3D printed former for 3DSS coil intended for Minipulse

[aeberbach]

I built the coil...



It measures 370uH, 1.6 ohms. The wire is MIL-W-22759/11 26AWG.

[Teleno]

Don't forget the option of having the former laser-cut on a plastic material of yoru choice. https://www.seeedstudio.com/service/...r=lasercutting

[Davor]

True. I'm considering investing some of my future time to creating an assortment of acrylic boxes done this way. Those give that "I have nothing to hide" look and feel, and you may get precisely what you need in mechanically superior material. And compared to 3D printing - for peanuts.

[Point]

i print allmost all my parts for my projects with PLA+ work fine and fast... 1mm strengh is not a probleme and the cost per part is not much depense how much filament i need but most time arround 0.20e

[Davor]

... and you need to print a house to break even the cost of everything else. OK, it becomes cheaper, but compared to laser cutting, we non-owners of a printer are better off with laser cutting:
- design is piece of cake,
- professional cutters are everywhere,
- while you draw out your wallet to pick a small bill, your design is already cut,
- it is mechanically superior to printing.

[aeberbach]

You're all correct, if my employer had not just bought a nice big 3D printer and boxes of filament I would probably be buying laser cut formers. As is I am going to need to jigsaw former pieces together since 8" round is about the largest single piece I can print.

But this is early days - 3D printing is at about the same level of advancement as the 9-pin dot-matrix printer was in the 80s.

[godigit1]

Very nice coil, Looks very clean.
That wire has a low resistance for 26 awg solid I am going to have to order some for experimenting. Most all my 26 awg coils with only 300 uh come out close to 3 ohms.
Thanks for your efforts and the link for the wire.
Best
Digit

[LukeJ]

Don't discount the possibility of just cutting out the 'former' with a vertical band saw. Or a more time consuming, Coping saw.


The 'former' doesn't need to be exact in dimension. +/- .030" is more than sufficient.


When I make my former, I first design it in a CAD system. (It could be hand drawn, but the tricky part would be the 37 divisions.) Then I print it to scale. If it's bigger than an 8x11" piece of paper, I position the part so I can print out a third or quarter of it and then print multiples and tape them together. Sounds low-tech, but works just fine. Once I have a scale representation of the former, I just glue it to a piece of ABS sheet (.062") with a few drops of superglue. Then I glue another piece of ABS sheet to the bottom of the first with five spots of superglue. One drop of glue in the center and one drop on each corner. The idea here is that I'm going to cut two pieces at the same time. So now I go to the band saw and start to cut. I cut the inside diameter first. I do this by cutting right through the side of the former and then cutting out the circle in the center. After the center is cut, I cut the 37 'slots' on the inside diameter. I cut my slots as a narrow "V", with the top of the V of about .125" width and the bottom the width of the wire going to be used. The slots are roughly 3/8" deep. I like the "V" shape and it just made sense to me to do it this way. Once the inside is completed, remove the former from the band saw blade. Then, carefully separate the two pieces of ABS with a butter knife. You'll find that not being too generous with the glue makes this easier. When they are separated, turn one almost 180 degrees to the other and line up the slots and diameter on the insides. What you will do is glue these two pieces back together with the intent of eliminating the place where the blade cut through the side of the former. Sounds a bit complex, but makes a lot of sense when you are actually doing it. Once the two pieces are glued back together, the outside diameter and slots can be cut. The former ends up being .125" thick and rigid enough to wind 21 AWG solid with no issues. I have made 6 coils in this manner. I can make a 3DSS from thought to completely wound in about 3 hours. The first one took a bit longer.

I wanted to mention this so that more people may be able to look around the house and remember some of their grade school craft skills and create a 3DSS of their own.

