Clamps for 144MHz EME array

A friend in the Netherlands asked me to make a few bits for his new giant 144MHz EME array

The first batch, sleeves, boom clamps, spigots, boom extensions and collars

Replacement Masthead Rotator adaptor

Mike asked me to make a stronger rotator attachment plate for his telescopic mast. The top section is thick walled GRP with 40mm OD. I made a collar and a central pin to fit inside the tube, and fitted the usual 12mm plate with 119mm PCD 8.4mm holes to fit Yaesu or Kenpro rotators. The collar was put in the freezer and the plate in the oven, then they were aligned and pressed swiftly into position to make a string shrink fitted join.

The completed assembly was fixed in place with gap-filling Loctite.

The completed assembly with original guy ring and stub mast and the internal (invisible) pin
All the things….
Rotator plate top side
Rotator plate underside
Collar and rotator-plate mount. The raised section is 0.03mm oversize for a shrink/press fit
Underside of the collar
HDPE bearing bush with guy plate in place
Stub mast inserted and top half of guy ring bearing fitted
Top side of the collar before drilling the centre hole
Underside of the assembly with guy ring HDPE bearings and retaining ring and centre hole
Complete assembly showing (L-R) stub mast, retaining ring, lower HDPE bearing, Guy ring, upper HDPE bearing, collar and rotator plate
Reinforcing pin to fit inside the GRP mast
Pin in the test stub mast which Mike helpfully sawed off for me to use as a template
Underside with the pin bolted through the rotator plate
The mount in place on top of Mike’;s mast with his Kenpro rotator.

Mandrel to machine large copper tube

A friend asked if I could machine the ends of a soft copper tube around 70mm diameter to be flat and square, and to an exact length. Not easy to hold in the lathe, so I made up some expanding mandrels from engineering plastic.

I made a silver steel shaft with an M12 threads on one end and drilled a centre. The other end mounts in a 12mm ER40 collet and there is a bracing tube so tightening the nut forces the the tapered plugs into the split mandrels and they open and press very tightly against the inside of the copper tube. The mandrels when uncompressed are a tight fit in the tube.

Using this technique allows full access to both ends and the whole outside of the tube for machining and polishing.

The raw tube ready to machine
Split mandrel with a tapered bore and a tapered plug on a threaded shaft
Mandrel in place on the shaft
Mandrels in place in the tube, there is a spacer tube inside to keep the mandrels apart
Finished product

Waveguide Adaptor for Octagon LNB to 22mm

The simple approach to attach an Octagon LNB to a circular waveguide is to saw off the ridged scalar horn and push the cut end into a split 22mm pipe, but I decided to do it the long way. I made up a conical plug from brass to fit against the cone of the horn, then bored a tapered hole inside the plug to match the 17.5mm ID of the Octagon to the 20.2mm ID of 22mm water pipe waveguide. Probably totally unnecessary, but I had fun doing it.

Parts of the adaptor and mount with the 22mm waveguide and bare LNB

First step was a CAD design

CAD Model of the Octagon LNB horn and tube section
The brass adaptor plug in place
Adaptor plug and the locking ring with the O ring compression seal
Front collar in place, without locking ring
Complete assembly with 22mm copper tube inserted into the plug with collar and locking ring
Tapered end of the plug
22mm bored socket for the copper tube
Collar slid over the plug
Collar showing the thread
Collar with locking ring in place
Collar, adaptor and locking ring in place
View into the tapered bore of the adaptor
Complete assembly ready to attach the dual-band POTY feedhorn