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May 22, 2020, 06:09 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
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Discussion

Machining Advice


While my question doesn’t apply to airplanes, it does to helicopters and cars that use clutches. I am trying to switch from a non-adjustable 3-shoe clutch to an adjustable 3-shoe clutch. The reason for the switch other than the adjustability factor is due to frequent clutch spring failure. I think the stock clutch would last a lot longer if the clutchbell ID was smaller, but these clutchbells are very specific to the truck I have and they’re discontinued and getting hard to find.

The new clutch I’m looking to convert to requires a 1.05” (26.7mm) ID; the brand new off the shelf clutchbells have a 1.08” (27.4mm) ID. That’s not a big difference, but it’s enough to cause the composite clutch material to delaminated due to an uneven contact patch with the clutchbell. There was talk of sleeving a clutchbell to reduce the ID, however the sleeve would be so thin that I can’t imagine it staying in place - or even getting it pressed in without damaging it.

How realistic is it to machine a sleeve that’s .35mm thick (to have an overall ID .7mm smaller) and have it actually work/last?
Last edited by 1QwkSport2.5r; May 22, 2020 at 10:27 AM.
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May 22, 2020, 06:48 AM
Registered User
earlwb's Avatar
I like your idea of making a slightly smaller diameter clutch bell. It makes sense with your reasoning.

Well it is possible to make a thin sleeve. What you would do is press fit in a more thick tube and then machine it down to 0.7mm. But as you noted it is hard to tell how well it would work. You would glue it in using a serious metal glue such as what Locktite sells, etc. Wait for the glue to cure good then machine it to size.

I just remembered that many many years ago, we used to glue in a thin fiber like strip of material into the clutch bell of RC cars or helicopters. It improved the friction for better grip. it would wear out after a while but it wasn't difficult to glue in a new one though.
Last edited by earlwb; May 22, 2020 at 06:49 AM. Reason: add more info
May 22, 2020, 07:42 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
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Quote:
Originally Posted by earlwb
I like your idea of making a slightly smaller diameter clutch bell. It makes sense with your reasoning.

Well it is possible to make a thin sleeve. What you would do is press fit in a more thick tube and then machine it down to 0.7mm. But as you noted it is hard to tell how well it would work. You would glue it in using a serious metal glue such as what Locktite sells, etc. Wait for the glue to cure good then machine it to size.

I just remembered that many many years ago, we used to glue in a thin fiber like strip of material into the clutch bell of RC cars or helicopters. It improved the friction for better grip. it would wear out after a while but it wasn't difficult to glue in a new one though.
Is this friction material you speak of still around or what the brand/kind it is? This might be more realistic for my needs, but ultimately Iím looking for something that will last more than a gallon of fuel. Thatís about what I get on a set of clutch shoes/springs before a spring breaks.
May 22, 2020, 08:48 AM
Registered User
Why not make a bell to suit what you want Tim , way better than adding bits , can be hardened and ground to size and will be nice and round and your clutch shoes and springs would appreciate it as well . I've ground a few internally for a couple of dirt racer guys out here , but they don't use springs .
May 22, 2020, 09:18 AM
Still gassin' it.
Quote:
Originally Posted by 1QwkSport2.5r
Is this friction material you speak of still around or what the brand/kind it is? This might be more realistic for my needs, but ultimately Iím looking for something that will last more than a gallon of fuel. Thatís about what I get on a set of clutch shoes/springs before a spring breaks.
Yes, that liner material is still availlable and I don't know the exact thickness, but around 0,7 mm sounds about right.
Amongst others, any shop carrying Align products should either have it in stock or be able to get it for you.

