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Tailstock DRO Part 3

The tailstock DRO is now completed. The last element was a block to bolt to the existing end clamp, to hold another rare-earth 12mm magnet which keeps the end of the scale firmly attached to the tab on the quill. See part 1 and part 2 for details

DRO attached to the tailstock casting by the four magnets under the wedge and the one in the end block
DRO in context in the tailstock
Collar and magnetic block
The magnet block attaches using the original end bracket cap
I left the magnetr slightly proud of the block in case of any misalignment
Milled finish will have to do, this isn’t jewellery!

Tailstock DRO Part 2

Having made the clamp collar and bracket to fit the quill (see part one), next step was to make the magnetic wedge to fit on the angled side of the tailstock on the Colchester 1800. It is inclined at 6.6 degrees. I wanted the digital display to be at 45 degrees to avoid glare and keep the LCD reading angle good for best contrast.

CAD sketch in Fusion360, showing the angled counterbores
The part in real lifer
Back view – the M3 mounting screws poke out of the holes by 2mm and screw into the backplate of the electronic scale
Four rare-earth magnets epoxied into the pockets so it will attach to the cast-iron of the tailstock
Bolted in place and ready for a test fit

Tailstock DRO Part 1

I needed a DRO (digital read-out) on the tailstock quill of my Colchester 1800 lathe. OK, the quill has an engraved mm scale and the wheel on the leadscrew is calibrated in mm, with 2.5mm per turn in multiples of 100 micrometres. Still a pain when you need to drill a hole 52.95mm deep. After watching a couple of Youtube vids, I saw a neat solution by ChrisB257. Make a collar to be a very close fit to the end of the quill, split it and put in some clamp screws, then fix a right-angled tab which can be used to attach the magnet on the end of a sliding electronic digital scale.

So, part 1 is just the quill clamp collar and magnetic tab. Collar is turned from 70mm EN3 steel round bar. Tab is from an offcut of EN8 I found in the scrap bin.

See part 2 for the magnetic wedge mount for the scale and part 3 for the magnetic end attachment.

CAD design idea in Fusion 360. Only one clamp screw modelled. Just getting some idea of scale
The first part, split collar and clamp with tab attached. I changed the orientation of the clamp to make access easier.
The main slit was made using a 1/16th inch slitting saw, the partial slit was done with the bandsaw
The collar pushed on to the tailstock quill and clamped in place.

SCAM12 elevation winch

A SCAM12 weights something over 90kg, and with a rotator and antenna system, it it rather too heavy to lift from horizontal. However, putting it to vertical then trying to lift the antenna up high enough to drop it into the socket on top is just too dangerous. Solution is a winch from the local agricultural merchant.

I has to make an adaptor from the double-flatted shaft to 17mm hex so I could use the original handle with a half-inch square extension
The adaptor, made from stainless steel
The winch uses a flat webbing strap, so I made up a wall-mount pulley to suit.
The big angle-iron bracket holds the SCAM in place once it is up. The bolts go right through to the inside of the wall where there are giant washers to spread the load on the old barn.
Ready to lift
Locked into position with the new az-el driven dish

VE1ALQ 1.3GHz PA heatspreader

A friend asked me to make a heatspreader for the 23cm amplifier board from VE1ALQ (SK)

Rather than mess about with a sectional spreader, we decided to do a large single block of copper to maximise RF performance.

Millled to sized and flat, not drilling and tapping the holes
Holes and FET/load slots tapped and drilled, extension block for input load, and output coax clamp fitted.
Coax clamp and output hybrid dump load
Input SMA mount and outboard resistor mount for input hybrid
FET groove
Test fit of an MRF286 FET
The FET fits!
Main PCB soldered tothe spreader with tin/lead solder paste. Now applying Bismuth/Tin 138C solder paste for the FETs
On the hotplate with spring clips to hold the FETS in place while soldering
FETs soldered to the spreader and gat/drain connections solder to the PCB. Resistors are for gate protection until the rest of the components are fitted.

Machining fixture for VHF PA Heatspreaders

Part of the design decision for the spreaders I made for the VHF PAs was to use pockets machined in the copper surface of the spreader to carry the MRF151 transistors, which protrude 2mm below the PCB. As I don’t have a CNC mill, I had to make a fixture to hold the spreader accurately in place while I machines the pockets on my Bridgeport.

Finished item, those pockets are at 45 degrees
Finished fixture with a spreader ready to mill
Slot where the spreader sits, before the holes for the clamps were made
Underside showing vice clamp
Cam to press the spreader against the reference surface of the slot
toe-clamps to hold the spreader in place for machining

Heat spreader for 4 x MRF151 VHF PA

These surplus high power PAs using 4 x MRF151 were originally used in watercooled industrial VHF drivers. The devices and some of the other components protrude about 2mm below the PCB lower surface.

To minimise the amount of copper required, I decided to make a heatspreader to go under the devices and make aluminium spacers for the rest. I also decided to make a fixture to hold the spreaders so I could cut neat pockets for the devices. Not sure that was a sensible approach. It certainly meant I had to do some tricky machining.

I have some more to make, I won’t be doing the fancy pockets this time, just transverse slots.

One of the completed PAs
Underside of the PA board
My over-complex pocketed heatrspreader
Underside of the spreader
Spreader bolted and slathered with Arctic Silver
Spreader and spacers showing the PCB-facing side
Output side aluminium spacer
input side spacer with driver device pocket
Assembled and ready to attach to the heatsink
I milled the giant heatsink flat and drilled and tapped some mounting holes
Two more of the finished items