Wobbler Pivot

[Paul AinsworthParticipant @paulainsworth93685]

Just started making a wobbler, my dilema is where to put the pivot point? I've seen them on centre of the cylinder and offset.

Does it matter?

Is one position better than the other?

If offset would you go higher or lower than center?

[Paul AinsworthParticipant @paulainsworth93685]

[DanielParticipant @daniel]

Hi Paul,

Are you following a drawing ?

[JasonBModerator @jasonb]

Single or double acting? Double are much more likely to be central where as a single acting can be towards the end.

Edited By JasonB on 26/05/2018 06:50:54

[HowiParticipant @howi]

surely the pivot point determines the inlet/exhaust ports position?

[John RuddParticipant @johnrudd16576]

I thought the op was building a steam engine….wobbler? Wiggler?

[JourneymanParticipant @journeyman]

Yes a spot of confusion between one of these, a wobbler or oscillating steam engine:-

and one of these, a wiggler or wobbler or centre/edge finder:-

Build article for steam engine *** HERE ***

John

Edit: Wrong photo

Edited By Journeyman on 26/05/2018 09:47:53

[HopperParticipant @hopper]

The further you place the pivot from the steam ports, the more room you have to play around with size and position of the steam ports. You have to make sure there is enough movement of the single steam port in the cylinder so that the two ports in the fixed body are far enough apart to prevent any overlap when the cylinder port is in the mid position. If there is not enough room there, steam will bridge straight from the inlet port to the exhaust port via the cylinder port without going into the cylinder.

[Paul AinsworthParticipant @paulainsworth93685]

Sorry for the confusion, yes a single action oscillating engine.

Following a youtube video and the only thing it doesnt give is either measurements for the pivot point or an explanation as to why it is where it is. I'll stick it just above center and see what happens, if I leave enough room at the top of the backplate it can be moved easily enough before I drill the ports.

Thanks for the link, that looks great for a second build.

[Paul AinsworthParticipant @paulainsworth93685]

Posted by Hopper on 26/05/2018 10:34:23:

The further you place the pivot from the steam ports, the more room you have to play around with size and position of the steam ports. You have to make sure there is enough movement of the single steam port in the cylinder so that the two ports in the fixed body are far enough apart to prevent any overlap when the cylinder port is in the mid position. If there is not enough room there, steam will bridge straight from the inlet port to the exhaust port via the cylinder port without going into the cylinder.

Right, better below center then as it would give a wider port spacing?

[JasonBModerator @jasonb]

Paul, can you put a link to the video, it may be a known design.

Best thing to do is draw it out as crank throw and distance between crank shaft and pivot will also affect how far the cylinder moves to open and close the ports.

[Paul AinsworthParticipant @paulainsworth93685]

It's a Tublacain one

https://youtu.be/Cgtjunt5bQo

 

The only measurements he doesn't give are the cylinder pivot and the offset for the cam. Is the cam offset half of the stroke i.e. stroke of 25mm cam offset from center 12.5mm?

Edited By Paul Ainsworth on 29/05/2018 09:43:04

Edited By Paul Ainsworth on 29/05/2018 09:44:01

[WearyParticipant @weary]

Hello Paul,

In this video, from 17:00 onward, Tubal Cain discusses making the cylinder. In the course of the exposition he specifically says that he doesn't use measurements! However, if you stop the video at 19:00 he holds his imperial depth gauge against the cylinder block and you can see measured position of the pivot hole = 9/16" above the open end of the cylinder.

You are correct about the 'cam' dimension.

Regards,

Phil

[Paul AinsworthParticipant @paulainsworth93685]

Cheers Phil, just measured where I put it and it's within a gnats (my only technical term) of 9/16", more by luck than judgement.

Time to crack on with it.

[HopperParticipant @hopper]

If you google around you should find free plans for an Elmer's Wobbler engine that might make a good starting point for working from a known design.

[Paul AinsworthParticipant @paulainsworth93685]

It lives, ran first time. Now for something more delicate

**LINK**

[Author]

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