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Prop Reamer

Old 08-07-2016, 04:19 AM
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dangtaylor
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Default Prop Reamer

I recently bought a Fox Metric prop reamer that is oversized on all three steps. The three measure with a micrometer 6.12 mm, 7.14 mm, and 8.13 mm. The result is props fitting the engine output shaft more loosely than I really want them to. Reamed props really do not center on the engine's shaft well but move around a lot before tightening .

Has any owner of a Great Planes reamer measured the reamer steps or the finished hole in the prop with an accurate means such as a micrometer for the reamer or gauge pins for the reamed holes in the props?

Dan
Old 08-07-2016, 04:31 AM
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Hobbsy
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http://www3.towerhobbies.com/cgi-bin...ox+prop+reamer

Which one, Thanks, Dave
Old 08-07-2016, 05:57 AM
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dangtaylor
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Dave,

I would find it most useful right now to know if the Great Planes Metric stepped reamer is closer to actual stated sizes ( 6,7,8 mm) but possibly knowing that any other Great Planes reamer in inch sizes was very close to nominal dimensions could suggest the metric reamer might be also.

Dan
Old 08-07-2016, 06:02 AM
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dangtaylor
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If I find out that all the readily available (Fox and Great Planes) reamers produce a loose fitting prop, instead of wrapping tape or some other material around the prop shaft, I'll probably try to alter my current reamer with an endmill sharpening grinder ( I dont have access to a surface grinder) or purchase some metric sizes of chucking reamers and do the job on my mill.

Dan
Old 08-07-2016, 06:31 AM
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jester_s1
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Make things easy on yourself and get a tapered reamer. I've used one for 10 years and I get perfectly fitted prop holes every time. If you ream the hole from the front, you also have the benefit of fixing a hole that was drilled crooked from the factory. Some worry about the fact that a tapered reamer only have a small amount of material actually touching the prop shaft. It's not a problem because all the hole is there for is to locate the prop on the backplate. 100% of the flight loads are born by the prop hub on the backplate. Theoretically, you could locate the prop on the hub properly and then mill out the hole as big as you want and you'd never notice that the hole wasn't touching the shaft in flight.
Old 08-07-2016, 07:35 AM
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dangtaylor
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I do have tapered reamers that I use for other things. I don't want to use one for this job. The problem may be only certain individual engines as I just reamed a 7mm (oversized) hole with the Fox reamer in a prop and it actually was not as loose on my Saito FA-50 as this has been on another engine with same sized shaft.

For that engine ( I did not re-check but may have been a S.T. GS-40 ) I ended up reaming a .375 inch hole in the prop and turned an aluminum bushing to bring it down to a nice tight 7MM fit on the shaft.

Dan
Old 08-07-2016, 04:11 PM
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Jennifer Curtis
 
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If you don't have any fancy equipment to grind
the reamer to the proper size, you can put it in
a drill press (or hand drill if you have a way to
hold it steady), and use a file to reduce the diameter.
Then by hand, re-sharpen the beveled edge
without further reducing the cutting edge.

Mostly it is the front edge of the step that does
the cutting and the length of the step in front
holds the reamer straight while the reamer is
going in, and the length of the step following
holds the reamer straight as the cutting part
goes past the halfway point and nears the
end of its cut.

Note that this is not the way tapered reamers work.


Jenny
Old 08-07-2016, 06:24 PM
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dangtaylor
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I do have an end-mill grinder which could do the job since it is designed to grind thesides of the flutes as well as the tip of an end mill. It is just that it is not a fast and easy job. That would be far more accurate than trying to file or stone the sides of the reamer in a drill press. The Fox reamer looks to be plated, besides and I have doubts that a file could easily do the job.

If I don't have an answer about the Great Planes reamer being manufactured to cut closer to even metric nominal sizes, my best approach will probably be to reamer the props for the problem engines to the next larger size and lathe turn an aluminum bushing to be a hand press fit.

Getting back to my reluctance to use a tapered reamer, the result of cutting a tapered hole is that a really small circle of prop material centers the prop. A hole in the prop that is a good fit along the full contact with the engine's shaft is a long column of contact. That's what I prefer.

Dan
Old 08-08-2016, 01:52 AM
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A piece of heat shrink tubing on the prop axis is often enough to get a snug fit. As said before there is no radial load, you just need a proper centering.
Old 08-08-2016, 03:14 AM
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dangtaylor
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This last suggestion is probably the most workable and easy, if the thickness of the heat shrink tubing turns out to be just right. I'll do some measuring of what I have.

Dan
Old 08-08-2016, 03:29 AM
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http://www.bennettbuilt.com/shop/Prop_Accessories.html

http://www3.towerhobbies.com/cgi-bin...&I=LXEGH6&P=ML

These would cover your needs.

