# Mini double-acting beam engine



## crueby (Jan 6, 2014)

While sketching up plans for my next big project, a 1" piston diameter, 2" throw double-beam engine, I decided to see how small a double-acting beam engine I could make, as a quick project since it will be a month or so till I start on the big one (in the middle of a carving project that I dont want to lose momemtum on).

Wound up with a 1/4" diameter piston, 3/8" throw with a 3" beam. Not a record setter by any means but the smallest slide valve I had ever made (3/32" valve throw). Came out to be a nice little runner - the throws were so short that I got away without needing a parallel-motion linkage, and it runs down to a very slow speed, which surprised me. Below is a video of it running. Having made a couple spool-valve engines and some slide-valve, I am now sold on the slide valve setup - much less air leakage, runs slower, just a little more complex to make.

In another month or so I'll put up build photos of its bigger brother.

[ame]http://youtu.be/6holUwugJAM[/ame]


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## mechman48 (Jan 6, 2014)

Hi Crueby
 I like your double acting beam engine, nice work; would there by chance be any plans available so that I can attempt one myself, if so would very much appreciate a set via e-mail.
 Regards
 George


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## crueby (Jan 7, 2014)

mechman48 said:


> Hi Crueby
> I like your double acting beam engine, nice work; would there by chance be any plans available so that I can attempt one myself, if so would very much appreciate a set via e-mail.
> Regards
> George



Hi George,

Sorry, but I do not have plans for this engine - it was a seat of the pants build. There are a couple other small beam engines in the forums and plans in downloads section.


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## GailInNM (Jan 7, 2014)

Very nice.  I like small engines and this one is great.
Gail in NM


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## ChooChooMike (Jan 30, 2014)

Do you have a build thread ? 

Very nice !!


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## crueby (Jan 31, 2014)

ChooChooMike said:


> Do you have a build thread ?
> 
> Very nice !!



Unfortunately while making this one I did not take any pictures - was done in one short session in the shop on the spur of the moment and did not think to take any. I was mainly curious as to how small I could make a double-acting engine, and this was about as small as I could go without getting into much smaller screws - the fastener size (2-56) really determined most of the dimensions. The slide valve itself is only 1/8" wide, little under 3/16" long overall - had to mill the recess in it using the tip of a nbr 1 center drill, and cut the fins with a jewelers saw. The design is standard double acting type, just done small. 

Could be a fun challenge to see what the smallest someone could go -i am sure it could be done smaller than this one. One interesting thing that helped is that the throw is so short that I got away without needing a parallel motion guide on the piston, since the angle travel on the connecting rod was so small.

The next engine, its much bigger brother, is in the planning stage now, and will have a full build thread with plans (hand drawn at least). That one will be a twin beam, 1" bore X 2" stroke fancy engine. Am currently working on a model/carving project for the next couple weeks, am planning on starting the next engine after that.


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## RichD (Jan 27, 2015)

Nice job and a smooth runner too.
Rich


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## davidl (Mar 13, 2015)

A very nice job - much smaller than I can attempt these days.  I came to machining very late in life, when hands and eyes are not quite they used to be.  I decided 3mm nut and bolt was the smallest practical fastner for me and that determines the engine dimensions.  I usually scale designs to suit or in many cases have a lot of fun designing and drawing up something based on a photograph.


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## m_kilde (Mar 15, 2015)

Nice little engine and a good runner.

Funny to see the massive air inlet compared to the rest of the engine


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## crueby (Mar 15, 2015)

m_kilde said:


> Nice little engine and a good runner.
> 
> Funny to see the massive air inlet compared to the rest of the engine



Yeah, kind of throws the scale! The engine itself is only 2-7/8" tall. Someday I'll carve a giant thumb to put in the corner of the pictures!


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