StephenC

Im struggling with a design problem for my HNC and no matter where I look on the internet cant find an answer. Wondering if anyone off here could help? Ive got a 5kw motor running at a speed of 600rpm driving a gearbox by a shaft. The shaft is 400mm long. We have been given a modulus of elasticity of 80 x 10^9 N/m2. I need to choose a standard shaft, well tube actually, that will be up to this job. Im running into problems as I cant find the ultimate torsional stress a mild steel shaft can take. Cant find any standard sizes anywhere. All ive got at the moment is a 100mm OD 80mm ID shaft and ive worked out the stress for this as 2.7099 MN/m2. Anyone shed any light on how to choose the optimal size?
thanks
Steve

M Brian

I can only just about remember doing a question like this and the standard size bit of it totally bolloxed me aswell...

IIRC correctly though it was just a round number - just go to the highest round number above what you work out? - and say it includes a factor of safety for example.

gutted I can't remember more - TBH think id stuggle to even do the formula now - its polar 2nd moment of area and angle in radians etc isnt it?

it would take me about 3 days to find my HNC notes as they're all boxed up. if it no ones answered and its sprung to mind then i'll try dig for you.

just take a standard mild steel for the modulus figures

foreigneRS

jesus, i'm glad that since graduating from Brunel over 10 years ago i've never had to do things like that.

why don't they teach you how to do things that you will do in the real world? things like that are taken care of by geeks behind cad screens these days

StephenC

Thanks lads, think Ive done it now, ive used a 200mm OD shaft with ID of 120mm and got a final stress of 418 N/mm2 which is below the ultimate stress of mild steel (430 N/mm2) so it'll have to do. Great innit considering its an Electrical Engineering HNC im doing

Westy

iTrader: (1)

Im currently doing a HNC in Electrical/Electronic Engineering.. About a week ago I had an almost identical question to that...had to find out torsion of shaft, angle of twist etc...
currently doing fluids...

what is electrical about this.. hard work tho..

M Brian

fpmsl...

i had to learn about faradays law some random ohm shit wtf that got do with mechanical?!!

sparkys stick their nodes right up their ass for all I care

Westy

iTrader: (1)

bernoulli's law ... wtf?? another tosser

Kirchhoff's Law - hero..

M Brian

ah kirchoff he's a cooooont inhe!?! oodjyanickyabollokoff!

is that the badger im thinking of with the circular poles, nodes and other equivalent bollox? current going one way equals current going another thank you please?