7mm On Heather's Workbench - a baby Small Prairie

Discussion in 'WR Action' started by Heather Kay, 2 August 2017.

  1. Heather Kay

    Heather Kay Western Thunderer

    Right. Time to dredge this build back up.


    I’m currently at the "staring at it on the bench trying to remember where I got to" stage. I think my first job is to get the chassis motorised and running. Then I’ll take a look at cylinders, brake gear is being sorted out through some third parties, and decide how I might sensibly fit some side control to the pony trucks.

    Has anyone seen my soldering iron?
  2. Paul Cambridge

    Paul Cambridge Western Thunderer

    When I made my 44xx in OF, I made the cylinder assembly removable. If I remember, there is a frame spacer below where the cylinder assembly sits. I drilled two holes in both the frame spacer and the transverse cylinder assembly. I soldered nuts to the top of the cylinder assembly. The unit is then screwed to the frame spacer. It’s not easy to describe, but I hope you get the idea. There is precious little space behind the cross head and leading crankpin. It is also nigh on impossible to remove the leading wheel set, unless you have arranged for the leading horn blocks to be dropped out of the frames or the cylinders are removable.
    Heather Kay and Peter Cross like this.
  3. Heather Kay

    Heather Kay Western Thunderer

    Thanks for the warning, Paul.

    Working to S7 standards, I think I may need to think about the front axle clearances quite a bit. I’ve already got the Slater's screws bedded down as far as they can be, and I’ll have to eradicate all sideplay on the leading axle. I hope the bosses won’t be a problem.

    I’ve settled on mounting the ABC motor/gearbox on the centre axle, with the motor to the rear. That way I can have some limited sideplay on the centre axle, and quite a bit on the trailing one. The client's layout has quite severe, for S7, curves so the more flexibility I can get in the chassis with minimal compromise the better.

    I think I’ll get the wheel sets chemically blackened next.
    Len Cattley and Paul Cambridge like this.
  4. Paul Cambridge

    Paul Cambridge Western Thunderer

    Heather, how you design how the leading crank pins and nuts to fit the coupling rods is worth consideration at this point. There’s next to no clearance with the cross head. I used CPL crank pin nuts.
    Heather Kay likes this.
  5. Yorkshire Dave

    Yorkshire Dave Western Thunderer

    Are you sure it's not a solderless construction like others on this forum ;).
    Heather Kay and simond like this.
  6. Heather Kay

    Heather Kay Western Thunderer

    No, I'm definitely in hot stick and runny metal camp.
    Len Cattley and AJC like this.
  7. simond

    simond Western Thunderer

    Hot stick, no problem.

    Runny metal, ditto.

    Invisible runny metal - err, that’s where my problems start.

  8. Heather Kay

    Heather Kay Western Thunderer


    This is where I got to yesterday. All the wheels have been blackened. I deployed my specially-procured countersink to bed in the Slater's screws better. I’ve also increased the depth of the crankpin screwheads in the rear of the wheels. Before I committed to epoxy resin to hold them in, I decided to test running on the test track.

    The pony trucks needed some fettling. Bearing in mind it is a test track, with faults and flaws, one truck insisted on derailing at speed. When I say "speed" I mean being rolled along the track under finger pressure. I tracked the problem down to balance: at this stage, the main wheel bearings haven’t been fitted with their springs, and I guess the chassis was rocking a bit depending on where my finger was at the time. Equally, the pony pivots aren’t fixed to the chassis, either. Anyway, the ensemble rolls freely, I’m happy with the motor and gearbox location, and I think I should mix some epoxy to fix the crankpins, then sort out electrical pickup.

    I’ve just spotted a potential problem with the hornblock spring screws: the heads won’t go down past the frames. I think a bit of Dremel time to make little troughs for them is required.
  9. Temeraire

    Temeraire Western Thunderer

    Mind if I jump and ask what your secret is for getting a nice even finish when blackening Slaters wheel Heather?

    I use Birchwood Casey fluid and cannot for the life of me get a finish that resembles yours. Mine is always pretty blotchy and inconsistent.

    I have another set of wheels to do at the weekend so any pointers gratefully received!
  10. Heather Kay

    Heather Kay Western Thunderer

    I know this has been covered before, and there’s about as many different views on it as there are members of WT!

    My "secret", if you like, is giving the steel parts of the wheel a good clean with fine emery or a scratch brush, then avoiding touching them until I apply neat Birchwood Casey Brass Black with the aid of a knackered old paintbrush. The first application will be sometimes be blotchy, but repeating the abrading process and another dose of chemical seems to cure that. I let the chemical dry on the tyre, then - avoiding breathing in the resulting puff of dust - use a steel wire wheel brush in the whizzydrill to buff the surface.

    This is my current brush:




    This pony wheel shows the dried residue well. As these wheels won’t be used for current collection, I haven’t cleaned them as rigorously as the drivers.


