing polyurethane, but thats a New Zealand brand, you might be able to find a similar product no doubt, but you want to look for a good quality one designed for floors. This stuff was touch dry in 20mins to less than an hour.
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Epoxy Coating Tutorial Video
