Doubling Dimensions

[lovenyc2600]

I got my new book on building the Pennsy a3 switcher today, i have decided to building in 1 1/2 scale.

I am kinda confused about the dimensions though, do I double the size of the parts and the tools, or just the dimensions in the plans?

I am using an excel file to give me on idea where to start i ordering tools and metal bar stock, but am unsure of the size / lengths since i will be building in 1 1/2

any help input is appreicated

nicky





1stclass.mylargescale.com/Slartibartfass/A3_Switcher/Material_Parts_Tools.xls

[kvom]

Read the errata section here carefully.

In general:

1) Lengthwise dimensions can be doubled, as can parts that do not bridge the frame

2) Crosswise dimensions that bridge the frame generally cannot. The issue is that the rail gauges are not 2x. For the 1.5 scale, the outer frame surfaces are 6-9/16" apart, while in 3/4 scale they're 3-1/8". A safe way to proceed is to redraw affected parts in CAD doubling the amount that a part measures from the frame and adding the separation.

The main parts that mount crosswise to the frame are:

- footplate
- cross member
- front bumper
- tee
- axles
- tie plate
- reverse shaft
- arm shaft
- cab front

Lateral parts unique to 1.5 scale like brake beams are dimensioned separately.

I didn't build the tender, but the same rules certainly apply.

Fasteners can be chosen according to your own preferences. I use a lot of 10-32 and 8-32 screws.

It will be better to use steel in this scale rather than brass wherever possible.

Many dimensions for holes and pins are non-critical. For example, doubling diameters for pins gives a mixture of 5/32, 3/16, and 1/4 pins and clips. In my view, standardizing all on 3/16 would be simpler both in terms of work and in ordering stock.

[kenrinc]

Totally agree with all that Kirk said. Once you get going on it some of it is self explanatory.

Best bet is Hot Rolled A36 for nearly everything accept for things like piston and valve rods etc.... Cold Roll nearly always curls up. I've had cold roll curl up just by drilling one hole in the center of the part!! Now there are ways to work around that but it's just faster to go with HR. "Dirt" steel is what I call it ;D Cheap and plentiful.
Some often bring up the subject of rust. It's a steam engine. Go visit a real steam engine. They ain't made of brass. Once it's coated with oil, it's irrelevant.

The downside to using A36 is the mill scale and the fact that you'll need to spend hours "thicknessing" stock to get it to the proper dimension just to get workable stock for layout and then machining. On small equipment, this can be a major headache. I spent weeks just cleaning up stock to make parts. But If you do it all ahead of time it will be worth it. Grind off the mill scale with a grinder or put it in a dilute solution of acid to remove the scale then machine to thickness. For instance, the main and side rods will need to come from blanks .400" thick by roughly 1.125" wide by 14" long. You'll start with 4 pieces of A36 that is 1.25 x .5" thick. If you go through all the parts beforehand and verify thickness you'll be able to prepare in advance.

Take note that the A3 is small engine so it behooves you to put as much weight as you possibly can on the drivers.

Ken-