Balancing act! Those darn props!

[mrwzrd59]

Has anyone else in here found that most all of the off the shelf props have the hole bored off center! I now start every balancing session with getting the hub close before ever moving out to the blades. Grim Racers seem to be the worst offenders with bad hub wobble that'll drive you insane until it slowly comes in. I made an indicator rig with a positive stop so I could repeat from blade to blade but that only is useful after the hub has been tamed. Hand working the hub is a huge challenge and I'm guessing at how round it is where it's hard to use the indicator close to the blade root. When I have the hub showing .010" total between each blade, it starts to settle down and allow moving outward on the blades. I gave up on using modeling clay to get the blades close and just keep going back on the indicator jig like a hundred times. I'm burning some grey matter on a better way to repeat the blade profile without fighting the knife-edge vs indicator tip battle. Maybe a fixed pivoting bar that rides the outer shape of the blade when you turn it??? Total indicator readings should look the same as it turns...Hmmm....Still thinking about that one.

Makes me want to break out the fourth axis on the cnc and make my own props from scratch! At least I could start with the hole in the center!

I used to have my own cnc pattern shop and learned to balance my long carbide ball end mills so I could raise up a clean finish from 18000 to 28000 rpm. That got revolutionized with hydraulic tool holders from Sandvik. No more set screws or lousy collets!
That got me thinking about the collets and set screws on the drives we see on RC boats...There has to be a better way...

I find airplane props to be waaaaay better right from the start! They take only about fifteen minutes to get right. Go figure!

Phil

[Mike Caruso]

Has anyone else in here found that most all of the off the shelf props have the hole bored off center! I now start every balancing session with getting the hub close before ever moving out to the blades. Grim Racers seem to be the worst offenders with bad hub wobble that'll drive you insane until it slowly comes in. I made an indicator rig with a positive stop so I could repeat from blade to blade but that only is useful after the hub has been tamed. Hand working the hub is a huge challenge and I'm guessing at how round it is where it's hard to use the indicator close to the blade root. When I have the hub showing .010" total between each blade, it starts to settle down and allow moving outward on the blades. I gave up on using modeling clay to get the blades close and just keep going back on the indicator jig like a hundred times. I'm burning some grey matter on a better way to repeat the blade profile without fighting the knife-edge vs indicator tip battle. Maybe a fixed pivoting bar that rides the outer shape of the blade when you turn it??? Total indicator readings should look the same as it turns...Hmmm....Still thinking about that one.

Makes me want to break out the fourth axis on the cnc and make my own props from scratch! At least I could start with the hole in the center!

I used to have my own cnc pattern shop and learned to balance my long carbide ball end mills so I could raise up a clean finish from 18000 to 28000 rpm. That got revolutionized with hydraulic tool holders from Sandvik. No more set screws or lousy collets!
That got me thinking about the collets and set screws on the drives we see on RC boats...There has to be a better way...

I find airplane props to be waaaaay better right from the start! They take only about fifteen minutes to get right. Go figure!

Phil

Hi Phil,

Welcome to boat propellers. I have found some really nice props with the mounting hole too big, tapered and dead on perfect.

It would be nice to have a small tooling kit piloted to bore the hole then press fit a bushing the hole so I can start at the center.

Hand file the slots in the prop for the drive dog which are out of balance along with the cable drive nuts.

Boating is good therapy just remember it is a hobby for me and I do it for fun.

Mike

[dana]

OCD much?

[KartRacer]

Mrwzrd59
If you ever machine your own please count me in. Does seem odd that with all of the extreme high tech and RPM, that the props look, well, rough cast!

[properchopper]

DSC03611.JPG

I get them as close as I can, balance & sharpen, then go racing. Heat race props, at least in my case don't need to be infinitly perfect. For SAW competition I just hang around Brian B. until he flips me a prop. Bolt it on & set records

[mrwzrd59]

Yea, I thought of bushing them but hanging onto it, centered (best guess) and starting to bore the hole would be a real challenge! I've been racing all kinds of stuff my whole life but when the critical working bits get real small (as in scale/hobby/RC stuff) Things get tricky real quick!
My mind never shuts off thinking about the problem and I'll find my chi limit with props before long... This is quite normal for me to not settle for what everyone else is doing and do the data mining for myself. It pays off huge in BS wars! It lets you know real quick who is a poser or a prof.
I'm getting my mind around the lack of efficiency of twisting thru a chemical medium to attain thrust. I'm used to lots of friction and contact patches doing the work. Physics are a constant and dont lie so its there to be dealt with. You just have to get a handle on the new medium your traveling in. The small size will always be a challenge.
We had this saying amougnst crew chiefs running in the SCCA Super Vee series; "Dont trick yourself right back onto the trailer...Stick with what you KNOW to be true". While we didnt have the budget to run with little Andretti and Unser Jr., we sure scared the hell out of them with being fast in the first qualifying sessions, then they would pull out the latest high dollar trick of the month and pull away...It helped that they were tigers behind the wheel too! They didnt have to pay for destroying equipment either!

[mrwzrd59]

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I get them as close as I can, balance & sharpen, then go racing. Heat race props, at least in my case don't need to be infinitly perfect. For SAW competition I just hang around Brian B. until he flips me a prop. Bolt it on & set records

P-Chopper, I'm sorry but I just cant do that...I simply MUST know how to do these things for myself. Its a cruel affliction indeed! My goal is always to NOT have to rely on someone else for the magic.

You're also talking "Racing" and I'd bet the driving is two thirds the battle... I used to HAVE TO buy "the good stuff" (Bertils or Schrick VW Engines and Ralt RT4 chassis) because I didnt have the time build those myself...I did however LEARN how to optimize what I had to work with. The side benefit was then becoming the "go to guy" when even the pro's had problems! How do you think I afforded to keep racing??? Consulting fees!

So far, in a very short time, I've learned that off the shelf "production" props suffer from poor tolerance control and are a pain to even get close...Since I have the equipment and know-how to do lots of stuff to MY standards, I feel real foolish banging my head against somebody else's suspect efforts. We will see where this battle takes me.

Phil

[mrwzrd59]

Ala-Kart,

Yea, I'd like to machine the first ones in aluminum and then try Ti. It will take a tiny ball endmill to get tight at the root. The helix is not hard at all with good software. I have Mastercam X6 and Surfcam Velocity 4 and both do 4th axis with the right data.
Adding it to "the list" is the biggest problem. I got into rc boats to relax and spend some quality time with my son-in-law...Now.... Here we go again! Yikes!

I'm under pressure to get a billet cylinder head designed for a top fuel dragbike (Korry Hogan) and a new cowling design for a acrobatic aeroplane (Daryl Arborgast) and .... It's nice to be needed but when does one RELAX?

On the water seems to work for now.