YachtForums.Com - View Single Post - CNC machined prop shaft versus old style machine shop techniques

K1W1 · 05-18-2007, 05:51 PM

Hi,

Unfortunately your pics are taken from different angles so it is difficult to compare apples for apples.

The thread count at 13 visible on each indicates that they are the same size and pitch, the old one was drilled for a castleated nut and the new has two nuts with a pin to retain them not penetrating the nut.

I would say that the keyway cut was done on the old one with an end mill and hazard a guess as I can't see the keyway that the CNC (Computer Numerically Controlled) one was done with a saw blade type tool- this could have been done by hand as well if the milling machine was set up accordingly.

What surprises me is the second split pin hole in the old shaft, it would worry me if I couldn't get the nut back where it was on an existing prop. I would find out why and correct it before reaching for the drill motor. If a new prop was used the boss length could affect this but it's a lot easier to whip 0.050" off the face of the nut than drill a hole through an installed SS Shaft.

CNC Machining is generally beneficial to the operator if more than one item the same is being made as someone has to sit and type the code to run the operation in the first place. There is no substitute to hand machineing and finishing if you are making something to fit an existing used component. Files,Emery Tape and lapping paste are the true jobbing machinists best friends.

05-18-2007, 05:51 PM	#2
K1W1 Senior Member Join Date: Sep 2005 Location: My Office Posts: 1,215	Hi, Unfortunately your pics are taken from different angles so it is difficult to compare apples for apples. The thread count at 13 visible on each indicates that they are the same size and pitch, the old one was drilled for a castleated nut and the new has two nuts with a pin to retain them not penetrating the nut. I would say that the keyway cut was done on the old one with an end mill and hazard a guess as I can't see the keyway that the CNC (Computer Numerically Controlled) one was done with a saw blade type tool- this could have been done by hand as well if the milling machine was set up accordingly. What surprises me is the second split pin hole in the old shaft, it would worry me if I couldn't get the nut back where it was on an existing prop. I would find out why and correct it before reaching for the drill motor. If a new prop was used the boss length could affect this but it's a lot easier to whip 0.050" off the face of the nut than drill a hole through an installed SS Shaft. CNC Machining is generally beneficial to the operator if more than one item the same is being made as someone has to sit and type the code to run the operation in the first place. There is no substitute to hand machineing and finishing if you are making something to fit an existing used component. Files,Emery Tape and lapping paste are the true jobbing machinists best friends. __________________ Cheers, K1W1