Mechanical Clutch

[Brian Rupnow]

My brain never stops!!! Not all of my ideas are good ones, but I never run out of mechanical things to think about. Playing about with my model sawmill has got me thinking about simple mechanical clutches. Not something that tightens or loosens a drive belt, and not something that creates "drag" when disengaged. Rather some device that totally and completely disengages the driveshaft from whatever it is driving, and can be engaged softly like the clutch on an automobile, not with a sudden "grab and lurch". It would have to be simple, cheap, small, and a minimum of moving parts. I have many small, single race ball bearings from disassembling various "things" over the years, and they will take a lot of axial as well as radial pressure without failing. I was doodling on a piece of paper, and where the levers are in the sketch, think about a Destaco style clamp. Not the ones with the swinging lever, but the push/pull type. I see the friction material as being oak or maple, glued into a brass or aluminum housing. Not sure if I will build something like this or not, but it is intriguing!!!

 

[Jasonb]

Very much like the cone clutches found on some hit & miss engines except a handwheel was turned to engage and isengage them rather than use a lever.

The make part of the cone had friction material on it

 

[aonemarine]

Some outdrives on boats use the same set up and some posi traction rears.....steel on steel!

 

[crankshafter]

My brain never stops!!! Not all of my ideas are good ones, but I never run out of mechanical things to think about. Playing about with my model sawmill has got me thinking about simple mechanical clutches. Not something that tightens or loosens a drive belt, and not something that creates "drag" when disengaged. Rather some device that totally and completely disengages the driveshaft from whatever it is driving, and can be engaged softly like the clutch on an automobile, not with a sudden "grab and lurch". It would have to be simple, cheap, small, and a minimum of moving parts. I have many small, single race ball bearings from disassembling various "things" over the years, and they will take a lot of axial as well as radial pressure without failing. I was doodling on a piece of paper, and where the levers are in the sketch, think about a Destaco style clamp. Not the ones with the swinging lever, but the push/pull type. I see the friction material as being oak or maple, glued into a brass or aluminum housing. Not sure if I will build something like this or not, but it is intriguing!!!

Hi Brian.
I have been following this build( and all your other ones)But when you say: "Not sure if I will build something like this or not, but it is intriguing!!!"
I know you will.;D

Best Regards
CS

 

[rodw]

Brian, I think back in the day they preferred to use laminated leather for cones in friction clutches. Back to my shearing shed experience, an overhead shaft carried a large friction wheel for each shearing stand. A leather cone was used to engage with this wheel to drive a smaller shaft at right angles. I can't find a photo but photo 3 on this PDF shows one on a single stand electric version. They do mention wood cones in this document but I never saw one. Leather eventually gave way to synthetic cones.

http://www.kondiningroup.com.au/web_multimedia/startDownload.asp?strMultimediaFileName=FA128-28.pdf

You might be able to get away with machining your clutch cone out of a plastic. I reckon that you could machine laminated discs of leather into a cone shape as it is very stiff.

I also remember a ride on mower we had as a kid that had a siimilar leather cone mounted directly to a 8 hp engine drive shaft that sat between two friction plates mounted to the rear axle, one on each side of the cone. Moving a lever moved the engine sideways. One side drove forwards, moving the cone to the other plate drive in reverse and of course, in the middle was neutral.

 

[myrickman]

The angle of the taper determines whether the clutch will lock or not. It depends on the coefficient of friction of the 2 materials. If you do a google search, there is a wealth of info out there. I'll have to check the angle on a cast iron clutch on a stationary engine which is currently removed.

 

[Brian Rupnow]

And moving from hand doodles to CAD doodles, we have this. What I have attempted to do here is to ensure that all axial loads are transferred thru the ball bearings instead of any sliding surfaces betwen rotating mechanical parts.

 

[Brian Rupnow]

Bad on me!!! I forgot to show the drive pin and slot in the shaft in the first drawing I posted.

 

[Brian Rupnow]

This is the first part I will make. As you can see, I have added a second groove to it, simply because I have the room. This entire clutch is not going to be a study in superior engineering. Its something to do to keep me from going nuts during the ensuing festive season. I THINK it will work fine and I will post drawings as I go along, because I have to make them anyways for myself. If it works really really great, then you can copy the drawings and save them. If it doesn't work, then at least it will have amused you.

