Flaring a bunker top

[Torper]

I'm building one of 52F Model's NBR C16 kits.  It has so far been a joy to build with every part fitting precisely, but I'm a bit stuck as to how best to flare out the back of the bunker, the top 5mm of which should be bent back about 1.5mm in a gentle curve to match the top of the bunker sides.  The material is nickel silver, approx. .38mm thick, and I'm having great difficulty achieving a nice gentle curve in such a small piece.  There is a thin half etched line in the piece to show where the curve should begin, but in a way that is a handicap as the material just wants to bend straight back from there.  Any advice would be much appreciated.

 

DT

[N15class]

There will always be a tendency to bend on any etched line. They are a pain.

I find the best way in this situation, is to anneal the part that needs to be curved. Find a bar a little smaller than the radius of the curve. Set it up in the vice by having the bulk of the material facing down and the etch line just below the the centre of the rod. The part that's to be curved and most of the rod out the top of the vice. Now with a heavy straight edge, something like a 1/2" square bar pull the flare over the rod.

It will spring back a little. Hence why you use something slightly smaller. It can be done without annealing, and the other way up, but is more likely to fold at the etched line.

[Torper]

I find the best way in this situation, is to anneal the part that needs to be curved. Find a bar a little smaller than the radius of the curve. Set it up in the vice by having the bulk of the material facing down and the etch line just below the the centre of the rod. The part that's to be curved and most of the rod out the top of the vice. Now with a heavy straight edge, something like a 1/2" square bar pull the flare over the rod.

It will spring back a little. Hence why you use something slightly smaller. It can be done without annealing, and the other way up, but is more likely to fold at the etched line.

 

Many thanks for that.  I haven't much experience at annealing but understand that I should heat the metal with my mini gas blowtorch (but ideally not so it gets red hot though that may be difficult to avoid) and then allow it to cool slowly.  As nickle silver is harder than brass, I anticipate that it may need a little more heat.  I will get on with it over the weekend.

 

DT

[N15class]

Yes annealing is getting it hot, red is ok, but not bright red. If you play the torch along the top part the lower bit won't get so soft. Which is better.

[brack]

If you have a gas cooker they can be useful.

[Daddyman]

I've devised an alternative to the rod method over the years. It might be good for experienced modellers, but there's an easier way for the less experienced. The two main problems with it are (a) once in the vice it's hard to see when the rod is square to the workpiece (though you could tack superglue rod to workpiece) and (b) it leaves most of the workpiece unsupported; only the point where the rod contacts is supported and that's problematical in your case where the bunker back wants to bend somewhere other than where you want it to. 

 

Below is the method I've devised. I've sketched it out as it's hard to get a clear photo. The basic method is trapping the workpiece in the vice jaws between two pieces of wood (I use the type used as backing by Eileen's Emporium), one of which has a radius slightly smaller than that required filed on it, which is positioned against the relevant part of the workpiece. 

 

 

 

For the actual bending itself, you can use a heavy bit of metal bar, or wood; but what I do is turn the vice upside down and press it (and the protruding part of the workpiece) against the bench. I find it's easier to get even pressure that way. 

 

This is photo of the bending about to happen, but as I said it doesn't show much: 

 

 

The results: 

 

 

Finally, don't get too stressed - you can always replace kit parts in sheet N/S if you damage them, using the original for dimensions. 

[Daddyman]

Oh, another thing about this kit: if you're modelling in 00, don't make the same mistake I did of following the instructions around the bogie frames! 

 

The instructions will have you position the dummy frames outboard of the wheels, when of course they should be inboard. This photo shows the error on my C15 - it ruins the front end look: 

 

 

This shows the real thing - the Glen at Riverside: 

 

 

The part in question (the large yellowy part with rivets top and centre right in the photo) is clearly behind the wheels (for obvious reasons!) 

 

I have a C16 to do but haven't worked a fix out for this yet. I'll also bin the boiler and replace with a length of tube, as I feel that the boiler-bands-in-grooves method (a) doesn't result in a neat or convincing look, and (b) is a solution in search of a problem. I'll simply represent the bands with transfers. 

[polybear]

I've devised an alternative to the rod method over the years. It might be good for experienced modellers, but there's an easier way for the less experienced. The two main problems with it are (a) once in the vice it's hard to see when the rod is square to the workpiece (though you could tack superglue rod to workpiece) and (b) it leaves most of the workpiece unsupported; only the point where the rod contacts is supported and that's problematical in your case where the bunker back wants to bend somewhere other than where you want it to. 

