# Re-grinding props

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#### rheuschele

##### Well-Known Member
Is there a place on the web that I can get tolerances and measurements for propellers to be ground down to?
Ron

#### Dan Thomas

##### Well-Known Member
Is there a place on the web that I can get tolerances and measurements for propellers to be ground down to?
Ron

Other than the FAA's TCDS database, which gives only minimum length for any certified prop, nothing that I know of. The propeller manufacturers will sell you manuals for prop overhaul and these have tables for minimum blade width and thickness for various stations along the blade. Maintaining such dimensions is critical; props that are taken outside these parameters can develop destructive vibration or flutter.

Dan

#### TFF

##### Well-Known Member
You have to be a prop repair facility to get that information if you are trying to rework a prop. That info is not for the public. The guys that can reshape blades are artisans of the first order. You have to be careful with messing with a prop blade. It use to be real popular to cut down props, the T-18 guys did it a bunch; they also lost a lot of blades. Changes the natural harmonics of the prop.

#### Geoffrey Thorpe

##### Well-Known Member
You have to be careful with messing with a prop blade. It use to be real popular to cut down props, the T-18 guys did it a bunch; they also lost a lot of blades.
And a couple pilots as a result.

#### rheuschele

##### Well-Known Member
Guys, I actually have no intention on regrinding props, I do however like to learn what I'm looking at in different situations.
Ron

#### wally

##### Well-Known Member
The best and safest bet in case you are concerned about the condition of a metal prop is have it evaluated by a certified propellor shop. They should be able to tell you if it is still within serviceable dimensions, overhaulable or scrap.

Of course the risk is they will say it is scrap and you have to buy another prop for maybe $1500 or more. The larger and unknown risk is if the prop fails in flight and you become a statistic. Wally #### Dan Thomas ##### Well-Known Member The best and safest bet in case you are concerned about the condition of a metal prop is have it evaluated by a certified propellor shop. They should be able to tell you if it is still within serviceable dimensions, overhaulable or scrap. Of course the risk is they will say it is scrap and you have to buy another prop for maybe$1500 or more. The larger and unknown risk is if the prop fails in flight and you become a statistic.
Wally

We pay \$2800 or more for a prop to fit a 172 (McCauley 1C160DTM7553). And we have the manuals to keep track of prop blade width and thickness. In a flight school that sends its airplanes into some unusual areas (mountain strips, gravel and all) our props get dinged up and the subsequent dressing takes metal off them.

And that leads us to another subject: Nicks in propellers. A nick causes a stress riser, where the lines of force in the blade are forced together and can start a crack. A crack can cause blade loss. Lose enough blade and the vibration tears the engine off the airplane. Lose the weight of the engine and the CG shift way aft. With the CG so far out of limits, the airplane won't even glide.

All because of a nick that was left to do its thing. In my class I use some strips of thin, hard aluminum flashing. I cut them about six inches long and an inch wide, smooth the edges, and hand one to the biggest, strongest guy in the class and ask him to tear it in half. He can't do it unless he flexes it to work-harden and fatigue it. I take another strip and file a tiny notch into one edge with a triangular file and hand it to one of the girls, who promptly tears it apart with her dainty fingers.

And after that, those students pay way more attention to that propeller. That prop is the most highly-stressed part of the whole airplane, yet the inattention of some owners and mechanics to prop maintenance is astounding. It's a wonder we don't see more failures. I've seen props that looked like they were used to mix concrete.

Dan