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Onwards and upwards

Posted by Kenton , 23 October 2009 · 289 views

kitbuild footplate frames
The footplate of most loco builds is the platform for the rest of the locomotive and needs to be a substantial structure - I have seen (and built) several kits where the footplate is so flimsy that an inevitable curve is later introduced by the addition of the superstructure. I am not expecting such problems with this kit, however I am aware that there are parts in the design that may cause me some challenges - not least the use of some serious overlays (buffer beams) and the nuts and bolts (literally).

Once again we start by identifying the parts on the frets. The footplate is made up of an overlay [7] which has very fine detail of the chequer-pattern floor on it and the footplate itself [6]. These need to be carefully removed from the fret, setting aside the sub-frets from the cab and engine cut-out areas. Pay particular care to removing the half-etched overlay as it is very easy to distort it. Don't be fooled into thinking that the footplate has shrunk, it is deliberately designed that way, being slightly narrower and quite a bit shorter. (Not so noticeable in the photograph). Carefully file off the fret tags and tidy up the edges before cleaning all the greasy fingerprints off.

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The footplate, and ultimately the whole body, will be bolted to the frames using two 12BA nuts and bolts. Use the two holes in the footplate and overlay to align them - rather obviously the chequerplate half-etch is on the outside. :) I used the bolts themselves but you do need to ensure that they are coated in solder mask to prevent them being soldered into their holes. Do note that the footplate is "handed", there is an extra hole on the left-hand side that needs to be matched.

While being held together, and ensuring that the footplate is flat, run solder along the inside edges of the cab and engine cut-outs. There is no need to apply heat to the outside edges at this stage, though I found that the fluxing of the solder was more than adequate for it to spread though the entire overlay. The most important thing is to try not to ruin the chequer-plate etching with stray solder.

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The 12BA nuts were then soldered to the upper surface of the footplate - I used a toothpick to keep them aligned to the holes. Use the minimum amount of solder here as the cab and engine casing base plate has to be fitted later around these nuts.

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Sounds easy and looks it too - but behind that is hours of grief. Sometimes you just have to walk away from something and come back another day - well after several days actually. It took no less than nine nuts and bolts to finally get there. A combination of soldering nuts off centre, getting solder inside the threads, cross threading the bolts, snapping the heads off el cheapo bolts, having to re-tap nuts .... :( All that and I just know that there is a lot more of this to come.

The footplate was bolted to the frames checking that the half-etch on the ends lined up with ends of the frames. They did, but all that rough handling had introduced a very slight bend across the footplate. Something I hope will straighten once the buffer beams are soldered on.

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Michael Edge
Oct 23 2009 12:52
You seem to be having a lot of trouble soldering the nuts to the footplate top, I don't knowwhat sort of soldering iron/flux you are using but the method I use gives no trouble at all. Some grease under the footplate helps but is not essential, I bolt the parts together, run a little flux (phosphoric acid) around the nut and touch the soldering iron to the side of the nut and footplate. The solder quickly flashes round the nut as long as enough heat is applied (40w iron for this) and the screw can then be removed. We supply steel screws and brass nuts to make this easier and they are the best quality available (and quite expensive)
Michael Edge

You seem to be having a lot of trouble soldering the nuts to the footplate top


I hope I did not give the impression it was the fault of the kit - It most certainly was not.
All down to my hamfistedness I am afraid, that and trying to do things at the wrong time of day (for me).

I use an RSU for most kitbuilding soldering tasks with solder creams. Though here used my usual Antex 25W - sometimes it is just easier to wield what is at hand and i had just used that to run round the inner edges of the footplate.

Having made a mess of one of the nuts and cross-threaded one of the "expensive" bolts into it - I resorted to what I had in the spares box - some poor quality brass :( Obviously a mistake - and now need to stock up again with some of better quality. I have had similar problems with this in the past so it is not new. Hopefully with the other's in the kit I'll be more careful.
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Michael Edge
Oct 25 2009 14:22
That answers my question, rsu and solder paste is definitely not the way to do this, most solder pastes have very active (and corrosive) flux in them. Phosphoric acid is much safer, also your rsu heats everything up, what you want is local heat (quickly) just around the nut.
Michael Edge
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Miss Prism
Oct 25 2009 15:44
In my experience, an RSU is precisely the thing for applying local heat. On most settings however, it probably applies too much rapid heat, and this can tend to 'cook' solder pastes, resulting in a joint that would have been stronger with ordinary solder wire and an iron. I think to categorise most solder pastes as having corrosive fluxes is incorrect, but I agree that phophoric is sufficient for most brass and nickel work.

That answers my question, rsu and solder paste is definitely not the way to do this, most solder pastes have very active (and corrosive) flux in them. Phosphoric acid is much safer, also your rsu heats everything up, what you want is local heat (quickly) just around the nut.<br />Michael Edge


But Michael, as I said above:

I use an RSU for most kitbuilding soldering tasks with solder creams. Though here used my usual Antex 25W - sometimes it is just easier to wield what is at hand and i had just used that to run round the inner edges of the footplate.


Yes, used a 25W Antex - and in most things 4mm have never had any problems with heat output.
The solder cream (Carrs range) is actually far less corrosive than most phosphoric acid fluxes - it has an organic base.
The issue here was purely carelessness with the supplied nut and bolt followed by my own poor quality and brass replacements.

The RSU is superior for small items on larger items as it not only acts as a third hand (you can hold a part in place with the tip, apply heat, remove heat and then remove the RSU electrode) but also because the heating is very localised. It is also great for overlays and laminations. Its biggest downfall is in the ability to seam and patch/fill with solder.

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