 

Below is the method I've devised. I've sketched it out as it's hard to get a clear photo. The basic method is trapping the workpiece in the vice jaws between two pieces of wood (I use the type used as backing by Eileen's Emporium), one of which has a radius slightly smaller than that required filed on it, which is positioned against the relevant part of the workpiece. 

 

20181124_065356.jpg

 

20181124_065420.jpg

 

For the actual bending itself, you can use a heavy bit of metal bar, or wood; but what I do is turn the vice upside down and press it (and the protruding part of the workpiece) against the bench. I find it's easier to get even pressure that way. 

 

This is photo of the bending about to happen, but as I said it doesn't show much: 

 

20170709_094927.jpg

 

The results: 

 

20170709_095157.jpg

 

Finally, don't get too stressed - you can always replace kit parts in sheet N/S if you damage them, using the original for dimensions. 

 

I've heard that using a piece of wooden skirting with a rounded top can be used as the curved profile to bend against.  Take a wander around one or two DIY stores (don't take the missus, cos' she'll starting getting expensive, time-consuming ideas...) and look for a suitable profile.  HTH

[Daddyman]

I've heard that using a piece of wooden skirting with a rounded top can be used as the curved profile to bend against.  Take a wander around one or two DIY stores (don't take the missus, cos' she'll starting getting expensive, time-consuming ideas...) and look for a suitable profile.  HTH

Possibly in some cases, but the radius would be too large for many applications. 

[Torper]

Oh, another thing about this kit: if you're modelling in 00, don't make the same mistake I did of following the instructions around the bogie frames! 

 

The instructions will have you position the dummy frames outboard of the wheels, when of course they should be inboard. This photo shows the error on my C15 - it ruins the front end look: 

 

I'm modelling the kit in P4 and the bogie frames are correctly inboard of the wheels.  I think it would be difficult doing the kit in 00.  It's apparently "pitched at the competent EM/P4 modeller" and I'm not sure that, for example, the fold up chassis and the gearbox unit would be narrow enough for 00 - width of the fold-up chassis is 15.1mm without wheel bearings which would, of course, add a little more.  Having said that it's a brilliant design - not often (ie never) have I assembled a chassis, wheels and gearbox for the first time and then watched it freewheel down a slight slope without any tweaking at all.

 

In any event, many thanks to everyone for your help on this.  Annealing, I hope, will take place this afternoon and then I'll try to bend the thing, initially at least using Peter's method with the handle of a small file as the rod - it's a little smaller than the required radius.  If I don't get on with that, I'll see if i can sand a piece of wood to the required shape to try Daddyman's method.  Happily 52F supplied two bunker rears (dependent on period modelled) so I'll try it all out on the spare first!

 

DT

Edited November 24, 2018 by Torper

[PenrithBeacon]

I've devised an alternative to the rod method over the years. It might be good for experienced modellers, but there's an easier way for the less experienced. The two main problems with it are (a) once in the vice it's hard to see when the rod is square to the workpiece (though you could tack superglue rod to workpiece) and (b) it leaves most of the workpiece unsupported; only the point where the rod contacts is supported and that's problematical in your case where the bunker back wants to bend somewhere other than where you want it to.

 

Below is the method I've devised. I've sketched it out as it's hard to get a clear photo. The basic method is trapping the workpiece in the vice jaws between two pieces of wood (I use the type used as backing by Eileen's Emporium), one of which has a radius slightly smaller than that required filed on it, which is positioned against the relevant part of the workpiece.

 

20181124_065356.jpg

20181124_065420.jpg

 

For the actual bending itself, you can use a heavy bit of metal bar, or wood; but what I do is turn the vice upside down and press it (and the protruding part of the workpiece) against the bench. I find it's easier to get even pressure that way.

 

This is photo of the bending about to happen, but as I said it doesn't show much:

 

20170709_094927.jpg

 

The results:

 

20170709_095157.jpg

 

Finally, don't get too stressed - you can always replace kit parts in sheet N/S if you damage them, using the original for dimensions.

I’ve used this method for bending over the curve over the cab cutout for a Fowler engine; it works.

