Author Topic: Greene Automatic Cutoff Steam Engine  (Read 5364 times)

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #75 on: June 19, 2019, 10:46:14 PM »
Another hiccup on the way to Greeneville.  Looks like an air bubble in the cast, revealed when squaring the back side. 



This  looks to be possible to work around.  The core to the admission valves looks ok.  This gap is somewhat wider than the holes on both top and back.  Since nothing is attached to the back other than the exhaust valve plate at the bottom, I could cover this with a third plate so seal it.  The hole in the top is also larger than it appears, and is partially in the area where the steam inlet pipe would be.  Once again it should be possible to seal it, probably by a bridge between the two top valve chest covers.

I'm going to suspend work on this pending advice from Dennis and Jeff.


Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #76 on: June 20, 2019, 01:18:20 AM »
In the meantime I played with the SW model of the cylinder to see if I could use the honed hydraulic cylinder tube I used for the Muncaster.

It seems that if I turn down the OD to 1.625 (1/16" wall), I could use this as a cylinder liner.  Any larger I'd need to change the bolt circle for the rear cylinder cover.  If that can work, then the issue of bore taper goes away.

Offline jeff l

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Re: Greene Automatic Cutoff Steam Engine
« Reply #77 on: June 20, 2019, 01:50:15 AM »
Hi Kirk , I have no problem with replacing the cylinder casting .Jeff

Offline Ye-Ole Steam Dude

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Re: Greene Automatic Cutoff Steam Engine
« Reply #78 on: June 20, 2019, 02:02:52 AM »
Hello Kirk,

Sure hate to see the bad luck you are having with some of the castings. I see how much work you have put into these pieces. None the less your project is coming along nicely  :ThumbsUp:

Have a great day,
Thomas

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #79 on: June 20, 2019, 01:11:36 PM »
Thanks Jeff.  New casting seems to be the better option.  I will use this one to experiment on using the hydraulic tube as a cylinder lining.



Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #80 on: June 20, 2019, 11:26:13 PM »
Trying to make lemonade from a lemon, I mounted the cylinder block in the 4-jaw and adjusted by eye until the center of the cast bore was as close as I could get it.  The good news is that even  with the hole a bit off-center in one direction, the lathe doesn't shake at 500 rpm.   :D  The block measures straight on both sides to .004 over 4 inches.  I don't know if there is a way to adjust that, but the deviation shouldn't be significant .



As cast, the bore looks to be about 1-3/16" in diameter.  My current plan is to mill it larger on the CNC mill from both directions;  this will remove the flashing from the inside and provide a round surface for precise centering when back on the lathe.  Then I'll bore to 1.5" and test for taper.  If .002" or less over the length then no need for the hydraulic tube as a liner.

Online Jasonb

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Re: Greene Automatic Cutoff Steam Engine
« Reply #81 on: June 21, 2019, 07:15:33 AM »
is there any reason you are not just boring it as you have it now? Usual practice is to bung up the hole so you have something to mark out the ctr on and then set that point to run true. A bit of hardwood driven into the hole and filed flush will do or you can just hot glue or cyno a piece of 1/8" scrap plate to the end.

I would set it up so that the base clocks true and then bore, also take a skim off the end of the cylinder at the same setting ( crank shaft end) as those are the two critical faces, any differences between those and the bore won't be in line with the cross head guide.
« Last Edit: June 21, 2019, 08:30:44 AM by Jasonb »

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #82 on: June 21, 2019, 02:27:44 PM »
The hole itself isn't very round, and there is a lot of flashing inside.  It's also not precisely centered.

A skim facing cut would be part of my plan.  I just noticed that as currently mounted the wrong end is outside of the chuck.  The block is symmetric in that the valve mechanism can be attached on either side (as was the case with the original). The crosshead guide casting works only one way however.
« Last Edit: June 21, 2019, 02:34:09 PM by kvom »

Online Jasonb

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Re: Greene Automatic Cutoff Steam Engine
« Reply #83 on: June 21, 2019, 03:01:56 PM »
The hole itself isn't very round, and there is a lot of flashing inside.  It's also not precisely centered.

That is why you plug or cover the cored hole so you get a decent surface that you can accurately mark ctr on, then punch and finally clock the punch mark true.

Something like this where the core was rough, I hot glued a bit a aluminium over the end and marked out on that using the height gauge. This setup with faceplate and angle plate will also set your casting bottom true to the lathe axis and therefore your bore will be parallel to that.


Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #84 on: June 22, 2019, 08:29:02 PM »
Despite the good advice from Jason, I decided to pursue my original plan and machine the rough bore before finishing by boring on the lathe.

The block is just under 5" long, and I don't have any carbide endmills with 2.5" flute length, but I did find this HSS one lurking in a drawer (from a bulk lot I bought at a sale years ago and never used).  .75" diameter and 4" flute length.



Unfortunately, I found that the center of the core is in the wrong location, approximately 1/4" higher than the design location.  You can see the ledge created after the first pass at a diameter of 1.55" needed to encompass the entire core wall.



Then in milling the other end it was even more out, indicating that the core is at an angle to base of the casting that I used as the initial reference surface when squaring the block.  For the replacement block, perhaps a thin rod through the code could serve as a "level", or at least to check against the bottom face.


