Author Topic: Greene Automatic Cutoff Steam Engine  (Read 11144 times)

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #150 on: October 27, 2019, 09:10:47 PM »
The eccentric lever is supplied as a casting.  I was tempted to just make this on CNC, but decided to see how practical the smaller castings are to machine accurately.  The first op is to machine the longest lug round so that the rest of the ops can done by holding said lug in a collet.  One side is reasonably flat, so used that surface to clamp to a 2-4-6 block.  Centering the lug was done with the mark I eyeball tool.





The other lugs were machined thusly:



This lever pivots on a rod from the pedestal of the governor.  This pedestal is provided as a casting, but the matching of the two halves was such that I decided to machine it from 1144 steel.  The form was roughed on the lathe.



After parting, the top flange was turned to the proper thickness.



Then on the Bridgeport the top was machined and mounting holes for 3-48 screws.



A flat was machined for mounting a bracket for the exhaust actuator rod, and two mounting holes were drilled and tapped 3-48.  The location of the lug for the eccentric lever was spotted with an endmill and a spotting drill in the center.



The lug is a piece of 1/2" drill rod that will be loctited during initial assembly.  It will extend out the proper distance so that the eccentric  lever aligns with the eccentric on the crankshaft.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #151 on: October 27, 2019, 09:15:39 PM »
The bracket that mounts to the pedestal is next.  Its basic profile was machined into the end of some 1.5" 1144 rod.



I didn't take many pictures of the rest of the machining, or of the similar matching bracket that mounts on the standard supporting the crankshaft.  The bearings of the two brackets will need to be aligned to support the 1/4" rod that activates the exhaust.


Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #152 on: October 27, 2019, 09:41:21 PM »
Last week I designed a test piece to see how accurate Shapeways steel printed parts might be.  I received it yesterday:



A nominal 1" cube with 3/4" round and square through holes and an array of 1/8" holes at the top.  My findings:

In general smaller than designed in all dimensions.  So basically I'd consider this as a casting where any critical dimensions need to be machined.  So the STL model needs extra materials overall, but the holes can be left as dimensioned since being smaller they can be machined. 

The top and bottom surfaces were both bowed out in the center slightly, while the sides were quite flat and square to each other.  Side to side measured .960".  The 3/4" round hole measured ~ .738".  Top to bottom was .996" in the center, but .991" at the corners.


Offline crueby

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Re: Greene Automatic Cutoff Steam Engine
« Reply #153 on: October 27, 2019, 09:55:40 PM »
Very interesting experiment. Have you machined any parts they printed in steel?

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #154 on: October 27, 2019, 10:08:26 PM »
That is the only part thus far.  I'm going to see how well the cube can be machined next time in the shop.  According to Shapeways the metal is stainless steel infused with bronze, approx. 60-40.
« Last Edit: October 28, 2019, 12:11:52 AM by kvom »

Offline Jasonb

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Re: Greene Automatic Cutoff Steam Engine
« Reply #155 on: October 28, 2019, 06:46:25 AM »
Will be interested to see how you get on, I have heard a lot of this type can be difficult to machine particularly when it comes to things like tapping where you can't resort to carbide.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #156 on: October 28, 2019, 07:36:36 PM »
I don't believe this material will work for my needs.  It's quite hard.  I drilled through one of the small bottom holes to enlarge for an 8-32 tap.  While I was able to both drill and tap this through hole, I found that doing so heated up the entire piece.  So lots of heat being generated.

Taking truing cuts with the side flutes of the carbide endmill went OK, but again lots of heat generated in the part.

Final and disqualifying test was attempting to drill and tap a 3-48 hole. Spotting drill penetrated, but the small #47 drill made no headway.

I checked i.materialise, but they can't print my part in steel.

Offline crueby

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Re: Greene Automatic Cutoff Steam Engine
« Reply #157 on: October 28, 2019, 07:58:15 PM »
Bummer that it does not machine well - maybe one of the future versions (they are changing that technology very fast) will work out for us better. Thanks for sharing the experiment!

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #158 on: October 30, 2019, 11:58:30 PM »
Leaving the governor for the time being, I spent some time examining the casting for the steam inlet eccentric frame.  As castings go this one looks first rate, but knowledge that I can make this part from bar stock takes some of the pressure off.  The flashing around the edges was fairly easy to remove.  Where it was wide, I could clamp it in the bench vise and snap it off by twisting the casting.  Once the majority was removed I used the band sander to bring close to the outline.  I then milled away the sprue on the rod end.