[micknich2003]

"Daddyman's" method works perfect, I used the same idea many years ago to form the tanks etc on a 4mm H&BRly engine I home brewed. It's far easier to have the metal over long and then cut to exact size after bending.

[Daddyman]

I'm modelling the kit in P4 and the bogie frames are correctly inboard of the wheels.  I think it would be difficult doing the kit in 00.  It's apparently "pitched at the competent EM/P4 modeller" and I'm not sure that, for example, the fold up chassis and the gearbox unit would be narrow enough for 00 - width of the fold-up chassis is 15.1mm without wheel bearings which would, of course, add a little more.  Having said that it's a brilliant design - not often (ie never) have I assembled a chassis, wheels and gearbox for the first time and then watched it freewheel down a slight slope without any tweaking at all.

The fold-up chassis certainly works in 00 - my C15 chassis runs like your C16. I haven't opened the box on the C16 yet but I can't imagine it will be any different. The inner faces of the outer/main chassis are 12.5, so the inner chassis will be about the same. 

 

I'm surprised you even have to bend the bunker rear with a 52F it. If not exactly designed for beginners, they're designed for building without ...let's say "unusual" tools - bending bars etc. All the other parts, as you know, are pre-bent by Peter. 

[Torper]

The fold-up chassis certainly works in 00 - my C15 chassis runs like your C16. I haven't opened the box on the C16 yet but I can't imagine it will be any different. The inner faces of the outer/main chassis are 12.5, so the inner chassis will be about the same. 

 

I'm surprised you even have to bend the bunker rear with a 52F it. If not exactly designed for beginners, they're designed for building without ...let's say "unusual" tools - bending bars etc. All the other parts, as you know, are pre-bent by Peter. 

 

According tio the 52F website, there are two versions of the C15 kit, one for 00, the other for EM/P4.  However, there only appears to be an EM/P4 version of the C16, though Peter does say that if there is enough interest he'll do a 00 kit as well.  It may well be that that has happened and the website hasn't been updated, but perhaps you should check your C16 kit to ensure that you haven't got an EM/P4 version.

 

Yes, I have a little packet of pre-bent items which is very useful.  It would indeed have been nice were a flared rear bunker to have been included, but I am meant to be a reasonably competent modeller so it'll do me no harm to try and do this myself.  Certainly the kit has fully tested my soldering skills which has actually been quite satisfying.

 

DT

[Daddyman]

Yes, you're right - I've just had a look at the box: EM and P4 only. I'm sure it will be possible to adapt it - or maybe this is the moment for me to go P4... 

[Torper]

I doubt very much if it will be possible to adapt it - the gearbox/compensation unit folds up to an outside width of 14mm and fits inside the chassis, which is 15.1mm wide excluding wheel bearings.  That's bordering on being a little  tight for EM, but it's perfect for P4.  Maybe Peter would swap it for a 00 one if they really are in the pipeline, or a different kit if they're not?  I suspect you didn't order wheels with your C16 as if you had you'd have had to specify EM or P4. Anyway, every cloud.....as you suggest, now's perhaps the time for that P4 plank you've always wanted to do!

 

DT

Edited November 24, 2018 by Torper

[Daddyman]

Nah, it'll be easy enough to adapt - just need to copy the C15. There's nothing in the gear box that obliges the inner chassis to be so wide. And it's always possible to replace the gear box with a High Level and use that as an excuse to liberate oneself from the inner chassis thing in favour of beams which can move independently of each other - unlike those in the kit.  

[MarkC]

Peter's A8 chassis kit has two versions - one for OO and one for EM/P4. As the main assembly folds up from one piece, this makes sense. I'm thinking that this is also true for the C15?

[Torper]

Peter's A8 chassis kit has two versions - one for OO and one for EM/P4. As the main assembly folds up from one piece, this makes sense. I'm thinking that this is also true for the C15?

 

It is for the C15 but not - yet - for the C16, which is EM/P4 only.

 

Anyway, I've just completed annealing and bending the bunker rear section and somewhat to my surprise it went very well indeed and is now a perfect fit on the bunker sides.  Many thanks everyone - without you I would not have achieved such a good result.

 

DT

[Daddyman]

Good to hear! 

 

The ultimate test is to colour the curved part with a Sharpie pen - that will show if your curve is even. Better to find out that way if there's a problem than when you get topcoat on...