Starting design of the tender trucks

    The rather dark shot above is the tender truck portion of the C & NW 2-8-2 Mikado plans.  It is a copy of original C & NW build drawings.  Not all details are provided on this sheet as many sheets were needed to detail the truck assembly.  The journals and brakes are missing as is the detail of the truck wheels.  Those missing details will be derived from other sources.

 The axle detail is sufficient to prepare a detailed 3D CAD drawing.  The part is about 2.8" long and 0.26" in diameter.  It will be turned from 6061-T6 aluminum in the lathe.  Four copies are needed so the pattern will be programmed to run CNC on the lathe.  This will not only be the first part of the machine tool built locomotive, but will also be the first metal part the author will have made on the CNC lathe.

Setting Up Shop

    The author has recently added a set of Sherline CNC mini machine tools to his hobby shop alongside a BFB-3000 3D printer for building models.  The machine tools were initially an adjunct to the 3D printer to enable cleaning and shaping parts when necessary.  The new shop tools however are well suited to machining metals as well as plastics and a supply of various shapes of 6061-T6 aluminum rods, bars and squares were acquired along with Delrin sheets, rectangles and rods.
    The CNC capability of the two machine tools suggest that it would be interesting and fun to build metal models as well as the plastic version supported by the 3D printer.  For details of the 3D printer model locomotive project please visit my blog at http://electecnik.blogspot.com/.   Where the new mini-machine tools are used to support the 3D printer they will be highlighted there.

    The author has a set of plans for a C&NW Railway Mikado 2-8-2 locomotive and tender with limited structural details that will form the basis of the design of a "G" gauge model design.  This is a similar effort as is being done for the USRA Mikado design being done with the 3D printer effort.  The 3D printer design is being done in 1/2" per foot scale however and requires a unique track section to fit.  This is a display only model although wheels rotate and side gear moves, etc.
    The new effort for the "G" gauge scale model is not only intended to move, but may be powered at some future time, so the decision was to use available off-the-shelf "G" gauge track.  The scale will be set so that the 45mm "G" gauge track represents prototype American Standard gauge track spacing of 4' 8-1/2".   This results in a scale factor of 1 to 3189111 of the prototype locomotive.  The plans are sized for 7.5" live-steam model gauge track, so the Alibre 3D CAD software will be used to redraw and create a new set of drawings for all parts to be built.

    The Sherline model 4400 mini-lathe above provides the ability to turn parts up to about 3" and about 16" long.  The lathe is CNC controlled (or manual) in two axis able to move the cutting tool along the length of the part and diameter simultaneously if need be.  This enables shaping round items with tapers and contours and will be very useful in making wheels, axles, rods, round tanks, etc.
    Using available spacer blocks from the manufacturer somewhat larger diameter parts can be lightly machined.  The locomotive boiler sections will likely be about the larges diameters to need turning.  The prototype boiler is nearly 8' in diameter which would scale to a 3" diameter part, albeit a basically hollow tube.

    The milling machine is a four axis device which is equipped with a 4" turn-table, all axis being CNC driven.  This machine would likely get the most use in the project as most parts are not round.

     The CNC capability for both machines is controlled by a common computer with four stepper driver channels that drive either the lathe or mill, not at the same time.  The CNC action is controlled by a particular program language call "g-code" which the author must now learn and perfect.  This will take some time to master and likely only modest efforts will be undertaken during the learning phase.  The lathe being simpler will probably be undertaken first and various round items such as axles, shafts and wheels will be built.

    The turntable above is an accessory for the mill adding the 4th axis.  It enables the work to be turned to various angle during machining.  It will be very useful to make wheel spokes and round hole patterns.  It is also useful to make gears if needed.