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: http://www.g4dbn.uk/?p=1618 and this is the story so far of the machining,
The 100 x 100 x 150 mm aluminium blockFacing the block, bit of unnecessary slow-mo trickeryShiny!Nice rainbow causticFirst stage of turningForming the boss on the first sideTurning on a mandrel to form the second bossKnuckle finished and bored to take the pivot shaftPivot shaft machined to size, with flats for the grub screws and locked in placeMachining and tapping the bearing carriers. M10 spiral flute tap clearing the chips very nicelyI 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 anvilBlock fitted to the mandrel ready for OD machining and facingInitial facing done and OD completedRemoving the semi-finished bush from the mandrelOne half of the first bush pressed into one of the the bearing carriersBoring the completed carrier and pair of bushes to fit the shaft with a 5 micrometre clearanceTest fit of the first bearing carrier
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 DelrinFixed 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 feedhorn3.4 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
Machining and Ham Radio experimentation from VLF to SHF
