Ian_C's workbench - P4 and S7 allsorts

Discussion in 'Workbenches, including workshop techniques.' started by Ian_C, 21 May 2017.

  1. Threadmark: The cab roof
    Ian_C

    Ian_C Western Thunderer

    The cab roof is another job that's been continuously pushed down the to-do list in favour of easier stuff. Can't put it off any longer I'm afraid, and it did turn out to be a bit of a performance.

    I wanted the roof to be removable to make assembly of the cab interior detail and painting of the cab easier. The design intent of the kit is to solder the roof to the cab front and sides, so some modification was necessary.

    The kit provides an etched roof (flat), a sliding ventilator part and a half etched plate for the rear of the roof to represent the section that can be unbolted to enable lifting gear to get to the rear of the drag beam. The cab profile is not an easy shape to form, consisting of a sequence of curves and straight sections. After a lot of careful bending and tweaking I got a reasonable fit onto the cab but it was clear that I'd never get it to sit down perfectly. For fixing I'd considered small screws inside the cab, springy wire clips, micro magnets, but none of them seemed straightforward. The solution I adopted was to avoid fighting the springiness of the formed roof and make it a rigid lid that dropped into place and was retained by gravity and friction.

    First step was to make some stiffening ribs to hold the cab roof to the required profile. The etched cab roof rib that was already part of the cab assembly was unsoldered, tacked to a scrap of N/S sheet (0.7mm ish) and scribed around, and repeat. Piercing saw and files get you two very stiff ribs of the correct profile that can be soldered inside the roof. The etched rib is the uppermost in the photo below. I included some prongs at the ends of the rib, and they will locate in some slots cut in the cab side flange.
    roof and frames.jpg

    One rib was soldered in place just far enough back from the front edge to to be clear of the inside of the cab front sheet. The other sits just in front of the etched cab frame rib. This means that the longitudinal ribs provided in the kit that fit between the cab front sheet and the etched rib can't be used. They don't serve a purpose any more so bye bye. The kit intends the cab roof to be located by tab and slot. The tabs on the etched rib can be filed off and the slots near the front of the cab roof can be soldered up (the two small scraps of brass in the photo below). Now the roof is fixed to the exact profile, there's no springiness and it's become a rigid unit. The other bonus is that it can be held by the rather substantial ribs for the work that follows.
    roof with ribs.jpg

    With the ribs fixed, their positions on the cab roof flange can be marked. Well, almost. The etched cab sides have a flange above the windows to stiffen the top edge of the side sheets (I guess) and to provide something to solder the edges of the roof to. To prevent distortion of the window frames when the flange is bent there's a long relieving slot etched along the bend line. It certainly prevents the top of the window frames from being distorted but it all but negates any stiffening effect. Also the only areas where the flange is attached happen to be where the roof ribs are, so cutting a locating slot there makes the stiffening flange minimally attached. The remedy is to solder a length of 0.5mm wire inside the bend and fill the slot with solder (dotted line in the photo below). That makes the whole thing far more solid and we can cut locating slots without a problem. The locating slots are circled red in the photo below. If the slots and prongs are matched very carefully the roof can be a gentle press fit into position and be accurately located on the cab. A lot of words, but I hope it's clear from the photos.
    cab 1.jpg

    With that problem solved we can look at the cab roof detail. The Stanier roof is quite a dog's dinner of plates, angles, rivets, rain strips and beading and of course the ventilator hatch. The simple etched parts look a bit 2D and don't do it justice. More hairshirted tomfoolery follows of course.

    The rear edge of the roof (1/8" plate on the prototype) is finished with an angle section to stiffen it and stop rain dripping on the fireman. The angle is 1-1/2" on the prototype, and that's about 0.9mm in 7mm scale. I represented this with a strip of brass soldered to the edge and filed to shape. Rather than try and position a tiny strip accurately it's easier to solder on a wider strip in roughly the right place and file it back to size. It helps to anneal the brass first to make it easier to bend. Here it is soldered in place.
    roof rear angle 1.jpg

    File the lower edge of the strip flush with the inside surface of the cab roof first. Then mark 0.9mm offset from that edge and file the top edge of the strip back to that line. Finally cut the ends off the strip to match the edges of the half etched overlay plate.
    roof rear angle 2.jpg

    There's worse to come. The cabs had a beading section running from above the cab side wing plates (to which the cab doors are attached) up the rear edge of the side plate and following the roof edge curves around to butt up to the end of the aforementioned angle section at the rear of the roof. It's a surprisingly chunky section, measuring 2-1/4" x 3/4" with a sort of shallow 'D' profile. That's 1.3mm x 0.45mm in our world. That was made by making some 1.3mm wide strips about 60mm long from a sheet of 0.45mm N/S.
    roof and strips.jpg

