Z-axis design - help sizing materials please!

[Jonathan]

Forgive my stupidity, by why do you need all that z-movement for a wind turbine blade? If you're thinking of cutting them vertically 'on the hub' so to speak I think you run the risk of, as a minimum, the blade deflecting, or worse snapping off... anything that high a length to width ratio probably needs milling horizontally and adequately supported... or have i got the wrong end of the stick (or should that be blade?) :lol:

Yes you got the wrong end of the stick/blade there! :lol: I am intending to mill them horizontally. Near the hub, due to the twist on the blade, the Z distance is quite large. I'm intending to make a set of 3.2 meter (diameter) blades for a variable pitch wind turbine I've made. There are other things I want the big Z travel for, I just can't remember them at the moment!

I've found some 160x80mm steel box section. There's 5mm, 6.3 and 8mm wall thickness available. I think the 5mm should be ok. No idea how much it costs or if I can buy less than a 7.5 meter length....

http://www.steel-shop.co.uk/contentf...talogue(1).pdf
(page 7 - I live very near to them but I've never actually been)

[irving2008]

Yes you got the wrong end of the stick/blade there! :lol: I am intending to mill them horizontally. Near the hub, due to the twist on the blade, the Z distance is quite large. I'm intending to make a set of 3.2 meter (diameter) blades for a variable pitch wind turbine I've made. There are other things I want the big Z travel for, I just can't remember them at the moment!

I've found some 160x80mm steel box section. There's 5mm, 6.3 and 8mm wall thickness available. I think the 5mm should be ok. No idea how much it costs or if I can buy less than a 7.5 meter length....

http://www.steel-shop.co.uk/contentf...talogue(1).pdf
(page 7 - I live very near to them but I've never actually been)

Ah ok i see now... thats some serious machining you're planning! what material will these be made of (I know you said wood, but what type?). So each blade is 1.6m long approx by what at the root? the aspect ratio of a blade like that would be maybe 12:1 or more so the biggest cross-dimension is 135mm but I dont see that needs a 400mm travel. What am I missing?

[Jonathan]

Ah ok i see now... thats some serious machining you're planning! what material will these be made of (I know you said wood, but what type?). So each blade is 1.6m long approx by what at the root? the aspect ratio of a blade like that would be maybe 12:1 or more so the biggest cross-dimension is 135mm but I dont see that needs a 400mm travel. What am I missing?

Ash would be nice, maybe pine ... depends what I can get hold of really! Either way it's not a hard material, and anything I make which is a hard material won't be more than say 75mm tall so I think the making two of the bearings moveable and supporting in the middle is the way to go. Doing it that way would surely be sturdier than if I'd designed for 75mm in the first place - it will just take a bit longer to set up.

Here's one of my blade designs. This one was optimised for less Z axis travel but as you can see it's still quite a lot. The calculations show the root at an even steeper angle, and hence need a good Z travel. I agree this blade won't need 400mm, but I really don't want to be faffing trying to squeeze the blade into the available space!






The blade there is a 0.7m blade I made for a smaller with turbine. Plywood isn't so good...

Do you think the 160x80x5mm box section will be sufficient?