Going to build my first engine!

[clevinski]

Hi, All,

After lurking for a while, and gaining some more machining experience, I've finally decided I am going to attempt my first, small model engine. For a first attempt, I want to keep it as simple as possible, and thought I would go with a wobbler. I found plans from Western Kentucky University for what they describe as a "Lucy"-style wobbler. Any comments regarding whether this would be a good first engine project? It seems simple enough.

I recently read someone's comments on another member's design where two things were pointed out that seem to be lacking here.

First, this design seems to omit any packing. Is that an issue here?

Second, the piston lacks any spacer to keep it a fixed distance from the crankdisk and thereby prevent any side forces which could increase friction between piston and cylinder and accelerate wear. Perhaps this isn't an issue because the piston is the same diameter for its full length?

Anyway, I am looking forward to working on my first engine, and want to thank everyone here for the education I got reading your posts!

 

[crueby]

Hi Charlie,

On a wobbler, the end of the crankshaft usually just 'floats' on the crankshaft, finding its own position since the piston holds it in place horizontally. Even on a more complex engine the same is essentially true. It is important to get the crank pin as square to the crankshaft as possible - if it has an angle it will torque the piston back and forth.

There is no packing, it depends on a nice close sliding fit of the piston in the cylinder bore, and a smooth surface of the cylinder on the plate along with the spring to hold pressure.

Good luck on your first engine!

 

[vascon2196]

Charlie...I have built about a dozen of the "Lucy" style engines and have had my students build them each semester for the past 6 years. This engine is perfect for a first time engine. It has very little parts, can handle tolerance errors, and gives the builder the ability to make changes on the fly.

Here is an article I wrote in Digital Machinist Magazine a while back.

Thew original plans can be found online...Lucy the See-Thru engine...because it was made from Lucite (clear acrylic).

http://www.neit.edu/blog/wp-content/uploads/2013/02/Vascelanos.pdf

 

[clevinski]

Crueby, Chris,

Thanks for the suggestions and information. BTW, I love the transparent cylinder!

 

[Tin Falcon]

that would be a fine choice for a first engine.
no need to worry about side loads or packing. you can always ad a washer or spacer if you like.
My lucy has probably ran a few hundred hours at this point had it over ten years,
Tin

 

[robcas631]

Vascon, Excellent article!

 

[BronxFigs]

Just as an alternative...check out the "Little Husky" steam engine. Also a very simple, bar-stock design.


Frank

 

[clevinski]

Thanks, Tin!

Frank, the Little Husky looks like a great retirement project, but I think, with my limited machining expertise, I am going to start with the simpler Lucy. But I see a Little Husky in my future! Thanks for mentioning it...

 

[Tin Falcon]

The

McCabe Runner

Is another easy fun one.
Tin

 

[clevinski]

Wow... That McCabe Runner is really old school! Thanks for suggesting it...

 

[Tin Falcon]

You can make them in clear plastic as well here is one of my Builds from the McCabe plans.

Have fun
Tin

 

[clevinski]

Tin,

Beautifully done!

 

[clevinski]

Hi, All,

I have a couple of what are probably newbie questions, and I'm hoping I can get some advice here.

First, the Western Kentucky University wobbler plans specify a bronze bushing for the crankshaft where it passes through the valve plate. Does this really need to be bronze, or can I turn a brass bushing for this purpose instead? I was thinking of turning it from brass, pressing it in place, and then drilling an oiling hole from the top to allow lubrication to get into the running surfaces, but maybe that's overkill.

Second, I read in a post somewhere that one should select materials so that running surfaces were always dissimilar materials. This can lead to some oddball combinations. For example, I am going to make the cylinder out of aluminum, since I have material about the right size. The piston can then be either brass or steel, both of which I have, but if it’s steel, does that mean that the mating crankdisk pin would then have to be something other than steel? In my limited experience with loaded moving parts, running parts are often steel on steel but lubricated. Another issue; the valve plate in the plans seems to be aluminum, and the cylinder seems to also be aluminum. Since these two surfaces are held in contact with each other during operation, but they are like materials. Would this be an issue? I assume that the "like on like" restriction is intended to prevent the wear from occurring equally on two parts, but I'm not sure if there's more to it.

Many thanks in advance for any comments...

 

[Swifty]

Hi Charlie, with a wobbler a brass bush would be no problem. The problem with similar materials running on each other is galling. In my opinion you would have no problem making a wobbler out of the same material, there is not a lot of load or speed involved, and I doubt if the speed would warm up any parts.

Paul.

 

[Tin Falcon]

Do not worry too much about correct materials. These rules of thumb are best practice for working engines.
And remember you do have a shop if a part wears you can make a new one.
you can always put a brass tube sleeve in for the cylinder bore. in an aluminum block . I did that for my McCabe runner. (the first one.
cylinder to frame we often beak the rule and use like materials.

In engines that actually run on steam or in a pump galvanic corrosionfactors needs to be considered.
tin

 

[clevinski]

Paul, Tin,

Thanks for the valuable input!

 

[clevinski]

Hi,

Anyone know where I can obtain the barbed hose fitting and hose used to connect my air supply to the wobbler? I could make one, but the effort seems disproportionate to the result if I can get one locally. Is this maybe something from an aquarium store?

I finished the piston (very easy) and am almost done with the cylinder. I was, perhaps, overly cautious when clamping the cylinder to drill the bore; photo below. (In my preview, this image keeps coming out inverted, but the original is fine. Hopefully it's just an issue in the preview...)

I got the missing base plate and valve plate material from Exact Metals. Total of $16 for two aluminum plates 1/2" x 3" x 6" and four pieces of 1/4" steel rod 12" long, INCLUDING shipping. I think these guys are my new favorite metal supplier!

 

[clevinski]

Hmmm... Apparently it's NOT just an issue with the preview...

 

[vascon2196]

I sometimes use quick-disconnect fittings from McMaster Carr or any #10-32 air fitting for my air engines.

 

[clevinski]

Thanks, Chris...