Crossing vee soldering problem

[bjuleff]

I've been happily soldering up crossing vees for some years using the silver soldering process. I prefer silver solder as it prevents meltdown of the whole lot when I conventionally solder it to my Masokits chairs and copper clad timbers. It's all worked well until this week.

I have been trying to make up some very low numbered crossings, in the order of 1 in 1.5 etc., associated with diamond crossings. Despite multiple measuring of the Templot, confirmatory arithmetic and repeated double checks on the rail in my soldering jig, I am finding that once soldered the vee has reduced its angle by something like 5mm at 100mm from the nose. This has been consistent over four separate attempts and the error is too great for any to be used on the layout.

My conclusion so far is that it is associated with contraction of the piece after the red heat required of the silver solder. I would be interested to know if others confer.

Two other points come to mind. I have not had any problems like this when constructing the more usual angles (e.g. 1 in 8 etc), however the finished job sometimes has been just a tiny bit off the desired angle. So far I have put this down to my mismeasurement. But maybe it is actually the same problem and because the angle is much more acute, it does not show up so severely.

The other point is that due to the very diverging angle of the rails in my 1 in 1.5 crossing, the contact surfaces are very small and do not promise a strong soldered joint. For this reason I have allowed a fillet of solder to be deposited in the inside of the vee. I wonder if it is the contraction of this which is the culprit?

I'd value any comments particularly if anyone has themselves used the silver soldering process.

[steamraiser]

Try making a matching triangle of ply to push between the two rails that make the V when soldering.
This should prevent any change in angle.

Gordon A

[Terry Bendall]

I have never tried silver soldering crossing vees but I have in the past done a lot of silver soldering of metals. What sort of jig do you use and what grade of silver solder? There are three different grade with different melting points. The higher melting point one melts at between 770 - 825 degrees C, the medium grade between 750 - 770 degrees C and the lowest meting pint one at around 690 - 740 degrees C. I assume you use a miniature heating torch with a small flame?

Terry Bendall

[bjuleff]

Hi Gordon,

I won't be able to get the plywood very close to the vee end as it will be burnt by the blowlamp and red hot rails. I am happy the rails are not moving whilst being soldered, which makes me think contraction forces are at work. I suppose I could try filing up something like brass, but its' going to be tiresome for every odd angle I make. Thanks for your suggestion anyway.

Hi Terry,

You've got me there with the grade of solder. The piece I use goes back to the dawn of history and, to be honest, I don't think I was aware until now it came in several grades. So I've no idea what its melting point is other than very hot! I'm using a kitchen chef type of mini blowlamp which runs at about 1,000 degrees C. The jig is a homemade effort consisting of a flat melamine table and an adjustable clamp which holds the rails vertically and at the same time one rail can be slid closer or further from the other. The table is surfaced with a paper diagram showing lines radiating from a point, thus giving me the required crossing angle. The diagram was drawn separately before being cut exactly 50mm from the point and then stuck to the table, the cut edge being lined up with the edge of the table. Thus I can position firstly my point rail with its end 50mm, minus the nose to intersection point dimension, beyond the table edge. My splice rail is placed in the clamp and moved across the table and rotated until it lines up with my chosen line drawn on the table. The rail is slid fore and aft to contact the point rail in the right place. All tightened up and the business end, in free air, can now be soldered. It's worked well until now.

[davebradwell]

Perhaps just put much less solder on - no fillet. The silver solder would be strong enough for a butt joint so it isn't going to break, it's probably stronger than the rail.

DaveB

[bjuleff]

Hi Dave!

I am sure you are right about the strength of silver solder but, honestly, the surface area of the soldered part of the splice rail at this angle of crossing (1 in 1.5) is barely one square millimetre. Anyway, as it happens I've managed this morning to make an accurate crossing by factoring in my "error" and setting the rails up 5mm more than I need at 100 mm from the nose. Amazingly it shrunk before my very eyes and finished up exactly correct.

I am now of the opinion I need to factor into my crossings a variable amount for contraction. A 1 in 12 crossing I made a while ago came out exactly as anticipated on my jig and my 1 in 8s have needed a bit of "that's good enough" attitude. So I suspect the contraction issue is starting to make itself felt at this angle and becoming more noticeable as the crossing angle widens. I've never seen this referred to previously, so I wonder if there are any protagonists of silver soldered crossings who've met this little problem?

[davebradwell]

You could take the opportunity to test the strength of the joint as there's unused samples available for destructive testing. Anyway, you've found a way to win and that's all that matters. With the flatter crossings you're doing well to avoid burning the point off with the torch, although the melting point is significantly higher than brass.

DaveB

[Tim V]

Melamine has a melting point of 343 °C , but it gives off nitrogen so won't catch fire.
https://en.wikipedia.org/wiki/Melamine

I think you are being over cautious, I've used high melting point solder for vees, and lower melting point for the rest of the work.

Don't forget to solder the vee from the underside, this won't put a smidge of solder on the running surface - which will create a mucky surface on the top of the crossing.

[bjuleff]

Hi Tim,

Thanks for the useful tip about soldering the vee from the underside, although so far my exploits when soldering from the top have not resulted in any solder smudges! I'm not too worried about the melamine as the heat is very localised and not in contact with it.

Hi Dave,

Blackened but not melted!