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How do you make this

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BOB BLACKSHAW17/09/2021 17:01:46
430 forum posts
104 photos

16318934411324396504474087841076.jpgI am making this marine engine but I don't know how to make the eccentric. Its off set by 2mm with a 30 deg angle, I know how to off set 2mm but a bit lost with the 30 deg. Also the eccentric has a 1.6mm cut but the arm has a M2 diameter on the bottom.,is this M2 with a 1.6mm spigot to hold the two straps in place.16318933977505728651777667758850.jpg

I am self taught with turning and milling,so learning the hard way but get there in the end.

Thanks Bob

Edited By BOB BLACKSHAW on 17/09/2021 17:03:33

noel shelley17/09/2021 17:52:45
758 forum posts
19 photos

Is it a stuart D10 ? From the pictures it looks like one, in which case there is a small book on building this engine. Title, Building a verticle Steam Engine, published by Tee Publishing. I think it is still available. Good Luck. Noel

HOWARDT17/09/2021 18:11:56
778 forum posts
28 photos

You could either machine from one piece using offset centres to turn the part or create one eccentric with the boss and through hole, with another eccentric which can be fixed to the first with the correct angular position.

Ramon Wilson17/09/2021 18:18:48
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1194 forum posts
296 photos

Hi Bob, if you take a look here you can see how I aproached the same problem on the Stuart D10 rebuild I did.

I made the two eccentrics separately which gives independent movement rather than a double eccentric set forever as machined.

By making the sliding plate and using the faceplate the job becomes very easy.

Hope that helps - Tug

John Olsen18/09/2021 04:36:13
1196 forum posts
92 photos
1 articles

OK, this is not a Stuart. Not that that matters for the questions, and it looks like a nice design.

If the two eccentrics are being made in one piece, then the angle between them would matter, however if as is more usual they are made as two parts, then the angle only matters when you set them up on the shaft, one being set for each direction. Since your eccentrics are supposed to have a groove, there is nothing to stop you having a small grub screw set down inside the groove to bear on the shaft, so each eccentric can be set separately

The hole in the bottom of the strap is for a small screw with a spigot on the end. The thread only goes as far as the thickness of the strap, and the spigot protrudes into the groove on the eccentric strap. This stops the strap working sideways on the eccentric. Some designs make the strap with a groove and the eccentric with a ridge around it, which is more like full size practice and would provide more surface in contact. But that is more tricky to machine, especially in small sizes.

John

JasonB18/09/2021 07:06:03
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Moderator
21435 forum posts
2448 photos
1 articles

It's the J L Soumard design.

You can also do it by just marking out two positions rather than the usual one and resetting in the 4 jaw for each of the two eccentrics.

If you are only going to run on air then the 30deg may be a bit much so might be better to make them separate so you can adjust to get smooth running. If so make the inner eccentric with a boss the full 8mm long (might need to reduce diameter to say 7mm and then have a separate outer eccentric bored to fit the boss and set with a grubscerw

As John says the 1.6mm slot takes the core diameter of a turned down M2 thread

BOB BLACKSHAW18/09/2021 07:46:03
430 forum posts
104 photos

Morning all, thanks for the advice on the eccentric, as advised it's best to make them separate. It's a JL Soumard design, quite small.

Thanks Bob

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