But preferrably, I would use cork veneer. Basically there's two kinds of cork, the grainy kind and the smooth kind.
The smooth kind is excellent friction material for clutch friction material: Kawasaki used it for many years in their motorcycles, and I have used it for many years in RC helicopters.
Tough gasket material also works pretty good.
May 22, 2020, 10:10 AM
Registered User
Quote:
Originally Posted by 1QwkSport2.5r
While my question doesnít apply to airplanes, it does to helicopters and cars that use clutches. I am trying to switch from a non-adjustable 3-shoe clutch to an adjustable 3-shoe clutch. The reason for the switch other than the adjustability factor is due to frequent clutch spring failure. I think the stock clutch would last a lot longer if the clutchbell ID was smaller, but these clutchbells are very specific to the truck I have and theyíre discontinued and getting hard to find.

The new clutch Iím looking to convert to requires a 1.05Ē (26.7mm) ID; the brand new off the shelf clutchbells have a 1.08Ē (27.4mm) ID. Thatís not a big difference, but itís enough to cause the composite clutch material to delaminated due to an uneven contact patch with the clutchbell. There was talk of sleeving a clutchbell to reduce the ID, however the sleeve would be so thin that I canít imagine it staying in place - or even getting it pressed in without damaging it.

How realistic is it to machine a sleeve thatís .7mm thick and have it actually work/last?
Reducing a clutch bell ID from 27.4mm to 26.7mm requires a 0.35mm thick sleeve not 0.7mm, a 0.3mm aluminium foil glued around the circumference and the liner glued inside of the foil could do the trick. Try an aluminium foil from a soda can, I don't see why it shouldn't work...
May 22, 2020, 10:24 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
Thread OP
Quote:
Originally Posted by Geoff Potter
Why not make a bell to suit what you want Tim , way better than adding bits , can be hardened and ground to size and will be nice and round and your clutch shoes and springs would appreciate it as well . I've ground a few internally for a couple of dirt racer guys out here , but they don't use springs .
Because I donít have a lathe or milling machine. The clutchbell needs to accept radial ball bearings and has 2 pinions on it. Not to mention the cost of having someone make one would be prohibitive.
May 22, 2020, 10:25 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
Thread OP
Quote:
Originally Posted by ClippedWings
Reducing a clutch bell ID from 27.4mm to 26.7mm requires a 0.35mm thick sleeve not 0.7mm, a 0.3mm aluminium foil glued around the circumference and the liner glued inside of the foil could do the trick. Try an aluminium foil from a soda can, I don't see why it shouldn't work...
Good catch on the math - I forgot to halve the thickness; I was thinking the overall ID would be .7mm smaller, but the thickness of the sleeve indeed would need to be .35mm.

I’ll edit my original post to read correctly.

As to using soda can or similar for a sleeve - I don’t think this is going to work due to being much less ductile (I think that’s the proper term) than the hard steel bell. I think the aluminum would be too soft and not last very long even if it could be well adhered to the hard steel bell.
May 22, 2020, 05:08 PM
Registered User
Quote:
Originally Posted by 1QwkSport2.5r
Good catch on the math - I forgot to halve the thickness; I was thinking the overall ID would be .7mm smaller, but the thickness of the sleeve indeed would need to be .35mm.

Iíll edit my original post to read correctly.

As to using soda can or similar for a sleeve - I donít think this is going to work due to being much less ductile (I think thatís the proper term) than the hard steel bell. I think the aluminum would be too soft and not last very long even if it could be well adhered to the hard steel bell.
The liner material used in heli clutch bells is softer and brittle, yet it lasts a long time. Making the liner from a soda can is easy to cut, install and experiment with and replace/remove if required. In other words, you have nothing to lose if it doesn't work and plenty to gain if it does.
May 22, 2020, 06:36 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by 1QwkSport2.5r
While my question doesnít apply to airplanes, it does to helicopters and cars that use clutches. I am trying to switch from a non-adjustable 3-shoe clutch to an adjustable 3-shoe clutch. The reason for the switch other than the adjustability factor is due to frequent clutch spring failure. I think the stock clutch would last a lot longer if the clutchbell ID was smaller, but these clutchbells are very specific to the truck I have and theyíre discontinued and getting hard to find.

