AOG's first casting kit the PM 2A

[AOG]

It's time for my next build and I feel ready enough to tackle my first casting kit. I pulled the kit from the closet of castings and proceeded to perform some Jo approved fondling. I decided to start with the frame casting. Overall it looks to be a pretty good casting ( as far as I can tell with my very limited experience.) According to my machining plan I needed to start with flattening the base and establishing a reference point. There was a small problem with that. All of the surfaces were slanted as you can see in the next picture.



I thought no problem and set the part up in the vise and leveled the feet as best I could.



Then I took a good look at that setup and said to my self. "Are you crazy that's just asking for trouble" and promptly redid my setup. I used two parallels for the feet and an adjustable parallel as a jack to level the part.



What I didn't notice is that the casting was slightly cocked to one side. That will will come back to haunt me in later operations. With the bottom flat I put the casting up on parallels and flattened the tops of the mounting brackets.



Then the mounting holes were drilled.



It this point I was sick of having no reference plane so I squared up a piece of bar stack and drilled and tapped them to match the casting.



Then I promptly broke a tap in one of the holes so I flipped the piece and did it all again. I screwed the casting into the plate and put it back in the vise. I used another adjustable parallel to level the part and flatted one side per the print.



Then it was over to the surface plate to mark out the correct heights. I decided I would use the DRO on the mill to find the centerline instead of marking it out.



That was a mistake. If I had marked it out I would have seen my angle problem but more on that later. The next step was to set up the part vertically and mill the casting to height.



That's when I made my second screw up. I forgot to drill the intake and exhaust passages. This to would come back later an bite me. The next step was to flip the part over and machine the bosses for the cylinder pivot and crankshaft flat.



That completes the milling on this part. It's time to drill the holes. The part was flipped in the vise and the pivot hole and crankshaft hole were drilled and reamed.



Next I drilled the four port holes. That's when I realized I had forgotten the intake and exhaust passages. The ports were supposed to break into those passages and they obviously didn't



I pulled the part out of the vise and noticed my second problem.



If you take a look you can see that the to hole is in the center of the boss and be bottom hole is off to the right. Since the bosses are basically centered in the casting and I only translated in the y axis to drill the bottom hole it is obvious that the casting is slightly cocked even though visually it looks fine. I thought about plugging the hole and redrilling the hole but decided not to. It won't be visible behind the crank and flywheel but it's just something else to watch out for on castings. I went back to the mill and drilled and tapped the intake and exhaust ports.



It turns out that I screwed that up too. One side went down and intercepted the port holes correctly. The other one was totally off. In hindsight I think I used two different places on the casting to find the centerline. The difference in location was enough to throw the holes out of line.  Thankfully good old Elmer came to the rescue. To save the situation I used the Elmer method of cross drilling and plugging to save the day. The casting was flipped on it's side and connecting holes were drilled.



Then the outer holes were plugged.



When the locktite cured I filed the pins down to match the contours of the casting. Meanwhile I set the casting vertical and drilled the oil hole for the pivot pin.



Then I use some angle block to tilt the part to 45 degrees and drilled the oil hole for the crankshaft.



Here is the final casting after filing the pins.



Till next time.

Tony



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[crueby]

Lots done on it already!   

Wonder if the mistakes could have been avoided by more casting fondling time?   

[b.lindsey]

All in all I would say that is a great start Tony. The slight angle of the base casting shouldn't present a problem. Just think of the lessons you have already learned though. Well done!

Bill

[Gas_mantle]

Good to see you've made a start on your engine Tony, I've yet to make one from castings so I'll be interested to follow along with your progress.

As for drilling and plugging cross passages I've used that method a couple of times and find it works fine.

[Ken K]

  I have learned,over time, that some vendors, castings are not the best. I get the base flat, and mount it to a ref. plate, like you did. Paint the whole casting with layout ink, and with flat plate, lay out the whole casting, before I make any more cuts.
 With PM, I don't think you will have any problem, but I have found some vendors casting, are not the best. There has been cases were, during the layout, there is not stock, to cut, in some part of the casting. That is when things get tricky, and you have to determine what you need to do, to get a part, with this casting. In one case, the only thing I could do was cut a washer, the right diameter/thickness, to take up, the missing metal.
Ken K

[Flyboy Jim]

Good write-up Tony.  I'm following closely. Your build thread is going to be very useful when I build mine.

Jim

[mklotz]

Wonder if the mistakes could have been avoided by more casting fondling time?   

Perhaps, but a well-thought-out, written order-of-operations machining schedule would probably work better.

As Tony and others have shown, when working with castings, it's worthwhile to have some sort of bolt-on reference plane(s).

I discovered this trick early on too and decided to build a permanent piece of tooling to enable me to bolt a three-axis reference to a rough casting to maintain orthogonality between casting surfaces that require such.

My final design has already been documented here...

http://www.modelenginemaker.com/index.php/topic,385.0.html

but I'll repeat the reference to it for the benefit of future readers of this thread.

[AOG]

Time for an update on this project. The next part to be tackled was the cylinder. I started by facing the top side to length and then facing the bottom to .010 inches short of length.



Next I drilled out the casting to 3/8 to fit my boring bar.



Since I centered the casting on the outside rim the cored in hole was not quite in the center. I bored the hole concentric with the outer rim. On the last pass, I took a skim cut across the face to ensure that it was perpendicular to the bore.



Then I reamed the hole to size.



