Jim's 7mm workbench: Acorn BR Standard 3 Tank

[jim.snowdon]

With the last project complete bar the painting, time to start on the next, this time a kit for the BR Standard Class 3 2-6-2T (the 82xxx class). The kit comes in a box labelled "The Transport Age, designed and produced by Acorn", which to me is a euphemism for a Him Harris kit, and all the health warnings that go with those. I expect it to be a challenge.

 

To call it a Jim Harris kit might perhaps be a little unfair, as it does appear to have had some work done on it, at least in terms of there being a selection of brass castings that I would not otherwise have expected, and the frames are etched in nickel-silver, albeit still only 0.5mm thick. Whether the etchings themselves have been subject to any updating is something that will only come to light as construction proceeds.

 

First step is to cut out and consider the frames. As usual, I will be fitting hornguides and springs, using the Slaters components, and PFS plunger pickups. That entails a fair degree of preparation, best done whilst the frames are still in the flat, in terms of cutting out the openings for the hornguides and the necessary holes for the pickups.

 

Kits of this vintage predate the general availability of off the shelf hornguides and so the frames are quite plain - just the holes for fitting the brass axle bushes. Not surprisingly, these weren't in line, although only by virtue of the centre one being raised slightly - I have seen worse in other JH kits. Marking out the cutouts for the Slaters hornguides starts with locating the horizontal and vertical centrelines of the axleboxes. The former is worked out by measurement from a reference edge, in this instance the top edge of the frames, which is straight, using a vernier caliper to establish the hole diameter and the distance between the top of the hole and the frame edge. The vertical centreline of the centre axle is established by eye and the positions of the leading and trailing axles by measurement. The edges ofthe cutouts can then be marked out, leaving a bit extra on the width to allow for misalignments as the hornguides will be positioned from the coupling rods using extended axles. Getting the top edges of the cutouts in line is more important, as this will set the ride of the locomotive since the Slaters castings do not provide for any adjustment post-installation (not that I have ever found that to be necessary).

 

Before the cutouts can be cut, the olther step is to plan where the pickups will go and drill the requisite holes for these. The position of the plunger is fairly critical in ensuring that it contacts the back of the tyre. The mean radius of the tyre can be determined by measurement, but setting this out on the frames requires being able to pick up the axle centre. For this, I made up a brass button that fits into the hole already etched in the frames; this has a small centre mark machined into the face to take one legs of a pair dividers, thus -

 

 

 

With everything marked out, the various holes and corners are centre punched and drilled approximately 0.8-0.9mm. For what will be holes, these serve as pilots for the larger drill that will follow; for the hornguide cutouts, drilling the corners provides a space in which to turn the piercing saw blade, making life easier and reducing the rish of blade breakages.

 

The before and after result is -

 

 

I have long preferred plunger pickups to either wire or flat strip, not least because the presence of dummy springs and other gubbins beneath the frames tends to get in the way of the latter. The PFS variety has been my preferred choice for a long time, but I do modify them slightly by fitting up a plastic bush for the plunger. This both improves support for the plunger, which would otherwise tend to get locked cock-eyed in the hole in the pcb, and eliminates the possibility of its getting stuck in the hole due to traces of stray flux from when the backplates are soldered to the frames. These I machine up from a length of hard plastic knitting needle I acquired from the domestic stock some time ago, and are arranged to protrude through the frames to within about 0.5mm of the back of the wheel, making due allowance for any sideplay.

 

 

 

The tail of the spring pokes through the backplate and needs to avoid being in contact with the frames for obvious reasons. I used to recess the cut end using a grinding disc in the minidrill but partly as a result from the occasional shorted collector (alright if it is only one) and partly on account of the glass dust that was generated, I changed to drilling a clearance hole in the frames where the spring would come through. That ensures that so long as the pickup is aligned correctly, the cut end of the spring is in fresh air. The hole is usually hidden away, but if not, it is easily filled with a spot of epoxy, filed flush.

 

That gets the frames ready for erection, however at this stage, experience with kits from this era dictates that it is wise to check the frame stretchers for consistency. Sure enough, some of the stretchers were 25mm across the faces, whereas others were 24.5mm or slightly less. At this point the scratchbuilding part of these kits starts. Since the largest of the stretchers, the horizontal one between the cylnders and the motion plate that keeps the frames square, was the widest and tied in with the slots etched in the cylinder stretchers, it was chosen as the datum. New stretchers for the pony truck pivots and the rear body attachment were cut from scrap nickel-silver etch -

 

 

The difference in the length is noticeable, as is my provision of a slot instead of the original hole for the body mounting screw - I have been bitten before where the screwholes in body and frames do not quite line up.