The new clutch Iím looking to convert to requires a 1.05Ē (26.7mm) ID; the brand new off the shelf clutchbells have a 1.08Ē (27.4mm) ID. Thatís not a big difference, but itís enough to cause the composite clutch material to delaminated due to an uneven contact patch with the clutchbell. There was talk of sleeving a clutchbell to reduce the ID, however the sleeve would be so thin that I canít imagine it staying in place - or even getting it pressed in without damaging it.

How realistic is it to machine a sleeve thatís .35mm thick (to have an overall ID .7mm smaller) and have it actually work/last?
You can machine a thin sleeve but you are still going to have issues.

1) What material you think will work as the sleeve. Aluminum sleeve will probably be a bit soft. Brass may be ok and steel is better. Since it is such a small diameter rather than machining a sleeve just cut a thin shim stock and form a ring.

2) The bond of the sleeve or shim to the clutch bell may be an issue. I am sure the clutch gets hot so it will have to be some high temp tolerant glue. Loctite has some sleeve gluing compound but I have not checked what temperature they can tolerate.

3) Maybe getting some thicker lining material will work better. How is the original liner? Is it an endless ring or it has a gap? Machining a different clutch liner maybe an alternative if you cannot make a new housing.
May 22, 2020, 07:41 PM
Play that funky music right
kenh3497's Avatar
Is a steel bell really necessary? I've had several helicopters (a little different application) and all used aluminum. Never a failure. Still, you need somebody to do the work.

MY OPINION, A sleeve that thin would be doomed for failure. Just not enough material to be able to pres it in and have it hang together. Gluing to me is a bit sketchy, though it might work.

I have a small lathe and could do the work but my dayjob is taking so much time I would prefer not to offer my services, as when I am off work, home life is at a premium. I have yet this year to even start an engine no less put a plane in the year.

Ken
May 22, 2020, 08:27 PM
Scott
Pylonracr's Avatar
Tim, I think Hansen has your solution. Thicker friction material on the shoes. There are still places that reline trailer brake shoes and the lining is glued to the frames. I remember back in the drum brake days having the new shoes arced to match the radius of the newly machined (Larger ID) brake drum to give full contact. If you could get some friction material and glue it to the shoes, making a jig to sand it to the correct thickness and radius shouldn't be too tough.

Scott
May 22, 2020, 09:32 PM
Whats that drip ?
ClubFlyer's Avatar
Make a sleeve with an interference fit, and press it in with some permatex hi-trmp sleeve retainer. That clutch bell won't ever see 400 degrees / 3000 psi. Just clean / rough the surfaces. You will most likely have to make a mandrel to hold / support the thin wall sleeve while you press it together.

https://www.permatex.com/products/th...eeve-retainer/
May 22, 2020, 09:48 PM
Registered User
earlwb's Avatar
Yup, Align still sells it under their brand. They use it on their Rc helicopters with glow engines. I am sure that other Rc helicopter brands using glow engines also use it too.
ref https://www.amainhobbies.com/align-c...xoChr8QAvD_BwE

Latest blog entry: yes I still fly airplanes too
May 23, 2020, 02:37 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
Thread OP
The clutchbell is hardened steel without a liner. The clutch shoes are aluminum 6061 or 7075 typically, or composite. I’ve used different combinations of composite and aluminum shoes with varying spring pressures to get the clutch to feel right. The problem and the reason for changing the clutch is due to adjustability. The stock clutch isn’t adjustable without pulling the whole thing off. The clutch I’m trying to switch to is adjustable without taking anything apart. Spring pressure is adjusted with an Allen wrench. Far and away an easier way!!

See attached photo of an I assembled 3-shoe OEM clutch. I don’t think the heli clutch liner will work due to the different style of clutch shoes. My truck weighs 13 pounds and the engine is a 4hp .28 monster. I really think I’m stuck here because my head says the shin needs to be hard steel and it’s gonna be too much hassle to make this work in any sort of timely fashion. Adding friction material to the shoes is not an option. The new clutch and shoes can be seen here: https://www.bukupower.com/ClutchHPI.aspx
Last edited by 1QwkSport2.5r; May 23, 2020 at 02:47 AM.


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