Author Topic: Biggest problem with carving blades  (Read 2633 times)

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Norm

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Biggest problem with carving blades
« on: September 21, 2004, 04:06:17 PM »
  Since I didn't have templates for the various stations I made some crude templates of my own.

  Ah! Sawing kerfs at the proper angle and depth for the flat or windward side is easy ( I can even make a jig for that).

  Now sawing the kerfs for the rounded side saw a little bit harder...(a little bit harder to make a jig for that.....)

  Okay here's the way I see it if you can make a series of cuts with a hand saw and a jig to guide the depth and curve of the cut from one end to the other about 1/2inch apart,chisel away the excess wood  hand-plane and scraper to a smooth finish.

  Jigs are easier to make...and cheaper than making or buying a duplicator with the arms and beams, cams and whatnots....in my opinion.

  I've seen the posting about balancing blades..just a thought...if you made your blades from a good grade of wood (no knots) and each one was an exact copy they'd all weigh the same wouldn't they?...there'd be no need for balancing? Excuse my ignorance if this isn't so....

   Okay I'm just wondering if someone already has made a jig like I just tried to describe or hopefully I gave someone an idea       ( :>) Norm.                  
« Last Edit: September 21, 2004, 04:06:17 PM by (unknown) »

wdyasq

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FYI
« Reply #1 on: September 21, 2004, 07:35:26 PM »
One can purchase a tree, have it properly cut, dry the "stack" together, make as close to identical blanks as possible and CNC machine them they will still not be "identical" and will still need balancing.


Ron

« Last Edit: September 21, 2004, 07:35:26 PM by wdyasq »
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domwild

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Re: Biggest problem with carving blades
« Reply #2 on: September 21, 2004, 07:39:56 PM »
Hi,

Good info is available from "Wind rotor blade construction" by Hugh Piggott et al. Can't give you the web page.

Go to

www.thebackshed.com/windmill/assembly2.asp   OR

www.randysworkshop.com


and on one of the two web pages the chap will sell you laser cut wooden templates for $US60, if I remember right.


Cheers,

Dominic

« Last Edit: September 21, 2004, 07:39:56 PM by domwild »

DanB

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Re: Biggest problem with carving blades
« Reply #3 on: September 21, 2004, 08:08:09 PM »
Blades are a weird thing...

you can make them as complicated as you want... and you could strive to have each blade "identical".  My blades never turn out identical... and I never know if one works better than the other two!  When Im helping folks carve and they screw up.. I often tell them, "who knows, it might work even better! - dont worry about it".


So long as the width and pitch is within reason - and the airfoil on the back is within reason, I think there will be minimal room for improvement.  


Some have much higher tolerances in their work than I do and spend much more time, but I really feel that a lot of people get intimidated by blade carving (and never bother to even try) because of how complex some would make it seem.


Curfing - and templates for the back side, that's something I'd never even consider worrying about.  Neither would I worry about getting each blade weighing the same... just stick a weight on it and it will be fine.  (perhaps Im wrong)  I've seen 3 blade sets where two completely different types of wood were used and in the end they came out fine.


It's not difficult to use someones blade calculator or follow a formula and work out 50 stations if you want to  - and pick an exotic airfoil profile and make templates for each station along the way...- but very time consuming.  You've got to draw the line somewhere... I draw it at the place where I feel I can get it done before I lose interest (I have a short attention span).  I think a person can make a blade which is the same from root to tip and it'll work fine.  usually.. I often work from 3 stations - the root (which is determined completely by the width and thickness of the board with some consideration for strength and appearance), the half way point, and the tip - and I often make nice looking twist between the root, and the half way point - by bending a piece of springy steel and tracing the profile.  I make the front side of the blades flat, the airfoil is a "nice shape" with its thickest point about 1/3 of the way between leading and trailing edges.  The thickest part of the blade is usually about 1/8 as thick as the blade is wide.. a bit more perhaps towards the root.


I could be wrong.. but I have a feeling it can be much simpler than many folks think, and still work about as well.  I think blades are pretty forgiving.

« Last Edit: September 21, 2004, 08:08:09 PM by DanB »
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Norm

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exact copies and still different weight
« Reply #4 on: September 21, 2004, 08:50:11 PM »
   Thanks for the input guys I kind of suspected that would be the case and always interesting to hear of your experiences.

                 ( :>) Norm
« Last Edit: September 21, 2004, 08:50:11 PM by Norm »

windstuffnow

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Re: Biggest problem with carving blades
« Reply #5 on: September 21, 2004, 09:21:04 PM »
  I agree, they don't have to be perfect to work good.  Even with my duplicator all the blades don't come out exactly the same.   So far they've all worked well.   I've used hand saws, jig saws, band saws, hammer and chisel and anything else I could find to hack out a blade looking piece of wood.  They all worked good!  I've spent lots of time trying to make them as perfect as I could get them and as little time as possible hacking out some blades and both worked about the same.  So, the perfect set of blades in my mind are the ones that take the least amount of time.( I also have a limited attention span ;o).  If you have a band saw, once you get the blade layed out you can have the basic form in about 15 minutes, the rest is finishing.


