Author Topic: Monitor, A Half Trunk Vibrating Lever Back Acting Engine  (Read 41644 times)

Offline Captain Jerry

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #15 on: April 26, 2016, 08:46:36 PM »
There is a lot of clever linkage going on there.  The inner most pair are the ones that control the cutoff.  They are on the inside so that the outside pair, which control the reverse can be manipulated to change direction.  That causes a problem because the cutoff valves are on the outside and the main valves are on the inside on the valve chest.  At the valve lever pivot, the switch positions, with one pivot riding over the other inside the bracket.

I do not plan to attempt the cut off valve setup but may install the linkage and valve rods as dummies.  Undecided.

On a single cylinder steam engine, the simplest way to reverse is with an eccentric that can revolve 180 degrees on the shaft.  The engine is stopped, the eccentric is rolled over and the engine is started in the opposite direction.  This is a two cylinder engine so there are two eccentrics. Stopping the engine and manually rotating the eccentrics is not possible on a 300HP Ships engine

Ericsson devised a way to do that while under power.  The two eccentrics are fixed together and they are rotated from the forward to reverse position by two pairs bevel gear segments that are driven by levers attached to a hub that rotates with the shaft.  The hub is driven in and out by a second hub attached to a worm gear which is driven by that pretty brass handwheel.  That is the engineering genius of  John Ericsson.

Rich Carstadt devised a way to do that at a 1:16 scale.  That is part of the craftmanship for which he has been awarded honors.

I will probably not even try to fake it.

Jerry
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Offline Art K

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #16 on: April 26, 2016, 09:38:21 PM »
Jerry,
This sounds like a great build and I think I'll pull up a seat for the show.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Captain Jerry

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #17 on: April 27, 2016, 02:52:19 AM »
Welcome Art. Plenty of room.  You might want to bring something to read when things get slow.

I said I had a plan for the piston.  This is it.  The trunk is a Steel tube .390"OD x .375"ID x 1.5" long with a .125" x .650" pivot boss at one end.  The boss have a slot that carries the piston pin and after the rod and pin are installed is capped with a CI cover to complete the assembly.  A morning trip to my main supplier (scrap yard) for material and we will see what the afternoon produces.

The tricky part part here is the tube.  The wall is only .0075" thick so the ID and OD must be perfectly concentric.  I plan to turn it with the pivot boss from a single piece because I don't want to risk distorting the thin wall tube with any heat or stress from a press fit.  The ID is not a critical surface or fit and is less than 2" long so It will be bored in the lathe with a series of drill bits 1/4", 5/16", 3/8".  Reaming is not necessary.

I will then part it off to 2" long and set it up between centers to keep the OD concentric.  I will bring it down to .650" for the full length and then leaving a .125" wide boss at the headstock end, take the rest of the length down to .390" going the last .0005" with finer abrasive strips backed with a flat file.  I expect some bell mouthing of the tube at the live center end, if it gets close to .390", so the tube will be made longer than the 1.5" length needed and the end near the live center will be left at about .410" to prevent that.  The extra will be ground off after the tube is polished.

I hope I made the clear enough to understand and I would appreciate any ideas or suggestions that would improve the process. I don't have any experience with thin wall parts like this.

Look at the PDF for better view.

Jerry
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Offline paul gough

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #18 on: April 27, 2016, 12:10:04 PM »
Hi All, There is another simpler arrangement for reversing with these types of engines such as that for the 'Artemis'. Fixed eccentric and cut off with a 'Kitchen Rudder' for 'reversing' the ship. This is from a launch build, not from a ship. See image of valve arrangement below, ignore the name of the file is just my indexing . Regards, Paul Gough.
« Last Edit: April 27, 2016, 01:21:57 PM by paul gough »

Offline b.lindsey

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #19 on: April 27, 2016, 12:21:43 PM »
Jerry, I am asking this out of curiosity (read ignorance), but why does the tube have to be so thin? I took a post it note from my desk, doubled it over and measured the thickness....0075" exactly! Man....that is a thin wall  :o even from steel.

Bill

Offline Ian S C

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #20 on: April 27, 2016, 12:51:24 PM »
I needed thin walled cup shape for a hot cap for a Stirling Engine, so I bored out the piece of 316 stainless(all I could get) to the required bore and depth, then made a mandrel,  and Loctited the hot cap onto it without remove ing from the lathe, I then took the outside down to the outside diameter, that gave me .010" on a 1 3/4" diameter cup 3" deep.
Got the idea from reading about making a pressure gauge, the tube started as a bit of rod, drilled down the middle, put on a steel mandrel and turned to the required thickness, it was then taken off the rod and flattened and formed to it's horse shoe shape.
This method pretty well ensures that the tube is concentric.
Ian S C

Offline Captain Jerry

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #21 on: April 28, 2016, 01:06:04 AM »
Paul, the Kitchen rudder is a steerable,  thrust reversing, clam shell device that reverses the direction of a boat, but it does not reverse the direction of the engine.  Is it really simpler?  How well would it work on a 300HP engine driving a 9' propeller?  It may have some manueverability advantage on small craft but on a ship the size of the monitor?

