Greene Automatic Cutoff Steam Engine

[Art K]

Kirk,
You are making good progress despite unfortunate casting setbacks. At least you had the one to practice on. At work we've had boxes come in very busted up & missing contents, which were later found and returned.
Art

[crueby]

Thats quite a complex valve setup, very interesting.  The 1144 would be a good choice, gets rid of the warping.


 

[kvom]

I was intending to start work on the lower fixed grid, which I'll make from brass.  Not having any 5/8" round, I'll start with 3/4" hex and turn down to about .65". then heat in a 500 degree oven for a hour or so before turning to .625" and machining.  We'll see if we get warpage then.

I had to help with some family house moving that took up most of the day.

Since with the valves installed one can't see them working, I have in mind a test fixture.

[crueby]

Doing the stress relieving bake for brass works out quite well, sometimes there is still a very slight bend, but no where near as bad as untreated pieces. Still, it can be worth leaving the final surface several thou tall then taking it down in a final truing pass when all cuts are made. On the 1144, I have not been able to detect any movement in the pieces I have cut.

[kvom]

I have plenty of brass rod to make the trial, so nothing lost in trying.   

[Captain Jerry]

Hi Kirk,


I have been watching this closely without having anything to say since I have absolutely no experience with castings.  My main interest is the valve mechanism.  I have doped out much of the Green design for cutoff but had never given much thought to the exhaust, assuming wrongly that it was like the Corliss design. Then when I saw that it was some kind of reciprocating mechanism, I was thinking spool valve but it had not occurred to me that it could be a slide valve.


Your work on the slides is nice. The slots are perfect. What sort of spotting bit do you use to locate them.  I am guessing that the fixed part of the valve will be much like the movable part and that you will use a relieving slot to reduce the depth as you have done on the moving part. It seems like a bit of clearance for the slide would be much preferred to a tight fit and that you could lapp the two faces together to assure a good seal.


All in all, this is a very interesting project and your documentation is much appreciated.


Jerry

[kvom]

Jerry,

The entire piece is done on my CNC mill.  I discovered that when only milling the slots, the endmill only pushed up a thin layer into the pocket.  So I altered the program to use the endmill to chain drill the  slots and extra .020" deep before profiling them.

[kvom]

While my brass rod for the fixed valves was in the 500 degree oven, I used this setup to attempt to flatten the sliding valves.



My height gauge was used to level the work on the v-block, and I took passes .002" at a time.  Seems a lot better but still can see a bit of light when laid on a ground surface.

I also made a start on the four little rod ends (tan color in the sw image) that are made from 1/4" square brass rod.  One of each pair needs to be tapped 3-48 left handed so that the connecting rod acts as a turnbuckle.  I ordered a LH tap on Amazon, and it should be here in a couple of days.

Once the brass rod had cooled, I turned it down slowly until it fit my "ring gauge" that I made from some aluminum rod using the drill and reamer I got last week.



I'll make the parts next time out and see if I get any warpage.

[kvom]

Started on the fixed exhaust grid, which is secured to the bottom of the through hole by three 3-48 screws.  The relief slots on the bottom are oriented to the side of the cylinder block that open into the exhaust core.



The slits on the sliding edge:



I left about .02" to be removed on the flat after determining that the piece did have some bowing.  After parting off the valve, I put it back in a 550 degree oven for another hour+.  Next time out I'll shave the remaining as I did with the sliding grid and see how flat I can get it.

[kvom]

The connecting rod between the exhaust crosshead and the swing arm that drives it is designed to allow fine adjustment of the sliding drid position.  As seen in the model picture, it is a length of .099 diameter rod threaded 3-48 on one end and 3-48LH on the other.  A fixed nut between the two thread allows expansion of the length of the rod when turned by a small wrench.  To make this I first had to order a LH 3-48 tap from Amazon; this arrived today.  I previously made the 4 rod ends, so first I tapped two of them RH and the other two LH.

Not having a LH die, I spent most of the afternoon generating g-code for thread milling 3-48 threads.  My CAM program generates the code easily, but I have to tweak the parameter to get the proper minor diameter, and I do this by sneaking up on it until the generated thread will screw into a tapped hole.  Nuts are looser.  Once I had the depth correct, I could easily generate code for LH threads as well.

