radical design change, got the z finally perfect

[jacquesm]

After mucking around for a few days now with small changes to the blank shape we (RonB and yours truly) had a pretty big breakthrough today.

The one problem that seemed to be chasing us all the time was an 'off center' blade shape which caused the cutter to bite air a lot of the time and a very large blank compared to the resulting blade.

We have made two major changes to solve these problems:

• the blade is now centered in the 'y' direction, which means that there is taper on both the leading and the trailing edge. This is at the expense of a very little bit of efficiency, but makes the blank much more efficient.
  
  
• the blade is now centered in the 'z' direction, which means that the whole blade 'side view' is a lot flatter while maintaining the required twist angle.
  
  The blank went from 95 millimeters to 51 ! That saves a lot of wood and cutting time.
  
  

The rationale for this is that the blade functions as an infinite number of small sectional blades that each have to have proper twist and taper for that particular station. Changing the blade like this makes it almost impossible to shape by hand, but for the computer operated router that is no problem (it uses 800 stations to calculate the toolpath), every station would have a different front and back 'drop'.

We spent the rest of the day working out a method that would allow us to maintain perfect 'z' registration at the moment of 'flipping' the blade over between passes and further optimized the toolpath by selectively speeding up when we know we're making small cuts (such as the cuts on the final passes).

I think we're getting really close to a final design now, one more blank tomorrow morning to see if we have it all perfect, and then - finally - some real blades. I'd better get on with it too, because snow has been forecast for the region.

pictures follow:

the new blank shape, much simpler than yesterdays:

Last pass on the back, looks pretty smooth

Backside finished: (note the funny little 'hump' caused by the segments rotating about their 'z' center)

Roughing out the front, you can clearly see the 'staircase' steps during the roughout phase here, in this foreshortened (25%) blade that is exaggerated even further.

The finished blade, backside:

The finished blade frontside:

[sh123469]

Looks like you're doing a great job there.  I know it has been a lot of work and to see something turn out reasonably good is wonderful.

Now, when are you going into business making blades for people?  Just kidding, I am sure you have plenty to keep you busy as it is.

[Galagedara]

Dear JAC,

It looks like a fantastic job! I am a guy with no mean of constructing blades, as I do not have the tools, place, etc. I have plans to make a wind mill for battery charging. After you have perfected your achevement is there a possibility of buying a set of blades for Hugh's axial construction.

Kind Regads! Keep the good work!

Leonard fernando.

[jacquesm]

You have no idea how many people have already asked me, and while I'm not planning to go into the all out production of blades we have definitely discussed the possibility and if we get all the kinks worked out we may do a small series, but I really emphasize that we have not made any firm decision in this. We very much want to be on the prototyping end of things, production really is not my game. Stay Tuned !

[Galagedara]

Of cours I really understand you, that you do not want to make comercial, but what I really want is a kind of help for a set of blades for a person really have no possibilities to make his own! So it is a great help if you kindly responce to my request. The small hint in your reply made me really happy saying may be in the future you will! If it is so please let me know OK. My e mail address is >leonardfernando@mail.dk< I am intending to take this set to Srilanka in the future. Well I am not pressing you, but it is only with your decission.

Kind regards!

leonard