PMR #3 started.

[tevans9129]

My first venture into model machining and I have an issue. What am I missing with the figures for this item?

​

 

[Tug40]

I just finished my PMR#3BI yesterday, ran it in with a drill motor & plenty of oil.
Got it running under it’s own power today.
I followed the prints & tried to get the measurements spot on.
When I tightened the crosshead caps i noticed the cross head would slightly bind up, so I left the screws finger tight while I ran it in.
After running under it’s own power for half hr or so I was able to tighten the crosshead caps down & there is no binding up now.
I will use a tach on it tomorrow, see how low it will idle.
It runs very smooth & has a wide RPM range.
This is my first engine build, took a lot longer than I thought it would, but was big fun.

 

[tevans9129]

Perhaps I did not make my point clearly so will try again...if I followed the dimensions on the drawing correctly, and it is possible that I did not, there is no way the model can work.
This image shows the crosshead as per the drawings. The piston rod is at the bottom of the crosshead.

The next image shows the crosshead after milling a rabbit to allow the crosshead to set lower on the rails and connects correctly with the piston rod.

Has no one else faced this dilemma?

 

[Tug40]

Read the prints again.
The .094 is machined off of the base, not the crosshead.
Although I do not see why it would not work the way you did it.

 

[Tug40]

Or you could make a new crosshead.
I do not see why a chunk of aluminum or steel would not work.
Do not feel bad, I finished the eccentric hub, then screwed it up, & had to make another one.
All part of the fun, eh?

 

[SailplaneDriver]

Perhaps I did not make my point clearly so will try again...if I followed the dimensions on the drawing correctly, and it is possible that I did not, there is no way the model can work.
This image shows the crosshead as per the drawings. The piston rod is at the bottom of the crosshead.

View attachment 121492

The next image shows the crosshead after milling a rabbit to allow the crosshead to set lower on the rails and connects correctly with the piston rod.
View attachment 121493

Your photo shows the base flat where the crosshead slides. There should be a rabbit cut for the crosshead to fit in. It's at the same depth that you decked for the hold downs. The drawing confused me as well for a while until I noticed the dashed lines with the "f" on them.

I'm waiting for my replacement cylinder so I can continue with my build after I drilled the steam passages a 0 deg instead of 20 deg. We all make mistakes. It doesn't help that I have a touch of ADD. I need to force myself to evaluate the drawings closer and pay attention to to all the details when working on the part instead of going from memory.

 

[djswain1]

I made lots of little mistakes (design modifications) on my build. It's a learning curve..
I tried to bore the cylinder to size with a two flute (slot drill) end mill, it was great at the top end but I hadn't noticed the finish deteriorated in the lower half of the cylinder. I left the cylinder in the mill vice & made the inboard head to plan and the raised registration face was a lovely fit in the top of the cylinder. Only when I removed the cylinder from the vice did I notice the poor finish in the lower part of the cylinder. Not too worry I hadn't made the piston yet and figured I could bore out the cylinder enough to get a good finish and still get the piston to fit OK. So I bored the cylinder in the four jaw chuck (should have done that in the first place) and made the piston which fitted fine. It was then I realised that the inboard head registration protrusion no longer centerd itself in the larger bore. I could have made a new inboard head from bar stock but instead put a steel pin/dowel in the end of the cylinder and corresponding hole in the head which gives enough enough location to centre on.
I milled the cross head guides too wide, but as the piece of brass supplied for the cross head (yet to be machined) is rectangular I can turn it through 90 degrees and it fits well between the "guide rails"
My latest mistake was milling the crosshead caps.. I had them both in the vice and was milling the underside with a 4 flute end mil, on a climb cut the cutter dug in without me realising and pulled the caps up out if the vice leaving a big gouge well below where the fished surface should be! I'm going to try & salvage them with JB weld but may have to make some custom ones if that doesn't work or try and order a new
pair!

 

[tevans9129]

Much thanks to all for your comments and especially the pictures as I see my errors now. I thought about redoing the crosshead as per the drawing but I believe the way that I have it now may work and I kind of like the looks of it. I can always redo it if a problem presents itself. I am making a number of items from my stock rather than using the parts that are in the kit so when it is all done and if needed, I can go back and use the parts from the kit. I know, extra work but I need the practice.

This has been a real learning experience for me and thanks to the contributors on this forum I am learning much quicker and less painfully than I otherwise would have.

 

[Tug40]

I also like your crosshead the way you machined it.
I suspect your engine will run just fine like that.
These are good little runners, mine runs fine between 200-1500rpm.
The sweet spot seems to be 300-700 on mine.
Keep us in the loop on your progress.
Cheers

 

[tevans9129]

My first one completed…almost. Some parts need to be adjusted to the proper size. And only 14.7 pounds of brass, steel and aluminum in the scrap box.

I wanted a forest green color but out of my wife’s couple thousand cans of paint, there was no forest green.

It was reluctant to run but I was able to coax it into movement before reaching the 175 PSI capacity of my compressor.

I learned a lot and enjoyed my time on the project. Thanks a million to those who post in this forum and are quick to offer help and suggestions. Just a great group of folks.

 

[Eccentric]

Awesome first time project. I completed the PM#1 Steam Engine last December and enjoyed the heck out of it. Yours looks very nice, I like the color.

 

[Tug40]

Tevans that turned out great.
Nice touch on the screws & Oiler cups.
This was also my first model build, i also made some subtle changes.
I used 6-32 socket head screws & used 5 outer head screws.
Although I botched a couple of parts, i really enjoyed this model & these #3 engines run great.
I just started the PMR #5 model, it appears to be a bit more complicated, wish me luck.

 

[tevans9129]

Tevans that turned out great.
Nice touch on the screws & Oiler cups.
This was also my first model build, i also made some subtle changes.
I used 6-32 socket head screws & used 5 outer head screws.
Although I botched a couple of parts, i really enjoyed this model & these #3 engines run great.
I just started the PMR #5 model, it appears to be a bit more complicated, wish me luck.

Thanks for the comments Tug, "botched" is pretty mild for my "mistakes". It was good that I had most of the materials as it was not a game-changer when I messed up. The base, cylinder, crosshead cap and connecter rod were the only items that I used out of the kit. I should have used the 6-32 or even the 6-48 screws as I have a supply of those along with taps and dies leftover from my gunsmithing, to use the term lightly, days back when the Dead Sea was just getting sick.

Good luck with the #5, it should be very interesting. I wanted to start with the #7 but my better sense vetoed that idea.

Next for me is a lower receiver that I need to get milled and put together.

Best to you.

Ted