Member postings for Andy Ash

I've not read the whole thread, so forgive me if I've repeated something someone else said. Looking at this, it's an ideal application for a "buck regulator". The problem you have is the relatively high power dissipation dropping from 12 to 2ish volts at 270mA.

That's always going to be 2.7 watts in any linear situation. Its not that you can't get a resistor or transistor to handle that, but it's wasteful - especially if you're using a 12V battery.

You can get a buck regulator ready made circuit from ebay, but you can make one too. Broadly it is an oscillator which switches a pass transistor through a diode and an inductor in a PWM fashion. You could use a 555 timer for the oscillator. There is a feedback loop and an error amplifier which are used to control the mark space ratio of the transistor drive. The error amplifier is just a simple op amp, and the transistor drive is a comparator.

If the voltage is too high then the transistor tends more off than on. If the voltage is too low then the transistor tends more on than off. The inductor smooths the output jiggles into a DC voltage.

By only allowing through the required charge, and switching very quickly, the resistive losses are eliminated. If you build the buck regulator from discrete components, it's quite a complicated task. If you buy a buck regulator chip you can just follow the instructions on the datasheet and it will work fine.

An example device is MC33063 which can be used in buck, boost and inverting configurations. It's a £0.40 8 pin part, easily available everywhere despite the chip shortage.

Edited By Andy Ash on 10/11/2022 01:45:52

Nice post. I've been waiting for an update on that for a couple of weeks now.

One of these fine days, the youngsters will realise that the UK is actually made of coal.

When they get cold and fed up, they'll figure out how to get it out of the ground and how to keep warm by it.

Good luck to them. If I'm lucky, they might even figure it out before I fade away.

The headstock bearing adjustment makes a big difference and it is worth getting it right. If it is too tight or too loose, the tapered bronze bush wears, and that is quite hard to replace and scrape back in.

Get the proper C spanner. Anything else just chews up the castellated nuts. Once those are gone get some new ones. You need to make a fine adjustment here, and it's just not possible without the right spanner and well fitting nuts.

Actually it's quite hard to get the fineness of adjustment if the bearings are shot too. If everything is good the line between too tight and just right is quite clear. If you can't find the boundary replace the nuts/bearings. Don't lose the shim between the two bearings when you change them. Make sure you fit the bearings the correct way around.

You don't need the bearings with the super duper ceramic cages. Brass cages are nice, but the plastic ones are just as good. I don't know about inflation but you could change the bearings and the nuts for less than £100. The whole machine can be transformed if the ball races were shot.

Mine gave better finish, more accurate work, and it was happier with a much deeper cut. It was also much happier (and quieter) at top speed.

Edited By Andy Ash on 09/05/2022 01:54:18

ACME is quite doable if you have a Myford 7, but there are a couple of things to think about.

Smaller than 1/2" you need to use a tap, but larger you can use a boring bar. I made a boring bar from essentially a tube and a rod. The rod is threaded on the end, and when you tighten a nut against the tube the rod is pulled through.

If you cross drill both the tube and the rod somewhere near the far end, then you can poke a bit of round HSS through both - sticking out sideways. By tightening the nut, the HSS round is clamped in place. You might make a couple of these with the hole drilled at different angles. A 45 degree angle is good for boring to a deep shoulder. 90 degrees is good for threading.

It saves a whole load of relief grinding.

The smallest easily available HSS round is 1/8" and this suits a boring bar of perhaps 3/8" in diameter. As you can imagine a 1/2" ACME tapping hole is pushing things quite a lot.

You can get ACME left and right hand taps from Tracy. I have found it is quite useless to try and drive them by hand with a wrench. They just act like reamers. Your really have to push them through.

It is much better to put the prepared nut in the vertical slide and have the hole central on the lathe axis. Then set up for screwcutting with a pitch the same as that of the tap. Put the tap in a collet chuck in the headstock so it cant slip. Drive the nut to be, onto the rotating tap using the lathe leadscrew.

The ACME taps I use are quite long. They won't go through in one go. You will have to back up and clear the chips. As long as the pitch of the tap is imperial, you will be fine on a Myford 7. The rules are the same with respect to disengagement of the leadscrew as they would be for screwcutting.

If the pitch is metric, then you will have more trouble. The lash is too great to simply back up by reversal, leaving the half-nut engaged. It will destroy your new thread as you back out and clear the chips. Instead, you will need to release the tap from the collet chuck. You can then wind it out by hand. To pick up again, set the tap to position manually. Take up the lash and then clamp the collet chuck before proceeding under power.

For a 3/4" thick nut and a 1/2" ACME tap you will need to clear the chips four or five times. The tap for this operation will be be 8 - 9" inches long. It will taper from nothing (core diameter) to full depth over a length of perhaps 6".

I get a really nice nut this way. Very little play - like a bought one.

Hope it helps.

Edited By Andy Ash on 17/04/2022 02:43:42

It's all about boundaries, I think.

If you look at an ice cube, then you're going to say "It's a solid".

If you look really closely then it has a little puddle of water on top. Obviously that isn't a solid.

