jester_s1

That works if one fits. But sometimes it's only a little loose and the tape works great for that.

blw

My Feedback: (3)

Maybe I'm too picky, but I'm not going to settle for tapered holes as long as I have a drill press. These props have a lot of energy when turning 10k rpm. Likewise, while using a drill press I can check runout and sand down the tips as needed. Next, sand a nice leading edge on APCs or similar props. Then, time to balance them as best as I can. No cheap pocket balancers as they will always give you wrong info. Every single time. If you have one of those go outside and throw it as far as you can. Or, drop it on the grass next to the guy who's on your hate list at the flying field and let him 'discover' it.

aspeed

As the OP requested, I don't think he got an answer for the dimensions of the reamer, but.. I machine up my own spacers out of aluminum if they are too big. APC holes are often too large to use with no spacers. I think the back hole was considered to be the most accurate for balancing, or locating from. In that case, maybe you couldl leave all the props on the field for me!!! I hope I am not on you hate list though. I have one of those magnetic prop balancers, and have checked out dozens of props in my drawer, and they all have balanced from the package after only removing the flashing. Some wood and fiberglass props have needed some time.

airraptor

My Feedback: (66)

Really no need to balance the APC props, the engine is more out of balance than the prop will ever be. Yes the larger hole on the back of the apc props is very accurate. Some like to tinker and balance the props to the ninth degree and not knocking it. I will measure my reamers tomorrow.

jester_s1

You may have gotten lucky, but I've had a number of APC props that were pretty badly out of balance. Early in my RC days, I didn't bother much with balancing, not wanting to spend the money on a proper balancer. My planes shook a lot less when I bought one and saw just how far out some of them are.

1QwkSport2.5r

I've had the same experience. Some were really well balanced out of the package, others not so much. What made things worse was using a TopFlite balanced initially. Found out that balancer can't balance itself! Went to the Dubro balancer and now see a true idea of how balanced stuff is.

aspeed

I seem to have a lot more M Airscrew props, as they take a noseover better. Some APC. Ya I have the Top Flight balancer. Maybe I should go back to the pointy thing you put between your fingers. It worked well.

1QwkSport2.5r

I ended up getting a new balance shaft and two sets of cones from hobby services for the TF balancer and it worked better with the original setup than with the new parts, but in the end I put the magnets from the TF balancer on the fridge and use the Dubro balancer. If you use the TF balancer side by side with a good balancer on the same prop, you'll see pretty quickly which one works better. I noticed a huge improvement in vibration when switching balancers. Is especially noticeable on the high revving engines.

airraptor

My Feedback: (66)

All engines are balanced to run at a certain rpm. If you are below or above that rpm it will vibrate a lot. having a prop run true and in the same arc to me is more important than balance. Example our Q40 engines vibrate really bad around 20,000 rpm or so and then when they get on step around 25,000 they dont have as much.
So for me I dont take the time to balance the props. Sure using a very good balancer you can find errors in most spinning object even spinners. If you like to balance go for it I am not trying to sway you either way. It is a hobby. I have seen people take the time to even balance their wheels on the plane. It takes a lot of time but their plane was very smooth going down the runway.

1QwkSport2.5r

If I didn't have bubble free tanks on all of my models, I wouldn't concern myself as much with prop balance. I've found the balanced props do vibrate less and as such don't make the tank as much of a bubbly mess. I do agree about the engine harmonics causing more vibration at certain rpm - I've noticed this with a few engines in particular. Seems to be more of an issue with larger engines.

Hobbsy

My Feedback: (102)

Out of balance props also require more power to turn, an out of balance engine will be out of balance no what the rpm. Of course it would show up less at lower rpm and more at higher rpm.

JPMacG

My Feedback: (2)

APC recommends using a tapered reamer: https://www.apcprop.com/Articles.asp?ID=259#balance

Actually, if you follow their recommendations you almost need a metal lathe to make a custom bushing for every prop and engine combination.

jester_s1

It's worth mentioning that there are different types of vibration in an airplane engine/prop combo. An out of balance rotating assembly creates a circular vibration which causes the most flexible axis of the fuselage to shake back and forth. We can eliminate nearly all of that with good balancing. But there is also a twisting vibration caused by the power pulses of the engine that we can't do anything about. You'll notice it when the plane is idling and the wing tips and tail are shaking. And yes, there are certain RPMs with any airframe when the frequency of the vibration matches the harmonic of the fuselage and it really starts to shake. Full scale planes use props with some flex in them to act as a harmonic balancer (like you car engine has), but at the scale we work at that's not practical. Hyde mounts or other soft mounts help dampen out this twisting vibration, but you can never eliminate it. 4 stroke engines create much stronger twisting vibrations than 2 stroke engines do, and higher RPM reduces it while lower RPM increases it.

dangtaylor

JPMacG,

Thanks for the APC link . I had not seen this. It may alter my approach. I do have and use a metal lathe and would not find it inconvenient to produce some bushings for a particular engine as I noted above.

I dont use APC props. Could be I am very far behind the times but all my propellers are wood. I had been away from the hobby for decades and when I returned , I employed some of my old and possibly out-of-date practices such as using only wooden props to protect me ( I still hand crank) and my engines' crankshafts ( long ago belief that ground strikes by other than wood props could damage the engine).

I will carry my mic along on future trips to the club field to ask if anyone is carrying a Great Planes metric reamer in their flight box............I'll measure it myself and avoid ordering a possibly useless tool. But after reading the APC info provided me by JPMacG, I wont feel like I am fixating on details if I fabricate a custom bushing for certain propeller/engine combinations.

Dan

jester_s1

I think if Webster's dictionary were to go looking for a good definition of the term "overcomplicate," they could just put a link to this thread in the dictionary and have it covered! Seriously guys, $5 will get you a cheap tapered reamer that will perfectly fit every prop you'll ever own to any engine you'll ever own. It really can be that simple if you want it to be. Of course, if you want it to be complicated you can machine precision bushings and then ream props to work with them. Either way, the props will work great and the engines will run fine and the planes will fly fine.

1QwkSport2.5r

I agree. I've always used a tapered reamer and it's always worked fine. Mine is about 40 years old, but it works just fine.

blw

My Feedback: (3)

Same for me and APCs that are not balanced right off the shelf.

Aspeed- I've heard the mag balancers were good. I have the DuBro one.

An unbalanced prop can do a lot of stuff to glue joints on those ARFs some guys are flying. I almost learned the hard way when I noticed 2 engine mount screws were gone and one backed out as far as the engine would allow it. Only one was tight. Balancing has a huge effect on servo life.

aspeed

Lots of the old steel piston motors were so far out of balance that a balanced prop was the least of the problems. The crank counterbalance had to be like twice what was used. We put the heavy blade opposite the crankpin on the old Fox .35s. If a cheek cowl was not used to beef up the front end, the wing joint would fail. The new ABC motors do not have this problem. I think the new ARFs are just engineered too light to take the vibration, and they shake a lot more than they should even with a balanced prop. They do fly nicely though. Sorry for getting a bit off topic, but thought it should be added.

blw

My Feedback: (3)

Not off topic at all, imo. You can hear it on some badly out of balance ARFs.

dangtaylor

I did eventually find a local club member whose Great Planes reamer measured right at or very close to nominal for the three sizes I wanted most. It was some time later that I ordered one for myself and can report the following on this recent purchase.

7 mm ------ 7.01
8 mm ------ 8.01
10 mm ----- 10.01
(12 mm -------12.014)

.01 mm equals .0004 inch The Great Planes reamer for me is far superior to the Fox mentioned in my first post.

Dan

jdmachinery

My Feedback: (1)

Mixing & matching props & glow engines seems to result in loose prop fits at some point. Another crankshaft bushing solution to use drinking straws. They are extruded thru dies when manufactured so are fairly precise uniform thicknesses and come in various diameters. Straws are easily cut to length & even split to get that littler bit larger diameter sometimes needed. Essentially no cost at fast food eateries.

Crazy Legs

Thank you for that information Dan. I have the same problem when using the prop reamer I somehow wound up with. To correct the situation I use a precision drill index and just opened up the hole a little at a time until the prop barely fits on the prop shaft. In fact, I actually loosely threaded the prop on the front of the shaft and there was absolutely NO slop. When I get it to fit then at that time I balance the propeller.

the Wasp

My Feedback: (1)

oppps

RCoffroadracer

why isn't the great planes reamer .250 like it should be? they made it .264. way too big for a 1/4 (.250) shaft. when I worked for a machine shop reamers are what you used to make a hole exact. drill bits are not round. the reamers we used were always exact. when they got worn to .248 we threw them away. you cannot make a fitted hole with a over or under sized reamer.

Jesse Open

You are spot on with your doubts!!

No benefit of a longer contact column? Absolute hogwash. That skinny ring is often only making minimal contact with the crest of one thread. And that point of contact is easily broken down. Far better to have a broader closely fitted area across several threads.