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Got a new prop balancer... and new questions Empty Got a new prop balancer... and new questions

Post  RknRusty Thu Mar 22, 2012 8:41 pm

I got this at my LHS today:
http://www.ebay.com/itm/Top-Flite-Power-Point-Prop-Balancer-TOPQ5700-/160736125326?pt=Radio_Control_Parts_Accessories&hash=item256c9ea18e

It is a magnetically suspended balancing shaft and should be pretty accurate. That's assuming the cones are balanced, and they appear to be. Besides, the small hole in 1/2A props fits tightly without the cones. I do use one because the Cox props have a wide hole on the rear side of the hub. I have tried with and without, and nothing about my upcoming questions changes.

I had a bag of props balanced with my home made balancer last week, so I started checking those. Most of them will hang perfectly level horizontally, but only on one side of the hub. Given any opportunity it will always flip over so the same side of the hub is on the bottom, with the blades still perfectly horizontal. This tells me the blades are balanced, but the hub is either drilled off-center or heavier on one side(I bet I can guess which). It should park at any angle, either where I place it, or when it finishes spinning on its own. The instructions say never to remove material from a hub, but to counter balance it by adding weight. This is a safety precaution. But I'm not balancing TF wooden props, I'm balancing the toughest freakin stuff ever molded into a propeller.

Any thoughts on taking one to the drill press and just punching the point of a small bit(not the body) into a Cox hub to balance it? It makes a nice clean cone shaped divot. I botched one, by drilling a small hole, and then another and another. I threw it away. Damn, it was a brand new 6x3 too. My next one came out perfectly after making one tiny divot. It will park any place I stop its rotation on the balance shaft. If a prop needs more material removed, I want to use the point of the next size larger bit, rather than making more divots. But I haven't done that yet, I figured I should stop and ask first.

I don't think tape is going to stick on a hub. Nor is CA glue or anything else I try to adhere to it. What thoughts, oh brilliant forum members, do you have to offer a novice prop balancing friend, whom y'all already know takes things to extreme details.
Thanks,
Rusty

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Post  Cribbs74 Thu Mar 22, 2012 10:06 pm

CA sticks like nobody's business to my cox props. Are your props oily?
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Post  RknRusty Thu Mar 22, 2012 10:10 pm

No, I just assumed it might not stick, I could be wrong, since you've done it successfully. Plus it takes a lot of weight to balance a hub as opposed to way out near the end of a blade. I could mix it with some metal filings to add weight. That could be dangerous too though.

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Post  Cribbs74 Thu Mar 22, 2012 10:15 pm

RknRusty wrote:No, I just assumed it might not stick, I could be wrong, since you've done it successfully. Plus it takes a lot of weight to balance a hub as opposed to way out near the end of a blade. I could mix it with some metal filings to add weight. That could be dangerous too though.


Bondo? JB weld? Or maybe you could scuff it an use 2 part epoxy.
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Post  RknRusty Thu Mar 22, 2012 10:42 pm

Yeah, both of those are pretty heavy. I'll let you know whatever I figure out.

I never worried about it too much before, but the other day before I made that Black Widow video, I tried a 5x3 out of my field box on it, and it wouldn't even turn 17.5k. Then I put that Topflite 5.25x4 on it and it screamed. And that day I made the video of it flying, it ran like crap.That must have been the prop too.

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Post  John Goddard Fri Mar 23, 2012 6:57 am

Cyano will stick to it like, well glue Very Happy Rusty.

However...
Cox props and acuarately dilled hubs are not (inmho) really two things that are synonymous in my limited experience.

There are some new props 'out there' which are simply humourous in this respect.

I've only found props from those awful Germans (Graupner) that are any good balancing straight from the pack BUT
you've still the the hub hole to contend with.


Very Happy
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Post  fit90 Fri Mar 23, 2012 7:04 am

I know many here shun APC props but I have had really good luck with them. I have even had good luck shortenng them. I have never checked to see if the blades or the hub were out of balance when balancing them. I take the lazy way and just sand the blade tips. If you think that sounds bad you should see how most aluminum props are dressed on full size aircraft.
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Post  John Goddard Fri Mar 23, 2012 7:21 am

Sorry Bob I think APC are fine but sometimes need a little help.
But the Graupners are (through gritted teeth) always spot on.
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Post  Ivanhoe Fri Mar 23, 2012 11:07 am

John Goddard wrote:Sorry Bob I think APC are fine but sometimes need a little help.
But the Graupners are (through gritted teeth) always spot on.

vorsprung durch technik! Very Happy
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Post  RknRusty Fri Mar 23, 2012 7:00 pm

I'm cross posting this at RCG.

