Greene Automatic Cutoff Steam Engine

[kvom]

I've decided to tackle at least the bottom part of the governor housing.  It's the part that houses the gears, and in addition it attaches to the side of the crosshead guide (or frame), and it this necessary to allow attachment of the part that connects a lever needed to operate the inlet valves.  I've also looked at the rest of the housing and I think it will be most easily done broken into 4 pieces.  I'll relay my efforts on that front later.

The profile of the part just barely fits inside a 1.5" circle, so again I'm milling it from 1.5" 1144 stressproof bar.  The inside cavity is spec'ed as .8", but I enlarged it to .8125 to enable me to use a 13/16 collet in making the cover later. 



Holes were drilled for the cover mounting screws as well as for mounting to the frame and for the pulley shaft.  I didn't photograph those ops.  But once done I moved to the Bridgeport to drill and tap the 3-48 hole for mounting the lower pedestal.



Then I used the side flutes of an endmill to remove the unused stock and bring the thickness of the part to .83".



The holes for the cover were tapped 3-48 on the tapping stand using a small chuck that I turn by hand and is quite sensitive.  Holes smaller than 5-40 can be tapped without a handle, even in steel.



All done for now.  It will require a vertical hole to be drilled to attach the other parts as well as convey the shaft for the pinion gear.



Beauty shot with the pedestal:

[kvom]

I divided the governor gearbox into 4 fairly simple pieces that can be fabricated separately and then assembled.  There would normally be a single casting for the gearbox, but that hasn't been delivered.  And in any case I suspect machining that casting would take as much or more time and effort as this composite approach.  Here are SW images of the 4 parts and their assembly:











I reduced the diameter of the center section from .800" to .75" in order to mate with the bottom.

[Johnmcc69]

 
 Nice work Kvom!
 What will you use for the governor gears?

 John

[kvom]

The plans specify a pair from Boston Gear.

[kvom]

I made some time for the shop today, with job 1 being the single easiest part requiring machining of the entire engine.  It's the governor pulley shaft.  A piece of 3/16" drill rod with .100" on one end turned to .125".  The reduced end rides in the 1/8" hole in back of the gear chamber, and the pulley is secured with two set screws.  The shaft is retained by the bevel gear when installed.





After that beast, I did the top part of the center section of the governor.  Its profile fits within a 1.5" circle, so again I can use a length of 1144 Stressproof bar.  There are 8 CNC ops to get this far:



I decided to add the top fillet as it is the most visible.  It was machined with a 1/8" ball  mill, the first time i've used such a mill in this way.  Also a test as to how will my feeds and speeds calculator handles these mills.  Worked fine as you can see.

[kvom]

I finished the middle piece of the governor but I didn't take any photos.  You will be able to see it in the following pics of making the top section today.  I took a length of 1144 Stressproof round bar, 7/8" diameter and cut off a 2" piece.  On the lathe drilled a #15 an inch and a half deep, then reversed to finish the through hole.  Reamed through .1885, and then faced one end to a final length of 1/94".



One end was turned to .625" diameter for .5"; this will be the top section of the piece.  The other end was turned to .5" diameter for .25"; this boss will connect to the middle sections hole.



Now using the top piece in a collet, I turned the remaining section to .75" diameter.



The half-angle for this section is 6 degrees, so I set the compound to turn it.  Test fit to the bottom showed I need to square the rounded corner of the boss with a parting blade and a file.



A 1/8" wide slot .3" deep was milled across the center of the top.  The counterbore at the top is shows as .356" diameter on the drawing.  For the time being I used a 5/16 endmill, and we'll see what is needed later.



The flat for the flange was machined. 



Beauty shot with the middle section.

[crueby]

Watching along quietly, great progress!

[kvom]

Before making the flange, I thought it prudent to check for clearances with the two parts that are situated between the two arms.



Close, but clearance is clarence as they say.  I also thought it prudent to investigate the governor top, which presents some issues in fabrication.



