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Old 29th Sep 2017, 2:32 pm   #1
astral highway
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Default Large inductor lathe wound to a spec?

Hi folks,

Some of you will be familiar with my large valve Tesla coil project, which has been on ice because of some health problems. I've just sat down and done a whole load of maths and have concluded that I will only get lacklustre results with the current main inductor. This is because of poor impedance matching with the valve and Q, which is partly a function of the high operating frequency of the current build, as well as some other parameters. Rather than bashing my head against a brick wall, I'm considering a new approach.

I'm interested in scoping out if anyone would wind a new inductor for me, to a spec. I don't know it exactly yet, but to give you an idea, something like
1000 turns of 0.4mm wire on a suitable former. This could be a postage tube, but I would source the dimensions. I would just be asking you to wind it, put an initial protective coat of polyeurethane varnish to keep it safe it transit and then leave the rest of the prep to me.

I have previously done this job by hand and have also made a winding jig in the past, but I no longer have access to facilities that would enable me to produce this.

Please could you indicate whether you'd be theoretically capable and interested in doing this, for an appropriate fee.

I am also interested in lexan or other high-dialectric cylindrical offcuts for winding large primaries. Please post and PM. All of this isn't huge urgent but would be nice to get something going in November.

Cheers,

Al

Thank you.
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Last edited by astral highway; 29th Sep 2017 at 2:41 pm. Reason: forgot something
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Old 29th Sep 2017, 5:35 pm   #2
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Default Re: Large inductor lathe wound to a spec?

If you give an idea of the diameter and length, people will know whether their lathe is big enough.

David
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Old 29th Sep 2017, 6:02 pm   #3
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Talking Re: Large inductor lathe wound to a spec?

1 metre diameter, 4 metres long??

Only joking, I'll leave that a 15kW broadcast transmitting tube thought-experiment.

But good call, David. I'll do a few calcs as soon as I can and update. Realistically, that will be some time next week if mods happy to keep this open?

Thank you
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Old 29th Sep 2017, 7:33 pm   #4
Ed_Dinning
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Default Re: Large inductor lathe wound to a spec?

Hi Al, there have been all sorts of tubes on ebay at different times, from SRBP/ Paxolin, glass(a very good material for coils) and a whole variety of poly*** types. as well as ceramic tubes.
The difficulty could be finding the material constants of these things, probably not quite so difficult these days with Google etc.

If you are going big for the coil, have a look at cable re-reeling machines!

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Old 29th Sep 2017, 7:34 pm   #5
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Default Re: Large inductor lathe wound to a spec?

Look up "Dean Smith and Grace" on this link and scroll down to an old photo "Main Assembly department" now you need to find someone with one of the ones nearest the camera....

http://www.lathes.co.uk

It can be done!

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Old 29th Sep 2017, 10:55 pm   #6
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Default Re: Large inductor lathe wound to a spec?

Tesla coils are pretty easy to wind by hand. A lathe makes it faster.

These two were both made by hand.

Joe
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Old 30th Sep 2017, 3:13 am   #7
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Default Re: Large inductor lathe wound to a spec?

Years (Well several score of years back, actually) ago I built a dual band antenna project for 40 & 80 M. from 73' Magazine.
I took a PVC pipe to a local machine shop and had them cut threads on it at a certain Turns Per Inch.
That made the coil so easy to wind, and the grooves kept the wire in place. Not terribly expensive at the time. Just a thought.
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Old 30th Sep 2017, 8:16 am   #8
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Default Re: Large inductor lathe wound to a spec?

Cutting a groove (about 64 TPI) for 0.4mm wire is a good idea, but "Local Machine Shops" are a thing of the past, at least they are round here.
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Old 30th Sep 2017, 11:46 am   #9
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Default Re: Large inductor lathe wound to a spec?

Quote:
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... "Local Machine Shops" are a thing of the past, at least they are round here.
Yes! I live in an aggressively gentrified part of London, and in the 20 years I've been here, even the lightest industry has gone - along with car breaker's yards, the lot.