    The Brass Black gives a rather pleasing deep brownish black to the steel tyres. It also gives a fair primer base to paint later on. I clean back the tyre tread and flange with some care, but just quickly buff the tyre face. With vigorous cleaning, you will find the blackening can be cleaned right back to bare metal, which I sometimes do if electrical pickup proves a little hit and miss. There may be other ways of making the blackening process more permanent, but this works for me. I rarely find corrosion a problem once this procedure has been done, but I know others wipe some lubricating oil over the blackened surface if the wheels are not going to be used straight away.

    I hope that helps. :thumbs:
  11. Paul Cambridge

    Paul Cambridge Western Thunderer

    Not for the faint hearted (Health and Safety look away now); I mount my wheels on a spare axle and run it in the lathe, using my heavy duty glass fibre stick and finest grade wet and dry. I dip a cotton wool bud into the blackening liquid, and bring it up to the revolving wheel. Wear disposable gloves when using this stuff as it’s nasty.
    Disclaimer here. Rotating parts are dangerous, so take all sensible precautions. This is the first job on a loco build, before anything else. DON”T fit the crankpins either. You don’t want them flailing about.
    I find this gives a nice even finish to the blackening.
    Peter Cross likes this.
  12. simond

    simond Western Thunderer

    my approach:

    Rubber gloves
    Thoroughly clean wheels, I have also used my lathe for this, with emery cloth or fibreglass brush (fully agree with Paul's safety advice)
    Degrease with acetone, (ventilation!)
    Apply black (watered down a little) with cotton wool bud. rub vigorously if needed.
    Allow time to react - a few seconds
    Dump in water
    Repeat as necessary for the rest of the wheels
    Drain water & rinse container, dispose of gloves.
    Rinse wheels under hot water.
    Dump blacked wheels in ultrasonic bath, and oscillate fiercely for 5 minutes.
    Rinse under hot water again
    Dry on kitchen towel
    Oil with beard clipper oil, using a new cotton wool bud.
    Wipe off any excess using kitchen towel.

    I have not found it necessary to polish the treads. I don't know if the chemical reaction forms a porous surface, but the oil seems to stick well, and not oiling seems to lead to them going rusty under the black. I recently refurbished a pal's air rifle using essentially the same process, and it came out rather well. The oil & black combination doesn't seem to be insulating. If it is, it seems to wear off very quickly.

    I have no view on whether the ultrasonic cleaner makes a difference. I have one, next to the sink, so I use it. It is likely to ensure there's no residual chemicals hanging around.

    Obviously avoid getting any oil anywhere near the crankpin holes as cleaning will be difficult and you don't want to prevent the epoxy getting a good grip.

    hope it helps
  13. Steph Dale

    Steph Dale Western Thunderer

    Surely it would be easier to reduce the size of the head, or cut them off even? After all, you're not using them for a fixing; they're effectively grub screws.

  14. Heather Kay

    Heather Kay Western Thunderer

    Quite correct. Since my post, though, I’ve found the heads do just pass through. Perhaps a quick spin in the drill against a file will be enough. I need shorter screws as well, as the ones I’m using are temporary while I set things up.
  15. Temeraire

    Temeraire Western Thunderer

    Thanks for the info folks! I suspect my cleaning of the wheels prior to chucking the blackening fluid at them hasn't been thorough enough.
  16. Heather Kay

    Heather Kay Western Thunderer


    It runs! Considering it’s all but a rigid 0-6-0 at the moment, it’s surprisingly smooth. A nice ABC gearbox helps, of course.

    Putting the rods on gave me pause: is the knuckle joint supposed to be there? Well, yes, it is. I checked photos, but with the connecting rod hiding it you’d be forgiven for thinking the rods were "hinged" on the driven crankpin. Referring to the drawings, there was the knuckle, leading. Fair enough. Next job, then, will be to sort out the cylinders and connecting rods.
  17. Scale7JB

    Scale7JB Western Thunderer

    For blackening?

    Clean with Bar Keepers Friend.
    Don't touch the metal.
    Pop into small container with watered down Birchwood Casey.
    Rinse with 'COLD' water
    Dry with paper towel.

    adrian and simond like this.
  18. Scale7JB

    Scale7JB Western Thunderer

    Heather, will you beef up the coupling rod bosses a little?

  19. Heather Kay

    Heather Kay Western Thunderer

    That’s a good point. These are PC milled rods. As is their way, they are pretty flat. I might look at adding the etched parts from the kit.
  20. P A D

    P A D Western Thunderer

    Hi Heather,
    Looking at the plan view on the drawing you posted at the start of the thread, beefing up the centre boss will give clearance for the connecting rod to pass the rivet at the joint. Unusual having the joint ahead of the crank pin on an outside cylinder loco.