Winner Pm Research Engine #7

[tomw]

Next was making the two valve linkage bits. These are made from 3/16" brass hex stock. This part is just a little bit of turning, drilling and tapping for the valve connecting rod, and drilling for the retaining pin.

The plan for the valve linkage.​

The linkage has been turned to the correct diameter for the correct distance, and is now being parted off.​

The part was put back in the chuck and held by the turned portion. It was then drilled and tapped for the valve connecting rod.​

The last machining step was to drill the cross hole for the keeper pin.​

The valve linkage bits in a soft, romantic focus.​

Next was making the two packing nuts. These are made from 1/4" hex stock. The stock is turned down to a .25 for the correct length. Then the clearance hole for the piston rod is drilled through. Then a hefty chamfer is placed on the end, and the turned portion is threaded with a die. Unfortunately, I did not have a very good die for this, so ended up using what is really a thread chasing chasing die. It worked fine, but is not ideal. The part is parted off, and the next one is made.

Packing nut raw stock and drawing.​

Turning the stock down to .25 for the specified distance.​

Chamfering the packing nut prior to threading.​

The clearance passage for the piston rod was center drilled and then drilled through.​

I ended up having to use a thread chasing die to thread the nuts. It worked, but was not ideal. Here the die is being held perpendicular to the part with one of my button die holders.​

The finished packing nuts sitting in their respective gland retainers.​

The last bits were 1) trimming the included copper pipe for the cross tube to the correct length and B) making a few pipe nipples for the steam/air plumbing.

The manifold tube trimmed to the correct length via parting off in the lathe.​

Various pipe nipples made for the steam/air plumbing. These are made from 3/16" model pipe and threaded 3/16-40 MP using a button die.​

And after all this, spread across 16 posts, I ended with 61 machined pieces. Next up, assembly!

All the bits necessary to make a PMR #7 steam engine!​

Cheers,

Tom

 

[tomw]

I ended up not taking any pictures of the final assembly. It is pretty straight forward. I would like to show you a picture of the final engine, but I can't seem to download any photos from my iPhone. So, instead, I am posting the video below showing it running on air at about 5-10 psi.

Thank you to everyone that has been following along. I really appreciated the encouragement and advice.

The next little project is replacing the 5-40 machine screws with 5-40 stainless or brass hex bolts. I don't like the look of the screws, and replacement hex head bolts will be simple to make. I think I will use SS for all but the crosshead caps. I think I will do those in brass or bronze (though I am not sure where to find bronze hex stock).

Cheers,

Tom

 

[Dataporter]

Pretty darn cool! Thanks for sharing your build. -- Dave

 

[T Bredehoft]

Congratulations, achievement is its own reward. Keep on playing, and keep on with threads about your progress. Even if we don't do the work we enjoy the products.

 

[kvt]

Congrat on getting it finished and running. When I get my garage back in shape then I will get to work on mine again. Problem is I normally do not do pictures and stuff so I will have to work on it. Again congrats, Also are you going to paint it and stuff while doing the screws, or leave it natural.

 

[jumps4]

Great job on the mill engine and a really good build thread.
Steve

 

[kvt]

Tom, question.
did you use th3 3/16 -40 MTP, pipes and fitings, if so where did you get it. or did you use the 1/6x40 ME or something like that.

 

[tomw]

Data, T, Ken and Jumps, thank you for your kind words. I really appreciate it.

Ken, I used a tap and die for 3/16" ME straight threads that I got from PMR.

I got confused in my posts above about what I was using. I just checked what I actually bought! Sorry about any confusion for the readers.

Tom

 

[kvt]

I was looking trying to find the MPTs fo rit and they are hard to come by, and you can by a whole lot of others for what it cost for MTP tap and die. But I was trying to figure out if I was to build this into a display that had things like the Tank, boiler, and water pump etc, if the ME would work OK or if the MTP would be required. Did the ME ones seal up good when you put it together?

 

[tomw]

Ken,

With a little blue locktite the ME connections sealed up great, but I was running with air. I would think that a bit of teflon tape would have also worked fine.

These are very low PSI engines, so your main worry is the velocity of the gas. I think any kind of thread sealing compound should be adequate.

Are you going to run your engine with steam? I am not sure how that changes things, as the PSI would be the same, but the temperature would be much higher. Would metal expansion under heat be a problem? I can figure it out, in an ideal situation, if you would like. Sort of like deciding the acceleration of perfectly spherical horse in a vacuum.

Or, if your a Monty Python fan, a perfectly spherical rabbit*...run away!

Tom

*I used this very example in grad school.