   If thats not fast enough use flat 1x boards at a reasonable angle (4 to 8 degrees).  Form your leading and trailing edge and mount them on angle cut boards.  The loss in efficiency is quite minimum, you'd be surprised.  You also loose a little speed depending on the angle you mount them.  With the ease of start up on the dual rotor machines a 4 degree blade would work just fine.


   I also hate sanding although I used to do alot of body work while building street rods.  To get the blade finished quick, I use an air powered board sander with 40 grit, takes about 2 minutes to run the wood down 1/8", forms the leading edge in just a few strokes.( have to be careful)  Then I use an air powered jitterbug with 80 grit to smooth out the rock scratches from the 40 grit and from there I go over it with a sanding block with either 120 or 100 then its time for paint.  Flat blades I form the trailing edge in a table saw... ( be very careful though, mine has a tendency to kick back when cutting angles the length of the board).


   Blade making doesn't have to be difficult, after you do a set, all other sets are boring.


Have Fun in any case!

Windstuff Ed

« Last Edit: September 21, 2004, 09:21:04 PM by windstuffnow »
Windstuff Ed

Reno

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Re: Biggest problem with carving blades
« Reply #6 on: September 21, 2004, 09:26:51 PM »
Norm can you explain that to the knots

I tried but they wont listen

darn knots.

All in good fun actually the balancing post was mine and I did not mention the sheet of fiberglass just as a safety measure in case of shear.
« Last Edit: September 21, 2004, 09:26:51 PM by Reno »

Flux

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Re: Biggest problem with carving blades
« Reply #7 on: September 22, 2004, 01:40:58 AM »
I have to agree with the rest of you on this, when I was a kid my blades were very simple with little taper or twist and worked ok. Later in life when I came back to wind power I found out about theory and found drawings of NACA sections and went to great lengths to produce accurate profiles with templates etc. Again it worked fine but I couldn't detect any obvious improvement.


I have gone back to the quick methods and as long as the angle and chord is about right at 0.7 radius it seems to make little difference what you do with the rest.


For higher tsr the surface finish seems to have more effect than the exact profile.


I try to keep the blades similar on the outside half, but if there is significant difference in weight I correct it as far as possible by removing wood from the centre part of the heavy ones to reduce the amount of weights needed.


If you are going to make a mould to mass produce blades it would be wise to make it as good as possible, but for one set of blades, keep it quick and simple.


Flux

« Last Edit: September 22, 2004, 01:40:58 AM by Flux »

Norm

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Re: Biggest problem with carving blades
« Reply #8 on: September 22, 2004, 07:26:02 AM »
but I really feel that a lot of people get intimidated by blade carving (and never bother to even try) because of how complex some would make it seem.


   So do I...just from my first experience it's so much fun...it's like getting a surprise package

by carefully unwrapping a hunk of wood there is that prop you were wanting....it was there all the time!

   Hopefully some will be encouraged and discover for themselves how easy it is!

                 ( :>) Norm.

« Last Edit: September 22, 2004, 07:26:02 AM by Norm »

Norm

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Re: FYI
« Reply #9 on: September 22, 2004, 08:14:57 AM »
they will still not be "identical" and will still need balancing.

....I guess I should have said balancing to a degree whereby just lightening the heavier blades by sanding would be sufficient.

    It's just that when someone talks of lead weights for balancing ....but not that I wouldn't do the same thing....I'd be thinking ....this'll work...but it just ain't right! LOL

                 ( :>) Norm    
« Last Edit: September 22, 2004, 08:14:57 AM by Norm »

DanB

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Re: Biggest problem with carving blades
« Reply #10 on: September 22, 2004, 08:25:18 AM »
I agree... it is like Christmas a bit!

... and I'm always the one that wants to open my presents on christmas eve ;-)


We put on a little two day workshop last weekend at a fair in Ft Collins.  Welding... and grinding wasn't really appropriate there (plus we didnt have power) so I did that part at home before hand, and I cut the taper and a bit of the thickness at home with the bandsaw before hand.  But otherwise -  we had about 16 different folks over the course of the fair who'd never done this sort of thing before - we had space for 4 to work at any one time. Other than pointing fingers and offering up opinions, they layed out the blades and had them carved (and they came out nicely) by sunday afternoon... perhaps 2 inexperienced folks working for about 6 - 8 hours with hand tools only.  On the other table we got coils wound, magnets mounted... casting done and in the end we had everything finished and assembled and quite workable.  It can go pretty fast and it need not be too difficult.

« Last Edit: September 22, 2004, 08:25:18 AM by DanB »
If I ever figure out what's in the box then maybe I can think outside of it.

Norm

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Re: Biggest problem with carving blades
« Reply #11 on: September 22, 2004, 01:36:40 PM »
     Wish I could have been there ...but it's not possible just have to be satisfied with pictures, a 5 to 15 minute mpeg that we could download of the highlights would really be nice!

                  Fun!  ( :>) Norm.
« Last Edit: September 22, 2004, 01:36:40 PM by Norm »