Baar cutting a colbalt chrome propeller

[Jim Allen]

Cobalt Chrome ASTM F-75 is a medium strength (130,000 psi tensile) , 34 Rockwell C, nonferrous cobalt alloy with goood stiffness & high corrosion resistance. The alloy is difficult to file & cut, therefore I use diamond files ( 40 to 600 grit) & coated carbide end mills for effective cutting operations. After re-cutting the driving slot & both the front & rear of the propellers hub, I set up a simple fixture to index the propeller for Barr cutting. Since the propeller is balanced before Barr cutting, it should be balanced after Barr cutting if the cuts are of equal amounts.

Jim Allen

 

[Ray Sametz]

OMG are those cutting chips on you machine !!!! Clean up your act, your slipping.

LOL

 

[Jim Allen]

That's what they are Ray & they are much more sharp than stainless steel chips.

JA

 

[Terry Keeley]

Hey Jim:

I got a couple props done in CoCr and had to use some diamond strips from 3m to finish them. To be completely honest I wasn't impressed with the shaft fit, it was quite loose. I resorted to holding the props in a vise in my mill and setting a shaft with JB weld, it worked for a while but wasn't a permanent fix.

How was the shaft fit on yours?

 

[Jim Allen]

All of the holes in the prop hubs are a little larger than .250" ID. Therefore, I have many tapered shafts of different sizes which allow the propellers to be driven on tightly. I also have different size shafts for use in the magnetic balancer.

JA

 

[Randy Rapedius]

Some of my CoCr prop shaft holes were 10 to 15 thou larger than .250.

 

[BobHorowitz]

Hi Jim,

Bob Horowitz here. Where did you get the diamond files in the graduated grits? I could use a set like that.

Thanks,

Bob

 

[shoboat]

Terry,

If the hub has a really loose fit, drill them out and press in a reducer piece

of stainless steel tubing. It works Very Well and does not take too long.

Just A Suggestion,

Mark Sholund

 

[Jim Allen]

Terry,

If the hub has a really loose fit, drill them out and press in a reducer piece
of stainless steel tubing. It works Very Well and does not take too long.

Just A Suggestion,

Mark Sholund

I think this is a great idea but reaming would be better because a solid carbide reamer of this size would have 6 cutting points compared with 2 cutting points found on a drill. Also the reamer could be easily re-sharpened with a diamond wheel.

JA

 

[Jim Allen]

Hi Jim,

Bob Horowitz here. Where did you get the diamond files in the graduated grits? I could use a set like that.

Thanks,

Bob

Bob,

I got them from Amazon. SE74330DF 6-piece diamond grit file set. 40, 80, 150, 240, 400, 600 grit & they are double sided. The 600 grit file can put an impressive edge on the CoCr material!!

JA

 

[BobHorowitz]

Jim,

Cool, Thank you.

Bob

 

[Terry Keeley]

Terry,

If the hub has a really loose fit, drill them out and press in a reducer piece

of stainless steel tubing. It works Very Well and does not take too long.

Just A Suggestion,

Mark Sholund

I think this is a great idea but reaming would be better because a solid carbide reamer of this size would have 6 cutting points compared with 2 cutting points found on a drill. Also the reamer could be easily re-sharpened with a diamond wheel.

JA

Great idea guys, thanks, but I have a better solution. I'm gonna make my own props!

 

[BobHorowitz]

Jim,

Nice and cheap. I found them for under $11. Not bad considering that most that I've used have a limited life span. Thanks for the tip.

Bob

 

[GraysonTaylor]

DMT makes great diamond stones and files. Much easier to do stainless. I discovered them from wood working. Www.dmtsharp.com