Chance PI coil...

[geoscash1]

Hey thanks for the suggstion Dan and 6666,


I used 6666's suggestion and used some string and just did 10 complete turns. It worked....

All I was missing was that pic of the over/under switch over from one side to the other. Now I got it and the pattern so it will be pretty straight forward to do..


This particular form was given to me by Don, one of the members here, not sure if he just gave up on it or had the same issue I had, missing the crossover. I made one 9.5 inch OD by hand with a hand held router for a template for later. I have access to a water jet so will be making some of my own in different sizes. This one has slots that are over double the thickness, 0.263, I assume because the idea was to use teflon coated wire. Other than that, it is to the spec seen on one of the other images here, 0.098 lexan, 0.4" deep, 37 inner and outer slots, although this one is 7-3/4 od, so it would fit into an 8" coil form I'm guessin.

I'll take your advice and when I do mine on the water jet I'll make the slots just over the thickness of the material, maybe 0.100 or 0.120 and then go from there..


Anxious for my teflon wire to get here so I can get these done and test them out..

[baum7154]

Hey thanks for the suggstion Dan and 6666,


I used 6666's suggestion and used some string and just did 10 complete turns. It worked....

All I was missing was that pic of the over/under switch over from one side to the other. Now I got it and the pattern so it will be pretty straight forward to do..


This particular form was given to me by Don, one of the members here, not sure if he just gave up on it or had the same issue I had, missing the crossover. I made one 9.5 inch OD by hand with a hand held router for a template for later. I have access to a water jet so will be making some of my own in different sizes. This one has slots that are over double the thickness, 0.263, I assume because the idea was to use teflon coated wire. Other than that, it is to the spec seen on one of the other images here, 0.098 lexan, 0.4" deep, 37 inner and outer slots, although this one is 7-3/4 od, so it would fit into an 8" coil form I'm guessin.

I'll take your advice and when I do mine on the water jet I'll make the slots just over the thickness of the material, maybe 0.100 or 0.120 and then go from there..


Anxious for my teflon wire to get here so I can get these done and test them out..

-----------------

Excellent result with the string! Now your are cooking!

Dan

[baum7154]

I made extensive use of BB Sailors paper in building/testing my coils.

The best coils I have built are in this thread. While they are more work to build, they pay off in exceptional speed (8"/335uh/6us) and the fact that they 'self shield' by virtue of the coil geometry. The self shielding removes a major task from the coil construction and improves speed and eliminates additional shielding losses. Take a look at Page 2, post numbers 30, 31, 35, 36, 47 and you will see pictures and description of the coil construction. This coil will not see your hand completely gripping around it with the detector set to 8us sample delay (evidence of effective shielding) as long as the outermost end of the windings are at system ground. I would use 600volt Teflon/PTFE insulated #26 awg silver plated stranded wire (EBAY) to wind this coil and .091" thick LEXAN (from Home Depot) to create the form. I would cut the slots no wider than 1/8" wide in the form. I use a continuation of the coil wire twisted with a cordless drill at a rate of 3 turns per inch to eliminate solder in the coil which can be detected at short sample delays, and to eliminate much of the capacitance inherent in the use of coax cable. As there is no additional shield the coil can just be profiled out with polyethylene foam, over wrapped with self adhesive cloth hospital tape, and then directly fiberglassed.

Best of luck,

Dan

[bernte_one]

i would go crazy when cutting the form
respect guys

[6666]

Hi bernte_one, there are a couple of ways to make the former, one of the alternatives is to use a jigsaw and make long cuts then glue a ring onto former, gives same result, I will post pictures some day.

[baum7154]

An alternative way to make the coil form using minimal/hand tools is to:

1. Lay out the form profile and slots on paper and glue it to the .091 to .125" thick LEXAN or polycarbonate material. Note: Other plastics that are brittle may break in the fabrication process but could still be used if care is taken in sawing and filing.

Form pattern is 1" wide with 37 slots equally spaced around the inner and outer perimeters with the inner slots staggered to the midpoints of the outer slots. Slots are .400" long and 1/8" wide. The .400" slot length is meant to accommodate at least 35 turns of #24awg 600volt PTFE insulated stranded wire. Smaller wire or less turns would allow a slot of .375" or even less but .400 is a good slot depth for most wire in the range of 24AWG to 28 AWG.

2. Drill 1/8" holes at the innermost end of the slots so that the innermost edge of the drilled holes meet the desired slot depth/length.

3. Saw (jigsaw or sabresaw)out the outer and inner circles using the glued on layout as a guide. Note: Use a fine tooth blade, one meant for thin metal is good

4. Hack saw or jigsaw the slots from the outer and inner form edges to hit the center of the drilled holes using the glued on layout as a guide

5. Then file the slots using a 1/8" file. With care the file will follow the sawed slot right down to the drilled hole at the termination of the slot.

6. Smooth out the slot edges with a file.

7. Remove the glued on paper layout and VOILA!! You have your coil form.

I hope this helps those who want to build this coil with minimal tools. It is not too difficult to accomplish.

Regards,

Dan

[baum7154]

To clarify:


"5. Then file the slots using a 1/8" file. With care the file will follow the sawed slot right down to the drilled hole at the termination of the slot."

I should have said to use a round file of 1/8" or 3mm diameter. A round file will follow the sawn slots.

Sorry for the omission.

Regards,

Dan

[6666]

Hi Dan

After you have wound on the wire, what is the total width of the wire bundle , like from outer to inner ?

[baum7154]

I have a new coil of 306uh wound with 29 turns of 26 awg 600 volt insulated ptfe wire that measures .677" across the windings width. Larger wire and more turns would be wider and smaller awg with less turns would be less width.

Dan

[6666]

measures .677"

Thats about 17mm, thanks Dan

[joop]

What is the self-resonance frequency of this type of coil? Thanks.

[baum7154]

My coil in current use is 8" 335uh and has a feed line made of a continuation of the coil wire twisted at a rate of 3 turns per inch. For that reason I cannot give you 'just' the coil SRF but with 33" of feed line the coil has an SRF of 1.056mHz. This information and some for other coils is in post #48 of this thread. The feed line runs about 1pf per inch so if you remove 30" of feed and it's capacitance of 30pf the calculated SRF without feed would be about 1.414 mHz. This of course ignores the loss of inductance in the 30" of feed so the coil only SRF is probably even higher.

Regards,

Dan

[joop]

Interesting read, sorry I missed that. It seems that shielding always influences the speed of the coil. And yes, the cable is also important, I will keep that in mind.

[baum7154]

I have built a 4" X 12.5" oval coil with 8.5" parallel sides in accordance with Eric's 3:1 profile recommendation. This coil is a fast spider coil using the instructions I posted in post #126 using only simple tools. The construction pictures are posted below. I will post test results for this self shielding coil in the next few days.

[Silver Dollar]

Wow A BigFoot Spider Wound Basket coil Nice!
I was thinking of doing a BigFoot Litz Basket Coil...