3d Printed Double Acting Engine

[a41capt]

I have some experience with 3D printed cylinders and pistons. The models are nice, but running them presents two problems - wear and heat.

If the pistons and cylinder are left as-printed, they are anything but smooth, even in the best, most finely tuned printers. Running the model in this condition will very quickly wear the piston/cylinder to the point where they won't hold air at any pressure. Even operating the the model by hand will put it into this condition fairly quickly.

It will help some to smooth (drill, turn, ream, bore, hone, depending on the quality of the model) the cylinder, and to a lesser extent the piston, and to plan for a lubricated O-ring piston ring or two to get the longest useful life out of the model. At this point the model isn't entirely 3D printed, rather enhanced after printing, but is certainly a better model. If you are going to this trouble, enhancing the rotating joints with metal pins is also a good idea.

If the model is run fast (more than say 10 rpm) for too long (more than say 10 seconds at a time) the friction will cause the cylinder/piston plastic will melt and seize together, ruining the model. Remember that you are dealing with plastics that are designed to melt at very low temperatures (relatively speaking). It doesn't take long to build up this heat with friction.

I have successfully "run" models that are entirely 3D printed for a few seconds at a time, at very low speeds, using bicycle or foot pumps, and only to illustrate how they work. Even at low speeds, an entirely 3D printed model has a total useful run time of maybe 10-20 minutes.

Thanks, all sound advice for sure! I used a brake cylinder hone on the cylinders to smooth them (I use the same type of tool on my CI cylinders for my internal combustion engines), and lubricate with a small bit of olive oil. All of the movable joints are fastened with 4-40 screws, but the crankshaft does not utilize bearings in the base, so it is prone to over heating and deformation if rotated too quickly. I ran it in with a drill motor and found this out!

I have a large number of dashpots (glass cylinders with graphite pistons) and have considered adapting one to an engine like this, as well as crank bearings, to promote longevity. This one is a proof of concept, was a fun print and build, and will be used at very low RPM to “amaze and entertain” myself, friends, and family.

Thanks for the thoughts, I have palexander609’s vertical twin on the printer as I type this, and it too will entertain and amaze!!!

Now, to get back to work on Rudy’s Pioneer…

John W

 

[a41capt]

Hi John,
Do you have a garden sprayer of the type with an air pump on the top which pressurizes the liquid. If so, you can use it to run your engine. The easiest way is to run the sprayer empty a few times to ensure only dry air is coming out the tip, then connect the tip to your engine using silicone tubing. The tubing is available from car parts shops in various diameters as petrol lines. Doing it this way means you can use the valve on the sprayer to turn the air on and off and throttle it to a certain extent. I have modified an old one to run some of my engines.
Regards,
Alan

Now THAT is a unique solution to the air problem! Cheap too in that I have several lying about used for weed control around the acreage (a never ending task I’m afraid).

Thanks for the tip Alan, I’ll give it a try!

John W

 

[a41capt]

Hi John
Could you possibly measure something for me ? What is the largest part?
I have a rather small printer. 150mm square or 6" square envelope.
Will it fit on my printer?

Thanks in advance!! Looks like a fun print, I would like to try it.

I remember seeing a foot operated bicycle pump that was rather large. 4-5" bore with a similar stroke. A big pedal to stand on to pump. You could hook that up to your tank. And then put the foot pump in front of the table at shows Make the kids pump it up. I'll see if I can find a picture of one.

Scott

Hi Scott, thanks for the thoughts regarding the large displacement foot pump.

As for the size, you should have no problem with any of the parts. The two largest parts are the flywheel (4 5/8”), and the base (5 1/4”), and your 6” print envelope should have plenty of room to handle them.

John W

 

[a41capt]

Wow, you've got a junk yard where you can go 'shopping', that sort of thing ended around here a while ago.

Not only a junk yard, but a recycling yard full of mill ends and other useful “trash”! The owner and I have become best buddies since I took a couple of my IC engines out and ran them for him. Scrap prices for “mystery metal” make my creations more affordable, and that’s something EVERY married retiree (and his wife) loves.

John W

 

[L98fiero]

Not only a junk yard, but a recycling yard full of mill ends and other useful “trash”! The owner and I have become best buddies since I took a couple of my IC engines out and ran them for him. Scrap prices for “mystery metal” make my creations more affordable, and that’s something EVERY married retiree (and his wife) loves.

John W

A while ago I printed a version of Elmer Verburg's Baldy engine, it's not double acting and it's not all printed but the Idea is there. The parts printed were the frame, crank counterweight and piston.

 

[a41capt]

A while ago I printed a version of Elmer Verburg's Baldy engine, it's not double acting and it's not all printed but the Idea is there. The parts printed were the frame, crank counterweight and piston.

That looks great! I’m redrawing Elmer’s Geared engine with the thought that I’d print everything except a cylinder liner and piston (I’ll use a glass and graphite dash pot), and bearings. I’ve already drawn the ring and spur gears and will start on the rest in the next couple weeks.

I’d like to have everything done by late spring, and will post the completed engine when completed.

Once again, that’s a GREAT looking engine!

John W

 

[Leonardo]

Thanks, perhaps I’ll find some info on a pump that’s big enough to do the job, quiet enough to keep from overshadowing the engine itself, but still small enough to put in the base under the engine when on display.

Time to keep looking!

John W

Hi all,

I started a new thread yesterday to share my experience and discuss another alternative but found that it seems to be no much interest in the subject (because I have not received any comments on that thread).

So I just would like to invite you to visit it...

https://www.homemodelenginemachinist.com/threads/small-air-power-supply-for-engines-models.34946/

 

[a41capt]

I finally got some air to this thing, in a rather half-@$$ fashion, but good enough to show it runs.

John W

 

[minh-thanh]

Another way to make engines
Thanks for sharing !

 

[a41capt]

I’m still working on the CAD stuff for Elmer’s #5 (geared) engine so I can print most of the parts. I’ve got the ring gear and pinion gears drawn, as well as most of the base. These, along with most all of the other parts, will be exported to .STL files to send to my printer. I’m still torn between a printed cylinder/piston or a cast iron or copper insert in the printed shell. I’ve even been knocking around the idea of a glass cylinder and graphite piston.

We shall see how it develops, but for right now I’d better concentrate on completing Rudy’s Pioneer!

Thanks for the comment Minh-Than,
John W