Author Topic: How does this clutch work?  (Read 4946 times)

Offline Brian Rupnow

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How does this clutch work?
« on: September 19, 2018, 08:45:58 PM »
After building the dog clutch for the drag saw, I asked for any friction clutch plans that people could find. Mike sent me this link. It looks like something I could use/build, but I can't tell how it works. It seems that the arm, part #A227 moves the slider, #A225 ahead and forces the comma shaped pieces #A223 apart. I assume that once the part #A225 is captured by these arms #A223, it will stay in place. Somehow the pressure of the spring #A238 must be involved here, to make the arms #A223 spring loaded to hold the expander cone part #A225 in place. There is a very faint dashed outline that shows these comma shaped parts #A223 in the position they would have if the slider cone A225 was not engaged. The only way I can figure a clutching action here is if there were gear teeth in the comma shaped part and a rack style series of annular grooves in the shaft it slides on, forcing everything to the right to put pressure on the friction disc #A189.  Maybe I'm overthinking this. Any other explanation of how this works will be gladly listened to.---Brian
http://www.herculesengines.com/hercules/NewManual/page_58.html

Offline Doc

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Re: How does this clutch work?
« Reply #1 on: September 19, 2018, 09:11:57 PM »
Looks to be the same clutch as on old garden tractors. Pull the handle in and it pushes the clutch faces together and spins the outer shaft.

Offline Brian Rupnow

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Re: How does this clutch work?
« Reply #2 on: September 19, 2018, 09:54:38 PM »
I've been studying on this thing, and I think I have it figured out. I'll have to make a model to confirm what I think. It seems that the secret to this mechanism is all in the spring and the comma shaped pieces. When those comma shaped pieces are forced outward by the expander cone, they not only trap the expander cone but a tit on the bottom of the comma shaped piece makes the whole stack up of parts become marginally longer--enough to put pressure on the friction disc. Of course the magic in this isn't in engaging the clutch--it's in also capturing the handle so it can't slip out of engagement.

Offline Brian Rupnow

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Re: How does this clutch work?
« Reply #3 on: September 20, 2018, 01:31:16 AM »
Okay--Burned a few brain cells on this one. The clutch which I posted a link to in post #1 is not an "over center" clutch. It does however, not only engage and disengage the clutch thru pressure on the friction material, but also traps the handle so it won't jump out of engagement. This is a very clever design, and I had to study it a lot to see what was really happening. I have modelled it in both engaged and disengaged positions. EDIT EDIT--I have updated these drawings based on information from Velocette.

« Last Edit: September 20, 2018, 02:37:52 PM by Brian Rupnow »

Offline 10KPete

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Re: How does this clutch work?
« Reply #4 on: September 20, 2018, 03:16:32 AM »
Beautiful drawings, Brian. And a lingering question answered!

Pete
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Offline dieselpilot

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Re: How does this clutch work?
« Reply #5 on: September 20, 2018, 02:03:04 PM »
This is essentially the same mechanism for most collet lever drawbars. Simple cam action.

Offline Brian Rupnow

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Re: How does this clutch work?
« Reply #6 on: September 20, 2018, 03:58:33 PM »
I think this is an ingenious design for a clutch. The only issue with it that I see is that while it may be great for 1" diameter shafts and larger, it would be incredibly difficult to miniaturize it to work on a 3/8" shaft like most of my engines have. True, most of the components are simply "turnings" that would present no difficulty to miniaturize, but the comma shaped pieces would get so small I don't think I could machine them accurately. Too bad, because it is a really slick design.

Offline dieselpilot

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Re: How does this clutch work?
« Reply #7 on: September 20, 2018, 07:13:55 PM »
The shape of the cam can be simplified. Only the contact points are functional.

Offline Doc

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Re: How does this clutch work?
« Reply #8 on: September 20, 2018, 08:24:06 PM »
This is essentially the same mechanism for most collet lever drawbars. Simple cam action.
Yes this mechanism is used in many things.

Offline BillTodd

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Re: How does this clutch work?
« Reply #9 on: September 20, 2018, 09:13:00 PM »
This  is an animation of the clutch pusher on a Churchill Cub lathe :
Bill
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Offline Brian Rupnow

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Re: How does this clutch work?
« Reply #10 on: September 20, 2018, 10:18:54 PM »
One of the nifty things about my software is that I can shrink or grow a part by whatever factor I want to. Since my model to develop the drawings from had a 1" diameter shaft, and my engines 3/8" shafts are roughly 33% of 1", I shrunk the comma shaped pieces by that factor to see what they would be like to machine. I don't think I could machine this repeatedly 3 times to have three comma shaped pieces 120 degrees apart.

Online Admiral_dk

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Re: How does this clutch work?
« Reply #11 on: September 21, 2018, 11:21:39 AM »
I will not in any way claim that I can make the part ….. But I would not start on 3 separate pieces - I would make one wide enough to cut 3 identical parts from with a slitting saw.

I'm not going to claim that this will make it easy, as even 3 identical "comma's" isn't a warrant for a working clutch - you need to get the slots and holes for the pins that hold them in place perfect too ….

I will certainly follow this closely if you should decide to have a go at it anyway Brian  :cheers:

Offline Brian Rupnow

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Re: How does this clutch work?
« Reply #12 on: September 21, 2018, 03:10:06 PM »
I suppose that if I were to get serious about making this part, the first step would be to rough it out as rectangular part  and drill the required holes as shown. You can see the shape it will become, and also the "first cut" of the metal. All of these cuts and holes can be made with great accuracy, using the DRO on my mill for positioning.

Offline Brian Rupnow

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Re: How does this clutch work?
« Reply #13 on: September 21, 2018, 03:20:10 PM »
In second stage of machining all of the grey area would be milled away--again with a good deal of accuracy using the mill DRO's.

Offline Brian Rupnow

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Re: How does this clutch work?
« Reply #14 on: September 21, 2018, 03:37:37 PM »
Final filing would look like this. The filing buttons would let me hold very good accuracy on the round ends.  The rest would have to be "filed to the line". Maybe I could make these.  Since they would be made from 1/8" thick cold rolled steel plate I "might" be able to stick three pieces of plate together and do them all at once to ensure they were all exactly the same. I have heard of folks soft soldering plates like this together, then doing all the machining, then reheating them to separate them. I have never done this and don't know how difficult it would be.