Tungsten chipping, silver solder masking?

[graffian]

trying to make some contacts for something. They are a pill of tungsten
soldered to a brass bolt.
It solders easy enough. Using Silver-Flo55.

The tungsten chipped really badly cutting the tungsten down. I was cutting with
an angle grinder with a diamond disc and wasn't at all surprised when it chipped.
The tunsgten is probably a red one.
Would a different tig tungsten make better contacts?
Do the different tungstens chip worse than each other, or was it just a disc for cutting bricks is ****?


I have used chalk dust and isopropanol as solder mask before, quite successefully. I tried the same
with the brass bolt and to my horror as the tungsten tinned the silver shot along the first few threads.
Anyone got any ideas on solder mask ?

 

[optima21]

carbon from a soot lamp or old school tippex that was solvent based, but its 20 years since I had that sort of tippex and I havn't used a soot lamp yet.

 

[hotponyshoes]

You would at least want a little cutting disk in a dremel or something to have any chance of cutting a clean slug from a tig tungsten.
High speed , run a groove around it and keep rotating till the bit falls off. Dress it up by holding it lightly and runjignit against the side of the cutting wheel.

How about drilling a hole in the end of the bolt, cut the bit of tungsten longer and put a dab of solder in the bottom of the hole before dropping the piece in rather than trying to solder it to the top?

Another option, I think I have some small tungstan balls somewhere if you want a couple? Put a center dot / divet on the end of the bolt and again, drop one into a small bit of solder?

 

[hotponyshoes]

Or what might be even easier..
Would tungstan carbide work?
I have got some tapered pins, about 4.2mm on the large end, drill a 4mm hole in the end if the bolt and drive one of those in there. No solder required.

 

[voipio]

Why tungsten? It's not a very good contact material.

 

[DAPPH]

Have you tried silver soldering it with the tungsten under the thread end using a red hot steel bolt as the heat applied or perhaps perhaps using some alu tapped to take the thread as the apron whilst you quickly silver solder it with the tungsten uppermost again use a bright red hot steel bolt for the heat .

Another thought is to flash/ spot weld it to the bolt using a car battery or heavy duty PSU , smear some flux & a tiny sliver of silver solder on the bolt ,slip the tungsten on align it using a roll of brown paper , tape it in place . flash power through the tungsten down through the bolt via the carbon stick out of a zinc battery cell as an electrode or even use some drilled hard wood as the guides if you are flash welding it .

 

[graffian]

Why tungsten? It's not a very good contact material.

I was aiming to spend nothing on this at all. So it's what I already have.

I looked at a few relays, the silvery contacts look good and can be removed from some of them.
But I tried running a relay [with unused contacts] as a buzzer and after 5 minutes the contacts looked very
used, so those are not a lot of good; I may try them as the induced voltage from the coil was pretty high.
I bodged some tungsten in as contacts, buzzer sounded the same and the contacts looked great after five mins.

The screw the bit of tungsten is soldered to is 4BA so not a lot of room to bury anything into it.

I like the drilling a hole and putting some solder filings in and dropping the tungsten in idea.

Got several ideas. I will crack on with the rest of thing and just put some brass bits in as contacts for
now.

 

[mikegolding]

I use a white permanent marker ( pentel 100w ) for silver solder masking. Works very well.
Mike.

 

[hotponyshoes]

The screw the bit of tungsten is soldered to is 4BA so not a lot of room to bury anything into it

I have got some 0.8mm tantalum balls.
Those are so hard you could probably solder the whole thing in then grind away the solder to expose half of it. The contact area might be a bit small on those though?

 

[Rrobson]

Just cut it with a standard aluminium oxide abrasive disc, it’ll make a neat enough job for what you want, no need for a diamond cutting wheel. After all most sharpen a tungsten on a grinding wheel (alu oxide)

And rather than soldering, why not drill a hole in the end of the bolt just smaller than the tungsten size then knock / press it in?

 

[Seadog]

The screw the bit of tungsten is soldered to is 4BA so not a lot of room to bury anything into it.

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