Rescaling Designs for 7mm

[Arun Sharma]

Some four or so years ago I designed a 4mm scale three car AM1 [Class 301] EMU set. This represented one of the original LNWR Siemens Broad Street sets after their conversion to OHLE on the Lancaster-Morecambe-Heysham route. I understand that an article has appeared some time ago in BRM regarding this model.

My major interest is really in designing 7mm kits/models and this particular AM1 DMBSO has some rather interesting features. It represents car M28222M which was unique in being fitted with BTH equipment as well as having much equipment fitted underneath the car rather than solely in a compartment behind the cab. Like other power cars it was fitted with a pantograph but a EM1/EM2 [Woodhead] type rather than the Stone-Faively type that other units had.

Rescaling models for etching is not just a matter of photocopying designs - For example, the width of etched fold lines is a function of metal thickness as well as the type of fold. In practice, 7mm designs are made of thicker metal than 4mm designs so substantial redrawing can be required. Similarly castings have to be rescaled and assuming Slaters wheelsets are being used, then motor bogies need to be redesigned for scale gauge rather than the 16.5mm of an 00 model as well as a different type of motor and gearbox.

 

Anyway, the lower one is of one of the early 4mm models showing the basic layout of the superstructure and the flat roof where the diamond pantograph would sit.

 

The upper photograph is of progress so far on the 7mm build - The gap at the end of the body is for the other passenger door of course.

The 7mm scale pantograph is one that Mike Edge already produces which will save an amount of work.

 

Edited June 2, 2023 by Arun Sharma
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[jamie92208]

It looks very good Arun.  I know that there were differencesbetween the four sets and one had the first semiconductor rectifiers but I've never looked at the details. 

 

Jamie

[Arun Sharma]

The basic bodyshell of the test build has now been completed:

 

Edited June 3, 2023 by Arun Sharma
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[Arun Sharma]

The underframe of this particular vehicle is especially complex but fortunately it was well photographed during its conversion to overhead power pickup and those photographs have allowed the full complement of boxes and cylinders to be drawn in 3D CAD. Once printed, a trial set will be stuck underneath. It should end up looking something like this underneath:

 

[jamie92208]

That looks great.  I just wish could do 3D cad for the underframe of my 1907 power cars.

 

Jamie

[Arun Sharma]

I've now just added the cab front castings - these are mainly lamps, lamp irons and various MU connectors. All were generated as 3D prints and then cast in brass via Birmingham's Jewellry Quarter.

The next stage is to add the side louvre castings once their moulds are done [they will be resin castings from 3D printed masters]. Since this is solely a test build of the etches and check for casting fit, I am not too concerned about populating the cab interior as those parts don't require holes to be drilled in the etches.

 

Edited June 10, 2023 by Arun Sharma

[Arun Sharma]

The seating unit for this car has been 3D printed commercially using an ABS filament. Although it has a somewhat rough surface, it can be sanded smooth easily and it is a small fraction of the price of printing the two types of seats individually using a SLA material/process. 

 

Next step is to smooth the surface, prime and top coat this seat unit.

 

 

 

[Arun Sharma]

The underframe is currently being populated with the various battery boxes, chokes, radiators and transformers. The resin parts have been glued in place but there are some lost wax brass tanks, oil filters and brake cylinder/actuating arms that need to be soldered in place in the empty space on the right, nearside [as you see it on the screen].

 

The underframe is just sitting [rather than secured] on top of the upside down body. The resin boxes are glued in place using Devcon 5minute Epoxy. Adhesion is enhanced by drilling some holes in the contact area [both on the part and through the metal underframe]. If required, further support can always be given by drilling a hole though the metal underframe and gluing a pin into the part through it. Such 'drilling and pinning' is often used when dealing with resin parts.

The electrical compartment side louvres are also now in place.

Edited June 22, 2023 by Arun Sharma
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