HEAVY METAL Gallimaufry - Making channel for wagon underframes

Discussion in 'Workbenches, including workshop techniques.' started by Brian McKenzie, 8 January 2018.

  1. Brian McKenzie

    Brian McKenzie Western Thunderer

    IMG_72959a Headstock Channels .jpg
    .........................................9" x 3-1/2" Channel...........................................................................Brass stock...................................8" x 3-1/2".....


    First modelling work for 2018, was converting strips of brass into lengths of channel section - to represent scale 9" x 3-1/2" steel channel, plus a couple of lengths made as 8" x 3-1/2".

    Wagons, of my 1/48 scale New Zealand Railways prototype, have very distinctive headstocks of steel channel - where the exposed ends show prominently.

    The channels were cut by 'flick milling' - a term used by some to describe using a shaped tool in the manner of a fly cutter - most commonly performed using a milling machine's horizontal arbour.

    Channel.jpg

    Brass sheet was first sliced into strips to the finished width of the channels.
    Slicing brass bar_68243a.jpg

    A pair of steel bars was prepared to support the sides and base of the brass material by cutting a groove along the uppermost edge. Pins were inserted at each end as alignment dowels.
    IMG_72933a.jpg

    Much effort was expended on grinding the end of short lengths of 5/16" square H.S.S. (lathe turning tool material) for cutting out the internal contour of the channels to show the tapering section of the flanges. This task was made more difficult by endeavouring to additionally trim the flange height at the same time and provide some rounding to the inner edges.
    IMG_72924a.jpg

    The cutting tool was secured in a small diameter arbour (machining time is usefully speeded up by arranging the tool to have the smallest diameter cutting circle), and carefully centered over the brass bar visually by taking a trial shallow cut.

    When all is well, cuts are made at full depth in a single pass - to avoid any collapsing of the thin channel section.


    -Brian McKenzie
     
    Last edited: 8 January 2018
    farnetti, 3 LINK, ceejaydee and 16 others like this.
  2. AndyB

    AndyB Western Thunderer

    Hi Brian,
    That's dedication to fidelity! I considered milling channel for gauge 3, which would leave a serious pile of chips for each!
    A couple of questions, if I may.... The video says that you use a single point tool for the slicing off. Is this shaped like a lathe parting tool? Why use that rather than a slitting saw? And do you use a clamp or anything to hold the loose end once you get >3/4 of the way along, to prevent it from sagging or flapping?

    Andy
     
    Brian McKenzie likes this.
  3. Brian McKenzie

    Brian McKenzie Western Thunderer

    Andy, yes - even in my much smaller scale, there was a pile on the floor. :)

    Slitting saws of a size or thickness (thinness ;) ) appropriate to my scale, are notorious for wandering off line and taking a path of their own, thus spoiling the precision and the finish desired. Yes, the cutting tool used is just like a lathe parting tool. It is mounted to cut in the smallest diameter circle, so that the spindle speed can be increased to take more cuts per minute of feed.
    Slitting tool+swarf.jpg

    Yes, you're on to it! :thumbs: And when the slicing cut is just about to finish, a finger was placed on top of the start end, to tip the newly cut strip upwards away from the spinning cutter (it pivoting at the clamp in a see-saw action).
    Slitting_68239a.jpg

    Cheers, Brian McK
     
  4. AndyB

    AndyB Western Thunderer

    Thanks Brian - more things to put on my 'to-do' list now!
    May I also ask what sort of mill you're using? - it looks similar in size to a Tom Senior, but with a wider table.
    And that ?Colchester Student? in the background looks a big lathe for 1/48 work!

    Andy
     
  5. Brian McKenzie

    Brian McKenzie Western Thunderer

    Andy,

    The machine is an Elliott Omnimill with both vertical and horizontal spindles. You guessed right about the lathe, but there is also a smaller (green) lathe creeping into one of the pics.

    Years ago, I made some underframe channel in a larger scale. Brass sheet was glued firmly (Ados F2) to MDF board clamped flat on the table. A side-and-face cutter was paired with a slightly larger diameter slitting saw, with a thin spacer in between, on the horizontal spindle. The channel was hewn out and parted off simultaneously in a single cut.

    Would you use brass or steel for Gauge 3? A (contoured) two-flute slot drill might make life easier for a vertical mill in your scale. Good chip evacuation would seem desirable. Keen to see how you might get on . . . .

    -Brian McK.
     
  6. Overseer

    Overseer Western Thunderer

    Hi Brian

    Very impressive. I presume you are building L-6 open wagons with the reversed headstocks. Victorian Railways had one group of wagons with the same detail due to a NZ connection. They were iron coal hoppers designed by Allison Dalrymple Smith in 1886. AD Smith was ex New Zealand Railways and brought some ideas with him. Only the first 50 of these hoppers had the reversed channel headstocks 9" x 3" x 3/8", the remainder had 10" x 4" x 7/16" channel headstocks mounted the conventional way round. All of them had 9" x 3" x 3/8" solebars. The reason for this rambling diversion is to ask if you would consider an order for a few lengths of the 9 inch channel as they are on my list of things to build in 1:48 and I don't have a large enough mill to make them (tempting as one is).

    Part of the GA for the 1886 batch-
    O 1886 crop.jpg
    The hoppers looked like this, although this is one of the later ones with conventional headstocks.
    O 166 c.jpg
     
  7. Brian McKenzie

    Brian McKenzie Western Thunderer

    Hi Fraser,
    The easiest and quickest way of obtaining 9" x 3" channel in 1/48 scale is to slit K&S 3/16" square brass tube longitudinally. I do this for wagon solebars - and reserve the labour and time intensive milled channel for the headstocks - where the profile is more visually exposed. Alas, I didn't expect to machine any more underframe channel and recycled some of the setup for making other items. :oops:

    I was very impressed with the great job David Foulkes of Steam Era Models made of your split-spoke wagon wheels Scale Wagon Wheels - A Saga, and his neat methodical tooling work in general for kits, when visiting once. Some years earlier, I was encouraged by the late Graham Selman (originator of North Yard Models) to make my own split-spoke wheels in 1/48 scale. These six-spoke 30inch diameter wheels have injection moulded centres of glass filled acetal, with stainless steel tyres. Moulding acetal successfully as a hobbyist proved quite a challenge compared to less demanding plastics.

    Cheers, Brian McK.
     
  8. Overseer

    Overseer Western Thunderer

    No problem Brian. The square brass tube is an option but has radiused outer corners instead of the sharp arris the real channel has. I will probably revert to my usual folded brass solebars (which I punch the rivets in before folding) with fabricated headstocks to achieve the sharp corners where they can be seen.

    Yes, David Foulkes is a brilliant toolmaker with his pantograph mill. His earliest kits were good but the recent HO kits lift the art form to a new level, I should post some more examples of them here. Acetal is strange stuff, I was surprised a while ago at how low the temperature needs to be for it to deform. I had some rolling stock in storage in less than ideal conditions and one piece bogies distorted, a combination of heat and some pressure. They were saved with a dunk in boiled water and twisting.