Since I tried working on some more Cox props, the drill turns out to be a bad idea. So I answered that question myself.

Plan B. I also have a table top belt sander, so I tried sanding off some material on the heavy side of the hubs. I did it on old ones I can toss if I botch it. I'm surprised at how much plastic has to come off. Trying to keep the curve neat, but it's obvious where it's been ground down. But they will finally balance before I get down to the drive plate and spinner facings. I'm going to go with this. As tough as the rubber duckies are, I don't think they are in danger of self destructing.

I have some old Windsor props, I see on their site, that's the same as MA props I've heard about. They were almost perfect right off the bat. I think I'll get some of those. They look more brittle, so I'll be more careful with them, but their shape lends to easy cutting down.

So if I don't get a blade through my eye and out the back of my head, I'll come back to see any warnings or advice that might pop up.

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Post  PV Pilot Fri Mar 23, 2012 7:18 pm

Personally, i wouldn't drill or grind on that hub area at all. Alot of load on that little area. Like you posted, you might have a time bomb just waiting for the most inopportune time. One little unseen nick creating a stress fracture and you might loose model and engine.

Just my .051 cents.
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Post  RknRusty Fri Mar 23, 2012 9:05 pm

PV Pilot wrote:Personally, i wouldn't drill or grind on that hub area at all. Alot of load on that little area. Like you posted, you might have a time bomb just waiting for the most inopportune time. One little unseen nick creating a stress fracture and you might loose model and engine.

Just my .051 cents.
Is that 2 cents adjusted for inflation?
Since the Windsor-Master Airscrew props I've put on the balancer all seem to not have the hub imbalance the Coxes do, I believe I'm switching brands.
Bare seems to think rather than balancing 1/2A props, just put the heavy blade directly opposite to the piston position(I think he means at TDC) and it will make up for the inadequate counterbalance of the crankshaft. There is actually some sense in that, but I think I'll keep balancing the blades and not worry so much about the hubs. Maybe I'll go so far as to put the heavy side of the hub opposite the piston. Can't hurt. And I'll be less likely to die while needling an engine.

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Post  PV Pilot Sat Mar 24, 2012 10:45 am

You don't want one of these,,with your fingers close by.

Listen to the evil sound it makes, when it parts company. Some light duty cursing.
https://www.youtube.com/watch?v=qQZpRHcmHtQ&feature=related
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Post  PV Pilot Tue Mar 27, 2012 12:17 pm

This looks like a good little unit here, just spotted it. Has the adjustable thumb screw so you can set that tiny gap needed between tip and magnet. The cones push together instead of threaded cones like the ones on my small balancer.
http://www.sigmfg.com/IndexText/SIGSH903.html
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Post  RknRusty Tue Mar 27, 2012 7:01 pm

That works exactly like my Top-Flite balancer. I like it.

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Post  PV Pilot Wed Mar 28, 2012 11:48 am

RknRusty wrote:That works exactly like my Top-Flite balancer. I like it.

All the good balancers have a magnet supported shaft,, Wink

I have the Dubro wheeled version,, where the shaft rides on some pizza cutter style wheels and it isint as accurate as my magnetic ones. I do a reset(prop to shaft) and the balance changes each time,,where it doesen't with the magnetics.

The Sig one there looks to have a smaller shaft than the Top Flight, so your prop hub probably would not touch that,,depending on the prop.

You could get yourself a drill bit blank and rig up some spacers for your smaller prop hubs, to use with the Top Flight.

I caught a glimps somewhere of folks using nail polish for a balancing media. I'll stick to the tape, it is working good for me and not flying off.
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Post  RknRusty Wed Mar 28, 2012 3:04 pm

PV Pilot wrote:...The Sig one there looks to have a smaller shaft than the Top Flight, so your prop hub probably would not touch that,,depending on the prop.

You could get yourself a drill bit blank and rig up some spacers for your smaller prop hubs, to use with the Top Flight...
I'm not sure what you mean. I have to press the props onto the shaft, it's a pretty tight fit. In my experimenting when I first got it, I even tried balancing without the cones, or at least the flat side of one cone against the hub to make sure it's not crooked, in case the hole in the prop is bored crooked. Since then I've gone back to using both cones, one with the tapered nose inside the wider back side hub hole and the other cone with the flat side against the front hub.
I hope my wording made sense in that statement.

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