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Dec 13, 2017, 05:58 PM
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Rcflyyer1's Avatar
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Reaming Prop from SAE to Metric?


Hello

I've been in this hobby for quite a while and I haven't got a good grasp on how to ream props. I've been using drill bits to ream until I recently dove into the topic and found out that you should never do that.

I've got an ASP 12A on the stand ready to break-in and upon receiving my MA 7 x 4 prop, I discovered it has a 4.76mm/3/16" hole pre-made. My engine has a shaft diameter of 5mm and from what I've found online, prop reamers are for strictly SAE to SAE or metric to metric reaming, no in between. Also, I only need to enlarge the diameter by 0.24mm so I'm not sure how I should go about doing this. The MA is factory balanced and I really don't want to mess it up .

Thanks for the help,

Adam
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Dec 13, 2017, 06:21 PM
Registered User
Rotten40851's Avatar
These are what I use , they are very good reamers

https://www.towerhobbies.com/cgi-bin...&I=LXEGH6&P=ML

https://www.towerhobbies.com/cgi-bin...?&I=LXEGH7&P=7
Dec 13, 2017, 06:29 PM
Scratch builder
I did used a fox propeller metric reamer but I think now is discontinued so you can buy a drill bit #9 (numbered 1-60 135 Split point), commonly used in aviation you can order it in the yardstore.com
Alberto
Dec 13, 2017, 06:46 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by Rcflyyer1 View Post
Hello

I've been in this hobby for quite a while and I haven't got a good grasp on how to ream props. I've been using drill bits to ream until I recently dove into the topic and found out that you should never do that.

I've got an ASP 12A on the stand ready to break-in and upon receiving my MA 7 x 4 prop, I discovered it has a 4.76mm/3/16" hole pre-made. My engine has a shaft diameter of 5mm and from what I've found online, prop reamers are for strictly SAE to SAE or metric to metric reaming, no in between. Also, I only need to enlarge the diameter by 0.24mm so I'm not sure how I should go about doing this. The MA is factory balanced and I really don't want to mess it up .

Thanks for the help,

Adam
For a 7 X 4 prop on a .12 engine you really don't need to over think. You are not going to see or feel that much difference with the prop balance. You are still in a relatively "sport flying" range and not with some high speed special applications.

If you cannot find a prop reamer, at least go get a set of numbered drill bits. You start with a 3/16" then take a #12 drill bit and twist it in the hole by hand. Then go up in size by doing the same thing with number 11, 10, and 9. You should be at 5mm by the time you hit #9. Unfortunately the plastic in the prop will shrink back a little when you pull the drill bit out. So if it is still a tight fit you may have to go to a #8 bit which is .199".

The reason why you don't want to drill out a hole in the propeller in one big step is because the bit will bite and cause the hole to go off center. However if you do it in baby steps you should be ok.

Sometimes even a reamer doesn't work that well. The reason is that most people keep their reamer for a long time and the reamer gets dull.
Dec 13, 2017, 07:06 PM
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Rcflyyer1's Avatar
Thread OP
Thank you all for your help.

The links above show good reamers but unfortunately they are too big as is the fox reamer.

The numbered drill bits is a great idea. Harbor Freight has a kit that's pretty cheap for what you get, so I'll be picking that up tomorrow.

https://www.harborfreight.com/60-pc-...set-61690.html

Can't wait to run this engine for the first time.
Dec 13, 2017, 07:07 PM
Closed Account
That size difference is smaller, than for example is used for screws in unthreaded plastic holes.
The threaded part of the shaft is not 5.0 mm, but closer to 4,9 or 4,95

I would typically just force that prop on the shaft, and be done with it.
Dec 13, 2017, 07:20 PM
///////
coriolan's Avatar
Quote:
Originally Posted by Rcflyyer1 View Post
Thank you all for your help.

The links above show good reamers but unfortunately they are too big as is the fox reamer.

