Had Another Go

[Andy StopfordParticipant @andystopford50521]

It looks like you’re making good progress, Nigel.

In “Traction Engine Design and Construction” G.F.A. Gilbert suggests full-size practise was to make the clearance volume 7 to 12% of swept volume, and the passage area 5 to 10% of the piston area (I can’t find the reference for the latter, so I might have got that from somewhere else).
Previous contributors to this forum have suggested that full-size proportions will correctly work with models.

Of course, as you mention, actually fitting sensible sized walls, etc., between the passages can be a challenge at small scales – I’m currently wrestling with designing the very complicated steam ways for a Fowler Z7S – what looks like a decent wall thickness on the screen can turn out to be 0.5 mm or something ridiculous when you actually check what you’ve drawn!

[Nigel Graham 2Participant @nigelgraham2]

Neil – Impressive! 3D printed?

 

Andy – Thank you for that guidance. I’ll examine my dimensions so far. I’ve not yet done the metalwork – I want to make sure I remove the right swarf from the right places.

[Charles LamontParticipant @charleslamont71117]

One way to think about modelling this kind of internal detail is to construct it all, here the ports and passages, as a complete separate part and then use a boolian operation to subtract it from the cylinder. It is particularly useful when modeling cored holes – just model the core as a part in its own right and then subtract it from the body.

[JasonBModerator @jasonb]

Unfortunately Nigel’s Atom does not have Boolian add/subtract ( only pro & Expert) though as you say good for coring complex shapes.

I quite often have to go with 1mm between cylinder and passage on the smaller engines so proportioning that to your larger engine should not be a problem. That cylinder in my post above only has 1mm between the two. As  for some of the IC engines they can have some long water cooling passages, this one is about 120mm deep (mark near top of drill) and about 2.5mm wall left.

As for cross sections also consider the sizes of your inlet and exhaust pipes which may be where the restriction is smaller and also if your ports will be fully uncovered.

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