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Member postings for John Doe 2

Here is a list of all the postings John Doe 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: Battery fire in electric cars after a collision
28/06/2022 19:10:50

Interesting thread. Lithium batteries can suffer from thermal runaway, where too much current flowing leads to greater heat which leads to more current flowing, which leads to greater heat......

Airlines have emergency procedures to deal with lithium battery fires - we cannot pull over and get out of an aeroplane in flight.......They involve submerging the laptop/cellphone in a bar-box full of iced water, and careful monitoring. This is also why the cabin crew will take it very seriously if your phone drops into the seat mechanism. It can get damaged by the mechanism and go into thermal runaway, which they are very keen to prevent !

Electric cars being still 'live' after an accident is a very good point. If there was a fire, then the throttle position sensor could easily melt and send a 'go' signal to the motor. I consider myself warned.

Electric car batteries should have an emergency cut-out. The battery packs I have seen have a linking busbar between each side of the battery pack. This busbar could have an emergency handle protruding into the internal cabin of the car somewhere, which when pulled would break the busbar and separate the two halves of the battery rendering it relatively safe - certainly against it powering the motor.

Thread: Arbor Press
28/06/2022 09:46:38

The 1 ton force of the arbor press is only developed between the "jaws" of the press, in the same way that the force of a G-clamp is developed only between its jaws.

Owing to lever, (or hydraulic action, depending what your press uses), force is multiplied so you won't push the lever down with 1 ton, you will only push a small fraction of that, and this is all your bench will be subjected to - plus the static weight of the press itself.

The maximum force your bench will be subjected to is your own body weight, (since if you lift yourself off the floor, that is the maximum you can push down), plus the static weight of the arbor press; so if your bench can withstand you sitting on it next to your arbor press, then you are good to go.

Thread: How to machine out a metal channel by hand?
26/06/2022 12:24:08

Gosh, thank you.

I have only ever had hand tools, so I guess I have learned a certain precision over years of practise. Also, you can plane and sand quite accurately to a line if you are careful to eliminate inaccuracies such as your wrist turning over.

We needed a stand for my wife's rocking horse and I find the normal rocking horse stand pattern with all the horizontal elements to be a bit clumsy, so I came up with a twin tripod design, which is more open. I was careful to design it so that all the loads are compression loads along and through the legs, and not relying on the joins, which only stabilise it rather than support any significant load.

The sequence below shows the process - all done with hand tools.

We are in the process of moving house hopefully, so all now has to be packed away, to be finished after we have moved and I have finally built a workshop !

I will post pictures of the finished piece.


Tripods will fit. I can use cut down pre-made staircase balustrade pieces made from Hickory.


Glueing the first two legs. (I did use a lot of clamps for the glue-up, not shown). 


Tops cut, planed and sanded to size. Adding the third leg


Routing a groove for the metal channel


The twin tripod stand concept


Edited By John Doe 2 on 26/06/2022 12:27:21

25/06/2022 22:37:11

Thank you.

Yes, I put tape over the wood before filing, and washed my hands about 5 times during the process, so I wouldn't get metal filings onto the wood. yes

Edited By John Doe 2 on 25/06/2022 22:39:11

25/06/2022 16:01:30

Well, clamping both stands together did not work because the two channels did not meet perfectly round but slightly oval, so I had to resort to filing each one by hand.

I filed the channels and also the hoops too, because the bar the hoops are made from did not have a very round cross section, so they jammed on part of their swing. I used a half-round file and a round file wrapped in sandpaper for the channels. For the bars I used a flat file with that opposite action one uses for filing a smooth curve where you move the file opposite to the curve you are filing instead of following round the circumference - can't think how to describe it but I expect you know what I mean.

It wasn't a huge job in the end, luckily, and it all fits very nicely and freely now. I will add a hint of grease on final assembly, and possibly a cover over the top of each hoop. Got to finish the wooden stand next.

Thanks again for your suggestions.


25/06/2022 11:51:38

Thank you all very much for your time and suggestions.

The first great idea was clamping the two stands together to form an approximate tube to machine out. I had not thought of that.

