Northumbrian

[jasonb]

Just a note to anyone making or thinking of making this model if you have not been following the posts on ME's website there are a number of errors & ommisions. Please check the posts before cutting any metal, particularly the frames as the drawing has them too short and new frames will be needed.

Jason

[steam4ian]

G'day Jason

You have raised an issue which is a major point of criticism.

The dimensions on the drawings are incremental and there is NO SET OUT POINT from which measurements are made. This is model engineering (underline engineering) and one could expect that good engineering practices will be followed.

It would not be too difficult to make every dimension referred to the front edge or the main axle centre line.

The result of this failure on the drawings is the issue you have raised.

I have another criticism too. There is no intro article giving overall dimensions, wheel diameters and cylinder sizes. We will have to wait until almost the final article to see what we have built and whether it will meet our expectations.

That said, it looks like fun but at 3.5G it will have trouble pulling the skin off a custard.

I would like to build it double size for 7.25G where it should be able to handle at least one passenger truck

Regards
Ian

[baggo]

Oct 23, 2009 22:09:22 GMT steam4ian said:

The dimensions on the drawings are incremental and there is NO SET OUT POINT from which measurements are made. This is model engineering (underline engineering) and one could expect that good engineering practices will be followed.

This has always been a major criticism of 'Model' engineering drawings and I suppose the excuse is that 'it's always been done this way'

My brother, who was a draughtsman at BR, was absolutely horrified when he saw the drawings for the Rob Roy that he decided to build. He was used to everything being dimensioned from a common datum point.

The problem is that on a drawing of a complex set of frames, for example, if every dimension is taken from one end the drawing becomes a mass of dimensions under the frames and you would need one sheet just for the frames. That probably would not be a problem but would increase the number of drawings required and the cost?

Maybe a compromise would be to measure all the important dimensions from a common datum i.e. cylinder centres, axle centres, etc. and then dimension less important positions from those?

I must admit that when I produce my own drawings I follow the ME route and dimension one position from another but I accept that it is possible to have accumulatve errors when marking out. As I use CAD it would be no problem to use the 'proper' method of dimensioning.

At the end of the day it's what you feel comfortable with

John