 

[Brian Rupnow]

Here is a little trick that works for me. When I want to go to a non critical flat bottomed hole in a part, which has a smaller thru bore already in it, I stick this 1" dia. 4 flute end mill in the tailstock chuck with my lathe on its lowest speed (about 150 rpm) and crank it in. This seems to put a smaller chip load on the lathe than cranking in a 1" drill bit, and I can go full depth in one shot without having to worry about a tapered bottom like you get from a drill. This side will now be opened out with a boring tool to 1 5/16" diameter, and then I will set my topslide over 25 degrees to make the final taper.

 

[Brian Rupnow]

There!!! Enough silliness for one evening. Time to go spend some wife time.

 

[hammer2100]

Brian,
First I like your idea, I like the idea of the Oak. My Grandfather's family used Hickory bands in Model T Fords, I have one of the bands. But I have a idea for you that might help.
I have seen something like your design smoewhere but they used the cone part of the clutch to sycronize the shafts than a splined collar slipped over the input shaft. This would then
take away the thrust load on the bearings. Just a thought.
Hammer

 

[sssfox]

Brian,

I have seen something like your design smoewhere but they used the cone part of the clutch to sycronize the shafts than a splined collar slipped over the input shaft. This would then
take away the thrust load on the bearings. Just a thought.
Hammer

It's called a synchromesh transmission. The gears are always meshed and the little cone/clutch thingies connect them to the output shaft.

Here is an explanation here:
http://en.wikipedia.org/wiki/Manual_transmission#Synchromesh

That would probably work well in this application. It wouldn't be necessary to maintain pressure on the lever.

 

[Brian Rupnow]

Thanks for looking and commenting guys. The plan keeps evolving!!! My whole premise behind this clutch is that the bearings do take up all the axial load. Ball bearings like the ones I am using (because I already have them) will take amazing radial loads, but they will take considerable axial loads as well, though not as great. As for holding the lever in to keep the clutch engaged, this latest drawing will show what I have in mind. On the extreme right hand piece the outer diameter of the body will have a 1 1/4" thread on an extended boss and will be threaded thru a plate with a 1 1/4" thread, which is attached to the baseplate. A handle on it will engage or disengage the clutch by swinging in an arc to advance the entire end (holding the bearing) on the threads. Since the threads on a 1 1/4" nut are quite coarse, a 45 degree swing of the handle should advance all the pieces sufficiently to engage the clutch, and it should hold its position there untill the handle is revolved 1/4 turn in the opposite direction. This is very hard to get your head around, but the drawing I have posted should make it clearer.---Brian

 

[Dave Sohlstrom]

From the Willamette Iron & Steel Works 1925 catalog they were using the same principal on there donkey winches used here in the PNW. Here is a scan of there friction device.

Dave

 

[Brian Rupnow]

Thanks Dave. And here's how the other side turned out. I am always amazed by the infinitesmaly (is that a word?) small difference between a press fit and a Loctite fit!!! This was supposed to be a "light press fit" . It turned out by about one zillionth to be a Loctite fit. No fear though. I had reamed the bore on the fabricated part and it was right on. So---I slipped a piece of 3/8" cold rolled shaft thru the fab'd part, slipped the bearing over that, slathered on a bit of 638 Loctite, and together it went. Concentricity gaurenteed.

 

[Brian Rupnow]

Some observant soul on "the other" forum just pointed out that the slot in the shaft should be centered on the pin to allow the oak disc and its holder freedom to move in either direction.---And he's absolutely right!!!

 

[Brian Rupnow]

 

[Brian Rupnow]

 

[Charles Lamont]

I don't think oak is ideal for this job. I would say it is too coarse and too open grained. Of course, if it is all you have, then it is worth a try. If you later decide to refine it, I would suggest something hard with a fine, even grain and preferably an oily nature. Lignum Vitae would have been ideal but is now unobtanium and if I remember rightly Goncalo Alves is a reasonable substitute. African Blackwood might be good too. Less exotic alternatives, without the desirable oiliness might include Rock Maple or Apple. Or Tufnol.

I think I would have used a smaller cone angle, but have done no calculations.