Author Topic: Line Shaft Double clutch  (Read 1644 times)

Offline Captain Jerry

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Line Shaft Double clutch
« on: October 18, 2016, 04:16:13 AM »
Recent  posts of line shaft clutches have captured my attention and I guess I won't be able to ignore the urge to make one so here is my tentative plan.  The basic concept here is the same as the other ones that have been shown, in that a sliding actuator forces a shoe into contact with the inner surface of a drum.  The outer surface of the drum can be driven by a round. flat. or vee belt or it could be a gear.

I would like to make it as small as possible so the shaft diameter is 1/4" and the inner surface of the drum is 1".  The OD can be anything larger than 1.25 inch.  To make it a little bit different, I have designed it as a double clutch which could be set up as a forward/reverse system or one that selects 1 of 2 inputs or outputs.  At this point, I have not designed any input or output or control mechanism, just the two clutches.

I will probably  make it out of cast iron but may use some mild steel.  The 1/4" shaft is steel.  The only items that are fixed to the shaft are the two clutch bodies (green) which are attached with set screws and the two collars (yellow).  The two drums (blue, only one shown) are free to turn on the shaft. Each clutch body has two semi-circular shoes  (dark gray).  Between the two clutch bodies is a sliding actuator (light gray).  There are two lugs extending from the face that slide in slots in the clutch bodies, and with a sloped face on the surface of the lug, forces the clutch shoes outward to contact the drum.  The distance between the two clutch bodies is set up so that only one set of shoes is raise at any time and there is a point between where neither set is activated. 

I don't think that it is possible to accurately make the clutch shoes and the slope of the lugs so that contact will be even without some adjustment so each shoe has a small hex drive set screw (4-40tpi) that will be the actual contact point between the lugs and the shoes to allow adjustment for engagement and wear.

I have been giving this a lot of thought since a little back pain has kept me out of the shop for most of the past week.  Take a look, please, and lt me know if you see any gotchas or goofs.  I hope to get back in the shop this week to play with this.

Jerry
There are thing that you can do and some things you can't do.
Don't worry about it. try it anyway.

Offline J.L.

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Re: Line Shaft Double clutch
« Reply #1 on: October 18, 2016, 02:14:49 PM »
Hi Jerry,

This looks like a very interesting project. You have designed it well. All the best as it is being developed.  :ThumbsUp:

Today, on my model, I will try to reduce the amount of lateral pressure the actuator requires to engage its little set screws on the arms of the shoes and continue on to rest on the actuator boss so that the shoes remain pressed against the inside of the drum as the clutch rotates.

We are working on approximately the same scale. A fly in the ointment with these small diameters may be that there is not enough friction to keep the shaft running while engaging the clutch.

Cheers...John

Offline Captain Jerry

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Re: Line Shaft Double clutch
« Reply #2 on: October 18, 2016, 03:47:48 PM »
John - As I see it,the force required is related to the slope on the actuator and finding the best angle may not be easy. It also seems that a greater contact area between the shoe and the drum will reduce the needed force. There will be fiddling.
There are thing that you can do and some things you can't do.
Don't worry about it. try it anyway.

Offline J.L.

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Re: Line Shaft Double clutch
« Reply #3 on: October 18, 2016, 05:05:43 PM »
Hi Jerry,
Good observations.  I think I must have looked at every vintage photo of actuators on the internet. Some are hanging from the clutches with bailing wire; others shown on shafts. Not one of them had a cone shape on the leading edge. Every one had a bullnose.  That tells me that there must have been so much torque in the line shafts that the arms of the actuator with their chisel shaped fingers could just be driven up the nose with brute force from the lever.

As you say though, in our scale, finesse and shape of the nose or 'cone' could be critical.

A good challenge.

John

Offline Captain Jerry

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Re: Line Shaft Double clutch
« Reply #4 on: October 18, 2016, 06:22:19 PM »

Here is the results of a little shop time.  Revised due to available material, the drums are 1" OD / .75"ID so the actuator fingers are a little bit fragile.

I was lucky to be able to get this to work without adjusting screws in the clutch shoes, just a little filing on the fingers produce a working model.

Engagement is smooth and easy and the clutch remains engaged with no force applied to the actuator. 

I may fiddle with this a while before deciding if I want to get a bigger piece of cast iron.
There are thing that you can do and some things you can't do.
Don't worry about it. try it anyway.