Stuart Compound Double Eccentric Sheeves

[Richard BParticipant @richardb44403]

I'm currently building a Stuart Compound with reversing gear which is going OK, however I seem to have screwed up the setting out of the eccentric sheeves as now when I try putting the motion together clearly I''ve got an issue which seems to be the eccentrics.

i used the Stuart castings which are not really that good so I think I will get some Meehanite bar as its easier to hold etc.

The throw is 9/64 (3.57mm) at 140deg. what is the best way of setting out and turning them.

Are there any old ME articles relating to this build ?

When I built a Double 10 with reversing gear the eccentrics were seperate sheeves pinned together, however with the compound there does not seem as much overlap to use for riviting the parts.

[Richard BParticipant @richardb44403]

Stuart Compound Double Eccentric Sheeves

[JasonBModerator @jasonb]

Usual method seems to be to put the hole in first and then mark two lines 140deg apart on the side of the stock. Clamp to an arbor with an offset spigot and one mark on it, line up one set of marks and turn the first one . Then rotate part on the arbor to line up the next mark and machine that.

You could use steel if you have it rather than buying in iron bar.

Build showing how to do them including making the jig etc , you will need to register to see the attached images

[JAParticipant @ja]

Years ago I made a Stuart 7A with a double eccentric. I kept on breaking cast iron double eccentrics so I used a short length of bright mild steel bar. One good double eccentric.

I did not use a jig, just a four jaw chuck with a lot of measuring and checking. I think I had a chucking stub on either side of the double eccentric.

Have fun!

JA

[RedsetterParticipant @redsetter]

Isn't it simpler to make the eccentrics individually, and pin them together afterwards?

Just use mild steel bar, no need for cast iron, and easier to work.

Why make it more complicated than it needs to be?

[John PurdyParticipant @johnpurdy78347]

Richard

If you have access to it Andrew Smith in his description of building the Stuart "Cygnet" (5A ) details a method of machining of the double one piece eccentric in the Apr '82 issue of Engineering in Miniature, page 377-378. I've sent you a PM.

John

Edited By John Purdy on 07/04/2023 17:56:31

[JasonBModerator @jasonb]

There is not a lot of overlapping metal to be able to pin separate sheaves together particularly on the IP pair as they have to be split in half lengthways and then be screwed together as they have to fit between crankwebs.

As there are 3 pairs to make the time spent on a simple jig like the one shown in Jo's posts I liked to is probably worth the effort

[RedsetterParticipant @redsetter]

If they are split eccentrics, they do not need to be pinned together, and the angles can be set individually after they have been fitted to the shaft.

[JasonBModerator @jasonb]

There is only just room to get one clamping screw in each as they are quite small.

EDIT forget that It's the compound so not split, My link to the jig was for one being used for the triple. But they are even smaller than the ones on the triple

 

Edited By JasonB on 07/04/2023 20:34:58

[Ramon WilsonParticipant @ramonwilson3]

Hi Richard B,

I rebuilt my double ten for a steam launch a few years back and made separate eccentrics for each end with small grub screws to lock accessed through the eccentric strap for setting. I made them from free cutting mild steel and off set them in a simple fixture held on the face plate to ensure accuracy of throw one to another and squareness to bore. The setting proved simple and easy to do on final set up.

I described this here on the build log on Model engine Maker forum at the time – you may find it useful.

Best – Tug

PS Though I haven't described it I have used the same method to make the eccentrics on the 'Marine Condensing Engine' thread described elsewhere on here to equal success.

Edited By Ramon Wilson on 08/04/2023 10:34:49

[Richard BParticipant @richardb44403]

Thanks for all the ideas, seems split eccentrics may be the best way to go – will report back when I have tried a few ideas out.

Here is a couple of pics of my steam boat (still unfinished) with the Double Ten – rather dusty ! Still thinking of a vertical boiler ?

Not sure why the pics are above and below text – sorry.

[Author]

Posts