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| Brass_Machine:
Thinking about up-scaling a model steam engine for grins. May want to make it it 50% bigger. What do people do to upscale it? Say the bore is .5"... does it automatically become .75" for a 50% increase? Or is there a good equation to figure it out. Help? Eric |
| Bluechip:
Hi Eric 50% increase in what ? Bore will increase by 50% for sure. But the cylinder capacity will be 2.25 times greater I think ( ?? ) if the stroke is kept the same. ie Vol = pi * r2 * h will become pi * 1.5r2 * h Say the original is 0.5" bore by 1" stroke the volume is pi * 0.252 * 1 = 0.196 cu. ins. Now 0.75" bore is p1 * 0.3752 * 1 = 0.442 cu. ins. Which is about 2.25 times larger. ( Should be exactly 2.25, but I've used truncated decimals .. ::) ) If you want to scale the volume only, keeping the same 1" stroke, I get this rather clumsy equation New bore RADIUS = sqrt ( ( Scale factor * Original Vol ) / pi ) = sqrt ( (1.5 * 0.196) / pi ) = sqrt ( 0.294 / pi ) = sqrt ( 0.094 ) r = 0.306 So, the new bore would be 0.612 ins. to increase the vol. by 50%. Which seems to work out ... unusually for me :lol: Good Heavens ... 23:02 hs ... me bedtime bevvy long overdue .. I'm off .. Where's Marv, when you need him most ?????? Dave BC |
| cidrontmg:
Scaling up double: the linear measures will be 2-fold, areas will be 4-fold, and volumes 8-fold. The weight will go 8 times higher, so will swarf production, and the cost of materials (if bought). Machining time, to some surprise, will hardly increase at all, and if the original was very small, might actually decrease. Some structural elements, shafts, bearings, air and oil passages, screws, etc. would be unnecessarily large, to the point of not functioning as intended. Also, tolerances would be best left as is, no scaling there :hammer: Scaling up with some fixed ratio might be best, that way the raw materials would be better obtainable. I´ve done some builds that way, when the original seemed like watchmaking. :wave: |
| John-Som:
Hi Eric All my recent builds have been upped by 50%. It really is as simple as increasing all measurements by 50%. Two engines in particular, Elmer's mill engines #32 and 33 were built in this way and they both run beautifully. Obviously material costs increase but other than that I have not encountered any problems. John-Som |
| Brass_Machine:
--- Quote from: John-Som on September 23, 2010, 12:45:41 AM ---Hi Eric All my recent builds have been upped by 50%. It really is as simple as increasing all measurements by 50%. Two engines in particular, Elmer's mill engines #32 and 33 were built in this way and they both run beautifully. Obviously material costs increase but other than that I have not encountered any problems. John-Som --- End quote --- So how did you determine the piston bore/stroke? Eric |
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