Here is the result.



The plans specify soldering the nut, but I think Loctite will work just a well.  I needed to drill out the threads of the nut with a .097 drill, which produces a sliding fit.  To hold these small nuts for drilling, I laid them on a flat surface and placed a a small drill chuck over it, then tightened.  The jaws of the chuck naturally aligned the nut.  The chuck has a 1/2" straight arbor that's easily mounted on the lathe/

[kvom]

My cast iron chunk arrived yesterday, so today I had a chance to work on it a bit.  The parts involved are the rear caps for the exhaust valves, and are colored in turquoise on the SW diagram.  After cutting the 12" long piece of 1/75" round grey iron into twp 6" pieces. I mounted one piece in the Monarch.  Faced the ends, and then turned a .625" boss .25" long on each end.



Then back to the bandsaw to slice off each end.



Then using a 5C collet and square collet block, the rest of the machining was straightforward.



The 5" piece left from cutting I cut into two 2.5" pieces; these will be used for the exhaust brackets.

[Dennis]

Hi Kirk,

Still following along, the valves are looking very good.  I like the revisions you made on the exhaust valves.  Also good planning on the machining process.

Dennis

[kvom]

Started on the first exhaust bracket, starting with a 2.5" piece of 1.75" grey cast iron rod.  On the lathe, I turned down 2" in order to remove the mill scale, then drilled and reamed the center hole .501" diameter and 1.75" deep.  After reversing in the lathe, the remaining 1/2" was turned to 1.125" diameter.  The workpiece was then mounted in a square collet block using a 1.125" 5C collet.

On the CHC mill, work zeros for all 3 axes were set at the end of the work on the centerline.  This allowed a consistent setup with a vise stop in that I needed to mill 4 sides 2 ops each with varying depths of cut.  I just set target depth as the dimension from center needed on each op.  Each side was machined at full depth with a 3/8" 4-flute carbide endmill at .050" stepover.  After doing each of the ops, I had this result:



Then I used the Bridgeport to cut back the edge of the hole by 1" on each side as per the plans.



There are several more ops to go before the part is released from the collet to work on the other end.

The second bracket is identical except that the last two CNC ops are done on opposite sides yielding a mirror image part.

[kvom]

My euphoria was short lived.  Some measurements are showing that the inner portion of the bracket is narrower than drawn by a significant amount:  .608" vs. .625".  Normally these aren't critical dimensions, but here there is a bearing at the narrow end, and the tapped holes for the bearing cap won't work as drawn.  I can make them closer together and may do so, but before starting on the second bracket I wanted to investigate where the error arose.

After turning and drilling the second blank, I made some shallow flats on opposite sides on the CNC mill, and was not able to get the proper  distance between top and bottom.  It appears that the issue arises because the work is not perfectly parallel to all 4 sides of the collet block when held on one end by the collet with 2" sticking out.  So rather than cutting with the work horizontal in the vise, I believe I'll need to do so with it vertical and not using the block. 

The Red Cross wants my blood this afternoon, so any further work will have to wait.

[kvom]

Today I had only a couple of hours in the shop, so since I'd already done the CAM work for this small part it was a good time to start in it.  This swing arm fastens to the end of the rod that is oscillated by an eccentric on the crankshaft.  It also attaches to the rod end of the exhaust valve crosshead and provides the impetus to move the sliding grate back and forth.  The angle at which it is attached to the oscillating rod determines the throw of the grate, and hence is a major means of tuning the valve motion. 



The part is small enough to be enclosed in a 1" circle, so I machined its profile in the end of a piece of steel that I believe is an 1144 offcut from when it was used for the Joy engine valve rods.  In any case it machines very nicely.



Then at the Bridgeport, cut the 3/8" slot 1/2" deep.



Then mount on the lathe with the 4-jaw chuck using the spot drill mark to center a wiggler held in the tailstock.  Once centered, a parting tool rounds the inner end of the slot.



Then reverse the work in the collet and being the other end up to the same stage.



Next time in the shop I'll part these off, then mill soft jaws to hold the parts for finishing the other sides.