Delrin: a most useful material

If you ever come to build antennas, you might well find yourself wondering how to physically join two elements together mechanically, whilst keeping them electrically isolated.

I revisited this problem this week because I wanted to make use of a successful multiband, end-loaded vertical that can see useful service at my alternative operating site.  The antenna is a twin-fed, homebrew version of the I-Pro 'Home' antenna.

Having used round timber brush handles for a temporary test run, I found it almost impossible to remove this from the aluminium tube!  The timber had been outside in the weather for perhaps four years or so, and it was to be expected it would now be rotten.

The only way I could get the timber out was to apply strong heat from a butane gas torch.  This worked remarkably quickly, the wood just falling out after a minute or so.

Remarkably, when I cut through the timber, which was a hardwood, I found it hadn't rotted at all.  So if you can find the correct wood, this coupling could last for a long time.

But I had now embarked on changing things.  The alternative material I have tried is Delrin, a plastic that is meant to be suitable as a replacement for metal.

Delrin has interesting properties, not least of which are its mechanical strength and remarkable heat resistance.  This latter property became apparent as I tried to figure out how to insert a Delrin rod into aluminium tube that was very slightly (about 0.2mm) smaller than it.  Superficially, Delrin looks and feels like nylon.

If you like mechanical engineering and 'slow TV', this video is moderately interesting.  Having seen a professional engineering friend killed by the simple act of polishing a metal tube on a lathe, I very strongly recommend you don't clear waste from a turning lathe as appears in the video.


Without a lathe, all I could so was to try careful, even sanding.  This worked quite well, enough to get the Delrin rod to line up properly inside the opening of the tube, but no more.

I then tried heating the aluminium tube quite strongly, which eventually causes the Delrin to start softening.  It doesn't melt as such, with only the slight excess width being sufficiently softened, a bit like thick tar, to be pushed aside and allow the rod to fit.  Even then, it takes quite a lot of physical pushing to get it to go in.

Perfect friction fit!

I found that after cooling, the Delrin could be removed easily by hand, but the fit with the aluminium was perfect, with no 'play'.  This is very useful to me, because there is no need to drill holes through the Delrin and aluminium to secure the fitting; friction is more than enough.  It also allows easy assembly and dismantling without tools.

The end-loaded vertical is quite top-heavy, and puts a reasonable stress on the Delrin rod.  But tests show it is easily capable of taking the load, although guying is needed in moderate to strong winds.