- Jun 5, 2009
- Reaction score
- Camp Verde, Arizona USA
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 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.
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…