Friction clutch for small engines

[Brian Rupnow]

A huge THANK YOU going out to "Cuttings" from beautiful British Columbia for two pieces of friction disc material that came in my mail today.---Brian Rupnow

 

[bmac2]

Hi Brian

I’ve been following along and am enjoying this build and thought it was time to drop a note. If anyone should ever ask that IS an oil groove and they are Very hard to make . As a side note if “the good wife” ever gets touchy about using her oven for workshop projects have a look around for a toaster oven. I picked one up cheap at Value Village a couple of years ago. Anything that is used to process food usually goes pretty cheap and I wanted something to bake casting cores. Its good up to 500 degrees but I have to use shielding as the heat is not well distributed. It’s also handy to be able to set it in the back yard if there could be fumes involved.

Glad to see the friction material arrived before Canada Post went out.

 

[Brian Rupnow]

This will be (more or less) the set-up for testing the clutch. An electric motor is going to drive the large pulley via a v-belt. The sprocket which is bolted to the driven hub of the clutch will drive a second smaller sprocket when the clutch is engaged, thru a #35 pitch roller chain. In order for a clutch like this to function properly, there has to be some resistance to turning. If there is no resistance to turning, then just the fact that the clutch sprocket is setting on a revolving shaft will make the sprocket turn also. The resistance in this case will be provided by a nylon pellet under a #10-24 set screw thru the side of the small sprocket shaft housing. I will be able to vary the resistance to turning by tightening down the set screw against the shaft which carries the small sprocket.

 

[MachineTom]

Since you have some material your good at the moment. I recently rebuilt a Tapmatic Tapping Head. The friction disks were cheap like $4 each, that was the small 30 size head, I would suggest looking at a 70 size disk, about the size you were looking for.

 

[Brian Rupnow]

And now we are in "wait mode". I can't do anymore until my case hardened expander hub comes back from case hardening.--And I can't call the guy and hurry him along, because its being done as a "favour". The set-up as shown lets the shaft revolve freely without turning the sprocket. it also lets the sprockets and chain revolve freely without rotating the shaft. I may have to adjust the width of the wooden stand, but won't know until the expander hub is installed and anchored in the correct place.

 

[werowance]

Brian, are you using regular size bicycle chain or do you have a source for mini scale sized chain?

 

[nel2lar]

Brian
Love your cad drawing and how much you do to make the demonstration model. Looking to the growth of this clutch.
Looking good.
Nelson

 

[Brian Rupnow]

Werowance--that is #35 pitch industrial roller chain. I can buy the chain, sprockets, and connecting links at Princess Auto in Ontario.--Brian

 

[Anatol]

regarding chain and the like, for those of us in US and maybe Canada - I've use the Surplus Center in Lincoln Nebraska for years, they have an amazing selection of surplus machine parts at low prices. I have no association with them except as a long time satisfied customer.

 

[Brian Rupnow]

Spent today eating turkey and pumpkin pie--House was full of adult children and grandchildren. Good wife cooked her usual fantastic thanksgiving dinner.--and when I wasn't actively engaged in being grandpa I was thinking about clutches. Earlier in the week I had looked up and studied on a wrap-spring clutch, which I have never heard of before but now I know how they work. Also looked at a number of "over center" manual clutches and electromagnetic over-center clutches. I have built cone style clutches and expanding shoe clutches and dog clutches. They all seem to work, but they all (except for the dog clutch) seem to have too many parts to "miniaturize" down to a point where they work repeatably and consistently on an engine with a 3/8" crankshaft. I also looked at a proprietary friction clutch which is sold for go-carts and mini-bikes, but couldn't really tell how it operated. I hope to get the final part for my current clutch build back from case hardening this week to finish it up.---Brian

 

[billco]

Spent today eating turkey and pumpkin pie--House was full of adult children and grandchildren. Good wife cooked her usual fantastic thanksgiving dinner.--and when I wasn't actively engaged in being grandpa I was thinking about clutches. Earlier in the week I had looked up and studied on a wrap-spring clutch, which I have never heard of before but now I know how they work. Also looked at a number of "over center" manual clutches and electromagnetic over-center clutches. I have built cone style clutches and expanding shoe clutches and dog clutches. They all seem to work, but they all (except for the dog clutch) seem to have too many parts to "miniaturize" down to a point where they work repeatably and consistently on an engine with a 3/8" crankshaft. I also looked at a proprietary friction clutch which is sold for go-carts and mini-bikes, but couldn't really tell how it operated. I hope to get the final part for my current clutch build back from case hardening this week to finish it up.---Brian

You could check your local hobby store. I believe the r/c cars use a friction clutch like the go carts only smaller .love your work and follow closely

 

[velocette]

Hi Brian
enjoying following your progress on this clutch. There is probably a problem here from Billco With the RPM that they engage at "You could check your local hobby store. I believe the r/c cars use a friction clutch like the go carts only smaller .love your work and follow closely".
Eric

 

[Brian Rupnow]

Today I'm just dickin' around. No real work and my clutch part isn't back from case hardening yet. Of all the different clutches I've designed, the expanding shoe clutch seems to lend itself best to installing on a small engine. It is relatively small at 1 3/4" diameter, and it doesn't put any axial load into the crankshaft. I checked out all of my engines, and the one most suited to adding a clutch to was the flathead engine I had featured in the Home Shop Machinist magazine a few years ago.

 

[Brian Rupnow]

It seems that my case hardening friend has let me down. I will give him one more week and then I will get the part back and use it unhardened, or else build another from 01 and harden it myself.---Sorry about the delay.---Brian

 

[nel2lar]

Brian
Sorry to hear the bad news. Maybe they are sick or just forgot about the part.
Hopefully you come up with positive closure.
I've enjoyed your build.
Nelson

 

[Brian Rupnow]

Nelson--I used to work for this guy about 20 years ago, and he was a really great boss. His machine shop ran into hard times and had to close about 15 years ago and he went to work for his competition right here in town immediately afterwards as a salesman. I know he had good intentions when he offered to have it case hardened, but he told me today that the company he now works for doesn't send as much stuff out for case hardening now as it used to. It's not a big deal. I have two projects on the go, along with an order I'm currently designing for a welding fixture for General Motors.

 

[nel2lar]

sounds like all is good
Have a great day
Nelson

 

[Brian Rupnow]

Okay--We're back in the saddle again on this project. I just went down to the machine shop that was going to have my tapered hub case hardened, and then didn't.--Moving on--I'm going out to my main garage right now and set this up with a motor to drive it, and see if and how well it works. A video and picture will be posted here shortly.---Brian

 

[Brian Rupnow]

And as I promised, here we have a still shot of the assembled clutch, and a nice video of it in operation---Brian

 

[Brian Rupnow]

As promised, here are all the engineering drawings to fabricate this clutch.---Brian
http://www.mediafire.com/file/x7shbmds6box782/FRICTION_CLUTCH_BASED_ON_DRAGSAW.zip/file