Member postings for Robert Atkinson 2

I think Trevor is on the right track. It looks like some kind of H field (magnetic) monitor or antenna. More likely for above ground power lines though. It's effectively a directional radio system.

Not Royal Observer Corps (ROC) who monitored for nuclear explosions. They did not use electromagnetic detection systems.

Robert.

In the aircraft Tachometer systems they are not called brushless DC becuase they are not run from DC they are called Permanent Magnet 3 Phase Generators / Motors. Magnetically and electrically they are the same as the "motor" part of a drone style Brushless DC motor. Some tacho indicators indicators use induction motors but PM ones are more common. the speed to pointer mechanisim is a magnetic drag cup the same as a traditional car speedo or tacho.

Robert G8RPI

No, I ment Brushless DC Motors. The type used in drones and RC cars. ALL motors are Alternating Current at the coil, they have to be to rotate more than 180 degrees. In brushed DC motor the brushes and commutor switch the direction of current. In a Brushless DC motor the switcing is done by electronic switches. In things like small fans these are internal so you put DC in. With he larger model / drone motors the switches are external in a "controller" if you take the basic motor it has 3 stator windings 120 degrees apart and a permanent magnet rotor. The controller produces 3 phase "AC" but it's typically not a sinewave. It also needs feedback from the motor. In earlier designs and simple items (fans) this is by sensors typically hall effect sensors. in newer designs the sensethe back-emf from the coils when the switches are off.

So if you have a Brushless DC motor without a controller you can use it as either a pemanent magnet 3 phase AC generator or a permanent magnet 3 phase AC motor. So connect 2 "back to back" , turn one fast and the other will turn at the same speed.
With the aircraft tacho-generators you change the strength of the magnet (old Alinco not modern rare earth) with a coil and capacitor to set the output voltage to the correct level.

Stepper motors will work back to back, but not nearly so well because of their magnetic design. They tend to stall and then won't "pick-up" again.

Robert.

Tim,
Your proposed "back to back" brushless DC motors driving a mechanical tachometer will work just fine. This is EXACTLY how aircraft remote tachometers work. I have repaired aircraft tachometers, generators and designed and built test equipment for them. Ignore comments about selsyns and synchros, these are for transmitting anglular information not speed (and the power need to drive the tacho).

Robert

Well this went off-topic fast!

I think I'll stick to my favourite Rocol anti-fretting compound (Molybdenum based) on the screws...

Looks like the best way to lock the ML2's spindle without causing damage while unscrewing the chuck/baseplate is to put a expanding mandrel up the back gear end. If I had a working lathe it would be easy to make one, but I have a plan. More later.

Robert.

Rather than just skipping or dumping things it's always worth trying ebay or even using freecycle/freegle. I'm stunned how much people will pay for stuff I was going to put in recycling. Old car / bike parts are valuable. Metal can always go to the scrappie or recycling centre. You local garage might even have a scrap bin that they don't mind donations to. Non ferrous, motors and transformers are normally worth cashing in though. Don't forget you are not supposed to put electronics into rubbish skips or bins. If you have more than a couple of boxes of scrap PCBs they can have surprising value. I use AWA refiners www.awarefiners.co.uk They pick it up and you get payment based on the actual metal content, not some "average" value.

Robert.

Myford ML2 re-commissioning.

