Saturday, September 01, 2012

How I repaired LGB pointwork

After a while I found that several of my LGB points (switches) lost electrical continuity across the point blades and/or the rails leading up to the frog. It seems I am not alone in having this problem as the welded or screwed bonding straps beneath the rails deteriorate. Rather than removing the points to resolve the problem, I opted for remediating the issues with the points in situ.

To repair the link between between the stock rails and the fixed rails leading to the frog needed repair on R3 and some of the older R1 points, I soldered fixed heavy gauge copper wires using my 75watt soldering iron. Neither of these rails moves and so I felt there was no need for flexible wires.

 To repair the links between the pint blades and the fixed rails leading the frogs I went for multi-strand wire as the point blades move and hence there needed to be some flex in the linkage.

 For most of the R1 points where the point blade is pivoted next to the frog, and the link between the stock rails and the point-blades needed renewal, I soldered a multi-strand wire from one to the other. Once the ballast is relaid this link becomes less visible.

On the older R1 points where the point blade is split into a moving and a fixed part (as with R3 points), I soldered a single piece of multi-strand wire between the two halves of the point blade and then looped it under the rail, soldering the end to the stock rail.

As above, the longer stretch of wire will be buried in the ballast.

My main piece of advice is to ensure the rail is filed clean before it is tinned - I used the end of a square needle file to rub down the rail until I get clean bare metal. I find that holding the iron hard against the rail for around five seconds and then feeding multicore solder in between the iron and the rail is usually sufficient to tin the rail without melting the plastic chairs either side. This is particularly important when soldering near the pivoted end of the point blade as softening the plastic sleeper and cause the blade to become misaligned (how do I know???). The wire is also tinned before it is then held next to the tinned part of the rail and the heat applied from the iron for around another five seconds or so - I use a small flat bladed screwdriver to keep the pressure applied to the wire while the solder hardens. I reckon I eventually got the entire remediation process down to around seven minutes per point - ten at the outside. 

I have now bonded all my points in this way, regardless of whether they have failed, as experience suggests that they will all fail eventually. 

No comments: