wind junkie

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Hi guys. I did a quick search but didn't see this spelled out anywhere: Do you often balance large props by moving the hole when you enlarge it for the motor shaft?

I remember seeing a balancer advertised which had a drill jig to re center the hole, but forget what that was.

At this year's WRAM show, I bought Menz and bolly 18x6 props from Desert Aircraft. Yesterday, I drilled out the props to fit my Saito 180. I then checked the balance as I normally do, but was kinda miffed that both props were very far off and indicated that simply painting or sanding one blade would not fix the situation. They balanced horizontally -- indicating the holes were drilled too far to one side of the hub. It was bad enough that I had to do something. I then kicked myself in the head mentally for not checking this BEFORE I drilled the hole because if the stock smaller hole was also offset, I could have moved the hole center from the beginning as I enlarged it. I also wondered if the DA guys would sell "discount" props that were way off balance this way at trade shows, but then I thought to myself, "hey, the DA guys wouldn't do that. They're all about quality and wouldn't try to make a few bucks on faulty props.... These guys make beautiful multi thousand dollar motors... "

So, what I did was fill the hole with a hardwood dowl sanded to fit and CA'd in place, and then drilled a small test hole where I thought it should go, checked the balance, noted the heavy side, then took a small rat tail file to enlarge that side of the hole. I then drilled the hole with the next largest size drill I had. I did this and was able to achieve perfect balance as tested by my dubro wheel balancer. Good balance was achieved by the time I enlarged the hole to 1/4". I then used a prop reamer to step it up to the largest size of the reamer. (I know reamers are superior than drills -- they have 4 flutes to center the hole better). Then I crossed my fingers and drilled the final 13/32" hole for my Saito 180 with a standard high speed drill bit on my drill press. I re checked it and it was perfect! The pic below shows the remaining half moon dowel sliver indicating the center was off by more than 1/16". Probably less than 3/32".

Is this how you guys balance props? (for those that do balance them yourselves?)

For the larger props and motors that have many holes around the perimeter drilled with the benefit of a drill jig, would one first move the center hole and then use the jig on the new centered hole?

This method seems like a lot of work, but I guess it's not so bad given you really don't need to do it that often. Big props on big planes tend to last a lot longer than the smaller ones.

Thanks for any advice/input.
Joe

Bob_S

There is a nice video here for balancing not only the prop blades but also the hubs. Works like a charm, easy and quick. http://www.downonthedeck.com/videos_instruction.htm

JoeAirPort

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I don't move the hole when the hub is off balance. I just ream it to what the engine shaft is then I balance the tips and then the hub (just like the video).

tail strike

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I balance the tips and then the hub as described in the video at Down on The Deck.com
But I have never been able to balance the hub with a little glue as they describe.
What I did was get an assortment of various size lead fishing weights.
I start with the smallest weight and tape it to the hub. When I find the one that will balance the
hub I drill a small indentation in the hub directly over the center hole and epoxy the weight in.
Then if it is a little heavy I just file a little of the lead off till it balances.
Works great for me.

Thats my story and I'm sticking to it.
If you don't like that one I have others

wind junkie

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Excellent advice guys. Thanks a lot!

Wow, velcro. Pretty cool.

mstroh3961

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That velcro trick works like a charm! and so does using the clear spray paint!

JoeAirPort

My Feedback: (41)

I've been able to balance the hubs of 18-22 inch props by just using 5 min epoxy on the side of the hub. Takes a puddle of it but it always balances. I sand the wood before applying the epoxy. Works great.

Bob_S

I use the fuzzy velco and thick CA. It just takes a while for it to dry but if you get too much on you can dab some off with a paper towl.

Which brand are you using that requires lead weights to balance the hub Tail Strike?

tail strike

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Here is a pic of some props and how much lead sinkers I had to use.
As you can see a lot on the Majclik

tail strike

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Hey Bob,
As you can see in the pick the Mejzlik took the most weight, the M3 a little less and the Xoar even less but a little thick CA on some velcro wouldn't work on thies props.

Bosch232

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I don't want to sound like I have wild-eyed paranoia, but the lead weight thing spooks me just a little.
Just think if that thing let go while you were doing a run up or something.

That being said, I know it's a common practice and probably proven.
With the velcro, at least it'd have a *chance* at not being a lead ball in the eye. [:@]

tail strike

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think about it the weight is on the hub not turning the RPM that the tip of the prop is
so the centrifigal force on it isn,t as great, and your spinner is covering the weight also.
Thats my opinion if you don't like that one, I have others

Bob_S

Wow! That seems like a lot of lead.

BTW the RPM is identical anywhere on the prop/spinner/shaft. The speed varies so the speed at the prop tip is far greater than at the hub. That speed is what makes the centrifigal force lower at the center and greater at the tips.

FreedomFlier

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A "dab" of JB Weld 5 minute works great for hub balancing too.

Panzlflyer

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What did you drill the props out with?

tail strike

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very short arm not much leveage so takes lot of weight, long arm lot of leverage not much weight. Give me a longenough leverage and I will move the earth [>:]

wind junkie

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Me? I used standard high speed steel 2 flute drills, which is probably why my hole walked so far off "ideal" center, but I'm not sure about that. I went up graduallin in sizes, in about 5 iterations, but 2 flutes are not very good at keeping the original center for larger holes. That's why I said I should have balanced it on the original hole before I started drilling.

Anyway, if you follow the video advice, you can go ahead and drill all the holes first, THEN balance the tips, THEN balance the hub. That method will always work, and you don't have a lot of trial and error like I did.

Panzlflyer

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I was curious.
Thats why I use a reamer, takes a little bit more time and then drill the rest of the holes.

wind junkie

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Where do you get a reamer that's the perfect size for your motor (or any motor in particular?)

I only have a Fox reamer and the largest size isn't big enough.

JoeAirPort

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http://www1.mscdirect.com/cgi/nnsrhm (home page, just type in REAMER into the Quick search and click GO).

I bought a 12mm reamer from these guys. I would recommend getting one a few thou over so the prop will slip on easier. If the reamer is dead nuts 12 mm, the prop's gonna be tight. In my case the ream only needs to be 5mm deep for the Moki engines so the prop goes on and off without too much trouble.

wind junkie

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Ok, now my lack of intellect is going to show:

If I get this reamer:

http://www1.mscdirect.com/CGI/NNSRIT...PMT4NO=5656310

It looks like the shank is thinner and the flutes make a constant diameter along the whole length of the flutes. How could I use this to enlarge a standard hole (say 1/4 inch) to the final 12mm size? I was expecting a tapered step arrangement with angled edges, like my fox reamer.

You just chuck this into a drill press? (it has no handle).

SeanCowan

Hey fellas,

I do this the simplest way I know how. First, I drill the center hole and/or prop bolt holes on a drill press. Then I balance the prop horizontally( I try to just sand the front, however, if it is way off, I use clear spray paint). Once it sits flat, I balance the hub. Instead of adding weight to the light side (I scares me and I don't want to wait for the epoxy and lead mixture to dry), I simple sand the heavy side on a belt sander. This flattens one side of the hub but is essentially doing the same thing as adding lead to the other side. Then I re-check both horizontal and vertical, and I am done. It takes me 2 minutes tops, and is ready to fly. I have never heard of the method failing and it works on all two blade props (even carbon fiber because they have a solid hub).

Sean

Panzlflyer

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I have 2 tapered reamers, one metric that go up to 10mm and the other 3/8 from Great Planes that fit my DA, ZDZ, Brison etc.
B& B also have drill bits with the tips shaped for starting in the small hole on some props and I believe they go to 12mm but v pricey

JoeAirPort

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http://www1.mscdirect.com/CGI/NNSRIT...PMT4NO=5659249
This one is a half of a thousanth bigger. Might help the prop slip onto the engine shaft easier. Depends what fit you want (.4724 or .4730).

You would not want to ream a 1/4 hole (6 mm) out to 12 mm. That's too much in one step. I'd use that Fox reamer and take it to like 10mm. Then use the 12mm reamer and slowly take it out to 12mm. I chuck mine up on a drill press. I just hold the prop down to the table by hand lightly so that the prop can center itself on the reamer. I feed the reamer very slowly at first to make a perfect start. Works great. I would balance it after I did all the reaming.

wind junkie

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Great. I think I got it now. Thanks again guys!