Prop Balancing Discussion

[longballlumber]

Hello All,

I would like to start a technical discussion on propeller balancing. I now have a Kintec balancer that is very sensitive. The Kintec is actually replacing an older style magnetic balancer, but it wasn’t as sensitive. I guess my question or topic for discussion would be what to do when the prop always stops “level”. So, neither blades are down or up, and the prop always stops on the same side. I would think there are two rules of thought on this.

1. If you imagine a plane running thru the center of the balancing shaft, horizontal to the plane (table) your balancer is sitting on; the ear and opposing tongue would have the weight in it.

2. The hub of the prop has the weight in it and material needs to be removed from the hub.

Thoughts, comments, and/or discussion????

[properchopper]

Good topic. I'm listening

[Darin Jordan]

I work to get the prop to balance horizontally first, then I start trimming down the hub. It's a LOT of back and forth, but eventually I am usually able to get them to the point where they don't stop in any particular place.

Now, I must confess, I don't go this far on MOST of my props... especially when I am first doing them and haven't tested them yet. Usually, a horizontal balance is good enough for me. With only one blade loaded at a time, I question the need to balance them to the nth degree anyhow.

Once I get a prop that works right for an application, I take it back to the bench, clean it up fully, get the balance right, then buff it up and it's ready to go.

One of these days I'm going to get setup to harden them as well.

[Darin Jordan]

I must ammend to this that it's possible the extra weight is in the leading edges of the blades as well, so while it may be horziontal, the part of the blades hanging down could be causing the imbalance. However, once you I'm pretty certain that the blades are balanced, I'll trim on the hub to get the final balance.

[longballlumber]

Another question that comes to mind on the topic, is what about props that have been de-tongued and is still ending horizontal? When you cut that plane from thru the prop, the ratio of tongue material verse ear/trailing edge material on that plane isn’t equal. Is this now when we move to the hub?

[Jeff Wohlt]

I clean the hub up first and check for balance then start working on the blades. The balance farthest from the hub is key. That is what will throw the rotational load out...not so much at the hub since that is closest to the shaft.

I only remove metal from the front of the blade...the convex side that faces the front of the boat. I also square the TE up.

I make sure my prop is the same length on each blade as well. You can only see this on a lathe...or something similar. Once all is sqaure and equal then I begin removing and thinning to get balance.

That is the way I do it...forget polishing unless it is looks you are after...does nothing but maikes water stick to it. Pretty is not the key but most want it for the bling and wow factor.

If you are getting horizonal after spinning then you are fine.

[longballlumber]

I clean the hub up first and check for balance then start working on the blades. The balance farthest from the hub is key. That is what will throw the rotational load out...not so much at the hub since that is closest to the shaft.

I clean the hub first too, and I like the additional detail on balancing furthest from the hub. Good Point!

I only remove metal from the front of the blade...the convex side that faces the front of the boat. I also square the TE up.

I agree

I make sure my prop is the same length on each blade as well. You can only see this on a lathe...or something similar. Once all is sqaure and equal then I begin removing and thinning to get balance.

Digital calipers and Micrometers can also aid in determining this. Another method that I have tried is using a piece of masking take cut to following the profile of the blade shape of one blade and then placing that piece of tape on the other blade. This will give you a general idea if the blades are the same. I recall someone doing the same but using playdoh to confirm the blades are the same shape.

That is the way I do it...forget polishing unless it is looks you are after...does nothing but maikes water stick to it. Pretty is not the key but most want it for the bling and wow factor.

I agree

If you are getting horizonal after spinning then you are fine.

I however, don't agree with this theory. If you spin the prop and it lands horizontally on the same side every time, the side pointing down is heavy. The questions is; in the blades or the hub???

What about manually standing the prop vertical on the balancer, letting go and it settles horizontally? That tells me the prop is heavy in the horizontal position.

This is good stuff guys!!!

[Doug Smock]

Another question that comes to mind on the topic, is what about props that have been de-tongued and is still ending horizontal? When you cut that plane from thru the prop, the ratio of tongue material verse ear/trailing edge material on that plane isn’t equal. Is this now when we move to the hub?

If the prop is hanging horizontal I remove material from the leading edge of one blade and the trailing edge of the other.

Doug

[properchopper]

Something Similar

I make sure my prop is the same length on each blade as well. You can only see this on a lathe...or something similar.

Nifty blade-length checker...

[Darin Jordan]

Nifty blade-length checker...

I check my blade shapes by pressing one blade into some modeling clay, then rotating the prop and seeing how the other blade fits into the impression. Takes a little patience, but it's a pretty accurate way to make sure the blades are shaped the same and the same length.

I do as Doug suggests as well, but to be clear, I believe he's talking about taking material off of the FACE of the blade at the leading and trailing edges of the respective blades to reduce their thickness. Just assuming that the blades are already shaped correctly, profile-wise...

[Doug Smock]

I do as Doug suggests as well, but to be clear, I believe he's talking about taking material off of the FACE of the blade at the leading and trailing edges of the respective blades to reduce their thickness. Just assuming that the blades are already shaped correctly, profile-wise...

[Flying Scotsman]

A very good thread and as Darin and Doug have mentioned the modeling clay method is important to verify length etc. especially on Octura props, as their molds I presume are old and have a lot of excess flashing material. But to be honest if the prop balances horizontaly, I am happy

Douggie