Author Topic: Marcher, a twin cylinder marine steam engine  (Read 4053 times)

Offline Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #60 on: November 01, 2018, 09:36:06 AM »
Thank you Thomas, that was a really fast reply. I hardly had my update finished when I noticed your reply.

Offline Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #61 on: November 15, 2018, 07:49:35 AM »
Next update includes fabrication of eccentric straps with rods and the expansion links.

A common casting strip for all 4 eccentric straps is provided. First it was milled into correct thickness. After that all the straps were separated from each other with a slitting saw. Holes for connecting bolts were drilled, and the straps were divided into upper and lower parts again with slitting saw.

It was very difficult to find a correct datum for boring the holes for eccentric sheaves, and finally I decided to use pieces of self adhering paper where centrum lines were drawn to show this. Straps were attached into 4 jaw chuck and centred as accurately as possible, and boring made.

Eccentric rods were turned conical using 3 mm silver steel rod, M2 threads cut at both ends, and rods installed into straps with threads & epoxy glue.

Expansion links were made using 3 mm mild steel. First I thought to machine them in the milling machine using rotary table, but finally decided to saw them out using jeweler`s saw. Quite slow process and many broken saw blades, but finally also this task was completed.

Offline Jo

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Re: Marcher, a twin cylinder marine steam engine
« Reply #62 on: November 15, 2018, 09:03:35 AM »
It was very difficult to find a correct datum for boring the holes for eccentric sheaves, and finally I decided to use pieces of self adhering paper where centrum lines were drawn to show this.

Yes it is very difficult to line up in the centre of the hole  :Doh: I like your use of the paper to fill it in.

I was trying to remember what I did on the Triple orphans I recalled there was zillions of straps to do  :facepalm: .. then I found a pic of using a stencil to draw on a circle so that I could see if the hole looked right, then checking again after I had got the centre hole round.

Jo
Usus est optimum magister

Offline Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #63 on: November 16, 2018, 08:04:17 AM »
Thanks Jo, that could have been also a very good method to find the right position to bore the hole.

Next a short update. Because I do not own a watchmaker`s lathe to make small screws, I had to find another way to fabricate the eccentric rod pins. First I tried to make them from 3 mm silver steel, but that didn`t work.  The needed thread is M2, and diameter of the cylindrical part is 2,5 mm, and then I should make the hexagonal bolt head, not possible with my skills and relatively big lathe.

After thinking hard to find a solution for this, I finally took a 12 mm long M2 bolt, screwed on it 5 pcs M2 nuts and attached that into 3 jaw lathe chuck. Then I turned the nuts into round 2,5 diameter nuts, and screwed those on another, shorter M2 bolt with hexagonal head. And finally secured those round nuts on the bolt with tiny drop of epoxy. And voila, I had the necessary threaded pins for eccentric rods. I have never seen anybody make the threaded pins like this, so this is why I publish this method. It might help some of you with equal problem.

Offline Jasonb

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Re: Marcher, a twin cylinder marine steam engine
« Reply #64 on: November 16, 2018, 08:53:58 AM »
The other option for those pins is to drill and tap the end M2 and screw in a bit of threaded stock, you get a thread all the way upto the shoulder. make the rest from hex stock if you have it or use larger round and hill the hex after turning the 2.5mm dia section.

Other option for the straps is to hot glue or superglue a bit of thin metal sheet to the face then you can scribe and punch the ctr position and use a spring ctr and dti to clock it in which is more accurate then a cross on a bit of paper or tape

Offline Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #65 on: November 16, 2018, 09:23:13 AM »
Thanks Jason for your comments. I agree that there must be several ways to make these pins, and I am sure that you more experienced guys have much better solutions for this. But because I am relatively new to the hobby and do not have long experience about machining, I have to find easy enough ways to do things.

And I am quite sure that your method of scribing and clocking the center for eccentric straps is way better than my humble method. But when making my first steam engine I have to find simple ways to make things and learn and learn again from you more experienced guys.

Offline Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #66 on: November 23, 2018, 06:00:11 AM »
A little bit filing sanding and polishing here and there, and finally the engine rotates and all parts are moving nicely.  I hope anyway that there is not too much slop in all the various joints to prevent easy running of the machine.