Thelen Tree Farm

Celebrating 17 Years - 2001 ~ 2018  



Spider Web Coil Form

This is the Spider Web coil Form that I used for my crystal radio.  Both the antenna tuner and detector coils are wound using this form design.  I used 1/8" thick white High Density Polyethylene (HDPE) sheet.  I bought this material at TAP Plastics in Portland, Oregon.  They have a scrap/surplus barrel that any plastic in it sells for $1.00/pound.  It is the kind of plastic that is used on cutting boards in the kitchen.  It has a relative dielectric constant of 2.26 @ 1 MHz.  See the table with Dielectric of Various Materials.  If you could find some Polypropylene, that would be good as it has a little better dielectric constant than the Polyethylene. 
I used some spray adhesive and attached a 1X paper print to the plastic and cut it out using a scroll saw.  When I am finished with the form I clean it well using Acetone.
If you are having problems with the print coming out at a different scale try printing the pdf file from within Adobe Acrobat.  Also you need to print it on a letter size (8 1/2" X 11") paper.  If you do this it "should" come out at 1X (actual size).  You might measure it just to be sure.
I used PTC Pro/ENGINEER® software to design this coil form and converted it to .pdf in Ghostview.  If you have the need for any other type of files; .ps, .igs, .prt, .dxf, or ? just let me know and I will see what I can do to help.

Small Spider Web Coil Form


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