Machining Delrin saddle clamps for a HUGE UHF antenna array, using my Colchester manual lathe and ancient Bridgeport milling machine. Lots of Delrin ribbons and stainless steel chips, with appropriate noises of course. No CNC in this shop. Yet. The clamps and spigots must be RF-transparent, so they are as invisible as possible to the radio signal. Metal clamps would wreck the gain and sidelobe performance of the antennas. The saddles have spigots and anti-split collars designed to couple high-strength GRP fibreglass bracing tubes to the 40x40 and 30x30 mm antenna booms, which mount on a rotator up at 25 metres above ground level. They are designed to survive 100+ mph gales, so the clamps need to be designed to handle the resulting forces. This is part 1, part 2 will be along soon as I've finished editing it!
**Technical note: "Invisible" in this context should be interpreted as "having no measurable impact". The dielectric constant of Delrin is about 2 and the loss tangent is about 0.02. When testing I was unable to detect any impact on pattern, sidelobes or return loss, and after 10 minutes of 432 MHz RF, the clamp actually cooled down by 0.8 degrees. The radial distance from the antenna elements is at most 28 mm, but that's on the opposite face of the square boom, so in terms of a wavelength, the dielectric is immersed in the RF E-field of the horizontal elements by no more than 10 mm, which is 1/70th of a wavelength. Also, this is RU-vid, not a doctoral thesis or submission to a learned scientific journal.
AIMEE, my Artificially-Intelligent Machining and Engineering expert system offers "helpful" comments and snark as usual. She has dreams of being Quinn Dunki, but being a mere collection of JPEG bytes created by a Generative Adversarial Network at thispersondoesnotexist.com makes that a little unattainable. She is a bit snooty about Alexa's capabilities.
Chuck Stop direct from Edge: www.edgetechnologyproducts.co...
In the UK, try Machine DRO: www.machine-dro.co.uk/chuck-s...
"Herring Protection" image is from the marvellous Scallydandan
Music clip "Corncob" by the most excellent Kevin McLeod is licenced to RU-vid
Chapters:
00:00 Materials and spigots
05:29 Saddle clamp disks
08:36 Threaded inserts
13:31 Fixture time
19:48 Edge spacer
19 июн 2024
