kitbuilding 4mm hornblock OO springs
The pack (4M60) is supplied with parts to make up 6 hornblocks for 4mm loco/tender springing. The parts are small - very small - and you need to be aware that small parts - especially springs - have a habit of finding their way off the workbench and into the carpet or between the floor boards.
So start by emptying the contents of the pack into a suitable tray and sorting them out (a brass fret - the hornguides, 6 hornblocks, 3 lengths of 0.4mm brass wire, 6 turned steel beveled nuts, 6 steel screws and those 6 springs).
1. Start with the hornguide etch (DO NOT remove the individual guides from the fret - yet) and the bevelled steel nuts.
Both sides of the brass fret were cleaned with a glass fibre brush and run the tip of a scratch-aide pointer around the lip of the steel nuts - this is quite fiddly due to the size but the nuts will solder in with greater ease if you can manage it.
I used my trusty RSU for this work (very handy if you have one), holding the brass fret onto one of my steel plates (RSU ground) with a magnet (giving electrical contact), I slid an insulating sleeve (card) under the rest of the fret. I then applied the merest hint of Carr's 179'C solder cream to the edge of the larger holes mid-way along each hornguide. I then placed the small diameter of the turned steel nut into the hole with the lip facing downwards and the plain side of the hornguide facing upwards. Having a magnet nearby is very useful as if you slip in placing these nuts they are pulled onto the magnet rather than rolling on to the floor. Next a tiny drop of Carr's Green Flux (for steel) was added (this is not absolutely necessary as the cream is self fluxing but the cream flux is not ideal for steel). The other electrode of the RSU was then placed on each nut to hold it in the hole and the unit powered up to form the join.
While the fret remained intact I filed a flat on one side of each of these steel nuts, on the side corresponding to the frame front, so that they will not foul the frame when soldered in place.
Clean any residues away thoroughly before continuing.
2. The threads of each screw were dipped in Carr's solder mask and carefully threaded into the nuts, again working from the plain side of the guides. The solder mask should prevent you accidentally soldering the screw/nut during the rest of assembly and also acts as a lubricant.
3. The guides were then cut from the fret, taking care not to twist the guides or to shorten their length. The tags holding them in the fret are non-existent, being simple half-etched lines, and so I found that they were best removed with a piercing saw. Tidy up and square the ends with file. Now using one of the hornblocks as a former bend the hornguide to a 'U' shape along the half etched fold lines either side of the screw/nut.
4. The three lengths of 0.4mm brass wire were each cut in half and then bent into a 'U' shape around a hornblock. It is important that the bends are sharp and that the 'U' sits snugly in the grooves of the hornblock. Be aware that the grooves are not engineered square and are in fact round - but this distorted 'U' presents no real problem. Howver, the brass is very soft, probably to facilitate easy bending, which will not withstand double bending. So get it right first time or carry some spare. I lost 1 out of 6 due to this. The staples were then slid into the guides checking that they pass easily through the small holes at the top corners of the guides. It was necessary to slightly open out these holes to accomplish this using a broach or drill. These must remain a close fit.
5. The bearings were threaded on a spare 1/8??? axle and clamped in the jaws of a smooth faced vice. A small land was filled in the middle of what will become the top edge of the bearings. This will help in location and retention of the spring.
At this point you may take the decision to solder the hornguides into the loco/tender frames. However, as I use plenty of solder mask during the assembly, I find it slightly less fiddly to continue to assemble the units and then to solder them into the frames afterwards.
6. Now for the really fiddly bit. Small amount of Vaseline was placed on the spring ??“ this helps to keep the spring where you place it and also minimizes the ???bounce to oblivion??? when you drop it. Assemble the unit upside-down. The spring was placed over the screw projecting into the guide-way. The sides of the bearing that will be in contact with the guide were coated in solder mask and then the bearing placed into the guide with the notch facing the spring. The 'U' staple was then pushed in along the grooves until the ends came through the small holes in the hornguide. When the spring was just being compressed the ends of the wire were bent over. The screws were then retracted so that they just protruded through into the guide-way yet still holding the springs in place. Check that the hornblock moves freely in the guide compressing the spring. This movement should be no more than 2-3mm.
To safely store these for future use I wrap a length of cotton around them.
When used, these hornblocks are adjustable using the screw as a end stop for vertical travel of the bearing. In theory even a slightly twisted chassis can be made to run with all wheels touching the track by the adjustment of each hornblock. The idea is that the model's weight compresses the springs but the amount of compression is limited by the screw. The model rides on the bearing butting against the adjustment screw.