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Silver soder joint breaking

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Baldric25/03/2019 08:21:02
143 forum posts
11 photos

I have had a few problems with making two parts that have a hole on each end of the rods, where the holds must end up exactly the same length.

My procedure was to drill and part of the ends for the rods, and put a counterbore in the side where the rod will go. The rods were created and machined to length, I made a jig so the rod ends could be located with the rod between them, assembled with flux ready for silver soldering.

Once silver-soldered, which seemed to go OK, I struggled to get the parts off the jig, to the point where the joint failed. The parts showed no signs of having being soldered to the jig, I assume it was flux or other "scale" created during the heating.

Questions.

1. What clearance should I have on the jig to allow for expansion/contraction?

2. Will the jig cause the joint to be weak as the part is put under tension as the rod cools and shortens?

3. If I was using free-cutting steel, would that cause an issue with silver solder? I know lead in steel can cause issues when welding & soldering to brass alloys with lead in.

4. Am I better off drilling the rod ends undersize to start with, then opening them out later using a slot drill to get exactly the correct spacing, allowing a bit more movement within the jig?

Unfortunately I can not put a picture up as I was going to re-do parts so took a file to the solder.

Baldric.

JasonB25/03/2019 08:30:51
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Moderator
16530 forum posts
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1 articles

I always coat jigs with Tipex to stop any risk of the solder sticking and make them in such a way that they can be taken apart eg separate location pins also pickle the part and the jig to remove the flux before trying to take apart. Never made any allowances for expansion.

One thing you do need to watch is that the part gets fully heated as the jig can act as a heat sink and stop one side of the part getting hot yet the other side you see looks hot and has a good solder flow.

A lot will depend on the part you are actually making but I usually drill the two end holes first and then do the shaping of the rod, a lot easier to hold and set the spacing on the mill while you have a rectangular section than trying to hold a round or even tapered rod to drill unsupported ends.

Free cutting steel such as EN1A won't be a problem but if you used Leaded steel EN1A Pb then that does not like solder.

CuP Alloys 125/03/2019 09:39:05
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200 forum posts

A properly made silver solder joint will certainly withstand the stress of parts stuck to a jig by flux residues!

If the joint failed there is something amiss. Examine your joint design, fluxing, heating technique.

To answer some of your questions;

1) any jig used must allow for the inconvenience assembly to move. That's a contradiction of terms but if the components can't expand they will distort. Redesign your jig.

2) the jig nor the alloy will cause a weak joint but thermal stresses during cooling might.

3) silver solder does not like lead. It affects the fluidity.

More information on this and other silver soldering issues can be found in the book "Every Thing You Wanted to Know about Silver Soldering but were afraid to ask". Available via CuP Alloys.

Keith

Baldric25/03/2019 12:15:40
143 forum posts
11 photos

Thanks for the replies, it does really confirm my thoughts. The rod its self is 1/4", but the jig was 1" x 1/2", so I fear would have put the joints under stress during cooling, that and the close fitting jig. I will look to make the jig with more clearance, or so it can be slackened of as the job cools.

Baldric.

John Haine25/03/2019 12:20:09
2693 forum posts
138 photos

Do you need a jig? Couldn't you stack the parts vertically so gravity holds them together while the solder melts and cools?

Jeff Dayman25/03/2019 12:20:48
1656 forum posts
42 photos

Two thoughts re jig - 1. suggest making jig from same metals as parts to be soldered, to minimize differential expansion effects. 2. Make one pin a slip fit in the jig, so it can be popped out with a punch (carefully) after soldering, rather than needing to lever the part off the jig.

J Hancock25/03/2019 17:14:17
320 forum posts

IF the free-cutting steel is of the 'leaded' variety then you will have a problem with silver solder.

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