 

Jim

 

 

[Sandy Harper]

This is Spooky Jim! See my latest post.

Sandy

[jim.snowdon]

These class 3s must be like buses - you wait for ages, then three come along all at once. One result of your post was my finding someone else on the RMW 7mm+ section looking to build one and being encouraged to do a build thread.

 

The other coincidence is that I have a Chowbent Stanier 2-6-2T in my build queue, although that,  hopefully, will be a more straightforward build to start with - they were better designed kits.

 

Jim

[JeffP]

Interesting start, and thanks. I like the centring button idea.

 

Jim, can I ask why you don't tack solder the frames together and do all the cutting/drilling as one, as I used to in 4mm? I picked up the tip from Rod Neep, supposed to be super accurate.

[pwr]

Jim

 

What motor gearbox are you using? The Scorpio instructions don't reference a motor at any stage in the build which seems strange?

 

Paul R

[jim.snowdon]

Interesting start, and thanks. I like the centring button idea.

 

Jim, can I ask why you don't tack solder the frames together and do all the cutting/drilling as one, as I used to in 4mm? I picked up the tip from Rod Neep, supposed to be super accurate.

Jeff,

 

I suppose I might have done if I was cutting a new set of frames from scratch, but with the frames already in the etch, it just seemed simpler to mark them up individually. A bit of a case of six and two threes.

 

Jim

 

What motor gearbox are you using? The Scorpio instructions don't reference a motor at any stage in the build which seems strange?

 

Paul R

Paul,

 

It will be getting a Canon 1833 + ABC VML2 gearbox (my usual choice). That the instructions don't make any reference to motors and gears is normal - there are very few kit designers that actually consider the means by which the finished loco will be driven. The other 99% just leave it to be builder to improvise his chosen favourite, which can be anything from old-fashioned worm drives to proper gearboxes. The latter are my preference, both because installation is much simpler, as well as facilitating the use of sprung axleboxes, and for their greater efficiency.

 

Jim

[jim.snowdon]

Last item before erecting the frames is to fit the pickups, if only because access for soldering gets more and more difficult from here on.

 

 

Interestingly, although these were designed to be soldered in place, and that is commonly what I have done with them, looking back over an earlier project, the LNW Prince of Wales, I found that I had glued them in place on that build. In fact either will do, and I would admit that using epoxy does eliminate the problem of getting the solder to flow into the joint, especially with the rounded tips of the bits on the Ersa soldering iron. In pre-Ersa days, I used a 75W Weller with a copper tip that I had to dress periodically, which meant that I could get it to a sharp edge that was much better at getting solder into the corners of joints.

 

That done, it is time to start on putting the frames together. Fortunately, there are a pair of stretchers in the space behind the cylinders that are at right angles to each other, which helps in getting everything square. They go in first -

 

 

after which the other frame plate can be added -

 

 

That will get the two frames set at the correct separation, and parallel, but not square to each other looking across the chassis. At the rear end, the frames are connected solely by two horizontal stretchers, and a brass bar screwed in place (or it would be were I not discarding it - I have no real like for old fashioned bar stretchers attached to the frames by screws). The result is that the frames are qeite flexible where they really ought not to be. To stiffen them up and maintain squareness, I cut a new vertical stretcher from scrap etch and fitted that into the vertical grooves on the frames that mark where they should be cut for the 2-6-0 version. These are helpful in that they will provide positive location for the new stretcher.

 

 

 

Fitting this to one frame shows just how out of square the frames can be. Once secured to both frame plates, the new stretcher will hold the frames square.

 

That just leaves fitting the two stretchers for the pony truck pivots to complete the basic chassis.

 

 

 

 

The front ends of the frames are still waving about in the breeze somewhat, but that will be improved in part once the cylinders are fitted, and by an additional stretcher I will add close behind the buffer beam later on. As designed, the body has no positive fixing to the chassis at the front end, the builder being left to improvise some form of clip. I intend fitting a screw under the front footplating, but as it will have to be soldered in place, head upwards, underneath the body, the stretcher that will receive it needs to be set down from the top edge of the frames to accommodate the thickness of the head. Because the position of the screw is still indeterminate, that stretcher will not get fitted until much later on.

 

The eagle-eyed will also notice the length of blue wire that is not a carrying handle. The rear set of pickups are immediately above the rear pony truck stretcher and would be difficult to get to after the latter is fitted. So, the leads have to go in first.