They say that a flame isn't a plasma because it isn't hot enough. If you get the flame hot enough it can be a plasma.

If you lower the pressure, then the flame doesn't have to be as hot to become a plasma.

It still has unburned reactants and combustion products in it, even at reduced pressure.

If you took the wet ice cube and crushed it into a Slush Puppy, no-one is going to call it solid any more.

I don't know about anyone else, but that makes sense to me.

My welder does plasma cutting. I don't know if that makes my machine a plasma cutter or a welder?

The plasma process is Direct Current Electrode Negative, just like the majority of TIG work. The air valve is the same for Argon/TIG as compressed Air for plasma cutting. To switch between you just connect the compressor instead of the shielding gas cylinder.

It does have a different positive connection for the clamp when you are doing plasma cutting. The plasma torch is set up for contact start even though the welder has HF start. I think the plasma clamp connection on the front of the machine excludes the HF start coupling coil, but it is a while since I had the lid off.

Edited By Andy Ash on 14/02/2022 00:25:02

I have a cheap Chinese mill, it's the next size down from yours, and mine was made badly.... In a bad part of China.

You might get away with more than I do, but I don't think I would even bother trying to hog this out of plate. I have ended up upgrading a stent cutter grinder so I can keep my cutters razor sharp. I get away with a lot more since I did that. I try to use the biggest cutter I can, to maximise tooth life. I have modified the mill so it can go fairly slowly and still have grunt.

In your situation with my machine, I'd have the blanks laser cut and finish them on the mill as option one. Second option would be to make a disposable MDF template and use the plasma cutter to burn them out of plate, before finishing them on the mill.

If it had been mild steel, or even tool steel, you would have got away with it. since it is Stainless, you probably would have had the same problem even if you had a strong milling machine. It's the cutter that's weak, and unless it's a nice thick side and face cutter, a slitting saw will be the same.

Use the time honoured technique of drilling with a nice fresh drill, then cutting away the worst of it with an HSS hacksaw. Then when you're done, finish it with the endmill, or a nice thick slitting saw (at least 3/32", especially if it can cut on the sides.

Given it would probably be a one sided finish cut after the hacksaw treatment, obviously plunge the slitting saw. You can still slice with a side/face cutter.

There is no way this is overkill. The early developers of space flight systems learned the hard way that satellites go into space and disappear. They soon learned that the need for meticulous quality is very high indeed.

The main problem for aircraft electronics is vibration, and the main problem for space flight is thermal vacuum.

Vibration causes work hardening and fatigue. Thermal vacuum causes the growth of tin whiskers and outgassing.

For space, most manufacturers use special PCB substrates that are not based on epoxy resin due to outgassing of volatiles. If they can, they avoid solder altogether in favour of gold plated mechanical connections. Otherwise electronic systems have to go through vacuum bake-out to ensure reliability "on orbit".

If the soldering isn't good enough the system won't pass bake-out, but it might still fail in space even if it passes. There's no mechanic up there to fix anything, and the launch alone will cost millions.

You have to get it right first time.

Edited By Andy Ash on 31/01/2022 18:52:53

It occurred to me recently that one of the few "high tech" nations that is reasonably environmentally sustainable is actually North Korea. I think they're "high-tech" on the basis that they have some kind of space/missile program and more than a passing capability in commercial and military nuclear power.

At the time of the Korean war, they had the bulk of the heavy industrial capability in the Korean peninsular.

All this time later their industrial goals have withered and although their per-capita carbon efficiency is quite poor, their lack of commercial activity means that they have a fairly low environmental impact overall.

No part of me wants to live like a North Korean. For me the truth is that this is the required direction of travel, to meet the environmental obligations that have been set out. I don't actually think people will put up with it unless it is brought on slowly. As I look at things, I have to conclude that's exactly what is happening.

Edited By Andy Ash on 11/01/2022 16:30:55

There is a lot of confusion about the meaning of CE mark. To a consumer, generally it has the meaning "of Commercial Origin".

The implication for the creator of the goods is the most significant. If the creator is found to be placing the mark inappropriately, then he/she can be legally pursued and stripped of his/her right to place the mark.

Basically anyone is allowed to place a CE mark (unless that right has been formally revoked). Generally non-commercial items should not wish to (nor should) apply one. Its non-placement absolves (to some degree) the creator of responsibility. Consumers should expect to see it on supplied goods, because it indicates that they can (perhaps) hold the creator responsible.

It would not be advisable to place the CE mark unless one had public liability insurance to cover the accountability/responsibility that it implies.

The CE marking has no specific meaning outside of indicating the scope of responsibility, should a problem occur.

This advice applies to any kind of product, not just pressure vessels.

Edited By Andy Ash on 04/01/2022 10:58:41

"The Myford ML 1,2,3,4, series were all hobby machines built to a price."

The ML1,2,3,4 must have been military spec too. Mine has an RAF "War Department" plate on it!

I would never claim that the ML1,2,3,4 were high quality lathes, mind you.

I think the Ministry of Supply would buy anything in those desperate days.

