Prop balancers

[Roflhat]

I've been looking at a couple of designs of prop balancers (static),
anyone on here got one? I'm considering making one. Theres a company called Stuhr that makes them and they look really good, but very pricey £££!

[Roflhat]

anyone got one?
I'd like one like this - 54292

[zul8tr]

anyone got one?
I'd like one like this - 54292

The image does not come up? Post a different way

[Roflhat]

oops, try this: http://www.rundquist.com/images/stuhrpb.jpg
54294

[zul8tr]

Those are the typical static balance devices. Not cheap but effective for stage 1 balance. While they will tell you where the heavy area is in one plane they willl not tell you where on the blade to remove material, i.e at what radius and area out from center, closer in remove more or farther out remove less, experience definatly needed here. Any object can be statically balanced and not be dynamically balanced and still cause problems.

[Roflhat]

That's what I'm after really, just to get props/flywheels a bit better balanced. I was just going to take it slow, remove tiny amounts of weight at a time until it's balanced.

[Roflhat]

I'd like to have a go making something like this: http://www.pinoyboats.org/forum/viewtopic.php?t=2531
any idea where I'd find discs like them?

[phillnjack]

the balancer in the video is the same as used on rc boats just scaled up.
very simple to make
BUT you have to get the balancer shaft balanced before use ? and make 100% sure the ground it sits on is level !!!
then just use it very simply and very effective.
dynamic is a wastoe of money, simple is all thats need for boats.
as we dont blance gear cogs gear shafts,bearing carriers etc etc,so stick to the simple balancer and enjoy.

first time out it will lose a certain amount of balance anyway.


phill

[zul8tr]

RC boats mostly use a static magnetic balancer (less friction for these small props that need a very sensitive balancer). Some sophisticated RCers use a dynamic balancer as well. As far as dynamic being a waste of time that depends on the size and weight of the prop and cost of the dynamic balance. Do you think the large ship props and aircraft are just static balanced? No way! They are or shaft bearings would go to pieces and down time is costly. Some examples:

http://www.centralhobbies.com/props/balancer.htm

http://www.rundquist.com/how_balancing.htm

http://www.modelpowerboat.com/content.php?138-propeller-balancing

http://balancemyprop.com/

As far as the small outboard and race props the static balance does work very well provided the prop tech knows were to remove metal to keep all blades close to the same dynamic balance by Experience. With surface piercing props there is an automatic out of balance that occurs because of it's operation in and out of the water and very variable blade loading, but still if dymanic balance was available for a reasonable price it would be worth while.

I know this is not a prop but would you run your car tires with just static balance? Might work but most likely will not and dynamic balance needed.

[Roflhat]

Something like that first link would be ideal (obviously scaled up). Especially if could do flywheels too.

Funny you mention tyre balancers, a similar idea went through my head- whether it would be possible to modify a wheel balancer to do props and flywheels? Because you must have to put in the wheel diameter, so maybe you could make it would?

[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