    There's a lot of bending in both planes and the strips need to be annealed to make that possible. Heat them to a gentle red with the mini torch, pick them up with tweezers and wave them around in the air for few seconds. That cools them fast enough to anneal them fully, and they're very pliable to begin with. I started at the top and worked my way around the cab curves and down to the wing plates. This time the strip has to be accurately positioned so that it's centred on the edge of the roof. No bodgery and filing to shape permitted here. I pre-formed the initial curve along the rear edge of the roof and tack soldered that in position first. Then it was a case of working along pressing the strip into position and tacking. Note that the more you bend and re-bend the strip the more it work hardens and may eventually fatigue through and break. It's easy enough until you get to the last bend where it runs down the rear of the side sheet. The roof has to be placed on the cab to form that bend and because it's quite a tight bend across the flat of the strip it's an a*s*.
    roof bead sequence.jpg

    Because the roof is to be removable the bead strip has to be cut near the junction of roof and side sheet. I chose to make the cut where the bend straightens out. It means there's a little bit of beading projecting from the cab roof corner and the roof has to be handled carefully thereafter to avoid bending it out of shape. The final short straight section of beading on the rear of the cab sheet is positioned to match. When it's all tacked in place it can be carefully soldered along its length. The final task is to create the D section by rounding the edges with files and wet & dry. You can see the break in the beading here, and I'm hoping it'll be less obvious when painted.
    bead gap.jpg

    The roof edges on the prototype were formed up into a semi-circular rain gutter about 5/16" outside radius. Can't really replicate that at this scale, but a flat edge doesn't look right, so a length of 0.3mm brass wire was soldered along the edge and blended in. Of course it's not the U shape of the prototype but it looks the part at a normal viewing distance.
    rain gutter.jpg

    The etched part for the roof vent was a bit clumsy so a replacement was made from a scrap of N/S closer to scale thickness. It took a bit of research to figure out whether there was any detail on the ventilator. The cab drawings in the Wild Swan book show that the whole ventilator hatch was riveted together. Eventually I found a good photo looking down onto the roof of a Black Five which had an almost identical cab. Looks like the small rivets were flush with the surface and don't show at all. There were four bolt heads along the rear edge and they were made from 0.5mm wire soldered through holes and filed down. Here's the finished roof in position. A lot more work that I'd imagined, and I hope the Modelu crew appreciate it when the scaleseven Toton drizzle doesn't run down their little resin necks.
    finished roof.jpg
     
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  2. Dan Randall

    Dan Randall Western Thunderer

    :)):)):)) That did make me chuckle! :thumbs:


    Regards

    Dan
     
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  3. Threadmark: More cab details - injector water valve control
    Ian_C

    Ian_C Western Thunderer

    Just for fun* , the water valve control for the live steam injector. The handle's about 3mm long. A bracket from NS scrap, a tiny turning, some 0.6mm wire and a little 0.5mm wire, all silver soldered together.
    Driver side injector control.jpg

    * - legal definition of 'fun' that you were previously unaware of.
     
  4. Threadmark: More oil boxes for the cab
    Ian_C

    Ian_C Western Thunderer

    When I made the oil boxes for the framing I forgot to make some for the cab. Two varieties; 2 x larger oil boxes with two outlets each, for the rear axleboxes I think, and 1x smaller oil box with three outlets, which I assume is there to lubricate the damper control linkage beneath the cab.

    A bit of 'how to ' for those wot's interested. The basic section (1.5mm x 1.8mm) was milled from some 1/8" brass strip. The angle on the top for the lid was filed on and the section cut into oil box lengths (2.7mm) and cleaned up. The outlet positions were marked on the bottom of the boxes by eye using a sharp scriber to make an indent. That's usually just enough of an impression to start a small drill. The holes were drilled using a pin vice, 0.5mm for the small box and 0.8mm for the larger. Short lengths of micro bore brass tube were pushed into the holes and snipped off over long. Some pieces of scrap etch were cut well over sized for the lids. The whole lot was cleaned and silver soldered together (Linbraze TOS155-HA30-W1 silver solder paste with flux , 630C, in 10g syringe applied with the tip of a cocktail stick - makes it easy). Various stages of finishing and cleaning up shown below. I have to say that taking photos of your work like this does show up all the carbuncles and provides some motivation to improve.
    cab oil boxes making 2.jpg

    That's definitely the last of the oil boxes. Unless there are some on the tender - I'm not going to check.
     
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  5. Threadmark: Cab interior progress
    Ian_C

    Ian_C Western Thunderer

    Here's where I've got to with the cab interior.

    cab interior 1.jpg
    cab interior 2.jpg
    cab interior 3.jpg

    Still a few things left to do. I see that the oil box on the reverser pedestal is a little wonky, needs adjusting. The cab windows need to be fabricated. I'll be trying to use microscope cover slides for the glass so they might be thin enough to make the sliding window actually slide. Slaking pipe and valve on the fireman's side. I think there was a section of steel tread plate beneath the firehole. Cab doors. Fall plate. Now I think about it there are quite a lot of things left to do!

    There's one minor mystery though, and something I overlooked when I was detailing the backhead. The official LMS cab photo shows (if you look carefully) a heat guard to the left of the firehole to save the driver's legs from intermittent roasting when the fire doors are open. I doesn't seem to be present on any of the preserved 8Fs so far as I can tell. Was it a 'great idea' that was quickly discarded? Something that's not favoured in preservation? Would it be present in BR day's (and I can't find a cab interior photo from the BR period)? Anybody know?
     
