Tuesday, June 28, 2022

You're Not Thinking Fourth Dimensionally

Having mentioned in a previous post that I'd carefully measured to ensure that the gerbox and motor would fit, I've now discovered a slight flaw in the plan.
That is the drawing I made which combines the plan of the loco from the instructions, the gearbox, and space for a nice chunky Mashima 1620 (16mm x 20mm) motor. As you can see it all fits nicely. Unfortunately not only was I not thinking in three dimensions, I wasn't fully thinking in four dimensions either.

There was nothing wrong with my planning and I could build the gearbox and the motor will fit inside the boiler just as shown. The problem is that I didn't consider how I would actually get from assembling the chassis with the gearbox and motor to the point where the body was fitted.

Yes, I'd checked that the gearbox would fit between the frames but the mounting lugs for the motor are wider than the gearbox. This means whilst I could assemble the chassis with the gearbox in place it would never fit through the hole in the footplate so I wouldn't be able to slot the body on. Fortunately the gearbox has two mounting points, so I could remove the lugs and it would fit through the chassis.
Except of course that the motor is also way too wide to fit through the chassis; in fact to make it fit I'd have had to cut off the rear of the splashers and left a much weaker chassis. Fortunately I have a Mashima 1215 motor in stock which will mount to the gear box and fit through the hole in the footplate... at least it will on an angle. I need to bolt it to the gearbox first and see if it will slide in or if I will still need to lengthen the hole slightly. It's a double shafted motor and while a flywheel would be nice I think I'll need to trim the extra shaft down to help fitting it in. We shall see.

Oh and I still need to work out how to keep the gearbox vertical as currently it will spin freely on the axle. Of course not being part of the kit there are no nice mounting brackets, but I think I have a plan to solve that problem

3 comments:

  1. Gosh. I've just caught up and I'm astonished at the detail involved. I marvel at your patience.

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    1. Thanks, although I have to admit my patience with this kit is quickly running out, but I'm determined to get it finished.

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  2. You need a proper 3D programme. It can still happen then as I know only too well. I have cuckooed with multibranch motorbike exhausts so often, I made five last year and two had to be chopped and sorted. The only quick way to avoid it is to 3D scan the bits you have and then load the scan into Fusion 360 or similar software. I don't know of small 3D scanners. The alternative is to sketch up as you did, then go to your physical piece and go round with vernier calipers. Then go round again a couple of times.
    Whilst I'm here I noticed that you hadn't popped centres in your axles. They allow quick and accurate set up for re-machining. A collet set for the lathe would help in the absence of centres and a face plate. A chuck is time consuming to use and the source of most errors. Tailstocks also have to be checked for lateral and vertical alignment, the first is easy, the second not so much as the height has to be increased by shims or decreased by scrapping. For bearing fits look in The Machinery's Handbook or the bearing suppliers catalogue. Turn the OD first and grip a solid bit, don't bore all the way through on your tiny bits, part off the piece you want.
    It's all good fun and the tiny loco looks as if it will be beautiful. Patience is a virtue. I don't have much of it but do have lots of special words.

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