Saturday, April 22, 2017

Making Big Propellers

John Abbott posted
Chuck Larkin They're cast bronze, then machined to size. There are some videos of the steps required to make them..
Michael Murray I ran large 5 Axis to machine a prop. at RRNM it was the most boring job I ever had...we could get one blade at a time under the machine bridge....I ran the CVN Carrier prop.
Chance O'Neil You should see submarine props. Way bigger and way less fun to work on. Cool to look at.
Steve Walker Went to Groton, Conn. to meet a mate. Had security clearance, but NO photos of sub props.
[I saw a Science Channel program on make the big subs. They showed an animation with the prop turning. I noticed it had many thin bladse and an exaggerated curve so that it can turn slow and avoid cavitation.]

David O'Neill One of the screws for the Queen Mary is on display in front of a museum in L.A.. according to the sign they were originally balanced to such a high degree they could be rotated with 2 fingers!
[That also speaks well of the construction of the bearing.]
Chuck Larkin commented on the above posting
Chance O'Neil Now imagine some 5"diameter threaded holes in the top of that propeller hub that are about 5and a half inches deep. The problem is that they should have had about 6" deep threads. Now picture a tap in that hole with a 100:1 torque multiplier on it with a cheater pipe long enough to reach a few feet past the edge of the blades. Now picture me and the other poor guy holding that pipe and pushing it around and around all night to tap the threads to the bottom of the hole. Ya. Propeller work is not glamorous.
In the new modern propellers that are milled, or even ground, you can still see each pass of the tool. I guess the key is that they machine along the flow of water across the blade.

I recognize Wartsila as the company that makes the worlds largest diesel engines for big ships.

Whoops, this thumbnail invalidates my conclusion that the machine ripples are OK because they are with the flow of water rather than across it.

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