I'm not an expert on Nuclear Physics, and this is probably a case of "Famous Last Words", so I'm knocking on a hardwood table to be double sure!

As I understand it the PWR reactors will be fine. The AGR reactors are showing problems with the graphite moderators cracking. I've seen some photographs on the internet in the past, but I can't judge if the cracks are bad or really bad. Obviously they would probably be much better better without them, but they're old ladies now!

All I know is that the worst thing for them is thermal cycling. I'm fairly sure that the main enemy for these reactors is "turning on and off again". This seems to be a common solution for many modern systems but not nuclear reactors, I'm sure.

Probably better flat out all the time, than constantly changing the power output.

I recently had call to cut a 2.5mm pitch thread using my Super7 QC box. I knew about this forum thread from way back and already knew which gears I would need to make the metric thread. Back when I figured it all out I didn't know what metric thread pitch I might want to cut, so I always assumed I would buy an involute cutter when I needed one to make the required gearwheel.

With Coronavirus and the supply shortage I have discovered that the correct involute cutters aren't easily available, nor are the gears. I had always assumed that my ordinary PLA filament 3D printer would not make a gear strong enough for metric screwcutting on the Super7.

Pressed by shortage of availability I gave the idea a try despite thinking it wouldn't work. I can report well of the results. I was easily able to cut an accurate 1.5mm pitch internal ACME thread, into a mild steel bush. It's a substantial thread and quite a long job, but the 3D printed PLA gear shows no sign of distress at all. I still wonder if the oil will affect it in storage, but even if it does I can just print another one.

If you're thinking this isn't worth the effort I can assure you that it very much is. I don't think I'll be making gears any longer unless it is for a model where the material actually matters for cosmetic reasons.

Edited By Andy Ash on 25/11/2021 19:46:42

All motors are different, which might sound obvious, but a windscreen wiper motor has been designed to wipe windscreens on cars.

So, they have to deliver high torque, and have to be compact, so as not to impact on the "look" of the car. On the up side, it's pretty easy to have them sited in a high flow air-stream.

A compact high power motor is always going to get hotter than a large heavy one. For the same number of wire turns, the wire can be thicker and the magnets stronger. Weaker magnets means more current required, and thinner wire means more heat for that current.

One way to fix it, is to attach your new saw to the front of your car, and drive around whilst sawing. That way you would get the required airflow.

A more practical solution would be a bigger motor, or different/better gearing.

I suspect you won't achieve cooling equivalent to the automotive environment with a practical fan setup.

Edited By Andy Ash on 16/04/2017 17:49:16

I don't know about Owl, but I have the drawings for Bat.

If you want to find out about Owl, then TEE Publishing do the combined book, "Introduction to Bat & Owl".

I expect you would find most of the information you want there. As Julian has said, the back issues of ME will carry most of the details too. If you're new to Curly's engines, expect to have to make leaps and jumps. His engines are quite deceptive, they look simple, but often there are critical details missing.

In truth, I think that might be half the fun.

Under my bench I have a half complete Bat.

The garden railway fraternity have moved on a bit these days. I must say that although the modern engines look superior, I'm not certain that they really are. As I understand it, many of these locomotives are purchased as kits. I have nothing whatsoever against kits, but it is much nicer to me to see a scratch built engine.

I think many of the kits are gas fired and often only have a single inside cylinder with cosmetic cylinders and motion outside the frames.

Say what you like about the appearance of these smaller gauge offerings from Curly, but they can usually be coal fired and the cylinders are in the right place. It depends on what you want to do, of course, but I'm pretty sure I know what Curly would have thought about the modern models.

Good luck with it. Nothing wrong with the old un's as far as I can see.

I don't know if I'm right, but I feel like saying, polished stainless pin, with a PTFE bushing in the brass wheel.

I'm an advocate of Citric, particularly hot Citric, which is every bit as effective as other more powerful acids.

Some of those more powerful acids don't benefit (as much) from heat, not that you would want to use them that way anyhow.

I've only ever used acid pickle on hard soldered joints. Mainly because the borax flux is so tough to remove.

For soft soldered joints, especially with acid flux, you can just use warm water to clean up. For that I usually use Fry's Powerflow flux and it just works very well indeed.

If you use Rosin cored solder, then you do get a residue. Meths is a disaster for that. It won't shift anything and you get a white deposit which looks really gross. The best stuff I've ever come across for rosin cored solder flux removal is from Electrolube. It's in an aerosol, called LFFR (Lead Free Flux Remover). It even smells fairly nice. Don't breathe it though, it's Cyclohexane. I've no idea what that is, but rest assured that one day someone will recognise it as being bad to small furry nylon bears.

Farnell Pt. No. 1098276

It will lift the sticky deposits. All you have to do is make sure that the solvent has been wiped away before it evaporates. Wherever the solvent evaporates, the Rosin residue will be left. The aerosol has a brush nozzle. You give it a squirt, mush it in with the built in brush, and then dry the solvent with a paper towel. Job done.

Edited By Andy Ash on 14/04/2017 23:00:04