So as I’ve said in my “introduce yourself” post, I’ve recently purchased new old lathe. While advertised on ebay as an ML4 it appears to be a late ML2 (or ML1 with upgrades). Seemed to be reasonable condition and right price, £200, but you don’t know until you see it in the metal. From the photos in the listing it had a nice round end cabinet stand and tumbler reverse. I’m an Electronics / aviation engineer and have used lathes etc before. I had access to a well-equipped prototype machine shop at my previous employment and have been missing it for small home jobs. The big decision was a new “Chinese” machine or an old British one. So that’s decided then. A quick look at the sellers when picking it up showed one significant fault – the fibre headstock V pulley is badly split and warped. Getting the lathe home and having a closer look revealed the following:
Headstock pulley is unusable
Spindle bearings have been greased
Cross-slide feed has ½ turn backlash
Chuck won’t unscrew with normal technique.
Spindle has a tight spot
The cross-slide backlash is in the endplate an screw. Should just be an adjustment but the handle, nut and dial have been soft soldered together so further investigation required.
Still thinking about how best to lock the spindle to get the chuck off. I know enough not to use the back gear. Given the state of the pulley I’m thinking an expanding mandrel and L or T handle in the back of the spindle would be best, I might take the chuck off the back plate and try gentle heat (hot air gun) on the back plate first. Spindle has to come out to clean out the grease and replace the pulley.
The good news is the tight spot on the spindle disappeared when I released the step pulley. Additionally it has a 1” diameter spindle and if the faceplate that came with it is correct it has the 12TPI 11/8 nose so can be adapted for later ML7/ML10 chucks.

I’m calling this a re-commissioning as it’s the intention to get a working lathe, not a restoration or significant modification. One thing I am considering is replacing the old induction motor and layshaft with a modern motor and drive. More on that later.

Robert.

Hi Andrew,

I'm in a Village west of Cambridge on the A14 with a big Tesco so pretty close to you. I was at the St Neots radio rally on Monday. I'll have to look up the ME club there.
Getting a bit old to look for a new employer.

Robert.

Muzzer is totally correct. The motor will run fine from a USA 220V socket intended for driers aircons etc. Brown to Red Blue to Black. No connection to the US neutral (white). Make sure you connect the earth wire as the moter neutral will now be at a 110V above ground and any insulation fault that might not show up in the UK will in the US. The setup i very similar to the 55V-0-55V 110 volt safety system used on UK building sites.

One thing to note is the motor will run 20% faster as the UK is 50Hz and the USA is 60Hz.

Robert (new to ME but I've designed equipment to work in UK and USA)

Hi,

Thanks for all the good wishes. I've had a closer look and some measurements and it's not an ML4. The bed ways are only 18.5" long. It has tumble reverse, 7" cross slide and a swing away change wheel cover (slotted style) so I think it's a late ML2 or an ML1 with upgrades. Now he bad bits. The fibre V drive pulley (3 section) is breaking up and warped and there is half a turn backlash in the cross-slide screw. The spindle looks like it's the later type with the 11/8 12TPI thread. This is nice because it opens up modifying the register for ML7 chucks etc. The size is based on the faceplate that came with the lathe as the chuck won't come off with gentle force so I need to make a spindle lock. I know enough not to use the back gears. Not sure what to do about the pulley, I need to investigate further. The cross slide backlash is in the screw / endplate. This should be just ann adjustment and maybe a thrust washer, but the handle, nut and indictor disk have beed soft soldered together so again investigation needed.
Anyway this is bit far from hello so when I hve done more I'll post to a more appropiate forum.

Robert.

Hi,
I've just joined the forum having just picked up my first lathe. It's a vintage Myford ML4. At let that' what it was advertised as on ebay, I've not checked the dimensions yet. It's got tumble reverse so a later model. The motor and countershaft are a bit rough so I'll probably fit a modern 3 phase inverter motor (actually a servo motor and drive as I happen to have them).
I'm an engineer by profession but electronics / aviation. First used a lathe, a Super Seven 40 years ago, ha some training at college too. At my Last employer I had access to a small, well equipped prototype machine shop but current employer won't even let me use a pillar drill for work jobs because I'm a "designer". Hobbies include electronics and instrumentation an the little Myford will do 90% of what I need. Looking forwarn to getting it sorted and running. Obvious faults from a quick inspection are the smallest step on the grooved headstock pulley is split and the spindle bearings have been greased. I'll check the play before deciding to pull the spindle or not.

Robert.