How to shorten a ferrite slug? - UK Vintage Radio Repair and Restoration Discussion Forum

stevehertz · 5th Jan 2018, 5:22 pm

I need to shorten a ferrite inductor core slug. The slug is presently c12.5mm long and I need it to be about 8mm. FWIW thickness is 5.8mm. Ferrite is very brittle, so I don't want it to break up during any attempt to reduce its length, although I realise that there will be no process that doesn't pose a risk, it will depend on how well, how carefully it is carried out. I can grind it?, fine saw it?

G6Tanuki · 5th Jan 2018, 5:44 pm

I've successfully cut them using a Dremel with a diamond-disc.

They are brittle, yes - the best technique is not to try and cut clean-through in one action but rather to start by cutting a groove all round the slug at the appropriate point, then gradually deepen this groove by progressively rotating the slug as you cut deeper.

This way, if it does crack the crack will probably end at the groove anyway.

Then once cut, lap the cut end on a whetstone to remove any sharp edges.

dseymo1 · 5th Jan 2018, 5:52 pm

Try immersing it in water while cutting, to dampen the vibration. It works with glass, so may well do so with ferrite.

stevehertz · 5th Jan 2018, 6:02 pm

Ah, good info guys. I keep forgetting about my Dremel for lots of jobs, and I have some fine cutting discs. I'll give it a go.

5th Jan 2018, 6:05 pm

The old method was to notch and snap.

paulsherwin · 5th Jan 2018, 6:15 pm

I've also used a diamond cutting wheel, but it's hard work. Snapping rarely leaves a clean break.

Lloyd 1985 · 5th Jan 2018, 6:58 pm

Where I work we use small ferrite beads for attenuation, we adjust the size of them using a sheet of wet and dry sand paper. We have a small jig to keep it straight, it's just a half inch or so thick lump of steel with a hole drilled down the centre the same size as the ferrite.

Regards
Lloyd

stevehertz · 11th Jan 2018, 5:22 pm

I did it. Based on the advice on here I used my Dremel with a very thin cutting disc in it (brown and c2cm diameter - are they diamond?). As suggested I took cuts all the way round rather than try to cut it through in one go. I held it in my fingertips on the carpet covered top of my workbench and the cutter went through it like butter, no brittleness issues, no probs whatsoever. Very pleased and thanks to all for the advice, and Frank (Nuvistor) for the slugs to use.

Nuvistor · 13th Jan 2018, 2:41 pm

Did the slug help with the tuner problem?

stevehertz · 20th Jan 2018, 3:15 pm

Quote:

Originally Posted by Nuvistor

Did the slug help with the tuner problem?

Unfortunately, no. The slug barely dropped into the end of the inductor tube as the existing one is too near the top. Also, I can see that the thread is different anyway.

I've asked a Tandberg friend if he can help with a spare inductor, tuner assembly or even a scrap set but no joy so far so I will also place a wanted ad on this forum.

Nuvistor · 20th Jan 2018, 4:03 pm

Hi Steve,
It was worth a try.

Station X · 20th Jan 2018, 9:01 pm

Two posts moved to what I hope is the correct thread here:-

https://www.vintage-radio.net/forum/...d.php?t=142924

5th Jan 2018, 5:22 pm	#1
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,831	How to shorten a ferrite slug? I need to shorten a ferrite inductor core slug. The slug is presently c12.5mm long and I need it to be about 8mm. FWIW thickness is 5.8mm. Ferrite is very brittle, so I don't want it to break up during any attempt to reduce its length, although I realise that there will be no process that doesn't pose a risk, it will depend on how well, how carefully it is carried out. I can grind it?, fine saw it? __________________ A digital radio is the latest thing, but a vintage wireless is forever..

5th Jan 2018, 5:44 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: How to shorten a ferrite slug? I've successfully cut them using a Dremel with a diamond-disc. They are brittle, yes - the best technique is not to try and cut clean-through in one action but rather to start by cutting a groove all round the slug at the appropriate point, then gradually deepen this groove by progressively rotating the slug as you cut deeper. This way, if it does crack the crack will probably end at the groove anyway. Then once cut, lap the cut end on a whetstone to remove any sharp edges.

5th Jan 2018, 5:52 pm	#3
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: How to shorten a ferrite slug? Try immersing it in water while cutting, to dampen the vibration. It works with glass, so may well do so with ferrite.

5th Jan 2018, 6:02 pm	#4
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,831	Re: How to shorten a ferrite slug? Ah, good info guys. I keep forgetting about my Dremel for lots of jobs, and I have some fine cutting discs. I'll give it a go. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

5th Jan 2018, 6:05 pm	#5
Guest Guest Posts: n/a	Re: How to shorten a ferrite slug? The old method was to notch and snap.

5th Jan 2018, 6:15 pm	#6
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: How to shorten a ferrite slug? I've also used a diamond cutting wheel, but it's hard work. Snapping rarely leaves a clean break.

5th Jan 2018, 6:58 pm	#7
Lloyd 1985 Nonode Join Date: Jun 2008 Location: Coningsby, Lincolnshire, UK. Posts: 2,819	Re: How to shorten a ferrite slug? Where I work we use small ferrite beads for attenuation, we adjust the size of them using a sheet of wet and dry sand paper. We have a small jig to keep it straight, it's just a half inch or so thick lump of steel with a hole drilled down the centre the same size as the ferrite. Regards Lloyd

11th Jan 2018, 5:22 pm	#8
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,831	Re: How to shorten a ferrite slug? I did it. Based on the advice on here I used my Dremel with a very thin cutting disc in it (brown and c2cm diameter - are they diamond?). As suggested I took cuts all the way round rather than try to cut it through in one go. I held it in my fingertips on the carpet covered top of my workbench and the cutter went through it like butter, no brittleness issues, no probs whatsoever. Very pleased and thanks to all for the advice, and Frank (Nuvistor) for the slugs to use. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

13th Jan 2018, 2:41 pm	#9
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: How to shorten a ferrite slug? Did the slug help with the tuner problem? __________________ Frank

20th Jan 2018, 4:03 pm	#11
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: How to shorten a ferrite slug? Hi Steve, It was worth a try. __________________ Frank

20th Jan 2018, 9:01 pm	#12
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: How to shorten a ferrite slug? Two posts moved to what I hope is the correct thread here:- https://www.vintage-radio.net/forum/...d.php?t=142924 __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.