I am also discovering that expensive wire may not always necessary to end up with a good working coil. I wound several coils with Teflon insulated wire with good results. Then, just to experiment a bit, I wound an 8" 3DSS with 26 AWG seven strand PVC insulation and so far it seems to be the best coil I've made yet. It's like $5 of wire and a couple hours of time to a coil that can be experimented with. I put it in a homemade vacuum formed housing and found a couple nuggets with it. To be fair, I could have found those nuggets with several other commercial coils I own, but the homemade one did find gold.

Luke

( Sorry I don't have a picture of just the former before winding. I always get excited to start winding and then realize I didn't photograph it until it's too late. )

[LukeJ]

I figure I may as well put these up too....

[WM6]

Very PRO LukeJ, congratulations.

[Koala]

Some nice coils there. Well done.

[aeberbach]

Really nice work Luke! Is the coiling the 3rd and 4th photos made on the same 37-slot former we are using here? The wire crossings seem more neatly aligned.

[LukeJ]

Hey, Thanks for the compliments guys !! I've learned quite a bit from this forum and I guess these days I have some 'extra' time around the house to play with my toys... I figured now might be a good time to hopefully return the 'favor'.

I also wanted to say that, like what the others said before, very nice work on that former design, Aeberbach. My only concern was possibly rigidity, which was mentioned, but you wound the coil and it looks great. WTG.

With regards to the 3rd and 4th photos, I believe you are talking about the Plexy coil pics. If I'm correct about this, then no it's not the exact same former. It's still 37 slots but I made the cross section larger by decreasing the inner diameter. My goal was to further lower the capacitance of the coil by having the wires cross closer to right angles. What I discovered is that when you spread the windings out like that, it requires more turns to achieve the desired inductance. By that time, you've added more resistance and capacitance by adding more wire. It didn't work as well as the others. Somewhere between 1" and 3/4" cross section seems to be the 'sweet spot'. Which I'm pretty sure baum7154 has mentioned at least once. For instance, the 12" coil pictured has a 10" ID. It also has 41 slots, my first coil with that number. 37 is a prime number and so I figured 41 might work too. The 12 inch coil is the biggest one I've made yet and with the increased circumference, it needed a few more slots.

When I look at 'designing' another 3DSS coil, I look at how the first layer of windings will lay on the form. What I'm looking for is the right combination of OD and ID and slot depth. What I want is for the wire to make an almost straight line from the outside slot to the inside slot and back to the outside slot. Once you get the first 'layer' wound, the subsequent layers begin to form the angled look and ultimately the 'basket weave'. For someone who has yet to wind a 3DSS, this language may be hard to digest, but once you go through the process the first time, it will all make good sense.

Thanks again for all the great knowledge that is freely passed around here on Geotech. It's a pretty great feeling to read and learn about what others are doing and then doing it yourself, especially when it actually works !!

Luke

[aeberbach]

Since I'm 3D printing I was thinking along the lines of adding alignment pins on the former face, perpendicular to the slots. That could force the wire crossings to be made perpendicular to each other, and the relative inner and outer diameters wouldn't be a factor.

[baum7154]

When I look at 'designing' another 3DSS coil, I look at how the first layer of windings will lay on the form. What I'm looking for is the right combination of OD and ID and slot depth. What I want is for the wire to make an almost straight line from the outside slot to the inside slot and back to the outside slot. Once you get the first 'layer' wound, the subsequent layers begin to form the angled look and ultimately the 'basket weave'. For someone who has yet to wind a 3DSS, this language may be hard to digest, but once you go through the process the first time, it will all make good sense.

Thanks again for all the great knowledge that is freely passed around here on Geotech. It's a pretty great feeling to read and learn about what others are doing and then doing it yourself, especially when it actually works !!

Luke[/QUOTE]
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You may have read my recommendation in the Chance PI Coil thread that the distance between the deepest points of the inner and outer slots should be 1/4" or 6mm. Also widening out the coil form spreads the coil cross section and is likely to diminish the self shielding effectiveness of the 3DSS coil. I try to keep the coil cross section circular to keep shielding uniform and effective.

Regards,

Dan