I do not want to file the hoop pieces as that might weaken them or leave stress risers on the metal - it's quite a heavy horse. Also, I won't be able to hand file them perfectly round.

I would rather not remove the channels as that will probably mark or damage the wood. They are epoxied in and I should of course, have double checked the fit before glueing the channels in. A classic case of "measure twice, cut (or glue) once" !! (but see below)*

I am going to try clamping the two stands together and then running a 10mm drill through, then emery paper taped and wrapped around a smaller diameter drill, or a piece of dowel to open out the channels. At least that will result in reasonably concentric channels, my hand filing won't be quite as good. Hopefully there is only a small amount to remove before the hoops will drop in.

Once they do, I will put some valve grinding paste in the channels and rock the horse to smooth everything out, then clean and lightly grease.


*Part of the problem is that this was originally all a secret for my Mrs, whose horse it is - it had no stand when we bought it. So I could not keep going back to the horse to check measurements or the fit, because that would have given the game away. I hope she appreciates all my work ! By the way, I do not like the traditional rocking horse stands with the long horizontal pieces running under the horse, hence my dual tripod design.


PS, I have a garage, with hand tools and hand held router and drills etc, but not a workshop, or even a vice, (yet). I made the wooden stands by using pre-turned baluster sections for making staircases and very carefully hand cutting them to fit together and glueing it all up.

The hoop rods really are 10.20 mm - 10.30 mm diameter - measured with callipers.




Edited By John Doe 2 on 25/06/2022 11:52:29

24/06/2022 17:13:26

Thank you so far, liking that last suggestion.


Just to reinforce, I have no workshop, so cannot make new hoops, and the channel is already glued in. (Yes, I's a cock-up on my part).


Edited By John Doe 2 on 24/06/2022 17:15:21

24/06/2022 16:43:59

Hi folks,

I need your advice. I am making stands for our rocking horse, but the channel I glued in, made from some metal pipe, is a slightly too small ID for the support hoops' OD. (I know, schoolboy error!).

How can I relieve the channel neatly to allow the hoop to seat properly?

I have no workshop or milling machine etc, so need another way to do it - filing by hand would probably be too hit or miss?

I was wondering about something I can put in my 1/4" router and move along, grinding out the channel from above, or maybe a parallel reamer?

The channel measured 10.00mm ID and the hoop OD measures 10.20mm, (I originally thought they were the same).

Any thoughts?



Edited By John Doe 2 on 24/06/2022 16:48:18

Thread: Fiber optic cable
14/06/2022 12:58:19

I heard that BT can 'blow' fibres down their existing cable ducts, using an air source to carry the fibre along the duct without having to dig up the roads. Clever stuff.

I am just back from televising the Leeds Triathlon, where we used the fibres installed at Roundhay park for some of our circuits crossing the site. We had a lot of problems, but to be fair, it was mostly the short fibre adapters of ours at each end that were duff.

Outgoing links were on satellite, so no problems there.




Edited By John Doe 2 on 14/06/2022 12:58:46

Thread: Milk container top colours
26/05/2022 15:55:56

I had to walk to the local shop to get some emergency milk, and on the way back, I suddenly wondered why the colours for full fat, medium and skimmed milk are blue, green and red respectively?

I would have thought yellow for full fat, cream colour for medium and, I don't know, clear for skimmed - would have been more logical and more closely reflect the colours of the actual milk. Too subtle maybe?

What about red, amber and green for full, medium and skimmed - at least that would use the traffic light system for fat content and sort of make sense.

But the present colours; where did they come from ?



Edited By John Doe 2 on 26/05/2022 15:58:42

Thread: Crates to transport Meddings MF4/5 ?
09/05/2022 12:24:24

Many thanks for all the suggestions - much appreciated.

I had not thought about using a pallet truck and will construct my crates accordingly. The min internal dimension between a pallet truck arms is 540 mm?

I will make two crates, one for the head and another for the base, drill table, chuck key rest, etc.

