Friction clutch for small engines

[Brian Rupnow]

While I was working on the dog clutch for my recently built drag saw, I put out a request asking for a good design for a friction clutch that could be "miniaturized". Some kind hearted soul from another forum sent me a link to a one page document, which shows setting up instructions for exactly what I was looking for, which surprisingly enough was a friction clutch used on a drag saw. It must be about 100 years old, and will totally make your head explode trying to figure out how it works. It is a great design, because it not only engages the clutch, but a secondary and very beneficial effect is that it "traps" the clutch handle and won't let the clutch accidently disengage until the operator wants it to. This is my interpretation of the mechanicals of this clutch, and an attempt to build one.
http://www.herculesengines.com/hercules/NewManual/page_58.html

 

[Brian Rupnow]

These two models show the clutch engaged and disengaged. the green expander cone is slid along the shaft by an outside handle (not shown) and when it engages them it spreads them open, thus making them rotate and put pressure on the red friction disc. the yellow flywheel is keyed to the shaft. The blue hub with sprocket mounted on it floats on the shaft.

 

[Brian Rupnow]

In about two minutes I am going to jump up and grab a piece of mild steel and make this expander cone. It's cold outside and good wife and visiting daughter are off to the mall. I don't have any 01 stock this large in diameter, so I'm not going to harden it.

 

[minh-thanh]

That's Great
I'm looking to combine my engine with a car

 

[Brian Rupnow]

First part made---the expander hub. I made it from a scrap end of material that I had left over from something.

 

[Brian Rupnow]

I was originally going to make this clutch with three comma shaped arms. However, looking at the slitting saws I have, I decided to make it with four comma shape arms. This way I can cut the 1/8" wide slots in the blue hub all the way across the face.

 

[10K Pete]

Now you have a design that is very interesting to me. I wuz gonna take yer two arm and make it more powerful but you have done it here!

Excellent work! The magic of CAD....

Thanks,
Pete

 

[Brian Rupnow]

I don't post very many set up shots anymore, but this is a worthy one. No, it's not a Maltese cross, it's the hub that will hold the four comma shaped arms. There is more work yet to be done on it.

 

[Cymro77]

Fantastic!

 

[nel2lar]

Brian
I believe you have the winning combination. The drag saw drags on. No pun intended.
Nelson

 

[Brian Rupnow]

Now, is that a beautiful thing or is that a beautiful thing? I chickened out at the very last moment and put the slots in with a 1/8" carbide endmill instead of using my slitting saw. This part is steel and I didn't want to take a years life off my slitting saw. I took 0.010" deep cuts with the mill running at 1300 rpm and hand cranked very cautiously so as not to snap the endmill off.

 

[Brian Rupnow]

Now it's my turn to ask a question. What can I buy for a friction disc. The disc stands alone and is not attached to anything, simply centered on the shaft. In a perfect world, I would like something about 1/16" to 1/8" thick. Whatever it is, it has to not only have very good friction surfaces on it, but must be durable and capable of holding it's shape. It needs to be 2 1/4" diameter. If I don't get a good answer to this question, I may default to a piece of 1/4" plywood for a friction disc.

 

[dtsh]

Have you looked at clutch pack material for limited slip or perhaps motorcycle clutches? You many have some luck finding some in that diameter.

 

[TonyM]

The old bike clutches had cork inserts. You could try epoxying a cork disk inside a thin aluminium ring and a small aluminium centre.

 

[Anatol]

Funny- this ad popped up in response to your question about what to make clutch disc out of

 

[Anatol]

but hard leather might actually work. (?)

 

[Brian Rupnow]

Maybe I'll go down in the swamp behind my place and catch a crocodile

 

[Brian Rupnow]

I went down street on a shopping trip today, and bought a 3 foot length of 1" x 1/8" precision ground 01 steel to make the comma shaped pieces from. Also bought a couple of very healthy small springs, one of them will work on the end of the clutch shaft, not sure which yet. Also picked up a sprocket which can be bored out to fit the appropriate clutch hub. I sawed off four 1 1/2" long pieces of the 1 x 1/8" 01 material, lined up the sides and one end, and clamped them in a set of welding vice grips. I will put a dab of mig weld on the ends which will be trimmed away after the fact, so I can machine all four pieces at the same time to ensure that they are all the same.

 

[Brian Rupnow]

I'm curious--those of you who have suggested leather, how would you use it. Would you glue it to the face of one of the discs, or just let it free float between the two metal discs?

 

[razor7177]

Brian, you'd probably have to epoxy the sucker onto a sacrificial piece( make sure you have afew of this as spares) just like a car dry clutch plate.
Hope this helps.