Category Archives: Mount

432 MHz Moonbounce array elevation mechanism

I’m working on an elevation pivot plate for a large 70cm moonbounce array for a friend. The design uses a 40 x 30cm plate with clamps and alignment blocks to carry GRP and aluminium tubes to support the array and LNA/phasing harness. This is the first stage, making the knuckle and pivot pin and bearing bushes/carriers. The bodies are aluminium, the shaft is 316 stainless steel and the bushes are phosphor bronze. It will have dust caps and grease nipples. The bushes are in two parts with a 1mm grease groove between them

So far, it is looking OK. More to follow.

One of the bearing bushes and mounting blocks being checked for fit

The original concept for the knuckle is here: and this is the story so far of the machining,

The 100 x 100 x 150 mm aluminium block
Facing the block, bit of unnecessary slow-mo trickery
Nice rainbow caustic
First stage of turning
Forming the boss on the first side
Turning on a mandrel to form the second boss
Knuckle finished and bored to take the pivot shaft
Pivot shaft machined to size, with flats for the grub screws and locked in place
Machining and tapping the bearing carriers. M10 spiral flute tap clearing the chips very nicely
I made a mandrel with a threaded hole to turn the bearings from a piece of an ancient slab of bronze that I remember my dad using in the 1960s as a soft anvil
Block fitted to the mandrel ready for OD machining and facing
Initial facing done and OD completed
Removing the semi-finished bush from the mandrel
One half of the first bush pressed into one of the the bearing carriers
Boring the completed carrier and pair of bushes to fit the shaft with a 5 micrometre clearance
Test fit of the first bearing carrier

Dish Feedpoint Mounts

Tony G8DMU has a 2.4m mesh dish on his van. He uses a variety of feeds, and they are all different diameters. I made up a quick-detach support ring to fit an RF Hamdesign multi-band ring feed, but Tony’s 23cm feed is larger, so I made up some extension blocks and a set of cheeks and spiders to support the different feeds.

The original ring feed, with the adjustable ends on carbon fibre struts, QD sockets and attachment brackets

First step was to extend the ring to fit the large feed

Blocks inserted into the ring to increase the diameter and provide attachments for the spiders and cheeks

I made up a stainless steel internally threaded clamp nut to fit on a stainless threaded bar fixed into the block with Loctite, so I didn’t have to worry about threads in the aluminium getting damaged.

The big 23cm band feed in the clamp ring

Next step was to make support cheeks/crescents to hold the multiband ring feed

Adjustable crescent with a knurled brass head on a pointed stainless steel thread, with a brass insert to spread the force and prevent wear on the Delrin
Fixed crescent, milled from Delrin and threaded M5

The 3.4 GHz feed is the smallest, so I milled a support ring and fitted support rods with threaded ends to fix to the holes in the outer ring. The threads were M5 so they fitted easily through the M6 threaded hole in the clamping block.

Clamping ring and spider for the 3.4 GHz feedhorn
3.4 GHz horn fitted to the main ring.

The 13cm horn is a little larger, and had to be made in two pieces to fit over the backshort.

2.3 GHz feedhorn in the clamp

I milled the rings on my ancient Bridgeport mill using a shop-made fixture plate on a rotary table with a sacrificial plate made from acrylic sheet.

Finally, a photo from Tony of the big dish in use on his van at a portable contest site up in the hills