Greene Automatic Cutoff Steam Engine

[kvom]

Back to work after some weeks away from home.  Today's target is the upper flyball arms that connects the flyballs to the top of the shaft.  It's basically two Us that surround the balls with a shaft between them.  The "tricky" part is that the upper and lower Us are offset from each other so that at the top they interlink but keep the shafts and lower U centered.  I imagined multiple ways to make these, so this is one possibility that if it fails I have other ideas.

I decided this was a good time to dust off my surface grinder that has been asleep for a couple of years.  After slicing off a a chunk of 2" diameter steel (I "think" it's stressproof), I faced both ends and then ground them as well.



I then turned on end down to 1.125" diameter for a length of .25" allowing the work to be held in a collet block.  Here's the setup on the CNC mill.



The Us were machined .25" deep (finished part is .19" thick).  The bars to the side will be used to accurately clamp the part in a mill vise later on.  Doing it this way means that the Us are the correct distance apart and offset correctly.



On the Bridgeport, .099" holes are drilled for the shaft.



A length of .097" drill rod is loctited for the shaft, and the Us are connected to the side bars with some CrystalBond, an adhesive with a melting point lower than boiling water.  Left overnight for curing.  Next a slice will be cut off on the lathe leaving a thin portion of the bottom, and this will be milled off until the part is free.  I'll then boil off the bond and bring to final thickness with the grinder.



The puck will be faced and ground again for the second one.  I'll need to drill cross holes on both Us for the mounting pins.  Because the space  between the interlocked top Us will be tight, I expect some fettling will be in order.

[Johnmcc69]

Pretty slick way of doing that!

 John

[kvom]

This attempt ran into a few glitches, mainly in separating the parts from the workpiece.    The Crystal Bond isn't stout enough to hold and I messed things up a bit.  Then the drive wire on my grinder came loose and I spent all afternoon figuring how to fix that.  While I can probably recover this try, I now have better ideas on doing the next and may just make two more instead.

[kvom]

Since the last post, I had some equipment issues to distract from progress.  First the X axis drive cable on my surface grinder came loose, and given that it had some decades of wear and some kinks, getting it back in place was frustrating.  Finally I took a look on youtube, and decided to order a replacement cable from McMaster.  Just got it today.  Bigger issue was my lathe quit working, and it took several days and assistance from the Monarch guys on Practical Machinist to get it going again.

Back on the engine, I started the third time to make the upper flyball arms.  For this trial, the bar holding the two ends would be 3-48 threaded rod, since loctite apparently isn't strong enough for tiny parts with little surface area.  Here, all 4 "Us" could be milled on the end of the 2" rod.  Note that the ends are all aligned and at the same distance from the center.



By doing this, I could use all 4 sides of the collet block for drilling, and with a vise stop in place the X value needn't change between moves of the block.







After parting off and freeing from the remaining material, each was brought to final thickness individually.



Initial test showing how the offset to the small end allows the connecting shafts to line up.



The small ends need some filing to make room for the ball on the center shaft.  To cover the threaded rods, I took 1/8" drill rod and drilled it with a .099" drill making a tube.  The two ends are then screwed down to touch the tube.  The same was done on the two lower ball arms.



Finally a test fit to the governor "family".



Now I need to make some pins to hold it together properly.

[kvom]

While waiting for some deliveries, I spent a couple of days working on the cylinder head assembly.  This consists of three close-fitting parts: the cylinder head, packing insert, and packing nut.



The cylinder head was turned from a piece of 2.5" round grey cast iron rod left over from another project.  While the turning and boring were straightforward, parting off was not.  With my 1/4" parting tool needing to stick out 1.25", it chattered so badly I wasn't able to find an rpm that was tolerable.  Because the work was only 4" long, I couldn't fix in my bandsaw vise firmly enough to saw through, and I certainly had no intention of hacksawing that thickness.  I ended up being able to clamp it securely in the Bridgeport's vise and milling halfway through with a 5/16" endmill, 50 thou per pass.  Then turned over to repeat.   

After doing this, it occurred to me that an easier way would be to mount my CNC 4th axis and mill downward as it turned, in essence milling a spiral slot.  Of course I'd need to vary the Z axis feedrate to maintain a constant SFM.  I may write a Java program to generate the g-code as an exercise.

The other two parts are bronze.  The insert was just the right size for a piece I had laying in a drawer, and the nut was from a length of 1" rod.

After drilling and tapping, here are three assembled.



Note that the "nut" isn't a classical threaded packing nut, but id instead tightened by the two screws.

[kvom]

I have been nibbling away at the crosshead guide (called frame in the plans) casting.  You can see the raw casting in this photo I posted on page 1.



This piece presents quite a few challenges, both from its size and also from the many surfaces that will need to be aligned just so.  To start, I felt that the edges of the side opening were the flattest and straightest. so I was able to mill parallel faces in two dimensions.  Here I've milled off the large sprue from the cylinder end.  1.5" removed 50 thou at a time with the side flutes of a 1/2" 4 flute endmill.



After today's efforts I have this:



The initial reference surfaces, red arrows are flat and parallel to each other and the two surfaces indicated by the  yellow arrows.  The sprues on each end, green arrows, are parallel.  Now I need to find the centerpoint on each end that will be the centerline of the piston rod.  The blue arrow shows the center of the cast angle where the slippers on the crosshead will ride.  So I'd like to set the vertical coordinate of the center point as close as possible to that line.  The other coordinate could be guessed via eyeballing the part lines, but since there's another cast angle on the opposite side, I intend to split the difference between them.