One thing I will need but cannot make and don't know how to obtain; is a short length of tube to fix the head to the collar piece that bolts to the base (foot). The head and the actual base itself in one crate will be much too heavy, so I am thinking to bolt just the collar piece to the floor of the crate and fix a short bit of tube to put the head on and hold it central in the crate.

I measure the Meddings support tube to be 80 mm / 3.15" OD, and it would need to be around 400 mm long - doesn't have to be metal, just strong enough to hold the head from falling sideways.

06/05/2022 14:17:09

Half question, half answer possibly.

We will be moving house soon and I am thinking I should make a wooden crate to make it easier and safer to transport my Meddings floor standing drill press. Well two crates, one for the head, one for all the other components, base, table, chuck etc, and the mounting post will be carried separately.

I am thinking a simple wooden box made from 9-12 mm ply, with a thicker base, reinforced at all the joins and with hand holds that will secure the head safely inside, and make it easier for two lads to lift. Ditto the other components - I might even remove the motor and put it in the second crate to lighten the first crate.

Any thoughts or tips?


Thread: New To CAD? No, but....
06/05/2022 13:57:59

Learning something thing such as a new CAD or a new smartphone operating system, is similar to learning a new language, I reckon.

Our young brains automatically absorb new languages, but after around 9-12 years of age, that system shuts down and it becomes much harder for us. I think this is why children seem so bright at programming the video, or sorting out their computers, but their parents or grandparents sometimes struggle with a new device or a completely novel system.

In my youth, I just absorbed computers and computer programming, writing my own code etc. Now, I don't find computers to be quite so intuitive, and I have to look up how to do things that I used to find easily by informed guesswork or trial and error.

What we learned in our youth can be built on, but if we had to learn a new foreign language in our later years, it would take conscious study, repetition and constant practise to become semi-fluent, because our language learning centres have shut down.


Edited By John Doe 2 on 06/05/2022 13:59:29

Edited By John Doe 2 on 06/05/2022 14:01:35

Thread: Emergency Radio Format
05/05/2022 14:11:08
Posted by Anthony Kendall on 04/05/2022 11:25:11:
Posted by SillyOldDuffer on 03/05/2022 16:33:22:

Britain's nuclear submarine commanders are allowed to launch their Trident missiles in the event they can't hear BBC Radio 4 on 198kHz. Low frequency radio not only has long distance ground wave, it penetrates underwater too. A submarine can detect BBC Radio 4 almost anywhere in the North Atlantic without surfacing and revealing it's position.

Unfortunately, the BBC has many enemies working hard to kill the institution. Be ironic if lefty comedians were stopped from pointing out political blunders and sleaze due to a "don't bother me with mere details" enthusiast not understanding what the Archers is really for!


Most of what you say is true about LF being received underwater.

Regret to distort a good story with facts but, communication with submarines is nothing to do with Droitwich Radio 4.

If there was no R4 LF, we would lose only the shipping forecast, Morning Service and cricket. All are available from other sources.

I think the point is that if the submarines do not hear the BBC and chimes of Big Ben etc., they will assume that London, at least has gone. But the military talk to the subs by other means. Or maybe 'The Archers' does in fact contain secret military instructions !! teeth 2

Even Putin - mad as he has become - knows that if he sets off a nuclear device, then Moscow and half of Russia will also cease to exist. My Dad was on Quick Reaction Alert on the nuclear armed Vulcan bombers during the Cuban Missile crisis, and his primary target was a small city in Russia of between 500,000 and 1,000,000 people.

03/05/2022 10:21:13

Can I just say, ChrisB, what a nice installation you have built there ! Good engineering to keep the heatsink cooling air completely separate from the electronics, and well done for lining up the front panel with the circuit board switches - that must have taken a couple of attempts.

And proof, if it were needed, that the front panel switches of a VFD are not designed for heavy use - you can see (the five yellow dots near the readout display); they are just tiny circuit board switches, not designed for heavy regular workshop use.

Thread: Electric bike fault
02/05/2022 10:28:09

Yes, or simply rig up a couple of wires piggy backed onto the battery supply, so the supply voltage can be read while the bike is operating. Obviously, be careful trying to read your meter while riding the bike !! - build a secure temporary rig that doesn't need to be held or anything to see the voltage.


