Greene Automatic Cutoff Steam Engine

[Dennis]

Hi everyone,
The uneven hole pattern on the cylinder heads on this engine is used to fool-proof the alignment of the cylinder head.  On the original engine, the piston travel ran up extremely close to the cylinder heads, I would guess this was to get as much of the expanded and cooled steam out of the cylinder as possible.  However with the piston nearly touching the cylinder head, the top and bottom of the cylinder head had to have a recess that would allow the steam into the cylinder to start pushing the piston.  A round cut was made across the top and bottom of the cylinder head and the hole pattern guaranteed that the steam passage in the cylinder head would always line up with the steam inlet and steam exhaust passages.  The Green Engine Model design does not include the steam passages in the cylinder head and the piston to cylinder head clearance is not very small because the engines will typically run on compressed air and at low speeds.  A  lot of the engines I have been fortunate enough to see original drawings on do have this feature.  It is good engineering to improve the performance of the engines AND to eliminate the possibility of the cylinder head being installed incorrectly.  If you encountered Pok-e-Oke fool-proofing programs in the 1970's and 1980's,  they were not the revolutionary new programs they purported to be, just a re-do of some very good 90 year old ideas with a new name to capture manufacturing' attention.

[Dennis]

Kirk,
I am glad to hear you have a way to save your cylinder block casting and all the time and effort you have put into machining it.  Your plan sounds like a good one.

[kvom]

To redrill the mispositioned holes, I center find on a piece of 5/8" drill rod.



Drilling with a .104 drill failed as the drill drifted into the previous hole.  So I used a carbide endmill to drill without drifting.  The endmill is a few thou larger than the drill.  Afterwards I was able to fasten the lower grill in the exhaust hole using the new screw holes.



Afterwards I turned towards starting the piston and piston rod using a piece of 2" bronze rod that happened to be just about the length required.  After facing it ended up .011" short of the .800" plan length.  A through hole was drilled with a #3 drill, which is the tap drill size for a 1/4x28 thread.  A cavity .8" in diameter was bored .381" deep, slightly less than the plan depth of .400".  Then the remainder of the hole was tapped.



Finally the piece was reverse and a 1/4" endmill bored a short pocket for the end of the piston rod.

The rod itself is 3/8" in diameter, with the piston end turned down to 1/4" and threaded.  Once fastened together, they are secured by a nut in the pocket, and eventually loctite.  I need to make the rod next, and it will be fastened in the collet chuck to turn the piston diameter to fit the cylinder.

[kvom]

Having received my 4" long .25" endmill yesterday, today I used it to mill the cylinder exhaust ports.  Basically this is just continuing the cuts of the admission ports down through to the exhaust valves' cross holes.

I decided to so this on the Bridgeport by doing chain drilling with a small overlap of holes.  Once the first cut wenth through I set a spindle stop for the rest.  After the chain was complete, I fed the endmill to finish the sides.



With the recent repair to my lathe, I am able to run it in reverse for the first time ever.  Since I need a 1/4x28 thread for the piston rod, I wanted to try single-pointing with spindle in reverse and tool upside down, feeding toward the tailstock.  I did a sample thread in some 1/4" drill rod, and I must say this is a lot easier than eyeballing when to disengage the half nut before crashing the tool.

[Art K]

Kirk,
I remember some time ago for work doing some nonstandard thread. Once the handle was engaged I had to leave it engaged and run it forward to thread pull it out run it in reverse to back it to the beginning & repeat, as I recall there was some hand turning the chuck involved.
Art

[kvom]

Art,  I believe that is required when cutting a metric thread with an inch lead screw.  On my lathe you'd need some special gears. 

I have decided not to singlepoint the thread on the piston rod as there needs to be a section of 1/4" rod after the thread to fit in the pocket in the piston.  That pocket is only .2" long, and to single point the thread I'd need to cut a groove as a starting place for the tool.  To ensure good alignment with the piston I want to use the full depth of the pocket.

So thread mill it will be.

[kvom]

To make the piston rod, I turned down one end of some 3/8" drill rod to a 1/3" diameter, then moved it to the CNN mill to thread mill the 1/4-28 threads.  I already had a CamBam setup for this thread, so the only work needed was changing the length of the thread.  I started conservatively with a .442 length. 



However, the piston blank would not screw on.  A  nut went on easily, so again a nut will attach where a tapped hole won't.  I changed the target minor diameter by .003, and that worked.  Now the blank would screw on, but not all the way down.



I used a feeler gauge to estimate the amount of additional thread needed, and eventually could get a tight fit against the rod.  Then over to the lathe to apply blue thread locker and cinch down both the blank and the nut.  This will sit until the next shop session where I'll turn it down to hopefully get a good fit to the cylinder bore.

[kvom]

Turned down the piston blank carefully to get an excellent fit, around .001" according to measurements of both bore and piston.  Slides  nicely the full range.



I needed to drill the mounting holes around both sides of both exhaust passage holes.  The pattern relative to the holes' center is the same, so I was able to use a single g-code program for spotting and drilling the 4 holes.  I used the 5/8" drill rod in each hole to center find.  After doing the right side using G54 work offset, I switched to G55 for the left hole (manually entered the G54 and G55 commands).  The for the spotting drill set Z0, switch to the other offset and zero Z, the run the program to spot drill.  Switch offset again and rerun the program.  Mount the .079" tap drill, zero Z in both offsets, and then run again, once per offset.  The advantage here is reducing tool changes.

Turn the block over, do it all again.

[kvom]

Today's project was to remake the catch housings that I attempted a good while ago.  I screwed up one of them and wasn't happy with the other.  Starting with some 1" diameter steel round, I faced it and mounted in the collet block.  Then the first CNC ops were drilling the holes for the catch and the set screws.



Finish was not great on the outside (3/16" carbide endmill at .9" DOC), but inside surface between the two was decent.

Then the block was turned 90 degrees to drill the hole for the valve rod and mill the profile.



Next, at the Bridgeport cut the two "steps".



While still in the collet block, tap the holes for the set screws.  The 3-48 tap is just long enough to do both ends of the through hole.



Then, cut off with a hacksaw and mill to final length.

[Craig DeShong]

Coming along nicely Kirk 

 

[kvom]

Thanks for checking in, Craig.

Today was time to start repairing the blowout section in the cylinder block.  On the Bridgeport, I used a 1/4" endmill and MarkI eyeball to cut out the lower abscess.



Not having any suitable cast iron raw material for a patch, I cut up one of the castings I didn't use and then reduced it gradually to about 5% of the original volume.  After getting the width, I developed a quick CNC solution to fillet the corners, and then gradually whittled down to a fit.



There should be plenty of surface area for Loctite to secure it.

The larger patch will be made from a piece of round.  To limit any possible air leakage I plan to more a cross passage rather than just a slot in the bottom.

[crueby]

Nice save on the casting.




  But, you just had to talk about cutting out the abcess. Now I am flashing back to root canal work at the dentist!  At least once I had the pleasure of standing on the crypt of the guy who invented the dental chair during a tour of Westminster Abbey!

[kvom]

Starting patch for the large opening in a piece of 1.8" CI rod.



After parting off, I nibbled to get a good fit with the width, then filleted.  Then gradual trim for height and depth leaving a few thou proud.



Next I drilled a 3/8" air passage across the width  to match the core, leaving enough on the top for a NPT tapped hole.  Finally applied Loctite to the bottom patch and clamped to await overnight cure.

[Craig DeShong]

If I remember correctly, Tony said he had a void in  his casting that he filled with Jb weld.

[kvom]

I don't think that would have worked here.