Next I used a brass lap and some timesaver to remove the machining marks



The cylinder was then rotated, semi centered and faced to length.



Then over to the mill where the part was leveled.



Then the ports and pivot hole was drilled and the pivot hole tapped.



The cylinder was put aside until the covers were completed. Speaking of which the next part was the top cover. It was roughly centered in the lathe, faced and the center boss turned.



Then the boss was chucked into the collet chuck and the outer rim turned.



The part was superglued to the cylinder and drilled to tapping size.



Heat was used to separate the parts and the top cap was drilled out to clearance size using the DRO bolt circle function and the cylinder tapped



The next piece was the bottom cover. The part was roughly centered in the chuck. Then the lower boss was turned round and the ends faced. It turns out that I made a little bit of a mistake. When I initially measured the casting  i thought I had enough material to make the the required dimensions. What I didn't account for was the fact that the boss was offset slightly. When the boss was trued up I realized that when I turned the rim of the casting to concentric I would end up .015 undersized. I should have used the four jaw and centered the part better.



Then the part was flipped and the top faced and the locating boss was turned.



Next the center hole was drilled and reamed.



Then the parts were separated. The cover was drilled to clearance size and the cylinder was tapped. I'll end this update with a family shot.



Till next time.

Tony


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[tvoght]

It's coming along fine, Tony!

--Tim

[b.lindsey]

You are coming along great Tony!!  You should have this one running in no time 

Bill

[mklotz]

Hmm, an aluminum cylinder oscillating back and forth against an aluminum frame.  Sounds like a great opportunity for galling to occur.  It's not just a guess; I had some experience with this on an oscillator I built early in my career.  I solved it then with a bit of Never-Seize and the engine is still running today.

Obviously, PMR doesn't think there is a problem but keep it in mind when you get to the stage of testing it.

[Gas_mantle]

Coming along nicely Tony.

It may be worth milling a very shallow flat band across the cylinder and the standard where the pivot rod enters,  I found on engines I've made it helps the ports faces to fit against each other better.

Peter

[AOG]

Thanks guys. Peter, the standard casting has a cast in counterbore around the pivot point that should do the same thing as the band your talking about.

Tony

[Ian S C]

Aluminium against aluminium, I think if I was building it(I don't usually build to plan even if I have one), I would be facing these areas with brass. Tony your doing great,  this is a good learning exercise, and as it is it will run, it's just that aluminium bearing surfaces is not good engineering.
Ian S C

[philjoe5]

Good work Tony.  You are discovering a lot about working with castings and you've recovered nicely from a few misfortunes.  An aluminum cylinder oscillating on an aluminum frame should work OK if you keep it lubricated.  I've run my oscillators for 8 hours a day, 4 days in a row at model shows without a problem.  BUT admittedly, I don't have highly polished mating surfaces so there's space to retain oil.  Your results may vary

Cheers,
Phil

[tvoght]

There's a lot being said about the aluminum-against-aluminum design here. It being my first engine, I built the PMR 2A to plan (I didn't know anything about possible galling). It's very well broken in by now and remains my best-running engine. I have seen it run on the breath of a very motivated 8 year old boy.

--Tim

[b.lindsey]

Mine was built from bronze castings but like Tim's experience, it is a great runner even at low speed. A drop of oil in the air inlet every 30 min or so should provide adequate lubrication. There is not a lot of friction between the two since PMR only uses a wavey spring washer ( I assume this is still the case).

Bill

[AOG]

Time to finish out the last few pieces of this build. Next up is the crankshaft . I got the crank reasonably centered and cleaned up the boss and the back face of the part.



Then the part was flipped and the front faced and the outer rim turned true.



The shaft hole was then drilled and reamed.



The crank was placed in a collet block and moved to the mill. The hole for the crank pin was drilled and tapped.



Next the shaft was loctited into the crank.



The next assembly was the piston. I started by turning down and threading both ends of the piston rods.



Next the piston itself was turned down and the grooves for throngs turned.



Then the center was drilled out, counterbored and parted off.



The last piece of the piston assembly was the connector. A piece of brass rod was squared up on 2 sides.



Then the crank pin hole was drilled and reamed.



The part was flipped 90 degrees and the hole for the piston rod was drilled and tapped.



That completes the parts for the piston assembly. They will be put together with the engine. Now on to the last part, the flywheel.

I started by getting the part as true as possible in the three jaw. Then I faced the rim and the center boss. Next I used a blind boring bar to clean up the inside edges.



Then the part was flipped and clamped on the machined surface. The other side was faced and bored then the outer diameter was cleaned up and taken to size.



The shaft hole was then drilled and bored.



Then over to the mill where the setscrew hole was drilled and tapped.



That completes the the machining for this kit. Here is a final family shot.



I assembled the engine and gave it a test run. Even with no gaskets or rings it ran like a champ.



Now I have to pull it all apart and paint it (something I hate). The next time you see it will be in the showcase.

Tony


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[Gas_mantle]

Well done 

Any chance we could see a video of it running once painted etc ?

[AOG]

I'll do pics and a video for the showcase when it's painted.

Tony

[b.lindsey]

Very nice Tony, looking forward to seeing it in the showcase once painted and finished!!

Bill

[AOG]

It's done. Here's the link to the final pics.

http://www.modelenginemaker.com/index.php/topic,6424.msg131377/topicseen.html#new

Till next time

Tony

[Gas_mantle]

Looks good to me and it runs nicely 

[Jo]

  Well done

And who was it said making engines from castings is difficult 

Jo