Offline Dennis

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Re: Greene Automatic Cutoff Steam Engine
« Reply #85 on: June 24, 2019, 01:49:02 PM »
Good morning Kirk,

You are finding a lot of problems with the Green engine castings.  I have been bragging for years about the quality of castings from the foundry that made these castings but I am sure embarrassed by the flywheel and cylinder block you have.  I can understand that we should see an occasional inclusion or void but I can't figure out how the core could be put in at an angle.  I have always tried to leave a lot of extra metal in cylinder bores to allow for things like this thinking a few extra passes with the boring bar are better than loosing all the work already in the part.

Whatever the cause, I will replace the cylinder casting or send one to Jeff if he has already sent a casting to you, and appologize again for the problems you are encountering on this model.

Dennis




Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #86 on: June 25, 2019, 01:07:07 AM »
Thanks Dennis. 

The location of the bore was partially my bad as I used the dimension from the top surface rather than the bottom to locate the center.  The latter is what should be used to make the piston rod at the correct height.  That said, I think using the hydraulic tube as a liner will work out well, and boring to 1.625 will cover the core position.

Since I had the current casting to experiment with, I drilled one of the exhaust cross holes using a 5/8 endmill.  The exhaust core "appeared" as expected, so that is OK.  The edges are at a bit of an angle to the base surface, once again indicating that the core isn't perfectly parallel to the base.  That should not be an issue.

I'll wait for you and Dennis to decide on the replacement, either your original one or one of his new ones.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #87 on: June 25, 2019, 01:12:30 AM »
For the next part to attack, I've been looking at the brackets for the exhaust valves (images attached).  There are two castings for these, and the brackets themselves are mirrors of each other.

In reality, I expect these are easier to make from bar stock than the castings, and I'm tempted to order to a piece of 1.75" round grey iron to avoid the hassles of squaring the castings.  The overall size of each is approx 1.5x1x2 inches.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #88 on: June 25, 2019, 10:43:43 PM »
I decided to make the brackets from grey iron rod, which I ordered from MSC.  So today's project is a small part of the assembly, the crosshead for the valve bracket.  Here's a 3D view:



The radius on the top and bottom is .250, so the parts are made from 1/2" diameter rod.  I chose brass as the wll ride on iron guides.  The length of the part is .65".  First step is to drill on the lathe 0.7" deep with a #47 drill for 3-48 tapping.  Both ends of the rod are used, one part on each end.  Then move to the manual mill with a collet block to drill the cross hole 0.110".



Next position vertically to mill a 3/16" slot and then the sides to reduce the width to 0.3".



Back to the lathe to part off, face, and tap.



Finished.



« Last Edit: June 25, 2019, 10:52:41 PM by kvom »

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #89 on: June 29, 2019, 03:39:37 PM »
Latest attempt at parts is the sliding exhaust valve grid.  That's the green part of the exhaust valve assembly:



The design of this part has some non-obvious features.  One is the two cross slots;  these are needed so that both are exposed to the cylinder's exhaust port regardless of the grid's position, as the port is only .8" wide.  The other is the width of the grid openings, which is .07".  This is constrained by the distance that the exhaust eccentric motion can move.  On the real engine there are many more thin slits.

An issue with making the part as drawn is that it requires the slits to be 1/4" deep, and in two cases be contingent with the wall of the cross slots.  All of my 3/16" end mills have a flute length of 3/16" and a 1/8" diameter shaft.  So I modified the part to have a pocket within the cross slots, moved the slits outward and within the pocket, and machine the slits from the bottom to a depth of .15" max.

I cut off a 5" piece of 5/8" drill rod and secured in the square collet block with 2.5" exposed (making two parts from one piece of stock).  The part itself is 2.05" long.  Use of the vise stop means I have to establish the part zeroes only once.



The cross slots and pockets are machined with the same 1/4" carbide endmill.



Then the collect block is turned 90 degrees and the bottom half of the stock is machined away using the side flutes of the same endmill.  Then after a further 90 degree turn the slits are machined.



Then the stock is reversed in the collet and the second part made the same way.  Then both are cut away on the lathe with a parting tool.

It appears there is a slight bowing in the part, and when laid on a ground surface light can be seen through the center.  Stresses relieved during the machining are a likely cause.  I will see if stoning or surface grinding can flatten the bottom, since that's crucial to a  good seal with the fixed grid.  Otherwise I might remake from some 1144 stressproof steel.

The fixed and sliding valves need to live in a 5/8" hole in the cylinder block.  I had to order a 15.5mm drill and 5/8" reamer to machine these holes.  The fixed grid is attached firmly to the bottom of the hole with screws, and the sliding grid needs to move freely, so I am hoping that the reamed hole allows this without too much trouble.  As long as the seal between the two grids is good, there is no issue with some clearance between the sliding grid and the hole.

I have the intention to make the valve brackets from bar stock rather than the castings and hence ordered some 1.75" grey iron rod from MSC.  The box arrived yesterday, but no iron inside (box looked to have been damaged in transit and resealed).  Did a chat session with MSC last night to get rod re-ordered.
« Last Edit: June 29, 2019, 04:13:42 PM by kvom »