Bill, the dimension of the tube is a  compromise between two requirement.  The ID must be great enough to let the outer end of the piston rod, where it is attached to the Vibrating lever, rise above and fall below the cylinder center line as it follows the arc of the vibrating lever.  On the other hand, the OD must be as small as possible, because it's size reduces the effective area of the piston. On a half-trunk engine, the reduction is only on one side of the piston and affects the balance of power between in and out strokes.  And, of course, is a matter of scale. 

Ian, thanks for the help.  A mandrel may be the answer but I would be worried about the mandrel sticking in the tube. How did you release it from the mandrel if it was epoxied on?

Jerry
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Offline Captain Jerry

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #22 on: April 28, 2016, 03:16:48 AM »
I got a little shop time today after the electricians left.  I've got power everywhere with no extension cord.  I've got so much light overhead that I may need to wear a hat.  And Ive got plenty of air conditioning.

I didn't get to the scrap yard for material so I hunted around here until I found a 3/4" Grade 5 bolt to experiment with.  I learned a few things about making a thin wall tube.  I have more to learn.

First cutting it to 2" length and drilling  through to 3/8" diameter was not a problem at all.  Going from  center drill to 1/4" to 5/16" to 3/8" was no problem with sharp bits.  I was a little worried about starting the 3/8" bit on center in the 5/16" hole because of the length of the bit so I used a 3/8" end mill to open the 5/16" hole to 3/8" to a depth of 1/4" before starting the 3/8" bit to help keep it centered.  The ID finish is not critical but I ran a 3/8" hand reamer through to help me believe that it was straight.

After that, I mounted it between centers and began taking the OD down to the target .390"  It went well, up to a point.  I am a strong believer that VERY sharp tools prevent a lot of difficulties but for some reason, while hunting for the bolt, I ran across a long forgotten carbide insert and holder  so I decided to give it a try, at least for a few passes to see how well it cut.  I had used a brazed carbide to to take the threads of of the bolt taking it to about .650"   Going from .650" to .400" in increments of .020" (.010" DOC) gives plenty of opportunity to evaluate the tool.

It was cutting free and easy with a nice finish so I kept using it.  It had no chip breaker and as I got closer to the target, I reduced the DOC to .005" and it was making an almost invisibly thin continuous blue curl.  I was paying close attention to the curl when I noticed an occasional bright spark at the tool edge.  Before I realized what was happening, the tube began to take on color and before I could back out, it had gone from bright steel to dark brown.  The color polished off with some 1200 grit paper but I think the damage was done.

By now the OD was down to about .025" over meaning a wall thickness of about .020" and I think that a cutter going dull combined with a thin wall section that could not dissipate the heat had drawn the material's temper.  I replaced the insert tool with a freshly polished brazed carbide tool and continued.  I might have been OK if I had not overshot my target.  Before I knew what happened, the Micrometer read .386" leaving a wall thickness of only .0045",  not enough to survive the forces of removing it from the lathe.  The .750" OD section that forms the piston tore off of the tube.  I also found that it was weak enough to crush with my fingers.

Round 1 goes to the opposition.  Tomorrow begins with Round 2.

Jerry




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Offline Captain Jerry

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #23 on: April 28, 2016, 11:38:18 PM »
Ah Ha!  This is now an actual build project.  I was not sure until I figured out the trunk piston, that I could do more than talk about it but today turned the tide.  The trunk piston can be made, wel I knew it could, but it can be made by me and probably by you if you wanted to.  Here is what it looks like:



I was a little better prepared and more concentrated and I had learned a few lessons yesterday but today was successful.  The picture includes the cast iron piston cap and a temporary piston rod.  I am celebrating with a Loudmouth so if I post anything else tonight, don't hold it against me.

Jerry
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Offline zeeprogrammer

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #24 on: April 28, 2016, 11:43:45 PM »
Congrats! And on the 2nd try! (I'd take at least 3.)

Ah Ha!  This is now an actual build project.

I didn't know there was a question about it. So let's not question that anymore. Keep it going.  :stickpoke:
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Offline b.lindsey

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #25 on: April 28, 2016, 11:55:02 PM »
So what did you do differently today Jerry other than watching the wall thickness closer. Congrats on getting it done!!

