Greene Automatic Cutoff Steam Engine

[kvom]

Continuing on with governor parts, I machined the profile of the "short link" that connects the governor top section with the cutoff lever.  7/8" 1144 rod .26" deep.



Next, 7/64" slots are machined on the Bridgeport.



After parting for the rod and machining the freed side:



There an issue with retaining the link and lever as there is no space for a screw between the flanges.  Most likely just some .150" diameter rod, as the bottom of the link never escapes the flanges.

I made a form tool from some tool steel previous used for another build.  After reducing the thickness at the end and milling a 10-degree relief angle on the face, I cut a 1/8" semi-circle using a 1/8" endmill.  Since it is cutting brass, I didn't bother to harden and anneal.



The cross arms for the top are from some .1" thick brass.



I am not certain the best way to attach this once I mill a slot in the brass turning.    Since it fits across a 1/4" hole in a 3/8" diameter tube, the walls are only 1/16" thick.  (The center of the part will be drilled out after fixing).  If I solder, the solder will reach only one side.  I am considering Loctite on both sides, then the powder coat will provide some adhesion as well.  Only problem is needing to heat to 400F for powder coat, and that may weaken the loctite bond.

[kvom]

The mounting slot was cut in the top using a long 1/8" endmill.  The resulting fit is close enough that the arms can hold position from light friction.



I then secured the arms with loctite and left to cure 24 hours.  Then I parted off extra material at the top, and put the piece into my sonic cleaner for 20 minutes. 



Then powder coated with a cast iron colored powder.  The arms seem quite firmly attached, but redrilling through the center tio open up the bore will be the proof.  I may decide to do a second coat tomorrow.  TBD.  I would want to do that before parting off the base.

[kvom]

Since it appears that getting a new cylinder casting might take some time, I've been considering how I might reproduce it from bar stock.  Since I have the Solidworks model of the part, I've come up with the following idea.  The block would be made from three separate pieces of grey cast iron.  The specifications of these parts was obtained by defining two planes through the part that represent the boundaries.  The three parts themselves were then generated from separate copies where one or two "extrude cut" features removed everything but the desired material.  Here are the top, middle, and bottom:







The top and bottom could be machined using a single piece of iron 1x2.5x12", $56.74 from McMaster.

The center would use a piece 2.625x2.5x12", $74.81 from McMaster (enough for 2 pieces as 1' is the shortest length).

So $150 with shipping. 

The casting took a good deal of work to square, and there's always the issue of ensuring that the cores are correct relative to the final dimensions.  Using bars, the pieces would be aligned with dowel pins, and as long as the mating surfaces are very flat there should be no issue with air leakage from one end to the other.  There's also a few places where the machining would be simplified.  For example,  the bottom exhaust ports through the cylinder bore would require a very long endmill, while with the bars they would be machined from the bottom.

Another advantage is that a booboo isn't as bad.

[kvom]

The next governor part is called the "rotating clamp".  Rotating because it attaches to the fly balls and rotates with them, and clamp because it goes loosely around the governor top and raises/lowers it according to the fly ball positions.  Like many other small parts, I first cut the top and bottom profile in the end of some 1.5" 1144 steel rod, to a depth of .25".



After parting them off at the lathe and cleaning up, they were clamped in the small vise using some 1/8" brass rod for alignment.



A hole was then machined in the center. I settled on .382" diameter after measuring the governor top.

It was then necessary to remove the powder coat where the clamp would mount, and make small adjustments until a good fit was attained.



The plans call for special pins to join the two halves, but I see no reason not to use 5-40 screws.  These long screws have non threaded sections that fill the slots, so only some shortening is needed.

[kvom]

After drilling out the center of the top and turning off the remaining brass from the bottom, I mounted the upper section of the governor in the lathe and bored the top to give a good sliding fit to the top.  Unfortunately my fears came true in the that 620 loctite didn't survive the power coat oven with sufficient strength, and both arms came loose.  I ordered some Loctite 633, which is supposed to fill in a loose slip fit better, but has even less heat tolerance (180C).  I'll recoat the top and then re-glue the arms when cool.

In the meantime came Cabin Fever and a pretty bad cold, so nothing done for a couple of weeks.  The next part is the governor cutoff lever, which transfers the vertical motion of the top to the rod that raises and lowers the cutoff catches.  For this part I used some 1/8" thick stainless 303 bar that Chris sent me.  I drilled and machined the profile while overhanging the vise.  The part is .1" thick so some material left for support at the end.



Then over to the Bridgeport to mill away the bottom that remained.



The next part is the damper pot.  The damper system smooths any rapid motion of the governor.  As the fly balls moves it, the top moves with it a disk that is a type of piston within this pot, which is filled with oil.  The oil's viscosity acts to resist the motion until enough oil has flowed through a hole in the damper disc.

