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Old 15th May 2023, 10:35 am   #1
Ian Bailes
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Default Fine wire gauge

I would like to try rewinding a coil from an old electric clock but how do I determine the gauge of wire needed? The original copper wire is very fine.
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Old 15th May 2023, 10:40 am   #2
wave solder
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Default Re: Fine wire gauge

There is lots of advice on here on refurbishing electric clocks such as this:- https://www.vintage-radio.net/forum/...ad.php?t=74480
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Old 15th May 2023, 10:44 am   #3
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Default Re: Fine wire gauge

Unwind a length, measure resistance and calculate the ohms per metre.

Then you can use wire tables to find the gauge - it's difficult trying to use a micrometer on really fine wire - especially as the enamel adds to the thickness and it's difficult to see if it's removed or not!
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Old 15th May 2023, 11:25 am   #4
Ian Bailes
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Default Re: Fine wire gauge

Quote:
Originally Posted by wave solder View Post
There is lots of advice on here on refurbishing electric clocks such as this:- https://www.vintage-radio.net/forum/...ad.php?t=74480
Thanks for the link, just had a quick look and it looks like the answer is all there.

Much appreciated.
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Old 15th May 2023, 11:26 am   #5
Ian Bailes
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Default Re: Fine wire gauge

Quote:
Originally Posted by kalee20 View Post
Unwind a length, measure resistance and calculate the ohms per metre.

Then you can use wire tables to find the gauge - it's difficult trying to use a micrometer on really fine wire - especially as the enamel adds to the thickness and it's difficult to see if it's removed or not!
Thank you, I'll give that a go.
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Old 15th May 2023, 11:58 am   #6
David G4EBT
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Default Re: Fine wire gauge

When you say 'very fine' the finest SWG gauge you'll find is 50SWG - I doubt it's as fine as that.

Here are the SWG gauges from 40 to 50 SWG, in mm and inches:

40 SWG = 0.121mm / 0.0048"
41 SWG = 0.111mm / 0.0044"
42 SWG = 0.101mm / 0.0040" (4 thou)
43 SWG = 0.091mm / 0.0036"
44 SWG = 0.081mm / 0.0032"
45 SWG = 0.071mm / 0.0028"
46 SWG = 0.060mm / 0.0024"
47 SWG = 0.050mm / 0.0020" (2 thou)
48 SWG = 0.040mm / 0.0016"
49 SWG = 0.030mm / 0.0012"
50 SWG = 0.025mm / 0.0010" (1 thou)

You'd need to measure the gauge (easiest on digital callipers).

At Wires&Co (Retail arm of The Scientific Wire Co), in the sidebar menu under 'Copper', what you need is referred to as 'enamelled copper magnet winding wire'.

It's best to get solderable enamelled copper, which you don't need to clean or tin. EG:

50 grams of 0.032mm (49SWG) Solderable Enamelled Copper Wire (approx: 139 km/kg, 21.25 ohm/mtr at 20C)

To put that into perspective, 50 grams is only 1.76 ounces, yet it's 6.95 kms long.

It would set you back £25.33 inc VAT:

https://www.wires.co.uk/acatalog/SX_0032_0090.html

When you've checked either the gauge or Ohms/Metre, you'll be able to search Wires&Co's website for the correct gauge you need. The less fine it is, cheaper it gets, (and of course the easier it is to wind), but the Ohms/Mtre drops significantly with each gauge. EG:

50 grams 0.050mm 47 SWG Solderable Enamelled Copper Wire (approx: 57 km/kg, 8.70 ohm/mtr at 20C) Price: £12.19 Exc UK VAT (£14.63 Inc 20% UK VAT)

https://www.wires.co.uk/acatalog/SX_0032_0090.html

Hope that helps a bit.

Good luck with it Ian.
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Old 15th May 2023, 3:33 pm   #7
Ian Bailes
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Default Re: Fine wire gauge

Thank you so much David for your detailed response. I didn't appreciate that I could measure the thickness with digital callipers, I thought the wire would be too thin. I've now measured the existing wire in several places and it pretty much consistently comes out at 0.05mm (so 47 SWG), and exactly the example item you described.

I'll now place my order with Wires&Co.

Thanks again.

Ian
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Old 15th May 2023, 4:23 pm   #8
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Default Re: Fine wire gauge

Hi Ian, a micrometer is often better for the finer gauges and do not forget you will be measuring the diameter over the enamel. Wire tables will give you the bare size/ gauge number.

Using 0.071 or 0.063 and filling the bobbin will give you about 10,000 turns plus. This seems to work fine without needing too much precision

Ed
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Old 15th May 2023, 5:56 pm   #9
Ian Bailes
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Default Re: Fine wire gauge

Quote:
Originally Posted by Ed_Dinning View Post
Hi Ian, a micrometer is often better for the finer gauges and do not forget you will be measuring the diameter over the enamel. Wire tables will give you the bare size/ gauge number.

Using 0.071 or 0.063 and filling the bobbin will give you about 10,000 turns plus. This seems to work fine without needing too much precision

Ed
Thanks Ed, That's really good to know.

Thank you for taking the time to share your knowledge.

Regards

Ian
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Old 15th May 2023, 11:11 pm   #10
David G4EBT
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Default Re: Fine wire gauge

Quote:
Originally Posted by Ian Bailes View Post
Thank you so much David for your detailed response. I didn't appreciate that I could measure the thickness with digital callipers, I thought the wire would be too thin. I've now measured the existing wire in several places and it pretty much consistently comes out at 0.05mm (so 47 SWG), and exactly the example item you described.

I'll now place my order with Wires&Co.

Thanks again.

Ian
To be sure about the gauge, before ordering, you might wish to measure the Ohms per Metre of your wire, to see if it’s about 8.7 Ohms per Metre, which would equate to Wires&Co 47 SWG.

Good luck with the re-wind.
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Old 17th May 2023, 9:52 am   #11
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Default Re: Fine wire gauge

For these very fine guages you can expect the insulation to add at least 10% to the overall (measured) wire diameter.

See e.g.

https://www.elektrisola.com/en/Produ...-Data#iec60317
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