Churchill Mk. IV AVRE with Small Box Girder Assault Bridge Mk. II

[Guest]

That’s what I’m afraid of, yes: that in a few years’ time, I’ll hear a crashing sound and find the bridge has fallen off the model. The main one I’m worried about it part X31:

[ATTACH]482190[/ATTACH]

The T-part of it will go into holes at the top of the bridge booms, so it will take all of the bridge’s weight. I intend to replace at least that whole part by one fabricated from brass, and perhaps the rings on the blocks as well. Though those are a bit thicker and seem to be anchored into the blocks by a flange at the end of their pins, so they probably don’t need it as much as the rings on the bridge.

This would leave the cables as the main weak points, because they will have plastic eyes superglued to the thread supplied in the kit, but I see no realistic way of replacing any of this by something stronger.

[Scratchbuilder]

That’s what I’m afraid of, yes: that in a few years’ time, I’ll hear a crashing sound and find the bridge has fallen off the model. The main one I’m worried about it part X31:

[ATTACH=CONFIG]n[/ATTACH]

The T-part of it will go into holes at the top of the bridge booms, so it will take all of the bridge’s weight. I intend to replace at least that whole part by one fabricated from brass, and perhaps the rings on the blocks as well. Though those are a bit thicker and seem to be anchored into the blocks by a flange at the end of their pins, so they probably don’t need it as much as the rings on the bridge.

This would leave the cables as the main weak points, because they will have plastic eyes superglued to the thread supplied in the kit, but I see no realistic way of replacing any of this by something stronger.

I would make the 'T' part (X31) from brass rod and soldered, obviously made oversize and then cut down to size - with the same at the other end for the ring. Part O11 could come from the brass shackles sold I think by Aber. And you have already demonstrated your ring making for parts O6. As an addition to the 'T' you could wrap a thin strip of brass over the 'T' junction for extra strength before you solder the joint together. This will not be that noticable once fitted.

[Guest]

I was thinking of brass shackles as well, but I suspect the plastic ones will be strong enough — at least stronger than the eyes at the ends of the cables, anyway

[Tim Marlow]

I would make the 'T' part (X31) from brass rod and soldered, obviously made oversize and then cut down to size - with the same at the other end for the ring. Part O11 could come from the brass shackles sold I think by Aber. And you have already demonstrated your ring making for parts O6. As an addition to the 'T' you could wrap a thin strip of brass over the 'T' junction for extra strength before you solder the joint together. This will not be that noticable once fitted.

Soldered butt joints are not always the most reliable Mike/Jakko. Another option is to find a large headed nail with the correct diameter shank and file the head to the required T shape. No soldering, and solid metal….used to make coach T handles like this when I were a lad If you can’t find a nail, look up lace pin suppliers. They make pins in a bewildering range of sizes and head types.
O11 could possibly be replaced with model railway screw coupling parts……not sure what size you would need, but they come in both OO and O gauge sizes. You don’t need working ones (threading 16BA bolts through the working Tommy bar parts is sheer lunacy. Trust me, I’ve done it!), just the D ring parts on a dummy coupling.

[minitnkr]

Dressmaker's T pins for holding patterns might work. I use them for indicating placement of dio trees. Cheap too.

[Jim R]

Wood looks excellent Jakko. I think you do have a legitimate worry about the strength of the plastic parts but I've no doubt you'll "invent" a solution.

[Guest]

Soldered butt joints are not always the most reliable Mike/Jakko.

I intend to test it by seeing if I can pull the thing apart or not It’s not like the bridge is overly heavy, and AFV Club apparently trusts the plastic parts … though perhaps more than I do

Another option is to find a large headed nail with the correct diameter shank and file the head to the required T shape.

It would not be as easy to solder the ring at the other end to that, than to brass, wouldn’t it?

O11 could possibly be replaced with model railway screw coupling parts……not sure what size you would need, but they come in both OO and O gauge sizes. You don’t need working ones (threading 16BA bolts through the working Tommy bar parts is sheer lunacy. Trust me, I’ve done it!), just the D ring parts on a dummy coupling.

You do need clasps with separate pins in this case, though, because they have to go through eyes and holes on the bridge parts and the blocks. O6 are the pins that go through the holes moulded into O11, and these are not the only ones — they also go at the tops of the poles and through the rings I already replaced by brass ones, for the cables that connect those:

[ATTACH]482206[/ATTACH]

The little rectangular holes at the tops of A-frame poles are for small plastic hooks that the T-end of X31 goes into.

[Tim Marlow]

Hi Jakko
I was thinking of the D rings from these type of couplings

to replace O11. It’s pretty much the same technology. There are several manufacturers of these in the railway scales. They usually come as lost wax castings in brass. As to the nails, you can get decorative tacks in brass that may suit the T requirement. However, you are much closer to this than I am, and may be seeing issues that I’m not.

[Lee Drennen]

Nice updates on the bridge Jakko

[Guest]

I was thinking of the D rings from these type of couplings
[ATTACH=CONFIG]n1201423[/ATTACH]

Aha! TBH, I was wondering what kind of couplings you meant, as I was having a hard time figuring out how something like this:

[ATTACH]482217[/ATTACH]

… relates to part O11

The ones you mean seem a bit long, but I imagine something shorter would be available too by looking around a bit.

However, you are much closer to this than I am, and may be seeing issues that I’m not.

At the moment, my thinking is that O11/O6 are probably OK: they’re not likely to be the weakest link in the chain, which looks to me to be the X31 followed by the eyes on parts O10 (of which there are at least six) and their glue joint with the thread that makes up the cable. If I had to guess, it’s probably the eye on X31, as that takes the whole weight of the bridge, while each O10 only takes half.

I think the best thing to do is see if there are any spares, and if so, use one of them to see how much weight it can take. If it will hold the bridge’s weight without deforming or snapping, all should be well.

[Tim Marlow]

Aha! TBH, I was wondering what kind of couplings you meant, as I was having a hard time figuring out how something like this:

[ATTACH=CONFIG]n[/ATTACH]

… relates to part O11 :smiling3:

The ones you mean seem a bit long, but I imagine something shorter would be available too by looking around a bit.


At the moment, my thinking is that O11/O6 are probably OK: they’re not likely to be the weakest link in the chain, which looks to me to be the X31 followed by the eyes on parts O10 (of which there are at least six) and their glue joint with the thread that makes up the cable. If I had to guess, it’s probably the eye on X31, as that takes the whole weight of the bridge, while each O10 only takes half.

I think the best thing to do is see if there are any spares, and if so, use one of them to see how much weight it can take. If it will hold the bridge’s weight without deforming or snapping, all should be well.

I did think that after I posted Jakko…..I thought “he thinks I mean knuckle or automatic couplers LOL”. Hence the picture to explain….. British railway practice was far behind European and U.S. practice in the realm of couplings until relatively recently, and it’s easy to forget that.

[Guest]

Luckily I’m not quite dense enough to think you really meant those couplings, but it also did not occur to me that you meant the chain-type ones, even though I do know they exist

[Guest]

Small update on the strength of the clasps, eyes etc. issue: I weighed the bridge, found it’s about 75 grammes, and then went and found something a bit heavier. I had a small plastic jar at hand that has some water in it (and a lid on), and that turned out to weigh about 90 g. Looped some copper wire around it, and then hung it by the wire from one of the clasps in the kit. The clasp holds it fine, both the U-end and the pin that goes through. However, I do think I’ll need to drill a small hollow for the pin to fit into, opposite the hole moulded for it in one side of the clasp.

Next I tried one of the cable eyes, and that also held the weight perfectly well, even though it’s thinner material than the clasps. As I said, each of these will only carry half the weight of the bridge (minus the part carried by the pivots on the tank’s nose, of course), so if a single one can hold over 20% more than the bridge’s full weight, there should be no risk of breaking.

The last thing to try was part X31, which will bear twice the weight of the clasps and cable ends, and that also held perfectly — both the eye on it and the crossbar. I won’t be replacing it with brass, as I don’t think it’s necessary at all (but I’m sure I’ll say something else a few years down the line when fatigue and/or the influence of UV light causes it to break anyway ).

[Neil Merryweather]

Gotta love your thoroughness, Jakko :thumb2:

[Guest]

Better safe than sorry TBH, I kind of expect things to hold, as I (mostly) doubt AFV Club would have put parts in the box too weak to hold the bridge — but you never know … Which is why I did the quick experiment, that now has me wondering if it was thorough enough, though. Are the forces working on the various parts as simple as I thought? The bridge will be at an angle of about 45°, but the winch cable will be much flatter than that — what does that mean for the clasps etc.?