I made this from some 5/8" brass rod, mainly to reuse the form tool on the rim.  I doubt that the form tool would be effective against steel.  Since I expect the pot to be powder coated, using brass wasn't an issue.  It's all lathe work.  The post is attached to the governor middle section with a flat head 3-48 screw.  The hole is countersunk to provide a flat bottom.





The damper disc is made from 3/8" drill rod.  The smaller damper hold is 1/16", while the larger hole is tapped 3-48 for its connecting rod.



The connecting rod is 1.5" of .099 drill rod threaded at both ends.  The rod end connects to the longer of the two arms of the governor top.

[kvom]

The engine requires a number of different size steel balls, including the fly balls and the ball joint for the exhaust eccentric.  Rather than buy large bags of each size at McMaster or MSC, I found this vendor on eBay that sells assortments.   I should find what I need in this lot for $8.

[Craig DeShong]

Great progress    and I think your idea of building up a cylinder casting is sound.

You might Want to test the balls you purchased because if they are hardened you can’t drill them.  I looked hard and found a vendor that sell brass ones I’ll use on my model.

[Jasonb]

The stainless steel balls are usually drillable and look like steel ones if those prove to be too hard. Heating will often soften the hard ones enough to work them though you may want to Loctite them on rather than risk a tap.

[kvom]

The test steel ball (used a 17/32" diameter) was hardened, and my attempt at spot drilling it came out bad for the drill.   

I ground off a bit to see if it was perhaps only hard for a thin coating, but that was not to be.

Finally heated it red-hot with a torch and allowed to cool.  This led to being drillable, albeit slowly, with a .104" drill.



Fly balls are .625" diameter so very thorough heating is likely needed.  The challenge of drilling a separate hole perpendicular to the first has yet to be addressed.

[cnr6400]

Hi Kvom, if you have a mill vise with a V groove across one jaw horizontally, the perpendicular hole is easy to do. Just place a rod a close fit in the drilled existing hole, then place the rod in the vise V groove with ball face touching the vise. Zero up on the outer side of the ball in line with the rod, and move as far as you need to across the ball to drill the perp hole. Remove the ball, loctite the rod in the existing hole in ball, wait for loctite to cure, then drill the perp hole. Re-Heat to release the loctite and remove the rod. Hope this helps. 

[Jasonb]

Hold in a collet block with say 40% of the ball sticking out of the collet.

Mount block at 45degrees in the mill vice and drill first hole then hold at 45deg the other way to drill the second which will put the two holes at 90deg to each other.

[kvom]

Jason's idea is clever.  I'll have to see if the collet will actually hold a ball.  One of the holes is a through hole for the pivot arms, and the other is partial penetration for the rod connecting to the collar.  I definitely don't want to drill into the interior of the collet when doing the through hole.

My own idea, after last post, was to clamp the ball in the machinist vise near to the edge of the jaws.  Drill the through hole, then  turn the vise 90 degrees for the partial hole.

In the meantime I competed the governor cutoff counter weight, which plays a large role in setting the engine's speed.



The weight at the Warwick RI museum appeared to be several discs on a rod, so the grooves give the idea of that.  As can be seen in the photo, the weight wants to turn the lever counter clockwise and thus apply a downward force on the governor top. 

As the balls spin and rise, the centripetal force applied to the collar will cause the top to rise as long as it's greater than the weight of the top and the force applied by the weight.  Once the two forces balance, the speed is determined.  There is some addition resistance from friction in the cutoff mechanism connected to the bottom of the lever, but that's assumed to be minor.

So it can be seen that adjusting the counterweight will affect the total force applied against the fly ball force.  Increase the weight and the engine slows, decrease and it speeds up.  Small adjustments can be made by sliding the shaft of the weight in and out.

Slowing the engine means the top lowers pushing the cutoff rod on the lever toward the cylinder.  This in turn raises the trips causing the valves to remain open longer.  The additional steam power then acts to speed the engine up.

The system provides a safety against a runaway engine in that if the speed is too high the trips will be lowered such that the catches miss the trip entirely.  The dash pots then pull the inlet valves closed.

I suppose that each factory powered by one of these engines had an optimal speed to drive the equipment, and that the engine was set for that speed.  Then the optimal cutoff setting could be set by adjusting the length of the cutoff rod so that the trips are at the desired height at speed.

[Jasonb]

I've held balls in the lathe 5C collet to drill and turn them so should be OK. If you need a bit of clearance for the through hole the two angles could be altered so long as they add up to 90deg.

Your last photo prompted another thought and that would be to place the ball onto the corner hole of a 123 block and clamp in position. then you can use the edges of the block to give your 90degree positions. May be a little harder finding ctr of the ball.

[kvom]

I went to the website of the ball supplier, and it seems that there's a mixture of hard chrome and softer carbon steel balls in the assortment.  Might get lucky with the 4 I need.

[jeff l]

McMaster Carr sells low carbon machinable balls.