| First off, a big thanks to this board and all who contribute, it's a great resource for us newbies. This seems to be the time for CNC blades so I thought it was a good time to share my experience.
After about years time, I finally have a set of three matched CNC carved redwood blades to go with the dual rotor, 48 mag, 72 overlapping coil, AF alternator I've been building. The blades were quite smooth right off the machine and only required a little finish sanding to remove a few tool marks and clean up the edge where front meets back.
The blades were laminated up from clear redwood with varying lengths and widths to reduce the volume of wood to be removed. The finished blank tapered in width from 17 inches to 6 and from 6 to 1 inch in thickness. The cutting was done in 5 steps, 1-rough cut front, 2- finish cut front , flip the blade, 3- rough cut back, 4- finish the back, 5- trim the root and drill mounting holes. Each carving step took about 6 hours, kinda long, but get it going then go do something else.
Rough cross cut
It has been quite the adventure to say the least. I had gained some knowledge of CNC with a 24 x 24 inch CNC plasma cutting table I made, and figured why not try a CNC router, and what better excuse to build one than to have one big enough to carve out the 8 foot blades I wanted. With the CNC you can get as crazy as you want with convex and concave curves in airfoils. I chose the GOE222 airfoil for its high lift to drag ratio but it still has a fairly robust cross section. I am fairly proficient with drawing in 2-D but 3-D with its planes and faces was another world. Ended up using RHINO to draw up the 3-D blade profile. MeshCAM was the final choice for converting the drawing into G-code, it will not only follow the shape outline in the XY plane but can sense when the front starts to become the back so it stops the depth cut, saving a lot of cutting time. Much time and frustration was spent trying to get, free or cheap or demo, software to work with each other. A lot of their limitations did not surface until sawdust was flying, as luck would have it I only had to throw away one blade, thank God for putty.
The CNC router has come in handy for cutting out other parts as well, such as the mold for the stator and magnet disc spacer/fan. The CNC plasma cutter is great for the flat metal turbine parts too. It takes a bit of time to learn to use these tools effectively but the accuracy of the part is worth it.
Here is a shot of the stator before casting.
Magnet disk
Router details are
X - travel 24", ACME screw drive, 60 IPM
Y- travel 97", 1/4" pitch timing belt set in a T rail, 80" IPM
Z- travel 5", ACME screw drive, 60 IPM
Machine control using KCAM with MaxStepper, GECKO Drives
Rough cut- 0.2" over size - 3/8" depth per pass with 1/4" step over, 1/2" x 1" 2 flute straight cut router bit.
Finish cut- 1/16" step over, 1/2" bull nose (bowl carving) router bit.
bits are 1/4" shank, set in a 1/2" dia 4" long extension.
I dabble in pattern making and sand casting with aluminum which made this router design possible.
More blade, router and stator detail pictures can be seen in my files.
Thanks again to all.
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