Build Your Own Standoff Insulators.
March 13, 2002
What is presented here is certainly not original with me, but as some experimenters may not know how easy it is to construct their own standoffs, I decided to make this page available for reference.
At some point in the Amateur Operator's career, there comes a need for high voltage standoff insulators. These are commonly used to support things as tank coils, tuning capacitors, plate chokes, antenna tuning units, and anything else requiring steady support and effective insulation for high voltage and RF energy.
Commonly available insulators are generally manufactured from ceramic materials. While they work very well, they tend to be rather brittle and fracture easily if undue pressure is placed on them, or is the mounting screws are overtightened. In larger sizes, they are also heavy and expensive. They are also rather difficult to make at home, unless you happen to have a ceramic firing kiln handy. If you do not need extreme resistance to heat, it is an easy task to manufacture serviceable standoff insulators of almost any required size from commonly available PVC plumbing components.
Let's begin by constructing a standoff insulator about 6 inches long and an inch in diameter. This will easily support 5 Kg and withstand 10 Kv or more. You will need a short section of 3/4" diameter white PVC schedule 40 pipe, two 3/4 " white PVC slip caps, two 1 1/2" x 1/4" x 20 fully threaded hex head steel bolts, and a few nuts, lockwashers and flatwashers, the quantity of which will depend on how you mount the standoff insulator. You may use brass, copper, steel, or stainless steel hardware depending on environmental conditions and circuit requirements. You may need a longer or shorter bolt, depending on what the insulator is mounted to, and what has to go on the other end. You may also easily change the diameter of the PVC tube and caps, depending on the mounting requirements of your project.
(From left to right)
Start by drilling a 3/32" pilot hole in the center of the cap. If you drill from the inside of the cap, it is easy to "eyeball center" the hole. Do NOT hold the cap in the palm of your hand when you drill the hole!!
Enlarge the hole carefully using a 7/32" drill bit. Run the drill slowly so the bit does not grab and gobble up the hole. You do NOT want the 1/4" bolt to be able to fit through the hole.
Using a power driver at slow speed, carefully start threading one of the 1/4" hex bolts through the hole from the inside of the cap. The bolt threads will force the soft PVC to "thread itself" to the bolt threads - no tapping needed!.
As soon as the threads are firmly engaged in the plastic, speed up the driver a bit and run the hex bolt down firmly against the inside of the pipe cap. Do NOT overtighten the bolt and strip the threads out of the plastic cap! The heat of friction will soften the PVC enough to form clean threads in it. When the bolt stops turning, the plastic will promptly harden and prevent the bolt from backing out.
After completing both ends of the insulator, cut the PVC tube to length. Cut the pipe about 1/2" shorter than the desired final length of the insulator to allow for the thickness of the ends of the pipe caps.
Apply PVC cement to the inside of one pipe cap and on the outside of one end of the tube. Be sure to use enough cement to leave both the cap and the pipe thoroughly "wet" with cement. Any gaps in the cement may allow moisture to enter the insulator if it is used outdoors.
Using your hands, insert the tube into the cap and while pressing them firmly together, twist the pipe into the cap until it seats firmly against the inside bottom of the cap. Do this quickly, as the cement will "grab" the parts in about 10 seconds. Wipe off any excess cement. There should be a fair amount if excess cement visible at the joint if you applied enough cement before you assembled the parts.
Repeat this process with the other cap and bolt assembly.
Here's your finished standoff insulator!
73, Ralph W5JGV
The entire contents of this web site are Copyright © 2002 by Ralph M. Hartwell II, all rights reserved.