Prop balancers

[zul8tr]

The tire balancer concept is sound but to take a tire balance machine and adapt it to balance small props would not be so easy if not impractical. First the tire machine is calibrated in the range of tire + rim weights that are expected to be placed on it, not light weight props. Second they spin at relatively low rpm. Third they would have to be revamped to tell where to remove weight and how much and not to add it like for tires for dynamic balance.

[Roflhat]

The tire balancer concept is sound but to take a tire balance machine and adapt it to balance small props would not be so easy if not impractical. First the tire machine is calibrated in the range of tire + rim weights that are expected to be placed on it, not light weight props. Second they spin at relatively low rpm. Third they would have to be revamped to tell where to remove weight and how much and not to add it like for tires for dynamic balance.

This is all very true, but do you think with some reprogramming it could be made to work? I'm sure the motor could be made to spin it to higher RPM, I'm just not sure if it could be programmed to tell you where to remove weight instead of adding it.

[Fastjeff57]

Being Mr. Crude, I spin balance my homemade props in a vise-held fixture with a 3/8 drill at about 600 rpms--thrilling!

I mark each blade for identification purposes, then duct tape a weight (flat washer) to each blade in turn and note how the prop reacts. After determining the heavy blade, I grind the backside until it spins as smoothly as possible.

It takes awhile--and is subjective (lots of guesstimating)--but I get them fairly smooth.

Jeff

[zul8tr]

How do you determine the heavy blade while going 600 rpm? Do you use a strobe? How do you determine that where you removed material on the backside is the correct spot? Ex. you could remove less farther out vs more closer in and still have dynamic balance. Do you have some device to check the vibrations or by feel?

More details of your process would be appreciated. Perhaps a video?

[Fastjeff57]

How? By guestimation and lots of patience. (Ever balance a ceiling fan? Same technique.)

Jeff

[Roflhat]

Got any pictures of this setup, sounds very interesting.

[Fastjeff57]

The prop shaft is in a steel bushing held by the vise. I've since improved on the set up with a nice, bronze bearing. The prop is my first homemade special.


Jeff

[Fastjeff57]

Just finished balancing my latest homemade prop. Weighed the blades (at the Post Office!) before welding them to the hub, getting them very close. The result was gratifying: the weight of a 3.8 flat washer on one blade smoothed her right out. A little grinding on the 'heavy' blade and she's ready to go.

Jeff

PS: Doing this with a two blade (vs. a three or four blade) is a bit easier!

[David Mason]

How do you determine the heavy blade while going 600 rpm? Do you use a strobe? How do you determine that where you removed material on the backside is the correct spot? Ex. you could remove less farther out vs more closer in and still have dynamic balance. Do you have some device to check the vibrations or by feel?

More details of your process would be appreciated. Perhaps a video?

ZUL8TR, thi sis part of that process that I try to convey. Sometimes it is not all theories and books. Sometimes a little old fashioned go by the feel of it, fly by the seat of your pants kind of thing is the right thing to do. And you can't explain it. Possibly instincts describe it best ? The fastest racing engines that i have seen in outboard racing today have never seen a textbook. It just comes from years of experience and learning by your experiences. There is no formula that will tell you the best prop. There is no dyno that can replace a good racers gut feeling on an engine. I watched Danny Kirts take a prop that was good (Pro Divison) and take a hammer to it on the hitch of his truck. No a single measuring tape was within sight. He beat it, looked at it with his eyes, put it back on the rig and went out and smoked the competition. How do you measure that ?

[Fastjeff57]

Well said, David. Balancing a prop in my sop is the same concept: by feel and intuition. Sometimes a weight placed on blade "A" is the right one and smooths it right out; other times it takes an hour of frustration to get it right.

Jeff