Syringes for flux dispensing

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John Palmer
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Joined: Fri Jul 15, 2011 11:09 pm

Syringes for flux dispensing

Postby John Palmer » Thu Apr 19, 2018 10:42 am

I'm interested in your experiences with use of a hypodermic for dispensing flux. This had seemed to me a Good Idea when I recently purchased a packetful of such hypodermics together with what I hoped would be suitable needles for just this purpose. Alas! in practice there proved to be a complete absence of control over the quantity of flux dispensed. I pressed gently on the plunger - nothing happened. I pressed a little more firmly - still nothing. I pressed a little more firmly - the plunger shot downwards in the tube and and the entire workpiece was soused in the jet of flux emitted from the needle.

So my question is: can anything be done to improve control over the amount of flux dispensed from a hypodermic, or should I revert to the 'bottle of flux and paintbrush' method I have used hitherto?

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Paul Townsend
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Re: Meeting report April 2018

Postby Paul Townsend » Thu Apr 19, 2018 12:20 pm

John Palmer wrote:I'm interested in your experiences with use of a hypodermic for dispensing flux. This had seemed to me a Good Idea when I recently purchased a packetful of such hypodermics together with what I hoped would be suitable needles for just this purpose. Alas! in practice there proved to be a complete absence of control over the quantity of flux dispensed. I pressed gently on the plunger - nothing happened. I pressed a little more firmly - still nothing. I pressed a little more firmly - the plunger shot downwards in the tube and and the entire workpiece was soused in the jet of flux emitted from the needle.

So my question is: can anything be done to improve control over the amount of flux dispensed from a hypodermic, or should I revert to the 'bottle of flux and paintbrush' method I have used hitherto?


I suspect you have needles which are too fine.
I have some donated by my deceased diabetic mother which work fine.
Take advice from a pharmacist.

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David B
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Re: Meeting report April 2018

Postby David B » Thu Apr 19, 2018 3:04 pm

John Palmer wrote:
So my question is: can anything be done to improve control over the amount of flux dispensed from a hypodermic, or should I revert to the 'bottle of flux and paintbrush' method I have used hitherto?


It depends how you hold the syringe, John. If you hold it in the conventional manner with thumb on the plunger, then this can prove difficult to control. Try as in the attachment, holding the plunger against the base of your index finger, gripping the syringe body between thumb, index and second finger and gently drawing the digits towards your palm. Practise with water first - it saves on flux!

Chris F mentioned a blocked needle at S4North. I can only say that I have had no problem with Carr's yellow flux over several years. The plunger in the syringe can become stiff in time (with the result you describe above) and I have replaced my syringe a couple of times, but the needle should lase indefinitely. Mine is 28 gauge (orange) which I can get a 9 thou guitar string through but not a 10 thou. I use Carr's yellow which I have understood to be phosphoric acid but may be zinc chloride based. Chris was talking of using 12% phosphoric acid which to our ears at S4N sounded strong.

Syringe_0589.jpg

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Paul Townsend
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Re: Meeting report April 2018

Postby Paul Townsend » Thu Apr 19, 2018 3:42 pm

I realise I hold mine the same way as David's picture. Mine is loaded with nominal 8% phosphoric acid diluted by me and the syringe is decades old.
The hole is less than .011" The needle is not colour coded or removable.....it is integral to the syringe.

When I moved house a couple of years ago, I lost mine for some months and David gave me one of his which worked just the same.

DougN
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Joined: Wed Sep 01, 2010 9:57 am

Re: Syringes for flux dispensing

Postby DougN » Fri Apr 20, 2018 12:53 am

Well I had this discussion with a relative and asked if he had any old ones he could give me..... lets just say nothing that small and some go up too 100ml :shock: but then again he is a large animal vet! :P
Doug
Still not doing enough modelling

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steamraiser
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Re: Syringes for flux dispensing

Postby steamraiser » Fri Apr 20, 2018 8:14 am

I bought a couple of small syringes from Eileen's.
They worked well with cream flux, providing you just wipe the tip of the needle at the end of each modelling session.
Not tried with liquid flux.

Gordon A

John Palmer
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Joined: Fri Jul 15, 2011 11:09 pm

Re: Syringes for flux dispensing

Postby John Palmer » Fri Apr 20, 2018 10:09 am

Thank you, David, for the alternative technique so clearly illustrated, but one with which I had no greater success, regrettably.

At the risk of degrading this thread into an excessively abstruse discussion, here is a picture of another way of holding the syringe with which I have had greater success, I believe because gripping the plunger immediately above the tube 'wings' has the effect of making them a stop that minimises plunger travel. As the picture shows, by this method I was able to limit discharge to a single drop: a considerable improvement on my previous performance.
Another syringe technique.jpg

I note that the piston in David's syringe appears to be made of soft black rubber. Mine is of some green material – possibly nylon or similar? - and I wonder how far differences in piston material affect the degree of control possible over the amount discharged. My syringe was from Railroom Electronics. Needle was from the same source: 20 gauge, or about .020”, which is probably too big a bore size to be ideal

I also note that David's syringe retains an air bubble, and I wonder whether this too may affect the degree of control. I pointed my syringe upwards and pressed the plunger until a spurt of liquid proved my bubble had been cleared. Even if this made no difference to the degree of control I was able to exercise, it was in best tradition of baddie about to administer the lethal shot.

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David B
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Re: Syringes for flux dispensing

Postby David B » Fri Apr 20, 2018 2:02 pm

I get my syringes from the local farmer's shop - not farm shop - where farmers get animal feed, chemicals, posts, wire and other things useful for the farm. It has a veterinary department where the syringes and needles are 20 - 25p each.

The air bubble is of no significance. It is where I have sucked some surplus flux back in or a bit of air when leaving it on the bench. If there is no air and the room is warm, flux can leak out of the syringe. I suck a bit of air back to clear the needle.

charleswrigley
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Joined: Thu Oct 01, 2009 5:49 pm

Re: Syringes for flux dispensing

Postby charleswrigley » Fri Apr 20, 2018 3:35 pm

This YouTube gives a useful alternative to syringes using the carcass of a highlighting pen. It works quite neatly.

https://www.youtube.com/watch?v=dIogzh8WDwo

Charlie

Philip Hall
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Re: Syringes for flux dispensing

Postby Philip Hall » Sat Apr 21, 2018 2:30 am

If you are going to use a flux pen, my preference is for the CPL one, which I have had for an awful long time and works very well, no drips or spillages, just needing a very small funnel to fill it up. The downside is the expense, but this is compensated for by the hilarious English translation of the Japanese (?) instructions.

When I don’t want to use a lot of flux, I do use a syringe, as recommended by David (I think he might have given me mine!) and that is very good at dispensing small amounts precisely.

Philip


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