Before quitting for the night I slid my milling vise over and aligned the work on the mill table.  Using a pair of ground rods designed to fit Bridgeport slots closely, I used the 2-3-5 block against them and the cylinder end surface I had just machined to align the casting.



Once I can determine the center dimensions, I'll need to drill both ends with a center drill so I can mount between centers on the lathe and eventually an indexing head.  Here's where one of those right angle drilling attachments would come in handy, but alas, I lack one.

[Craig DeShong]

Looking really good Kirk. 

Tony has his completed, but I won’t get over to his place for a while to see if he has it running.  When I last talked he was thinking the valve adjustments could be tedious.

[kvom]

Since you can't see the exhaust valves, they could be hard to adjust.

If you go to see it run, please take some pics/video.

[kvom]

To determine the 3rd plane as the centerline of the crosshead, I made this "tool" quickly from some aluminum.



Then I touched it lightly to the inside crease on both sides, and used the DRO to divide the difference.



Then I used a height gauge to measure the distance above the table.



This is the distance to the center measured from the two "feet" supporting the casting.  After milling faces on the sprue equidistant from the center, I did the same on the cylinder head side both for clamping and for center finding.



Clamping the casting vertically on the sprue, I was able to verify that the cylinder side is flat.  Don't try this on a mini-mill.



Center drilling.  The other side was done similarly.



Test mount on the lathe between centers.  I didn't as yet remachine the chuck's center, and I also need to fabricate something to clamp onto the sprue to act as a lathe dog.  The only turning will be on the round boss at the tailstock end.  This boss will then serve for chucking on my 4th axis rotary table chuck for machining the guide V's.



I still foresee some issues.  While the clamping was sufficient for center drilling, there was a bit of vibration.  When it comes time to open up the cylinder end I'll need something more rigid.

[kvom]

I decided that a rod inserted into the sprue would be effective as a lathe dog given how it lined up with the vise jaws.  I tried this setup in order to drill a 1/4" hole 3/4" deep.  It was quite rigid.



Cut some drill rod just the right length.



I ran the lathe at 450 rpm and took very thin cuts of 20 thou.



The setup to make further progress on this will take me a while, so I'm going to put further work on it aside for now.  There are some small parts I need to make that I "skipped over", and I want to finish the governor.  I can also start preliminary work on the crosshead casting.

[kvom]

Moving on to the crosshead, I decided that the casting provided would take more work than machining it from bar stock.  I had a piece of 2.5" diameter round rod .9" thick that was a good match for the crosshead size (which is .75" thick).  Here's a picture of the crosshead from Solidworks.



This design is different from all my previous engines where the piston rod screws into the crosshead and is fixed with a jam nut.  Here the piston rod is clamped by the action of two screws and the horizontal slit.  There will be a separate round boss added at assembly;  were it left on the stock  there was insufficient room for an endmill to profile it.

To start, I machined a pair of soft jaws to hold the iron disc securely. 



The profile was roughed out with a 1/2" endmill and finished with a 1/4".  I took some deeper cuts that I have in the past (.25" DOC x .2") and as a result I had the endmill pushed into the collet by 40 thou at the end.  That's a problem witn carbide cutters and R8 collets.

[crueby]

Interesting crosshead design, never seen that before. I wonder if the mating surfaces should be left a little rough for a good grip.


 

[kvom]

Finishing passes with 1/4 and 1/8 endmills.



To remove the remainder of the rod I milled a half inch from each side followed by using the side flutes for the rest.





The reverse side is milled similarly but has a small integral boss, as this side will be tapped for the cross pin.



The conrod end is hollowed out: 1x3/8 by 1.1 inches deep.  I made it a couple of thou wider to give the conrod end some room.

[kvom]

Interesting crosshead design, never seen that before. I wonder if the mating surfaces should be left a little rough for a good grip.

The"hole"  to be drilled is shown as two .166" radii separated by a 1/16" slit.  So it appears that clamping may spread the sides of the two half holes to increase the mating surface.  But the instructions say to machine to a close fit to the 3/8" rod.  The .166 radius doesn't make a lot of sense

I bought a collection of new-looking slitting saws at Cabin Fever, and have a 1" arbor on order from ebay in order to mill the 3 slits.

[kvom]

I drilled the holes for the conrod crosspin.  The outside side is 5/16 and the inside is drilled and tapped 1/4-28.  I then drilled the hole for the piston rod.  I decided that as drawn it didn't make sense, so I reamed .374.  When the cross slit is done, I'm assuming the .375 rod can be inserted without too much drama.  Since it needs to be fairly  precisely positioned to account for the movement of the conroad and the piston.

The cross pin itself is a piece of 5/16 drill rod, drilled and tapped 1/4-28 on one end and 3-48 on the other.  While the plans show the 1/4 threads as one piece with the rod, I cut off a screw to provide the short threaded rod.  The pin is inserted on the front side and screwed into the tapped hole on the other.  To prevent it from  coming undone, a retaining cap is show in the plans; this sits over the outside end and is attached with a screw or stud.