Last edited by Hobbsy; 08-08-2016 at 03:31 AM.
Old 08-08-2016, 04:48 AM
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Of the two, I would maybe go with the BB step drill. I will say that I use a drill bit in the inch or metric size needed. They are pretty cheap and accurate. I set it on the drill press with the surface square on the table. (the front face down is the best if the numbers are flat, then the hole will pick up from the back.) Slow steady feed. I do have a Fox reamer in the toolbox, but it just make me mad at the field. Can't get through, and it is still too tight.....
Old 08-08-2016, 04:59 AM
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cardinalflyer
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If you have access to a lathe, I would make a D drill for each prop shaft size required. I did this a long time ago for several sizes I needed and the benefit is the drill is guided by the correct size hole in the prop and the cutting portion is the exact final size.
Old 08-08-2016, 05:20 AM
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jester_s1
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dangtaylor- You may not care, but I responded to your concern in my post above. I have read many, many threads on prop reaming over the years, and aside from which is the best 2 stroke oil it has to be one of the biggest topics people fret over and debate. There is absolutely no benefit whatsoever to having a long column of bearing surface for your prop against the engine shaft. And there is actually a benefit to having a tapered prop hole, namely that if the factory drilled the hole crooked the tapered hole will still let the prop sit flush against the drive hub. All the hole does is locate the prop in the right spot on the drive hub and hold it there long enough for you to tighten down the prop nut. It does absolutely nothing after that and experiences no side loads of any kind.
For the solutions that have been discussed in the thread, I don't see a single one that is going to be better than a tapered prop hole, not even the idea of remachining the reamer to make the right size hole. Adding bushings is a major waste of time and with so much removal of material from the prop, could lead to an imbalance as the prop hole tends to drift away from center as you ream it. Using something soft like fuel tubing is begging for an engine that shakes as the prop will be able to shift over while you are tightening it, and the tubing could find its way between the prop and the drive hub, which will result in a loose prop in flight. And, of course, fuel tubing isn't exactly a precision machined product for thickness and uniform hardness, so it's unlikely you'll get the prop properly centered anyway.
I bought one tapered reamer 10 years ago, a really cheap one. I've fitted every prop I've ever owned with it, and have never had a prop hole get wallowed out in use. Every prop I have is perfectly fitted to the shaft of the engine it's being used on regardless of SAE or metric or whether or not things are in spec or not. I also can push the tapered reamer to one side to get hubs in balance. APC in particular is notorious for drilling their prop holes off center, but I can fix them in just a minute or two as I size the prop hole. The tapered reamer is truly the perfect solution for this particular task, so there's no reason to complicate things further.
Old 08-08-2016, 06:18 AM
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+1 to jester_s1
Old 08-08-2016, 06:32 AM
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Jes, offering up other options is not complicating things further, honest. It's just common courtesy.
Old 08-08-2016, 06:34 AM
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dangtaylor
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jester_s1,

Thanks for the added details. Your last comments were more convincing . I still have a problem with the use of the tapered reamer for this job, but since I do have two different sizes ( one much too large for any prop I would be using) I will try it on a prop and examine results firsthand.

Dan

Dan
Old 08-08-2016, 07:00 AM
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Use one of these with the correct diameters for your crankshaft and prop hole. Dan.

http://www.mcmaster.com/#counterbores/=13mx8o3
Old 08-08-2016, 11:00 AM
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dangtaylor
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Thanks, I considered counterbore tools before and you are right that it might be the best choice for a problem , particular engine whose threaded output shaft is some undersized. It was for the Super Tigre GS-40 that I bushed a prop before. I have the equipment for doing that and it is a relatively fast straightforward job.

I still don't have an answer to my original question about the actual sizes of the Great Planes step reamer. Possibly my referring to metric dimensions kept someone from measuring with an inch mic. Measurements in inches would be fine for me, it's an easy calculation.

Thanks for all the above responses.

Dan
Old 08-08-2016, 07:24 PM
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The fox prop reamer was for their engines which had standard sized shafts and most engines outside of the US had metric sizes. So either by a tapered reamer or by a metric one. I my self have two reamers one standard and one metric. I find I use the standard one all the time over the metric even on the metric prop shafts. The very small amount of slop isn't noticeable in being off center. Also APC props arilled much better than they were in the past as they have jigs now.
Old 08-09-2016, 03:04 AM
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I like Jester's solution to the problem. Myself I usually use a reamer, but I only ream it out 90% of the way from the back. I then turn the prop on letting the shaft cut its own threads. seems to work fine.

Calvi
Old 08-09-2016, 03:50 AM
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I have a Fox reamer for English units and a Great Planes reamer for metric. Both work perfectly for their purposes, and I've reamed holes for lots of different makes of engines. I recently got a tapered reamer for my flight box so it's nice to hear from those who like them.

Jim
Old 08-09-2016, 09:34 AM
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I use a tapered reamer myself. If I am using a prop reamed for a 5/16" shaft on an engine with a 1/4" shaft, I will use heat shrink tubing on the 1/4" shaft to get the desired fit of the prop. As was said - the most important things are having the prop balanced completely after reaming and having it centered on the prop shaft.
Old 08-09-2016, 12:02 PM
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jester_s1
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FWIW, a simple solution to a prop hole that is to big is tape. The key is to make a straight cut where you start and come fairly close to the starting seam where you stop without overlapping it. It's not a normal practice for me to do that, but it's handy when I want to test a prop that was previously reamed for a different engine.
Old 08-09-2016, 12:38 PM
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in that situation I will also use the approriate size of one of the adapter rings that come with a spinner.

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