  6. Dave Holt

    Dave Holt Active Member

    I've searched through all the likely books I have and also cannot find any photos of the cab interior in BR days. All Stanier classes had these heat shields when built. They had a tendency to work loose and there were official modifications to the fixing arrangements. However, I can't find any thing to suggest there was a modification to remove them. Perhaps if they became too loose, they would be removed from individual locos by the shed fitters?
    In preservation, I suspect that, like our (not Stanier) loco, people just haven't got round to making and fitting the guard. Also, in our case, the railway isn't keen because the guard makes it hard to fire from the wrong side and perhaps amateur firemen don't all master firing left handed, as required to fire from the right hand side. In addition, the guard can make fire cleaning more difficult, Again another disincentive to fit one in preserved locos.
    Not conclusive I'm afraid, but on balance, if it were my model, I'd fit the heat shield.

    Dave.
     
    Len Cattley likes this.
  7. paulc

    paulc Western Thunderer

    Hi Ian , my microscope slides tend to fall to pieces if i look at them the wrong way , i wish you luck with a sliding window .
     
  8. Threadmark: Fixing the backhead and another small cab fitting
    Ian_C

    Ian_C Western Thunderer

    How to fix the backhead into the cab and still have it easily removable? A magnet glued to the inside of the backhead, and a piece of steel fixed to the cab front sheet spaced off so that they just make contact when the backhead is in place. The magnet was from Eileen's Emporium. Hopefully the pics make it clear.
    backhead mag 1.jpg
    backhead mag 2.jpg

    In other news... there's a small valve or tap that controls the supply of water to the slaking pipe/coal watering pipe/fizzle pipe/whatever. No castings that look anything like or can be butchered, so have to make from scratch. Some tiny turned parts, scrap etch and bits of wire. Silver soldered together.
    slaking valve 1.jpg
     
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  9. P A D

    P A D Western Thunderer

    Hi Ian,
    Nifty idea using the magnet to fix the backhead. I usually go for a screw through footplate into a tapped hole in the base of the backhead, but that is simpler, so I'll file it away for future plagiarising. Lovely work on the slaking pipe valve.
    Cheers,
    Peter
     
  10. Threadmark: Window glass from microscope cover slides - a method for cutting very thin glass
    Ian_C

    Ian_C Western Thunderer

    Here's one way of cutting microscope cover slides to size. Daresay there are other methods, but this seems to work most of the time for me. You can get cover slides in various thicknesses, look on Ebay or Amazon. The ones I have are by Amscope and between 0.12mm and 0.16mm thick. You get a box of 100 for £peanuts. That's pretty thin, and they're correspondingly fragile, but they're close to scale thickness (about 1/4") so window frames don't have to be over thick and the glass edges are not obtrusive where they're visible.

    This is how I cut them...
    window glass 1.jpg

    You need something to scribe the glass. I use a tungsten carbide tipped scriber sharpened to a dead sharp point with a fine diamond abrasive hone. Some folk use a diamond record player stylus in a pin chuck, but I've never tried that. You need to work on a rigid surface. Any bending of the glass as you scribe causes it to break in uncontrolled directions. I draw the shape I'm cutting in fine pencil on a scrap of printer paper (90g/m2, but I don't think it's critical as long as it's not too thick and squishy). The paper is placed on something solid and flat, in this case a turned steel blank I use as a an anvil and mini surface plate. I use a lollipop stick as the straight edge to guide the scriber. It's kinder on the glass than a steel rule. Position the cover slide over the pencil marks. Hold the non-waste side under the stick, firmly enough to stop it sliding around but not so hard that it breaks the glass. I've found that the section of glass held under the stick is less inclined to break. Draw the scriber gently over the glass. You don't need to press down at all if the point's really sharp. It creates an almost invisible line on the surface of the glass. Often it'll break as soon as the line's scribed. If not, then pick it up and place the line over the edge of the stick with the waste section overhanging and gently bend the glass. It'll snap along the line. I use a lump of BluTack to pick up and move the glass pieces around. The diamond abrasive honing stick is also good for smoothing or shaping the edges of the glass, radiused corners etc. Light touch required and work along the edge of the glass rather than across it. You break a few to begin with, but once you get a feel for it it's surprisingly easy. I find the reject rate is about one in three. Make a few spares as you go! Better wear safety glasses as well, sometimes bits ping around when you break them.

    The sliding window frame's a bit of a head scratcher at the moment. You're only defeated once you've given up, and I've not given up yet. Next post probably!
     
  11. paulc

    paulc Western Thunderer

    I don't have any problems cutting standard windows , it was the fact that you wanted to make a sliding window with all its flexing that got my attention . Any luck yet ?
     
  12. Jim pairman

    Jim pairman New Member

    The finer the “scratch” on the glass the better the break as the former concentrates the stresses better.
    Jim P