The top is nearly 2" long and requires a through hole .25" in diameter.  The bottom section (dark blue) is .375" in diameter meaning a wall thickness of .062" to which the two asymmetric arms must be attached.  I have considered approaches using 2 or 3 individual parts, but at this point my approach is two parts, the body and the arms.  After the body is slit to allow the arms to be inserted, they will be soldered in place.  Then the 25" hole must be extended to eliminate the part of the arms that cross it.

The shape of the top is a bit arbitrary as long as the vertical dimensions of the part are observed.  The section between the two rounded "ribs" will be encircled by a two piece bracket than can rotate freely.  It will be connected to the flyballs as they spin, and as they expand outward, the top rises.  Its connection to the link in the flange is how the motion is conveyed to the cutoff mechanism.

To form the top, I imported its outline into my cam program, and used a function to create a list of points evenly spaced along the curved portion.  The spacing chosen was .050".  I was then able to print a list of the XY values of the points, where X would be the distance along the length of the part and Y the radius of the part at that point.  With some 3/4" brass rod mounted on the lathe, I drilled the .25" hole about 1.5" deep, and using the free end as X0 cut the bar to the specified radius at each point using a 1/8" parting bit.



To avoid overcutting I needed to use the left edge of the tool on the right side and the right edge on the left.  Then with a file and some 80-grit sandpaper I got the main portion of the steps removed.



The rest was cut using the same parting tool.



I then parted off leaving half an inch of 3/4" bar still attached.  This allowed reversing the part in the collect and drilling the through hole the rest of the way from the bottom.  The two ribs need to be rounded off so I'll make a small form tool.

[fumopuc]

Hi Kirk, always a pleasure to follow your set ups and machining operations.

[kvom]

Last machining of 2019; start of the flange.  As before, 1.5' Stressproof bar.



After parting, the width was adjusted at the Bridgeport and then the .25" slot milled.



As it turns out, I need to widen the slot slightly so my smallest .25" countersink bit will fit after the mounting holes are drilled.

[Art K]

Kirk,
That all looks good, though it is a bit  convoluted to make and assemble. You make it look simple.
Art

[kvom]

Short session today to finish off the flange.  I widened the slot by .01" on each side.  Since the mounting holes are not in the plans, I modified the SW model to position them so that the full width countersink would be completely inside the bottom of the slot.  The holes are .15" from the center of the slot.  I'm using the same 3/16" 3-48 undercut screws from McMaster that I did for the cover.



There is about 1/8" of material between the mounting face and the interior hole of the upper segment.  I set the drill bit visually so that it would just avoid penetrating.  I needed a bottoming tap to get enough threads so that the screw heads are flat with the slot bottom.

[Craig DeShong]

Nice work!  I like your straight forward methodical approach to the problem.  Still following along 

[kvom]

Chris, Achim, Art, Craig:  thanks for looking in.

Continuing with governor fiddly bits, we have the cutoff lever:



And its shaft.  With some 3/16" drill rod chuck, I reduced the diameter to .150" over a length of .45".  End is drilled for 3-48 tap.  I used the edge of a parting blade in order to get a flat surface at the inside edge.  Then parted, reverse in the collet, and drilled the opposite end.





Test assembly looks good.

[Dennis]

Good Morning Kirk,
You have made good progress over the holidays.  I like your approach to building the governor.  The results look better than the castings I have.  I have three castings that I had miss-match welded up and annealed but haven't been able to machine them to look acceptable.  I think Jeff is still having trouble getting a good looking casting from the foundry. 

As you are finding out, there are a lot of small detailed parts on this model that are challenging to make.  When the model was designed, I wanted to make this part and several others on the Green engine lost wax castings.  I think they are ideal candidates for the process.  However when I started looking for a supplier, the prices were quite high and some would not accept waxes that I made and sent to them.  They wanted to charge $3000 to make tooling for each part.

There must be low volume lost wax foundries willing to work with model engineers but I was not able to find one.  All of the models I designed have several parts that would be ideal for lost wax castings so if anyone knows a good source it would be a great thing for the model engineering hobby.
Dennis