 

Even with all of the stretchers in place, the middle section of the chassis is quite flexible, more than I would like. The need to leave space for the gearbox precludes putting much in there by way of stiffening, but once the hornguides are in, I will probably add a longitudinal stiffener of some sort, primarily to counter the thinnessof the frames - 0.5mm is a little too thin for frames, but is a common standard amongst earlier etched kits, probably because it was cheaper and avoided the complicatins of having to lay the artwork out on two different sheets of metal.

 

Jim

 

 

[pwr]

Jeff,

 

I suppose I might have done if I was cutting a new set of frames from scratch, but with the frames already in the etch, it just seemed simpler to mark them up individually. A bit of a case of six and two threes.

 

 

Paul,

 

It will be getting a Canon 1833 + ABC VML2 gearbox (my usual choice). That the instructions don't make any reference to motors and gears is normal - there are very few kit designers that actually consider the means by which the finished loco will be driven. The other 99% just leave it to be builder to improvise his chosen favourite, which can be anything from old-fashioned worm drives to proper gearboxes. The latter are my preference, both because installation is much simpler, as well as facilitating the use of sprung axleboxes, and for their greater efficiency.

 

Jim

 

 

Jim

 

Just out of interest what gear ratio are you using?

 

Paul R

[jim.snowdon]

Next would be fitting the hornguides, but to that, the coupling rods need to be made first.

 

I have elected to use the etched rods from the kit, although as is typical of the age of this kit, the representation of the knuckle joint is nothing to write home about. It is, I think, salvagable by dint of adding a small cast crankpin nut to the front, but I will leave that until a bit later. The rods themselves are etched as three layers, and at least the designer took the care to put the cork on the middle layer. Building them is straightforwards and what you end up with is -

 

although they still need cleaning up.

 

Since they introduced tham, I have been quite taken with the Slaters cast brass hornguides (7960B) and am now using them as standard. The castings are very good and the bearings simply dropped in without any cleaning up being necessary. The clearance is enough to allow free movement but not such as to be sloppy. From discussion on another forum, there seems to be some debate as to how best to fit the spring retainer plates to the top of the axle bearings, with at least one contributor advocating simply leaving them free, trapped between the spring athe bearing and retained by being engaged in the tongues on the horncheeks.

 

I have always soldered them to the tops of the bearings, and after some early headscratching, settled on the method below.

 

First step is to tin the backs of the retainers whilst they are still in the etch fret -

 

 

then, after re-fluxing both surfaces, set bearings down on every alternate retainer and line them up with the edges and slots -

 

 

then warm the whole lot (which is standing on a refractory block) with the gas torch until the solder melts, when each bearing will visibly settle down flat on the etch under its own weight.

 

 

When they have cooled, those three are cut from the etch using the piercing saw, and the process repeated for the remaining three. It isn't possible to do all six at once as the bearings are slightly wider than the pitch of the retainers.

 

The result -

 

 

I doesn't matter greatly if the slots in the retainers do not line up exactly with those in the bearing - there is a bit of latitude available, and if they are too far out, it is a case of either running a thin file up the grooves, or filing back the ends of the retainer.

 

 

With all six bearings dealt with, it is time to fit the hornguides to the frames. For this, I thread the extended dummy axle through a compression spring (and several washers and spacing collars) so that the hornguides have to be squeezed together a small amount to fit between the frames. The spring wants to be compressed sufficiently to hold the hornguide in place whilst it is tack soldered, but not exert so much force as to distort the frames (bearing in mind that they are relatively thin)

 

 

 

For a six-coupled locomotive, it is best to start with the middle axle, as then any tolerances in the coupling rods do not accumulate. Unlike some, the Slaters castings have a U shaped rib cast on the frame side of the hornguide, so that, providing care was taken when making the frame cut outs to cut the tops accurately to the line marked on the frames. The sides of the cut outs do not need to be so accurate as they are not used for referencing the hornguide position - the extended dummy axles do that. I actually make these cut outs wider than is necessary to allow for some fore and aft latitude in postioning the hornguides.

 

Because the rods in this kit are articulated on the centre crankpin it matters not whether you start with the front or back sections; where the rods are jointed at the knuckle, the section that coveres two crankpins has to be set first. That section then has to be held in place on two dummy axles whilst the third axle in the set has to be used to position it.

 

 

All done.

 

Apart from soldering the hornguides in properly the cast keep plates need to be fitted; the springs I will leave until a little later, as they are too easy to lose at this stage. What I will do in due course is to put a tiny spot of epoxy in the recess on top of the retainer and set the spring into that, thus fixing it to the axlebox.

