Here is my "piston rod" on the right of the picture;
On the bottom is a base that sits within a CAST ALUMINUM gas piston's dish area. That is then welded in place to the gas piston face and ground smooth. The gas piston is then non powered and only being used as a piston guide (along with the rest of the short block as a contained lubricated assembly) to move the powered piston within a true vertical plane.
Without going into it in great detail on the head.
The head has 6 sections that separate for maintenance. They are held together with 4 exterior threaded rods similar to a hydraulic cylinder.
The fixed parts are the Vent, Upper top head, Lower top head, Cylinder, Lower upper head, Lower bottom head.
The moving parts are the valves, bearings, and the 2 piece piston rod itself. The piston never touches the wall it stays 1.5 microns off the wall and is guided by the upper and lower bearings.
The working piston is double acting with a central exhaust.
Temperatures within and around the cylinder will not exceed 371C/700F. Max working temperature is 287C/550F.
The force exerted on the piston will not exceed 5039psig. The max working is 4400psig.
The cylinder and heads are made of STEEL. The cylinder is sch120 and the heads will be made of the same material/thickness.
The bearings are SILICON NITRITE.
The piston never contacts the heads in any way.
Working max rpm is 3500. Max rpm is 6000.
The rod that guides the piston controlled by the upper and lower bearings is 1/2" in diameter.
The piston is 2" diameter by 1/4 thick. It has no rings.
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Now that you have a background on to the question.
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In order to service and remove the lower head the "piston rod" itself will need to separate.
The means I am looking at currently are through the use of threaded rod. Where to place that threaded section is the question.
I have two places I can separate the piston rod.
The plan was to have the aluminum treaded section(one piece base/threads welded to the cast aluminum non powered piston) be threaded inside the entire length of the (one piece)piston rod then be retained by a nut/retainer at the top.
This will require perfect machining of both the one piece piston rod internal threads and the male threads of the rod welded piston base.
The total length is less the 10“. But the threaded rod or piston rod are uneven in any part of that will cause increased bearing wear and friction.
It eliminates any chance of vibration working the threads loose. But the complexity of the machining involved has me second guessing if it is the best choice.
The second option(shown poorly in the picture) is only threading a small section into the bottom of the piston rod and some how retaining it.
This allows for easier machining.
But creates a pivot point for increased wear and friction as well as possibly allowing the threads to back out due to vibration which would move the piston upwards causing failure.
I am not a engineer. I am not even a student. I am just a person trying to build something in my garage for fun more then anything. With that being said any recommendations if if I am worrying to much about the machine work involved in threading the entire internal length of the piston rod or any advise in general would be greatly appreciated.
Thank you for your time.
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