I love the idea of going into such a shop, but it would have to be after 1.21 GigaWatt hook-up Back To the Future! Flux capacitor charging!!
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Old 30th Sep 2017, 11:48 am   #10
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Default Re: Large inductor lathe wound to a spec?

Quote:
Originally Posted by joebog1 View Post
Tesla coils are pretty easy to wind by hand. A lathe makes it faster.
Hey Joe, I've made four (secondaries) by hand in the past, and I no longer have the facilities or capacity to make a jig here. I don't feel minded to wind another one, especially of the size I'm intending, by hand!
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Old 30th Sep 2017, 12:25 pm   #11
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Default Re: Large inductor lathe wound to a spec?

Several forum members, including myself, have screwcutting lathes, but we need more details of the job.
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Old 30th Sep 2017, 1:00 pm   #12
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Default Re: Large inductor lathe wound to a spec?

There are still some small machine shops in Slough, proper ones too.
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Old 30th Sep 2017, 5:23 pm   #13
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Default Re: Large inductor lathe wound to a spec?

Quote:
Originally Posted by Station X View Post
Several forum members, including myself, have screwcutting lathes, but we need more details...
Hi there, that's encouraging. I'll do some more inductance calcs next week and see if I can source the former in lexan, my preferred material , and the dimensions . I think it would be nice to have perfectly uniformly wound turns , especially given the voltage gradient between adjacent turns.

The previous one I made is a beast - it weighs a few kilos , including multiple coats of polyeurethane varnish and then potting compound for good measure. It took ages including the hardware I devised to secure it in position - so the next one I have to get spot on !

Mods can we keep this open until I update with the spec please ?
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Old 30th Sep 2017, 7:05 pm   #14
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Default Re: Large inductor lathe wound to a spec?

Quote:
Originally Posted by Radio Wrangler View Post
Look up "Dean Smith and Grace" on this link and scroll down to an old photo "Main Assembly department" now you need to find someone with one of the ones nearest the camera
Ah DS&G! Did my training in 1973 on one of their toolroom lathes. Happy days.
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Old 30th Sep 2017, 7:43 pm   #15
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Default Re: Large inductor lathe wound to a spec?

1000 turns of 0.4mm dia wire in a single layer will occupy 400mm so the former will need to be a bit longer than this to allow for terminations, mounting points etc.

Most amateur lathes tend to have a centre height of less than 5" and to do this job the lathe's saddle will need to pass under the former. So a 6" diameter former might be the limit.

I expect someone will now respond saying they have a gasometer turning lathe.
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Old 30th Sep 2017, 7:54 pm   #16
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Default Re: Large inductor lathe wound to a spec?

Hi Al, the thread method should work fine, but from dim memory I think you may get better results if the wire is pitched at twice its diameter. This is easily done if you cut a 0.8mm pitch thread.

Ed
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Old 1st Oct 2017, 3:00 pm   #17
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Default Re: Large inductor lathe wound to a spec?

Hi Ed, thank you, so you mean the wires shouldn't actually be contiguous (touching side by side) but have a gap of one diameter? Is that right?
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Old 1st Oct 2017, 7:13 pm   #18
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Default Re: Large inductor lathe wound to a spec?

Hi Al, yes that's it.
There will be some theory about it somewhere and I think twice wire dia was the optimum, dead easy to achieve if the tube is screwcut.

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Old 2nd Oct 2017, 10:16 pm   #19
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Default Re: Large inductor lathe wound to a spec?

If you have to, you can do it the way I did.
Wind the wire AND some string, the same size as the wire diameter to keep the spacing.
Ed Dinning has it

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Old 3rd Oct 2017, 8:28 pm   #20
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Default Re: Large inductor lathe wound to a spec?

Quote:
Originally Posted by Ed_Dinning View Post
There will be some theory about it somewhere and I think twice wire dia was the optimum
That's interesting, Ed. Thank you. I'll have to model the change in inductance and also consider how easily I can accommodate the doubled length! Alternatively I may have to find a wider diameter former.
I'll do some research and come back when I've made some decisions!
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