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More Lead Tape

A

Anonymous

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There is some more lead tape up for auction on eBay. See: Item # 1833139743 and Item # 1833139999 3M, LEAD FOIL TAPE, Type 422, 3/4" X 36 Yd 1-mil acrylic adhesive. Foil is 5.9 mils thick and 3/4 inch wide by 36 yd long. 1.5 lb per roll. This stuff makes a fantastic Faraday shield and it is nice and easy to use. Don't forget to leave an air gap in your shields!!! Dave. * * *
 
HI Dave
How are things going over there. I am back from holidays but didnt find much gold at all. It is getting very scarce. I found almost as much in the local gold field in two hours as I found in two weeks on the Central Victorian goldfields. Am preparing a post for this forum on gold and detectors.
Cheers
Steve D
 
of an air gap is usually enough? If using 22 gauge wire for instance. Can you just put some foam over the wire and then wrap it with the foil? Haven't built a PI coil before so need these answers. Thanks, John
 
A bit of clarification is needed as to where the gap is. Having wound your coil, you then wrap the lead tape around it. With 3/4in wide tape you would need to wrap in a spiral with each turn just overlapping the other. When you have gone all the way round the coil and are meeting up with the point you started, you cut the tape to leave a small gap (about 1/8th inch), so that the lead wrapping does not form a complete ring. Without this gap, eddy currents would flow in the ring and superimpose their own decay signal on the coil response. Spiralling the tape around the coil takes a bit of time to get it even and gradually peel off the backing tape as you go. I use 1in wide tape and just fold it around the coil without spiralling, which is much quicker. For convenience, the start and finish of the shielding is at the point where the coil wires terminate.
Having completed the shielding, you then solder a piece of stranded hookup wire to one end of the shield. You have to work fast as prolonged touching of the iron on the lead tape will just melt a hole. Best to practice on a spare bit of tape first. The lead from the shield is then soldered to the shield of the coax, as is the ground end of the coil.
Any problems and I can post a picture.
Eric.
 
I appreciate your detailed and easily understood answer. Thanks much, John
 
Hi Eric, I am interested in this lead tape idea for a faraday shield. Myself and some other people have been making coils and I have used a method by Frank Wallis. That is using a very thin wire I spiral it around the coil at about .25in gaps and then come back the opposite way in a cris-cross fashion. This seems to work fine. I know that in VLF detectors you completely shield the windings as with your lead tape but I would have thought that completely covering the coil on PI coils would render it less sensitive if not deaf? How thick is the lead tape? My mate uses nickel spray and we would prefer zinc but is almost impossible to obtain. I know that coiltek use a screen printed design similar to a flyscreen pattern. What is the most efficient for Aussie conditions in your oppinion?
Regards... IY
 
Hi All
I have found that for very large coils (2ft or bigger)the sheild and how it is applied is very critical,in so much if it is too heavy that the coil will not ground balance correctly.
Regards Frank Wallis
 
The lead tape I use is 6/1000in (0.16mm)thick, including the adhesive layer. Aluminium or copper tape would make the detector deaf, but the low conductivity of lead means that the shield eddy currents are much faster decay than the shortest sample pulse delay time used.
I have used nickel loaded paint, but you have to be careful as it is magnetic, and sometimes you can see the magnetic viscosity decay.
Eric.
 
Interesting what you said about the nickel paint. How would lead paint go (that's if it was available)...? Would you spray it light (like nickel) or thick like the tape?
Regards
IY
 
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