Silver Paste

Posted on December 14th, 2009 by Dave under Bikes.
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Fortunately I have been very busy since August with  car restoration work. I received some of Fred Parr’s much touted paste based silver about that time and I was anxious to try it for myself after seeing the pictures that Dave Bohm posted about his first run with the product.

Nearly all the frames in the past 6-7 years have been fillet brazed, the jig I use allows me to add one tube at a time if I choose to do it that way versus mitering everything and doing it all at once, the brazing that is.  For this trial I thought that I would use the paste to solidly tack the seat tube to the BB.

raw BB shell and seat tube

raw BB shell and seat tube

In the picture above, I have smeared a small bead of paste all around the inside of the seat tube and on the edges of the miter.

Paste silver tack

Paste silver tack

The above photo is the post heating result. I used no additional flux beyond the paste.  All surfaces were pre-cleaned with Parr’s Metal Prep product.

My thinking at this point was to also attach the chain stays in a similar fashion then remove that assembly from the jig and finish the fillets on a bike stand so I could get a clean shot at the underside.

So after asking Mr. Parr if it was ok to swab the entire area with flux, to make clean up easier, he said it was fine and could add rod at the same time too. I wanted to avoid additional filler at this stage and since the seat tube went well I didn’t anticipate any problems.

Internally pasted, externally fluxed; pre heat

Internally pasted, externally fluxed; pre heat


At this stage, after heating everything looked good, though I could have probably used a bit more paste, but I was going from Dave B’s tutorial where he thought he may have used too much and I was, after all only meaning to tack the stays and seat tube for a later final fillet.

Final joining complete

Final joining complete

Well, the verdict is, well mixed.  When I took the assembly out of the jig, I managed to knock one of the stays off the BB. The other was fine. I’m going to chalk it up to gross inexperience with the product, though I’ve seen enough silver flow over the years to think that my heat was sufficient to accomplish the task at hand. The fact is that the interior wetting was great and I was impressed by the natural fillet that formed and can only blame myself for the lack of adequate heat to the much thicker wall shell to obtain a good bond.

I intend to try it again some where else during this build up and I really want to use it for some silver-smithing projects. Especially were extremely thin gauge silver is being joined as this stuff doesn’t require much heat to flow as compared to getting a 1/16th rod to go liquid.

I have since talked with Freddy and he advises that if one wants to use the paste as a pre-placement vehicle, then it is best to NOT completely flow the joint as the eutectic ratio properties will be exhausted and further capillary travel is unlikely.  So, hope this was as good for you. I learned something new today.

Drop a line if you have any questions.  Double click on the photos for a close up view.


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