In order to get the first reference surface, I clamped the end away from the rod end in the BP vise and took 25 thou off both sides of the central boss.  Since I didn't move it in the vise these two surfaces and parallel and flat.



Then I clamped the vise on these surfaces and used side flutes of an endmill to remove equal material from both sides.  Again, flat and parallel.



The next requirement will be to establish a center line for turning the rodd end, and a horizontal cut line at right angles to it.

The finished front half is to look like this:


« Last Edit: October 31, 2019, 12:05:09 AM by kvom »

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #159 on: November 03, 2019, 09:53:33 PM »
With lateral reference surfaces established, I used the position of the rod end to establish a centerline and reference surface on its end.  The CNC mill machined the boss to 7/16" diameter.  Plans call for a 12-28 thread, and of course I didn't have a tap.  But McMaster come through with .219" drill rod and the tap.  I think the NC 12-24 is more common, but in this case it's irrelevant.  I'm sure both 10-32 and 1/4-20 would serve as well, but perhaps this is close to the prototype.



Once I could mount the casting in a collet block, I could do additional machining.  I didn't take pics of all the various ops, but they were a bit tedious just trying to carve the eccentric strap out of the casting.



I cut off the small end by milling with a 1/8" endmill.  I cut almost all the way, then sawed them apart.  The machined portion of the faces allows or cleaning up without losing flatness.

This eccentric strap using a central interior groove to retain the eccentric disk.  Plans call for a 1/16" wide groove .05" deep.  I will use a 3/32" Woodruff cutter as that's what I have on-hand. I bought the cutter at an moving sale last year and had never used it, so it was time for a trial before working on the casting.  I mounted a 2" disk of cast iron that I had previously used to test my broaches, milled out the center to 1.36" diameter, and then tested the cutter.  Luckily G-Wizard can recommend f&s for these, so I cut the groove in .01" deep passes at 2.5 ipm and 450 rpm.


Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #160 on: November 05, 2019, 09:45:19 PM »
Time to suck it up and machine the center of the strap.  First I set the vise stop as shown, then lightly clamped the collet block and strap without the inner piece.  The center of the hole to be machined is the surface of the flange (and also the movable jaw of the vise) for Y and the center of the collet block for X.  Then I removed the collet block to attach the inner half, and then clamped the ensemble using the vise stop to ensure the repeatability for X0.  Then the hole was machined using an outward spiral from the center and light cuts (17 thou) to 1.35".  Then a finish pass at 1.37".



The inner groove was then done in the same manner as for the test piece using the 3/32" Woodruff cutter.



Next time in the shop I'll work on the eccentric itself.

Offline Craig DeShong

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Re: Greene Automatic Cutoff Steam Engine
« Reply #161 on: November 05, 2019, 10:38:10 PM »
Nice work Kirk, I've never made an eccentric with the center grove.  Looks like the woodruff cutter did a fine job. 
Craig

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #162 on: November 07, 2019, 12:05:06 AM »
The plans saw to make the eccentric itself from cast iron.  But I can also make it from brass or possibly bronze.  Any thoughts on the best material?

I put that question aside and so decided to start on the exhaust eccentric strap, and altogether easier part and casting.  The casting has a "cut line" indicating where to separate the two halves.  I used this line as a means to clamp the casting straight, them cut off the sprue with endmill side flutes.



Then I could reverse the casting in the vise and set it level using a square.  This allowed me to machine a surface flat and parallel on the opposite side.  Once this was done I could measure across these flats to see how much to remove to get to the design width of 1.8".



Then I could use equal passes on each side to bring the casting to final thickness  on the upper half.



Next time I'll invert in the vise and thing the other half, then drill 2 mounting holes on each end before cutting the parts in two.

Offline Jasonb

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Re: Greene Automatic Cutoff Steam Engine
« Reply #163 on: November 07, 2019, 06:59:43 AM »
Steel would be ideal for the eccentric, that is what I have used in the past with CI straps. Just about all the larger scale model traction engines use that combination and they are not display models.

It will also look correct on a scale model rather than blinging it up.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #164 on: November 07, 2019, 11:59:24 AM »
Thanks Jason.  Steel it is!   :ThumbsUp: