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Old Feb 13, 2013, 01:50 AM
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Collet holding prop on is slipping - how tight can/should I make the nut?

Hi,

I have a prop generating about 2.5kg of thrust on a 5 mm motor shaft, using a aeronaut 55mm folding prop turbospinner with collet adaptor.

Statically, I can pull about 7 kg on it without it slipping at all. I haven't tried pulling harder.

But when I held the plane and ran it at full throttle for 30s-1 minute, and stopped, it had slipped forward 3-4 mm, presumably due to vibration.

I've been advised that loctite will potentially make it near impossible to get off in the future, so I want to avoid that.

I can make the nut tighter pretty easily since I have some damn big spanners, but I am afraid of breaking something. How do you guys know how tight you should make it? Or how tight you can make it?

I would appreciate any advice here.
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Old Feb 13, 2013, 03:41 AM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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First off make sure that it is the right size collet. If it literally can drop onto the motor shaft then the hole is likely too big. A too large collet will only have three lines of contact instead of the entire surface. A good fitting collet should actually require a moderate finger push to slip onto the motor shaft.

Next ensure that the collet and motor shaft are squeaky clean. No oil or anything else. Clean the inside of the collet and the motor shaft with a good de-greaser or strong cleaner then be sure to rinse away any possible soapy residue.
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Old Feb 13, 2013, 04:33 AM
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Originally Posted by BMatthews View Post
First off make sure that it is the right size collet. If it literally can drop onto the motor shaft then the hole is likely too big. A too large collet will only have three lines of contact instead of the entire surface. A good fitting collet should actually require a moderate finger push to slip onto the motor shaft.

Next ensure that the collet and motor shaft are squeaky clean. No oil or anything else. Clean the inside of the collet and the motor shaft with a good de-greaser or strong cleaner then be sure to rinse away any possible soapy residue.
well in terms of collet diameter, I'm pretty sure it's correct - there is a tiny bit of friction, in terms of play, there is nothing visible when I fully untighten it and shake side to side, but you can hear a light clicking from a little play. The size down would never fit I imagine. So I don't think it's a size too large by mistake. So barring aeronaut making a machining error of a tenth of a mm or so I'd guess it's correct.

Regarding dirt, I'll degrease and clean it before I fly next. Any other advice?
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Old Feb 13, 2013, 09:34 AM
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"Any other advice?"

Push the collet all the way in until it bottoms out; then pull it back about 1/32 or so. If it is bottomed out, it will have no where to move back when you tighten, and it will try.

Les
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Old Feb 13, 2013, 11:18 AM
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Originally Posted by LesUyeda View Post
"Any other advice?"

Push the collet all the way in until it bottoms out; then pull it back about 1/32 or so. If it is bottomed out, it will have no where to move back when you tighten, and it will try.

Les
I'm not sure what you mean exactly? All the way down on the motor shaft, or all the way into the circular thing that the screw tightens down into it to make it clamp?

If you mean onto the motor shaft, unfortunately the shaft isn't long enough at the moment since the motor is inset a bit from the front of the plane, not that much shaft pokes out. Is that a problem? I can modify it with some cutting back of the front of the plane if that is the reason for the issue.
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Old Feb 13, 2013, 01:07 PM
I don't like your altitude
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Originally Posted by Nereth View Post
I'm not sure what you mean exactly? All the way down on the motor shaft, or all the way into the circular thing that the screw tightens down into it to make it clamp?

If you mean onto the motor shaft, unfortunately the shaft isn't long enough at the moment since the motor is inset a bit from the front of the plane, not that much shaft pokes out. Is that a problem? I can modify it with some cutting back of the front of the plane if that is the reason for the issue.
Sounds like that's your problem.Not enough shaft into the collet.
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Old Feb 13, 2013, 10:06 PM
B for Bruce
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Les' adise applies to one type of collet adapter but not the other type I've seen and used. So some of this will depend on which collet adapter you have.

I wasn't suggesting that you have the "wrong size" but that the size you have is possibly not an accurate fit to the shaft even though it was labeled as being the correct size.

You say you don't have much motor shaft sticking out. Are you able to FULLY seat the collet? If you're only grabbing a short length of the motor's shaft then you won't have the proper support and you won't have the full measure of the friction needed to provide the grip. And worse yet, since many of the collet adapters I've seen are aluminium if they are not fully seated you run the risk of deforming the part that is in contact from the pressure. And if that occurs then it'll never grab the motor shaft correctly even if you do mate them up correctly later on. So there's a good chance that the adapter is ruined at this point.
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Old Feb 14, 2013, 12:14 AM
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I want to thank you guys for taking the time to help me, but this is starting to worry me, so I think it's time for some pictures.

Note that there are 20mm of shaft before the collet would hit the circlip of the motor shaft, but I have only been using about 11mm of it for that most recent test where it slipped, because I was purposefully leaving an air gap. I could go up to about 15mm of it before the spinner would hit the planes fuse right now. The depth of the collet itself appears to be 19.67mm before a tiny ledge is hit inside. There is a much more significant narrowing ~1mm after this ledge.

Pictures:

I have attached pictures of the inside of the collet (I didn't know what you meant by type of collet, hopefully this will help you identify it?), and the motor shaft with the collet in ~ a position parallel to where it would be if I pushed it as far down onto the shaft as it could go before the spinner hits the nose elsewhere.
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Old Feb 14, 2013, 01:23 AM
B for Bruce
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That's the basic sort. You can push that style on fully. There's no need to back it off with that style.

Try degreasing the motor shaft really well as well as the inside of the collet. Then put the thinnest possible smear of grease on the inside conical hole of the prop driver. That should let the tapered driver slip on the collet and apply the most possible pressure.
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Old Feb 14, 2013, 01:35 AM
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Originally Posted by BMatthews View Post
That's the basic sort. You can push that style on fully. There's no need to back it off with that style.

Try degreasing the motor shaft really well as well as the inside of the collet. Then put the thinnest possible smear of grease on the inside conical hole of the prop driver. That should let the tapered driver slip on the collet and apply the most possible pressure.
Ok, given that I can't go more than 15mm on (as shown in pic) will that be ok? Because that isn't full depth. I assume 10mm (what I was using when it slipped) is too little?

Edit: Oh, purely out of curiosity, what's the other style that can't get pushed on fully?
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Old Feb 14, 2013, 10:02 AM
B for Bruce
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The picture makes it look like you can push it on fully. Or is it the spinner and other bits that limit the amount?

The key to getting the collet to avoid moving and walking off is to go for full depth engagement. The clamping force might only come from the split portion but the part deep in the end still provides support against any vibration walking the adapter around or off the shaft by limiting the amount of flex in the adapter to shaft joint.

To get full engagement can you cut away at the nose a little? Even if it's just a rebate like ring around the edges for the skirt of the spinner?

Given your description of the trials so far I'd say it's likely that you've deformed the inside of the adapter and it's likely you won't get a full and proper grip. You may need to buy another adapter and this time ensure that it's fully on the shaft.

Some motors allow you to remove and flip the shaft around. If you can do that it would be well worth it. Or as suggested cut away at the nose as needed to let the adapter go on the shaft to full depth. Anything much less than full depth is asking for vibration and the problems you've had.
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Old Feb 14, 2013, 09:21 PM
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It's the spinner and other bits that limit the amount.

I can't get completely full depth. And unfortunately as I realised yesterday, the bit that is stopping me cannot be cut away. About 15mm is the best I can do. That's the amount you see in the picture with the ruler in it.

Why flip the shaft? Is it the adaptor, the sahft, or both that would be deformed? I can check the shaft with a micrometer or vernier caliper if it could be a problem.
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Old Feb 15, 2013, 12:55 AM
B for Bruce
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The shaft is hardened steel on any sort of even half way decent motor. So it's not the shaft. But if you've been playing with less than optimal engagement of the adapter it's quite possible that the vibration and other factors during the adapter walking off the shaft during running as deformed the inside of the collet area so that you're not getting full and proper contact all around the shaft and inside surface of the collet. And when that occurs you simply won't get optimum holding power even if you fully install the adapter at this point. Aluminium is simply too easily deformed by such things.

Often times the motor shafts have a notch for the locking screw that is not right at the mid way point of the shaft. So flipping it around could well give you another few mm's of extension out the front of the model and allow you to achieve a closer to full engagement length for the adapter. If this proves to be the case and the adapter STILL walks off the shaft then the adapter was damaged during previous trials and needs to be replaced.
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Old Feb 15, 2013, 01:20 AM
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Originally Posted by BMatthews View Post
The shaft is hardened steel on any sort of even half way decent motor. So it's not the shaft. But if you've been playing with less than optimal engagement of the adapter it's quite possible that the vibration and other factors during the adapter walking off the shaft during running as deformed the inside of the collet area so that you're not getting full and proper contact all around the shaft and inside surface of the collet. And when that occurs you simply won't get optimum holding power even if you fully install the adapter at this point. Aluminium is simply too easily deformed by such things.

Often times the motor shafts have a notch for the locking screw that is not right at the mid way point of the shaft. So flipping it around could well give you another few mm's of extension out the front of the model and allow you to achieve a closer to full engagement length for the adapter. If this proves to be the case and the adapter STILL walks off the shaft then the adapter was damaged during previous trials and needs to be replaced.
Ok thanks! I will look into swapping the shaft around. It's not likely I will ever get full depth, but maybe I can get closer. I hope it will be ok
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Old Feb 15, 2013, 12:54 PM
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Is there anyway you can move the motor forward?Pack the mounting?
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