 

Next will be fitting the wheels and starting on the motion.

 

Jim

[doilum]

Hi, I have just rejoined the forum. Santa brought a class 3 tank kit via the Scorpio model stable. This is my first mainline loco in almost ten years having concentrated on breeding NCB Hunslets. I am interested in Jims progress with the cylinders and motion. Anynews yet?

[jim.snowdon]

Next, in fact , is addressing the situation as regards the cylinders - the wheels can wait, and to do the motion, you need the cylinders.

 

Like most kits, the basis for the cylinders is a pair of etched cross members, profiled to the cylinder block outline and designed to be fitted into slots in the frames, with corresponding slots in the cross members to locate the cylinder block across the frames. The depth of the slots sets the vertical position of the cylinder block, or not in this case -

 

Not entirely unexpectedly, their position is nowhere near where it ought to be.

 

 

Putting a rod through the holes that correspond to the cylinders, using a couple of bushes I turned up for the purpose, shows that the cylinder centre line is nowhere near pointing to the centre of the driving axle. By reversing this approach, and comparing against the drawings, it is possible to set the two cylinder block profiles to what should be the correct vertical position and mark the frames accordingly.

 

Another problem to be dealt with is that the castings for the motion brackets do not line up with the cylinders by about a millimetre. Checking the dimensions, initially against the with of the loco itself, the conclusion was that the cylinder etches are under width. On top of that, the holes provided for locating the cylinder front and back covers are way too large compared to the castings that will fit into them. Now, we are into scratchbuilding, as the only practical solution is to cut a new set of cylinder profiles. That allows the dimensional issues to be sorted out.

 

 

There is still the question of how to mount them and get them in the right position. Going back to the marks on the frames from the first trial alignment, and adjusting these for the shape of the new cylinder profiles, the frames were marked with where the tops of these should be. To support them, a new frame stretcher was going to be required, simple enough except for thinking how to get it in the right place.

 

The solution I adopted was to solder two lengths of brass angle inside the frames, lining them up with the marks on the outside whilst holding each one in place with a hairclip. (Useful things where normal clamps just won't go.)

 

 

Fitting them is a delicate operation, and once done, the surplus is trimmed off to leave the frame slots clear.

 

 

The frame stretcher is then cut and fitted underneath the angles. This is cut from a piece of 1mm nickel silver left over from a much larger project (the 7.25" Class 14) as it will ultimately be drilled and tapped to take the screws I shall use to secure the cylinders.

 

The new cylinder block is essentially an inverted U fitted over the top of the new stretcher, with the profiles soldered under the edges of the top plate -

 

 

To stiffen the assembly, two longitudinal spacers are fitted between the front and back profiles, outside and clear of the frames.

 

 

Clearance to the frames, and avoidance of stray solder locking the whole lot into the frames, was achieved by the simple expedient of using a scrap frame stretcher as a spacer.

 

The result, albeit only tasked together at this stage, is a complete cylinder block that will drop into the frames and be secured by four 10 or 12BA screws through the top plate.

 

 

 

In due course, I intend attaching the motion brackets using screws, so that the whole of the motion can be lifted out if need be (hopefully not too often).

 

Jim

[doilum]

Looks like I will be binning the cylinder assembly I built at the weekend. The scorpio instructions lack a scale drawing and hint at a "make it fit" approach.

What is the overall distance between the cylinder centres?

Are the wrappers the correct width?

I may be lucky. The scorpio kit uses parts from a brass etching leaving the ones on the nickel silver frame etch unused. Is this a correction?

[PAD]

Hi Jim,

Nice work. Is there  any  particular reason why you  use 4 bolts to retain the  cylinders instead of  one  bolt in the centre?

Cheers,

Peter

[jim.snowdon]

Looks like I will be binning the cylinder assembly I built at the weekend. The scorpio instructions lack a scale drawing and hint at a "make it fit" approach.

What is the overall distance between the cylinder centres?

Are the wrappers the correct width?

I may be lucky. The scorpio kit uses parts from a brass etching leaving the ones on the nickel silver frame etch unused. Is this a correction?

The new cylinders scale at 8' 8", slightly wider than the prototype 8' 6 5/8", but better than the original kit etches, which come out at 8' 4". The cylinder centres on the kit etches are 6' 5", instead of the prototype 6' 8", which dimension I have managed to achieve with the new cylinders. That also points to the motion bracket castings being correct for the frames as designed as they were used as the datum for the new cylinders, being effectively unalterable.

