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Where to procure meters?

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Proud Mary

Thu May 12 2011, 06:36PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Ash Small wrote ...

Proud Mary wrote ...

If you have the skill, know how, and facilities to make, for example only, a pocket watch out of metal stock, you might very well be able to make an accurate moving coil meter, but who can say?

It's around 35 years since I stripped one down and repaired it (when I was 12 or 13), but I remember it was very simple.

If I was Magnet18, I'd get one, even a non-working one, strip it down, and have a look at what's involved.

Maybe the simplest way to settle this 'debate' would be for me to make one and post details in the 'projects' thread?

You clearly have skills a whole order of magnitude greater than my own very modest capabilities, and it was wrong of me to judge you by the standards of ordinary men.

Ash Small

Thu May 12 2011, 06:56PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Flattery will get you nowhere, PM.

But seriously, the hardest part I can see is being able to operate a centre-punch correctly.

I generally use a CAD package to print out a template, then sellotape it to the metal stock. It's hardly 'rocket science', but it does involve a modicum of 'skill and dexterity', which generally comes with practice (or is it perseverance?).

magnet18

Thu May 12 2011, 07:47PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

I can make a clock out of 40xx chips, does that count?

I think winding some galvos might be the best option if I can pull it off, though I think I'll go with the stationary coil/ iron needle design.

Patrick

Thu May 12 2011, 08:03PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

magnet18 wrote ...

I can make a clock out of 40xx chips, does that count?

I think winding some galvos might be the best option if I can pull it off, though I think I'll go with the stationary coil/ iron needle design.

If you can do any of this -- ill be impressed, im not so foolish to even attempt it.

Ash Small

Thu May 12 2011, 08:23PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

magnet18 wrote ...

I think winding some galvos might be the best option if I can pull it off, though I think I'll go with the stationary coil/ iron needle design.

Thinking about it, I think the one I pulled apart all those years ago may have been a stationary coil design. Not sure, but I may have been mislead by the fact that they are generally referred to as 'moving coil meters'. (It was a long time ago....)

I think it's certainly worth considering, especially if you want 15 of them, and don't want to pay much for them.

And calibrating them yourself means they will be as accurate as you choose to make them. (ie, they should be a lot more accurate than 'cheap' ones from Ebay). Plus, they will all be identical.

Just my 2 cent's worth.

Proud Mary

Thu May 12 2011, 08:40PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Designing and manufacturing those spiral springs so they provide a linear and proportional reaction across the whole scale looks a ticklish business, even for those who breezed through the selection of ferromagnetic alloys, machining, tapping, annealing, degaussing, and all the rest.

magnet18

Thu May 12 2011, 08:42PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

I'm thinking this doesn't look too bad
02246

Wrap the coil around a pencil, careful cutting of tin-plated steel for the needle, the hardest part I see is a low-friction pivot...

Ash Small

Thu May 12 2011, 09:09PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I did describe a simple low-friction pivot above.

I also agree that this would be the hardest part, but I think I've provided enough info.

If you require more info I'll be happy to elaborate.

EDIT: I seem to remember the one I rebuilt had what looked like a 'bow tie' on the bottom of the needle.

magnet18

Thu May 12 2011, 09:15PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

It would appear that you did... I'll give it a go.

As for the spring, how bout this, mount the whole thing sideways and throw the spring out altogether? Gravity is still good for a couple things I guess...
(for what it's worth I have access to lathes, band saws, drill presses, mills, plasma cutters... ect.
Friends are good, especially when they're directors of large corporations.

)

Ash Small

Thu May 12 2011, 09:33PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Try it, but planar springs (watch springs) aren't that difficult to wind, especially if you incorporate a tensioner mechanism. (they usually have a 'zero' adjustment) You just have to utilize the same method for all of them for conformity.

I doubt you'll need access to the other equipment, but it may come in useful for batch production once you've developed the prototype.

I'd still reccomend getting hold of one and taking it to bits, even if it doesn't work. Maybe your school has a defective one? (that's how I got my first one)

EDIT: Maybe this thread, or the majority of it, should be moved from 'sale and trade' to another forum?

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