First Model Engine - Elbow Engine

[Scott_M]

Well I'm gonna do it. I've been hanging around here long enough, I guess it is time to actually build something. I am still about 10 years from retirement so shop fun time is limited. I spend all day in the shop working to pay bills but am determined to sneak in some fun time. I have been looking around for plans for something fairly simple and somewhat interesting at the same time. When I found the elbow engine I thought it would be a great place to start. I found a set of plans and solid modeled it. It really is pretty simple. Not too many parts and none of them are very complex. Plus it is pretty cool to watch. When I first saw it I was thinking "How can that work?" It looks like it would just tangle itself up. So it intrigued me, that is good. I think I have all the needed materials on hand. I have a nice 3D model that works so now all I need is some time. I will try to get pictures along the way and document as best I can.

I uploaded an animation of my solid model it should be below. I also did a high quality rendering and will attach it as well. I hope the finished model looks as good as the render !

Scott

[ame]https://www.youtube.com/watch?v=bVY3dt1LNdo[/ame]

 

[vederstein]

Scott,

Alignment on these suckers is critical. Last year I tried to make one and either (probably both) my skills weren't good enough or my tooling was suspect. It looked ok, but it never ran. Make sure you have enough engagement on the pistons so that they won't bind in the cylinders.

So I wish you good luck in your endeavours. I hope you have better luck than I.

...Ved.

 

[Scott_M]

Hi Ved

Thanks for the heads up. But I was pretty sure alignment would be real critical on this design. After I finished modeling and started my assembly, things were not going together well. It turned out one hole in the entire assembly was out by .00027" and it would not go together. So it was pretty apparent that square, true and perpendicular are the keywords here. My equipment is good and my skills have kept me in business thus far, so I hope I have a good chance on this. My biggest concern is bending the pistons to a perfect 90. I have a tubing bender like fixture in mind to do this. but time will tell. I usually start a project like this with the most worrisome parts first. So I do believe that the pistons will be first.

Thanks again for your input !

Scott

 

[Brian Rupnow]

Scott_M---You have chosen one of the most difficult engines out there for your first engine. Good luck and some advice.--Try a simple wobbler first.

 

[Scott_M]

Hi Brian
I am not afraid of close tolerance work, have been doing it all my working life. Is their something inherently wrong with the design? That makes it a hit or miss proposition ( no pun intended ) on weather or not it will run ?
I have never built a model engine before but I do believe that I have made far more complex and tighter tolerance assemblies in my previous endeavors.
In any case I do like a challenge. And I am going to persevere. And if the model engine gods choose to smile upon me then all is good.

My compressor puts out 150 psi and if that's not enough I can always hook it up to the argon bottle on my TIG welder @ 1400psi That ought to get it going ! just kidding

Thanks for your concern and hopefully I won't be eating crow.

Scott

 

[toolznthings]

Hi Scott,

Knowing you I'm sure you will get the engine to work, but I got more satisfaction building the three engines I have pics of under the " engines " listing. The elbow engine I did a few years ago with multiple pistons worked o.k. but never was a keeper. Nice to see your posts !

Brian & Tormach in Kent

 

[Blogwitch]

Scott,
Please don't take a cavalier attitude towards what looks like a very simple engine. I have known a lot of people who have tried to make this engine, and very few have made a running version.

With regards to bending the pistons, I just 'waisted' mine in the middle, heated the thinned down part until cherry red and then bent it around a rod held in a vice. You will find that just dropping one gently on the bench will knock it out of square so that the engine just locks up. You have to gently tap one end onto a hard thing and that will gradually get it square. It took me a few days until I could get it to rotate freely either way under pressure.
BTW, I would suggest when it is assembled, you don't try to turn it over by hand using the flywheel, even that will be enough to knock the pistons out of square.

Here is mine running, unfortunately, like most my engines, I have given it away to someone who liked it.

https://www.youtube.com/edit?o=U&video_id=5ZRKNlY7enM

John

 

[Scott_M]

OK
Concerns are duly noted.

Brian ( Kent ) Good to hear from you ! hope all is well.

John
Your link is a little messed up it should be [http://www.youtube.com/watch?v=5ZRKNlY7enM] It looks like it runs great.


I will keep my progress updated.

Scott

 

[mayhugh1]

Go for it Scott. The final 5% of the build might take 95% of its time, but with patience you'll have something few others have been able to accomplish. - Terry

 

[Scott_M]

Thanks Terry !

 

[Scott_M]

I had some time today to actually make some parts. As I said I started with the pistons. I made a couple extra while I was at it because I was not sure how the bending would go. It turned out that was a good idea. I bowed one while bending. I was also unsure if I would be able to get a consistent bend radius or if I could hit the specified radius so I left the legs a little long and will mill them to length after they are bent. I'm glad I did, they are all a bit different. I made a simple block to hold them and bored a rod to bend with. I heated them with a little oxy. acet. torch. After the initial bending ( by eye )I trued them up checking against a 1-2-3 block and got them real close. I then checked them in the mill with an indicator. I got them all within .001" except the bowed one. I had also turned and reamed a small piece of brass to check my reamer size against the stock I was using. With the .250" reamer I have about .001" slip fit. I am thinking that may be a bit too tight. I also have .252" - .253" and a .254" reamers if it turns out I need more wiggle room. I still need to mill the ends to the proper centerline length. So far so good.

Scott

 

[toolznthings]

Hi Scott,

Wish I would have seen plans for the elbow engine you are doing. The one I did was five pistons and they were .500 diameter. Never ran good and lost way to much air. I did my pistons pretty much the same way you did yours.
Looks good !

Brian in Kent

 

[Scott_M]

Hi Brian
Thanks. For reference the cylinders are 1" dia. and the flywheel is 4".

I saw a video on YouTube where someone made one out of a .44mag cylinder I thought about it, but decided to go with fewer cylinders.

Scott

 

[Blogwitch]

Scott,

Even though you have checked them for squareness, I would almost guarantee that by the time you use them, they just won't do the job, you might have to adjust each one individually to get the engine to turn over correctly on pressure.

If you have DRO's fitted, don't be tempted to use the PCD function on the cylinders, as even being a minute amount out of square will kill any chance of the engine running. The only real way is to use an RT that has also had it's top face trammed to make sure it is perfectly level before starting, and make sure your mill head is also perfectly trammed at the same time.


John