Tom Mallard's Workbench - Lynton & Barnstaple Manning Wardles 7mm scale

Discussion in 'Workbenches, including workshop techniques.' started by Tom Mallard, 27 December 2013.

  1. Tom Mallard

    Tom Mallard Western Thunderer

    MW parts 8.JPG

    Progress on some Manning Wardle smokebox/boiler/firebox assemblies. Normally these would be aligned with a screw along the centre line to hold things in place. I wanted the assembly to be unimpeded by this type of construction so ring type formers are used with pins arranged around this area as shown on the face down smokebox of YEO.

    The saddle for the smokebox is fabricated and will have to be very carefully set so as to maintain a boiler parallel with the frames and tanks. After testing the tanks against the cabsides and smokebox, I think it will be safer and simpler to add the tanks after the boiler assembly has been attached to the cab and footplate assembly.

    For the brass firebox front and rear I invested in a radius milling cutter to generate a consistent radius on these parts. I machined them on my pantograph milling machine (quite a cold day or so stuck in the garage!) as a secondary operation during manufacture, and they came out alright. It would certainly have been a substantial headache to profile the internal radius on the backhead area. The firebox fittings will likely be attached to a separate plate representing the firebox front.

    Best regards

    Tom
     

    Attached Files:

  2. Tom Mallard

    Tom Mallard Western Thunderer

    YEO EXE cab 2.JPG MW castings 1.JPG

    There are some bits and bobs to fill the footplate of these engines now, all machined, turned and fabricated as required. Not entirely sure the 0.5mm hex heads on the brake standard are worth it but at least we know they're there. The cab interior is going to be on view on the models, yet remains almost invisible in nearly every photograph of the prototype due to glare from the glazing and the nature of outdoor photography.

    The castings are made directly from 3D printed waxes and are largely as hoped for, though I was expected a less matte finish. I am particularly pleased with the motion brackets which are nice and flat, and the coupling pockets.

    Best regards

    Tom
     
    Last edited: 23 February 2021 at 17:53
  3. adrian

    adrian Flying Squad

    They are very nice and crisp. Did you 3D print them or was that all handled by the casting company? As you mention I'd have expected a slightly more glossy finish based on other work I've seen. Is this a subtly different brass composition or have they been finished post casting. I'm aware many jewellery casters use various surface treatment processes after casting.
     
    AdeMoore likes this.
  4. Tom Mallard

    Tom Mallard Western Thunderer

    They are certainly nice and crisp, and so they should be based on the cost of the prints. It is also of course a function of eliminating the mould making step and the subsequent small loss in resolution and chance of wax deformation during handling. It’s an expensive approach but in my opinion for small duplicated and handed parts is very worthwhile.

    The prints are by Precision Wax, the casting by Slaters if that’s of any use.

    Investment castings seem to show highly variable surface finish depending on the investment selected by the company, brass composition and post processing. Slaters assured me that a gentle process is used to remove the investment.

    I’ve used 5 or 6 different casting companies over the years. Slaters are close to the best so far and nice to deal with. Sanspareil had the best finish by far but are much too opaque for me to be happy dealing with on a regular basis. They are also the only two companies who seem to understand the importance of the work we send them, and our expectations of the results.

    I didn’t have an opportunity to view the waxes prior to casting as I had them sent direct to the caster, but their resolution capabilities didn’t give cause for concern about surface finish. However there does seem to be seem creep or wander evident in the castings which can only be a result of the prints not being totally consistent left to right.

    It’s my first set of finished castings following an unsuccessful test enquiry with a Scottish firm, but based on results so far should work successfully. The learning curve is steep, if including learning to use a new piece of solid modelling software, but I got there in the end. It’s quite likely this process will be used again...

    Tom