It might be worth knowing that some electric bike companies are taking advantage of the "green" and "eco" revolution and charging a huge mark-up.

I nearly bought an add-on electric bike kit, comprising a replacement wheel with an electric hub, the battery and control etc. The company said they normally charged £1,000 but as a special introductory offer, the price would be £500.

Some research by myself and my son revealed that the components are readily available from China for a few hundred pounds retail - presumably less wholesale. So I shelved the idea.

So I am extremely suspicious about a battery costing £600+ That sounds like blatant robbery to me. If it were mine, I would look into purchasing new cells and re-cell the battery myself. And/or research a good quality balancing or rejuvenating charger.



Edited By John Doe 2 on 02/05/2022 10:41:22

01/05/2022 13:35:06

In my professional and personal experience, about 80% of electrical and electronic faults are caused by bad electrical interconnections, not the actual circuitry or components themselves.

My approach would be to disconnect and clean with switch cleaner spray, (WD40 now do one), as many of the electrical interconnections as you can - ideally all of them - both on the control side and the high current motor circuits. Use an old, clean toothbrush to carefully clean all the connector pins. Allow the connectors to dry out, then reconnect and disconnect a few times to 'wipe' the contacts against each other - all with the battery disconnected.

The problem might be in the controller, which might use conductive plastic switches - similar to the sort in your TV remote. These might have got condensation in the switches; causing spurious demands to the controller. They might be tricky to get to and clean. If so, maybe put the controller in a bowl of (uncooked) rice or desiccant, and/or in the airing cupboard for a week.

You might have a problem with the battery - but unlikely since you say a new battery does the same thing. Could be the battery internal control board - if you can get to it, clean all the connections as above. Rechargeable batteries usually require a few full charge/discharge cycles to achieve their full capacity; perhaps one or both batteries just need fully charging and discharging a few times - worth a try anyway. If the batteries are cheap, or if 6 years has gone by; individual cells might have become discharged, in which case a battery balancer might help, but only if the batteries and charger are designed to do this.

Finally, have a careful visual inspection of all the components and the wiring - something might have got damaged or pinched somewhere.

Good luck !



Edited By John Doe 2 on 01/05/2022 13:43:12

Thread: Galvanic Corrosion
01/05/2022 12:52:08

Turn fitting over and build a dam out of plasticine or some thing around the screw head. Fill with penetrating fluid and leave for a few days. Remove and dry off the surface fluid and gently heat the surrounding metal. Then try an impact driver, (electric or air), set to its' lowest force setting, and applied in alternate directions a few seconds each way?

Thread: Seeking advice on mains equipment earthing
22/04/2022 10:10:47

Something I was taught many years ago is to make the earth wire longer than the 'live' wire inside a plug or a machine connection.

So in a 13A plug I make the 'live' wire just long enough to reach the live terminal but I make the earth wire longer than it needs to be with a loop or a fold so if the whole lead got pulled, it would tear out the 'live', leaving the earth wire still connected. Or if the lead was completely ripped out, the earth would be the last conductor to be disconnected.

This sort of follows on from properly designed mains plugs in which the earth conductor is the first to make contact when plugging in and the last to disconnect when unplugging - owing to the earth pin being longer than the other pins.


Edited By John Doe 2 on 22/04/2022 10:17:18

20/04/2022 12:02:36

Yes, The fuse in a mains plug is there to protect the cable from the plug to the device from overheating or melting, so the fuse needs to be rated for the cable size, not the plug capacity. Not many plug connected household appliances draw 13A, which is about 3 kW ! But too many small devices are, or used to be, supplied with a 13A fuse.

My understanding is that unless a device is double insulated, (and shows the double square logo), any external metalwork should, ideally, be connected to earth.

The earth lead is there to carry sufficient current to blow the fuse in the plug if the metalwork becomes live, thus disconnecting the device from the supply.




Edited By John Doe 2 on 20/04/2022 12:07:12

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