The numbered drill bits is a great idea. Harbor Freight has a kit that's pretty cheap for what you get, so I'll be picking that up tomorrow.

https://www.harborfreight.com/60-pc-...set-61690.html

Can't wait to run this engine for the first time.
You will be pleased, the ASP .12 is a surprisingly good little engine! As Brutus1967 said 5mm is just a tad over 3/16"

Quote:
That size difference is smaller, than for example is used for screws in unthreaded plastic holes.
The threaded part of the shaft is not 5.0 mm, but closer to 4,9 or 4,95

I would typically just force that prop on the shaft, and be done with it.
Dec 13, 2017, 07:32 PM
Whats that drip ?
ClubFlyer's Avatar
Quote:
Originally Posted by Rcflyyer1 View Post
Thank you all for your help.

The links above show good reamers but unfortunately they are too big as is the fox reamer.

The numbered drill bits is a great idea. Harbor Freight has a kit that's pretty cheap for what you get, so I'll be picking that up tomorrow.

https://www.harborfreight.com/60-pc-...set-61690.html

Can't wait to run this engine for the first time.
Be careful using the drill bits, I would not use a hand held electric drill, and if you have a drill press make sure you secure the prop to the table well, don't hold it in your hand, if the dill bit grabs the prop, for one the prop could twist out of your hand and cut you, as well as the hole will become off center. Take your time and step up the bit size gradually, use the appropriate bit speed, and be safe!
Last edited by ClubFlyer; Dec 13, 2017 at 08:36 PM. Reason: Clarification
Dec 13, 2017, 07:35 PM
Master re-kitter
SRQFlyer's Avatar

Reaming/hand drilling


Quote:
Originally Posted by coriolan View Post
You will be pleased, the ASP .12 is a surprisingly good little engine! As Brutus1967 said 5mm is just a tad over 3/16"
Hi Adam,
Jim here. Welcome back!
If you do decide to "ream" the prop with a drill bit by hand, work from the back to the front. Any prop reaming should always be done from the back.
Dec 13, 2017, 07:40 PM
The runway used to be longer
Mad_Mike's Avatar
The difference between 5mm and 3/16" is about .009".
As said, just screw it on.

Don't buy cutting tools from HF, they belong in the recycle bin.
Dec 13, 2017, 08:07 PM
Registered User
Rcflyyer1's Avatar
Thread OP
Wow, tons of great advice and thanks for the welcome Jim!

At first, I was thinking maybe I should just screw/force the prop onto the shaft, but it didn't feel right. I did order two props though, so I can try both methods.

I'm interested in seeing how low I can get this engine to idle once broken in.
Dec 13, 2017, 11:07 PM
Registered User
I use a drill press and pinch the hub with my thumb and 2nd finger and the correct drill. Anything up to maybe .030" will centre itself pretty well. For your example, I have a rat tail file about that size that I spin ccw by hand to remove the .010" or so. I hate tight props on the shaft, I have so many used motors with plier marks on the drive washer because of laziness. A nice 3/16th" round file can be carefully used by gliding up and down and turning the prop 1/8th turn every couple swipes. Not rocket science. I like the little ASP motors. Kind of a modern low budget Cox replacement with a throttle, muffler and better performance than even the TD of similar sizes.
Dec 14, 2017, 04:53 AM
Closed Account
Quote:
Originally Posted by Rcflyyer1 View Post
Wow, tons of great advice and thanks for the welcome Jim!

At first, I was thinking maybe I should just screw/force the prop onto the shaft, but it didn't feel right. I did order two props though, so I can try both methods.

I'm interested in seeing how low I can get this engine to idle once broken in.
If it were a 1.20 or a 1.50 engine, or even a .60, yeah, I would not do that.

But this is a .12, and it is not going to generate a lot of power by any standard (of course, for its size it really is a nice amount, but in absolute numbers, it ain't).
I can fully guearantee you, just force it on untill the thread protrudes enough to get the propnut on, then push it down with the nut, and you will have the most precise fitting, exactly centered reamed hole you have ever seen.

I have done it all the time back in the days when these little engines were all that I could afford.
Dec 14, 2017, 06:05 AM
Closed Account
Wow, a thread for enlarging a hole in a prop....
Dec 14, 2017, 06:34 AM
Closed Account
Yup, isn't it something?
Now if it were something like my 18 x 8 prop that needed to be reamed from 5/16 to 12 mm, OK, I would understand: I had that done by a friend that is a machinist that has access to CNC machinery.
But these small props, they are not that critical....


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