ORIGINAL: rageman
What is actually done when sharpening and cuping a model propeller?
Which faces of the raw propeller blades do you grind off and which ones do you leave alone when sharpening. Leading edge only or both leading and trailing edge of the blade sharpened? To a fine thin edge or to a clever shape
What exactly do you grind/bend? to "cup" a propeller?
Do you only sharpen the propeller edges or do you grind the whole blade to make it thinner as well? If so how thin?
Do you try for an aerofoil blade shape like a planes wing or unifom thickness across the blade?
What tools work best? Dremmel tool? Air grinder? What dremmel/grinder bits to use for what operation? All by filing? Wet dry sand paper? Stone?
How and with what do you polish the prop when done shaping?
Etc? Etc?
A lot of this stuff is kind of subjective. I would love to do some testing with all this, or read about anyone that has done some testing.
Anyhow, about polishing...I brought this up before. It is said that a polished finish on the bottom of your boat will slow it down. So...why do folks polish their props, rudders, and turn fins to a high shine?? You will get answers on both sides of the fence on this...
As to cupping...I don't think most RC boaters cup their own blades. I think this is a more advanced method of working a prop. Problem being, you would need to cup both of the blades EXACTLY the same. There are some prop duplicators out there, but I have not seen one for props as small as most folks here seem to be using (for RTR type boats).
As to which side to work...I have heard of some folks not touching the front of the blade at all (the front actually is the part facing rearward when mounted in the boat). But, every picture I have seen of props seem to show that it has been worked. If you think about it, this is the side of the blade that makes the most contact with the water. It is actually pushing your boat. Personally, I use a dremel to remove any flashing from it...other than that, all I do is polish it when I polish the rest of the blade. I am not saying that what I do is right or wrong...just saying what I do....
As to what bits to use...I use a small diamond bit to remove any flashing off the barrel of the prop. I use the sides of a cutting wheel to remove flashing from the edges and flatten the rear of the blades. Then I use 2 or three different grit sanding disks to shape, sharpen, and balance the blades. Then I use dremel polishing compound if I actually polish the blade. One of my blades was just worked down to 600 grit sandpaper, and then left alone.
I think if you ask 10 different people how to do it, you will get 10 different answers.
As a disclaimer, I am pretty new to this. What I do either came from reading, from folks here (one in particular), or from figuring it out on my own.
Sean