|View single post by William Dunlap|
|Posted: Wed Sep 2nd, 2020 04:20 am||
|I've been tasked with reproducing the above mentioned blade as accurately as possible. Normally a project like this would include dismantling the sample blade and having the hub cast by Cattail or other casting services.That's not possible with this one. There simply isn't much demand for these, perhaps 5 in ten years, something like that. So the project involved keeping the sample intact and using it for a guide.
I don't have a water jet, plasma cutter, CNC machine, or even a mill or a lathe. Not to worry. It can be done with simple tools and techniques and the end product will resemble the original under inspection in every way and be perfectly balanced and functional.
I first started on the wings as the material was available at a local Ace hardware. I've already ordered a sheet brass disc .250 thick and 5 inches in diameter in 260 brass for the hub. This stock can be difficult to source from the usual outlets like McMaster- Carr. I chose 260 brass because it is formable. 360 brass would fracture when twisting the fingers to put the pitch in the spider. But that's for later in the week.
Today I made the wings.
I made a stencil from stiff construction paper and traced the wing shape straight onto the 6x12 sheet of brass.This is also 260 brass .025 thick or 22 gauge.
Then I used my high speed cut-off wheel to rough cut the wings out. The sheet of paper was used to determine the size of the sheet brass needed for four wings.
Next, I carefully laid out the holes for the rivets and drilled them into one wing, which I used as a template to drill the rest. Then I riveted the four wings together, colored the edges with a large black Sharpie and used my disc/belt sander to make all four wings exactly the same size and exactly the same weight.
After that a polish with tripoli to remove burrs and scratches. The wings are now ready to be riveted to the hub which I will finish later this week after the stock arrives. In this last pic, you can see the tube brass I had on hand which will be the center of the spider. It is fabricated to be dimensionally correct for this type of application. The ID is right at .375 and the rotor shaft is .373. This is nominally 3/8". Outside diameter is .625 or 5/8" nominal and exactly the same as the sample.
More later this week, hopefully.