Now for the second jig. The final blade will really be a wedge for our purposes. Mine will be 15mm thick x 8" across at the tip. At the hub (400mm point), it will be about 35mm thick. It's that simple. This wedge is attached to our hub part at an angle. Thats the only reason we have to chainsaw or carve... the wedge is at a different angle than the blade mount. If we were to use constant pitch along the blade we could just mount the blades with a 5-10 degree packing spacer, and achieve the same kind of thing.
So the second jig has to just achieve the second side of the wedge... within the confines of the blade material.
So first we need to place the blade on a new jig bed of 8x2. We place the blank on it (newly planed face down), and the butt will sit ok, but the tip end will be askew.
I use two screws to space the blade back up to the original height like this.
When the blade is place on them, they should sit square with the butt end, so it essentially sits flat as if we had not mangled the front side of the blade:
Doing it this way, if the boards were different thickness as they are here, it does not matter, as we will have effectively thicknessed them with the first chainsaw cut. The picture looks wonky, but the blade is positioned correctly and pretty flat on the top.
If you scribble the rough (mine was 15mm) blade thickness on the end, try and imagine at the hub end (400mm in) the same thing in the same plane at 35mm thick.... it's that simple. Using the offset you worked out with the chainsaw blades, just sketch it along the blades sides and place the guides to match.... remember to include the offset.
The trailing edge will look something like these two pictures
and the leading edge will look something like these two
Don't forget to drive in the stabilising screws. We don't want to have a belly in the unsupported middle. 3 screws as before will be sufficient. You can see the end one ready to drive in. This is important so that the blank is held firmly.... clamps are not a good idea for this, as they may distort the blank in the second jig in particular.... unless you make a heap of spacers to stop them dragging it down..... too much like hard work for no gain at all.
and after you hack away for about 3 minutes, it looks like this:
Tidy it up a bit with the planer.. should only take a minute or so ... including the drop off area at the hub end.
This side once the jig is built is only about 5 mins... damn quick way to make blades, however, the planing starts soon, and will burn up about 10 mins... so off we go.
Notice, I did not cut the taper first . It would seem to be a good idea too do that, as it will be less to chainsaw...... wrong!
The problem is that it is much easier to keep the blade pinned into the jig easily with the wood the full 8x2. If we had tapered it, it would be difficult to screw it to the jig. The chainsawing may be slightly slower, but the repeatability of the blade making is enhanced considerably, by being able to support it properly...
Now it's time to taper.
Sketch out the taper you want... I decided on 5" tip, straight back to the hub area. It looks like this:
I'm a doddering old fool, so I leave a few mm to plane down
Now for the airfoil.... and it is simpler than it looks.... just plane work. I set mine pretty aggressively so it only takes about 10 mins to do the trailing edge, and 5 mins to do the leading edge.
So draw a line 1/3rd in from the leading edge. This will be your reference line.... make sure you are using the down wind side of the blade... not the windward side!!
In my case about going from 37mm in from the leading edge at the tip, and about 64mm in from the hub end.
Draw a profile of what you expect it to look like on the end like this (I make the trailing edge thinner later on, or if I slip up a bit now.....
Ok now plane away. I set the planer for far too much (about 1mm cut) and the trailing edge is a 5 min job. Just start at the edge with a 45 bevel, and then flat plane with a pressure bias towards the edge, and it seems to work itself out in no time.
There are no fancy angles or anything here, just flat planing. Blend it into the hub area, and I lose interest about 1/2 way down the edge, and start to thicken it back up towards the hub area. It will look like this:
If you use some imagination, you may see that the trailing blade edge is thickening in the region above the tablesaw blade, the outer 1/2 of the trailing edge is only about 1.5mm thick/thin.
The leading edge is both quicker and faster. Just do a 45 degree bevel, and as Hugh Piggott rightly put it, just keep taking the edges off. It will round itself up in no time at all...
They are not sealed or painted as they are wet. They don't even remotely weigh the same at the moment, and it's not much point trying to match them either, They are too wet..... like this... oozing resin from their first spin drying session at 3kw or more.
Once the jig was done.... the next 2 blades were done in about an hour... then the holes
So, yes.. heathen that I am, I mounted them unsanded, and tested them out.
They are a staggering improvement over the better designed ones I did last time.. and they were damn good 5kw ones). These have better low end power generation, and are dead quite. This I don't understand. The ends are still square cut, and yet almost silent.... go figure. They have done over 3kw on their maiden flight, and I didn't think it was very windy either.... must have been, but it didn't feel it.
They come off at night so they don't take up moisture, rebalance them in the morning... and there off. I use Zubbles counter balance technique, so individual blade weights are immaterial.
Why would you use plastic pipe??? these are 4m blades, and still only a couple of hours to build once the jig is sorted.. and once done once, is a soda next time up
Have fun..... It's too long to proof read at the moment, I'm posting it as is until I get a chance to look it over a bit..... before I lose it all
Jonathan ( imsmooth on the forum ) has put together a excellent series of pages that explain part of the chainsaw method in detail. You can check it out here.
Mark ( Throgdor on the forum ) has modified a electric plan to give a nice final finish to his set of chansaw made blade. I think you could use a modified plan like this to do the complete job, it wont be as fast as a chainsaw, but more of us would have a electric plan in the workshop.
Max's technique should work well with Oz's chainsaw method. Once the jig is made, you could cut out a blade in a couple of minutes! All that's left to do is clean up the trailing and leading edges and your done.
I now have an update. I was already announcing that I would make a video on making my style of blades with the chainsaw and it it on youtube now: