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Old Nov 12, 2012, 07:54 PM
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Razor_Racer's Avatar
Northern Virginia
Joined Jul 2007
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Mis-drilled propeller holes

I'm wondering how to deal with mis-drilled propeller holes. I have a 13x6 APC prop and the hole is visibly mis-drilled by 1mm, resulting in huge vibrations.

I know propeller reamers exist, but won't that only make the hole bigger instead of re-centering it?

Also, I guess I could drill it out, but then the hole would be much bigger than the propeller collet.

What do you do with mis-drilled props?
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Old Nov 12, 2012, 08:03 PM
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FlyingW's Avatar
Long Valley, NJ, USA
Joined Dec 2001
1,713 Posts
Razor,

Drill the hole bigger until it is centered, then use a bushing to get a snug fit to the collet. A simple but effective bushing can be a strip of electrical tape wound around the prop shaft enough winds so that the shaft becomes thick enough to give a snug fit in the prop hole.

Good luck,

Paul
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Old Nov 12, 2012, 08:05 PM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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APC electric prop holes have two sides. The front is just a rough drilled hole which may be very, very inaccurate, and the back is an extremely precise, larger-diameter molded hole that you place an appropriate locating/sizing ring in (several are included in the package). This is the part that counts; occasionally you need to do a very small bit of reaming in the sizing ring to fit your prop shaft but the holes are perfectly centered as molded.

If the front hole gets in the way of anything due to its inaccurate positioning, just drill out the offending region.
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Old Nov 12, 2012, 08:31 PM
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Latvia, Ventspils pilsēta, Ventspils
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I know APC give out a lengthy blurb about using the rear hole as the accurate point ... but as the props are moulded - they really are accurate enough both sides ... who's going to make a mould that bad ?

Anyway - there is only 1 way to drill props - and thats with a drill guide or pillar drill. You are not first to ruin a perfectly good prop by drilling.

If you can get to a pillar drill ... can centre the prop accurately - you then drill out the prop to re-centre the hole.
A bushing is then needed to centre the prop on the shaft ... and I have to say that a 13" prop with tape ?? You gotta be kidding ... Sorry but to my mind that's not a good idea.

There may be a chance ... IF the rear shaft hiole is still larger than the drilled hole you made ... get that pillar drill to drill fully through centred on that rear hole ... same size as the rear hole. Then insert bushing. The prop nut washer will hold all together.
The reason I say drill all way through ... is that centre hub is way off balance with any hole off-centred.

I have 2 14" props that the drill wavered - pillar drill but drill bit was too long and flexed while drilling ! created off-centre holes ... they stay on the shelf waiting for a shaft bigger than that !! I will not use them on intended shaft.

It may be that you have to bin them ... lesson learnt.

Tapered Reamer is the best way ... or get a decent pillar drill.

Nigel
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Old Nov 12, 2012, 08:50 PM
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United States, LA, Angie
Joined Apr 2009
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I believe Nigel is talking about a drill press and he is absolutely correct! And NO, you can NOT hold the prop by hand , the bit WILL grab and get it out of your grasp in an instant. NO!!!! tape!!!!NON!!!! APC prop does have exact hole in rear and a proper sizer that fits in it. The sizer has a bevel, LOOK!!!!CLOSE!!!!!!Bevel side into prop. Hub balance is critical especially with a larger prop, balance blades, then hub. You do want your motor to be with you for some time????? Treat your props like you would treat your tires on your car when your children are going to ride in it! When in doubt..... trash it, or make a folder, it will be a rainy day project... Wait till you get into high RPM ducted fans ...can you spell dynamic balancing? or...EXPLOSION...enjoy, Dave/ZZ
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Old Nov 12, 2012, 11:00 PM
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Australia, ACT, Kambah
Joined Feb 2001
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APC has advisories on mounting aligning balancing props - worth reading: http://www.apcprop.com/v/html/tech_s...html#holealign

IIRC the pilot hole thru APC E props is 1/4"/6.34mm. For the larger props, the bore for the precision ring is .375"/9.5mm. That gives enough to ream out typical misalignment of the through hole and still use the locating ring. The main thing is the shaft should be a loose fit on the thru hole, and located entirely by the precision ring for electric or the correct diameter at the mounting face only (ie tapered hole). See http://www.rctoys.com/pdf/APC-Landin...age-Insert.pdf

I have been very happy reaming both APC and wooden props with the Great Planes stepped reamer from Tower, mounted in a drill press.
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Old Nov 13, 2012, 12:19 AM
Yea, I fly dusty planes..
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United States, LA, Angie
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HIP, HIP ...+10 on that .....ZZProp
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Old Nov 13, 2012, 07:53 AM
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Azarr's Avatar
Dayton Intl, Ohio, United States
Joined Jan 2000
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Quote:
Originally Posted by solentlife View Post
I know APC give out a lengthy blurb about using the rear hole as the accurate point ... but as the props are moulded - they really are accurate enough both sides ... who's going to make a mould that bad ?
Nigel
The props are molded, but the front hole is drilled which is why they say to use the precision molded hole as a guide. No idea why it's done that way, something to do with the sprue during the molding process.

Azarr
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Old Nov 13, 2012, 08:24 AM
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Australia, QLD, Grantham
Joined Oct 2012
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I found if you drop an APC Electric prop on its' tip it will snap off real easy. One new prop in the bin...
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Old Nov 13, 2012, 12:59 PM
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United States, NY, Cortland
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Quote:
Originally Posted by Grantham Kid View Post
I found if you drop an APC Electric prop on its' tip it will snap off real easy. One new prop in the bin...
You can take a half-inch off the ends with almost no loss in power.
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Old Nov 13, 2012, 03:07 PM
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They're cheap. Get a new one..
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Old Nov 13, 2012, 03:45 PM
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United States, NY, Cortland
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They're priceless, when the weather is good and the hobby shop is closed...
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Old Nov 13, 2012, 03:55 PM
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Lawrence, Kansas
Joined Dec 2001
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I have been flying APC props for more than a decade, never noticed many balance problems. I have to say that the last couple years, it seems like many of the APC electric props I have purchased have hub balancing problems. On my balancer, WITH the precision ring installed with the bevel facing the right way, I still get them balancing with the blades level (horizontal), same side of the hub always up. They actually seem to be centered--haven't measured but am pretty sure I could see a 1 mm deviation--so I wonder if there is some problem with glass fiber distribution, or voids in the plastic or something. This has been true of the last 2 or 3 APC E props I have tried to balance.

As far as tape as a bushing, been doing it for decades. Once talked to an engineer about it. He said that the prop nut and backplate are doing all the work of transmitting force to the prop, if the prop is balanced there is no significant force moving the prop side to side on the shaft. It is really just there to get the prop centered on the shaft before you tighten the nut. If you think about the difference between the vibration of an IC engine and the smooth rotation of an electric motor, we have even less to worry about. All that said, I would hesitate to use more than 2 or 3 layers of tape, because if the tape layer is too thick, I'd worry that it might not give a very precise center. Have used tape bushing on 12" and 13" props that have served for many years with nary a problem. If you think about it, this is not that different from what APC does with the locating ring, they even advise tapering the hole so only that locating ring touches the shaft, and I don't think that itty-bitty piece of plastic is designed to resist much force.

- - Dave
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