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N Gauge Brass People Mover (Extreme Close Up....!)

Will J

Entry posted by Will J

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Hi everyone,

 

in yesterday's blog, TomE asked 'Is there any sign of the original 3D printed mould on the final brass models? Tom.'

 

See: http://www.rmweb.co.uk/community/index.php?/blog/351/entry-16019-3d-printed-brass-objects-n-gauge-class-139-and-z3-gauge-hunslet/

 

To answer your question Tom, there is no sign of the original wax that the 'master' was printed in, it seems that the brass artifact is very thoroughly cleaned before it leaves Shapeways. Looking very closely, you can discern the 'stepping' on curved surfaces that you get in any printed material, to different extents. For the following photos, the usual disclaimers apply...

 

..in that it looks much nicer to the naked eye! In the moments since the bare brass body has been cleaned some more, and given a tentative dusting of grey etch primer, which adds to the realism while sadly eliminating the brief jewel-like 'bling' effect..... I'm thinking that with some gentle sanding and a few coats of paint, the stepped effect can be almost eliminated but rest assured, from any normal viewing distance it is not that apparent anyway.

 

The next step is the livery. I'm tempted, having already got a decent looking prototypical London Midland version, to do a version more suited to a Cornish branch line. With Kinlet Wharf appearing at Taunton later this year,

 

http://somersetrmc.org.uk/Rail-EX/layouts.html

 

it would be nice to have a 'Great Western' version, perhaps in FGW deep blue, or perhaps an interpretation of the forthcoming DfT specifified GWR livery. Does anybody know if this is still going ahead, and what colour would be used for branch line services?

 

Anyhow, here are the cruel close ups...

 

blogentry-1601-0-75590700-1430336536_thumb.jpg

 

blogentry-1601-0-46612300-1430336545_thumb.jpg

 

blogentry-1601-0-96499300-1430336556_thumb.jpg

 

blogentry-1601-0-56886800-1430336568_thumb.jpg

Stay tuned for more on the little Hunslet.

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D869

Another question :)
 
How does it compare dimensionally to what you drew?
 
The late Phil Kerr who was a member of our group used to be a pattern maker and I remember that he had several different rulers depending on the metal for which the (wooden) pattern was intended. Each ruler was scaled slightly larger than the true dimension to allow for the contraction of the metal during the casting process.
 
So I wonder if Shapeways are scaling the master up by a few percent when printing it to allow for the contraction of the brass.
 
Regards, Andy

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Will J

Hi Andy,

 

it seems pretty good, with minimal shrinkage, though it depends on how minimal your idea of minimal is....

 

The CAD model has a length of 66.04 mm, the model measures 65.89 (with callipers)

 

The CAD model has a width of 21.68 mm, the model measures 21.45 (with callipers)

 

I'm not sure whether Shapeways give the dimensions a tiny boost pre-production to keep things accurate, I suppose it would be quite an easy thing to automate if the effects of the casting process were predictable. The fractions of a millimeter involved are not going to be visible, but of course affect the fit of small interlocking parts, I am going to try some printed small gears which will test how well the brass parts perform in a more 'engineered' application.

 

One thing I noticed was that the same Kato chassis fits snugly in the plastic bodyshell, but had to be 'encouraged' more forcibly to fit into the void in the brass version. This might have to do with the shrinkage, but remember that the plastic version is also much more flexible which is probably the bigger factor!

 

Edit: decimal point in the right place in the dimensions!!

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D869

Thanks Will - probably as near as makes no difference given the accuracy of a set of calipers.

 

I suspect that they must allow for shrinkage when printing the casting master. As Mr Scott used to say... 'you cannae change the laws of physics'.

 

Whether it's accurate enough and has a good enough surface finish for mehanisms is another question though. I reckon that you're blazing a new trail there.

 

Regards, Andy

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