 

Hi Jim,

Nice work. Is there  any  particular reason why you  use 4 bolts to retain the  cylinders instead of  one  bolt in the centre?

Cheers,

Peter

Peter,

 

Thank you. Is there any particular reason.... well, no. Four small screws just seemed "right" - two would have done just as well, and one just seems a tad parsimonious. I would just put it down to "engineering artistry".

 

Jim

[PAD]

Well Jim, it  does look more elegant than one would, but  I guess I am just tight!

Cheers,

Peter

[Sandy Harper]

That's a pain Jim and a lot of work for what should be a straight forward job.

I didn't have that problem with the Stanier but I had issues with the large cast motion bracket that was too short, in the width, to attach to the frames when it was attached to the ends of the slide bars. I think this may have been because I made sure that I had the cylinder rear castings as close to the outside of the cylinder etch as was possible to try and avoid clearance problems later. Like yours, the etched holes were way too big for the casting stub. It didn't resolve the clearance issues that I had expected and I am going to have to revert to my usual 10BA replacement crank pins, and reverse fitting Slaters bearings, to get the clearance I need behind the slide bars and cross head.

 

Sandy

 

The red is where the clearance issues are and the green is where I had to extend the casting. Still a bit rough and needs cleaning up!

[jim.snowdon]

Sandy,

 

I am a tad surprised that you ever thought you could get away with a nut and washer on the leading crankpins. Still, useful to know about the motion brackets.

 

Jim

[doilum]

Just had a chance to get back to the workshop.

The scorpio brass etching gives an overall width of 60mm or about 8'7'' in old money. The cylinder centres are 49mm or 6'11''. Mocking up the motion brackets, they seem as if they will match the cylinder assemblies.

This is all a bit hypothetical as I havent soldered up the frames as I await a birthday to cash in the IOU for wheels and pickups at Slaters.

Meantime I shall look for some 25mm brass frame spacers to provide a temporary fixing via the plunger pickup holes before soldering up the chassis .

Yesterday, I managed to punch the rivets on the cab sides and chopped out the bunker floor to clear a switch that will allow me to fit my first ever dcc chip for running on the club layout.

[jim.snowdon]

That rather suggests that what I have got, labelled as Transport Age / Acorn, isn't from the same parentage as the Scorpio one.

 

Jim

[Sandy Harper]

Sandy,

 

I am a tad surprised that you ever thought you could get away with a nut and washer on the leading crankpins. Still, useful to know about the motion brackets.

 

Jim

I'm NOT surprised but, as this is a test build, I am trying to build it with what is available in the kit or, normally available to the 'average ' builder, and only deviating when there is no alternative! These deviations will be highlighted in the instructions for the benefit of builders not as savey as some of us!

 

Regards

Sandy

[doilum]

The "surplus" nickel silver cylinder ends on the main frame etch are 58mm overall and 46mm between centres.

[jim.snowdon]

I'm NOT surprised but, as this is a test build, I am trying to build it with what is available in the kit or, normally available to the 'average ' builder, and only deviating when there is no alternative! These deviations will be highlighted in the instructions for the benefit of builders not as savey as some of us!

 

Regards

Sandy

Oops! I had forgotten about this not being one of your usual builds.

 

Jim

[doilum]

Having an hour or so with the scorpio bodywork.

If our kits have a common parentage, this might be a heads up.

Instruction 8) take body/cab (68) and trim one millimetre off the inner face of the tank to clear the firebox /boiler.

Much easier to do neatly whilst still a flat sheet.

There is no provision for inner sides to the tanks, so now might be a good time to make a pair in case the are needed later.

[doilum]

A successful hour.

Trimmed back the tank tops having realised that they are not straight, but taper in two sections to match the profile of the firebox and boiler.

Next step was to fold the tops back and solder up the tank fronts. The fronts bend easily giving the rounded edge of the prototype.

I decided that this was a good time to fold up the cab doorways and add the handrails whilst everything is flat and accessible. Time now to quit whilst I am winning.

[doilum]

Another good morning. Having braced the gap between the tanks with a temporary strip of brass, I folded up the body sides. Top marks to the original draughtsman, it was like those models on the back of a cornflakes packet. Only a tiny adjustment to the floor section and everything is sat strong and square.

I have decided to add all the steps,handrails and lampirons to the rear whilst it is still flat on the bench.

The instruction drawings are not entirely clear, so can anyone advise me about which direction the lamp irons curve, and is the middle one curved also?

I have found an excellent picture of 82041s82041in the september 2017 issue of steam railway magazine. Lots of clear detail of all the motion and plumbing on the nearside, but no rear view.