Bill

Offline bruedney

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #26 on: April 29, 2016, 12:41:49 AM »
Just a thought but could you not change the size of the piston rod by say 0.04" (1mm - 0.5mm off each side) and the decease the id of the trunk by 0.04" :shrug:

Bruce
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Offline Captain Jerry

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #27 on: April 29, 2016, 03:09:47 AM »
So what did you do differently today Jerry other than watching the wall thickness closer. Congrats on getting it done!!

Bill

I did a few things differently.  First, I realized that there are a few operations on the piston face that should be carried out before turning down the trunk.   There is a slot for the pivot pin that needs to be milled and it is a lot easier to hold before the trunk wall gets thin.  There is also some  milling of the inside of the piston cap that clamps the pivot pin and to clear the end of the piston rod.  Now that I think about it, I should have gone ahead and drilled and tapped for the screws.

Another lesson learned yesterday is, if you don't really know a critical dimension, find a way to measure it.  I don't know about yesterday, but today, my 3/8" drill bit made a .379" hole.  With no inside micrometer, I had to take a steel rod and make a gauge that I could measure with a standard micrometer.  Starting at .400" and taking very light cuts with a very sharp tool, it slipped into the bore on the third try and measured .379" so if I wanted a .0075 wall, I would have to stop the OD cut at .395" and leave .0005" for polishing.  Trying to get to .390" OD would have failed just like yesterday.  Maybe I should have drilled under size and reamed to .375" but this is just for fun.

The other thing that I learned is to stick with what you know,  I know how to shape, grind, and polish a brazed carbide lathe bit and I know when it is cutting right, at least on my equipment.  I never should have experimented with the insert bit on a critical part.

You might think that the piston rod would be next on the list but not so.  I have not decided on how I want to  make the bearings at either end of the rod and I need to get to the cylinder and the cylinder heads  and the trunk glands.

Just a thought but could you not change the size of the piston rod by say 0.04" (1mm - 0.5mm off each side) and the decease the id of the trunk by 0.04" :shrug:

Bruce

Sure could.  It begins to just be a matter of what looks right.  I came to the rod dimension that I used in the design by starting with what I thought looked right and then reducing it to where I could get it to work.  There is also the consideration of what can you make.  I don't know how to make a .371"  by 1.7" deep hole.  (I guess I don't really know how to make a .375" hole either)

The cylinder offers plenty of design challenges of its own.  There is a shared head between the two pistons inside the single cylinder.  Routing steam and exhaust passages to the inner shared head for each cylinder sounds like it will need some tricky cores in the casting but I'm doing this from bar stock.  I have a plan.  I have had other plans.

Jerry
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Offline Captain Jerry

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #28 on: May 02, 2016, 02:55:29 AM »
I made a lot of chips today.  Actually, it was long stringy stainless steel swarf.  I wasn't really happy with the way the 2nd try at the trunk piston worked out.  The bolt holes for the piston cap did not leave enough room for the bolt heads and there was also a problem with the piston rod centering slot in the cap.  I might have said that this project is a design proofing build.  The plans are fairly complete as far as the geometry is concerned but the fine details may need some tweeking so this is Try #3 on the trunk piston:





The trunk piston is 316 Stainless Steel from a scrap yard bolt.  It has a .398"OD and a .008" wall thickness.   There are 4 bolts holding the piston cap in place.  They are scale #2-56 hex head, bolting through the trunk head, into the cast iron piston cap.  The second photo shows the 3/16" wide slot that will retain the piston rod in the center of the trunk.

I think I am happy with this one,  I will do the second one tomorrow.

Yesterday was spent searching down a noise in the lathe.  It didn't take long to find.  I only showed up in the lower speeds and was worn bushings on the low speed intermediate shaft.  They are very thin bushings to begin with and when badly worn, are paper thin.  A real pain getting them out completely.  There are two bushings, one from each end of the pulley with a gap between the ends when installed that gets oil from a hole in the shaft provided through a fitting in the end of the shaft.

QUESTION!  The shaft is stationary and the oil distribution hole is on the top of the shaft.  Wouldn't it be better if the hole were on the bottom of the shaft so that oil could flow from the shaft to the space between the busshings?

I ordered the bushings from Grizzly and should have them by the end of the week.  In the meantime, all lathe operations are at 1100RPM.  That's OK for most things but parting of 1" cast iron piston caps can be exciting.

Jerry
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Online crueby

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Re: Monitor, A Half Trunk Vibrating Lever Back Acting Engine
« Reply #29 on: May 02, 2016, 03:19:17 AM »
Wow.  :NotWorthy:   :popcorn:

I wonder how many times Ericsson remade his full size ones till he got it to work?

 

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