Author Topic: Marcher, a twin cylinder marine steam engine  (Read 3481 times)

Offline K.B.C

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Re: Marcher, a twin cylinder marine steam engine
« Reply #30 on: September 11, 2018, 12:22:31 PM »
Moxis

Don't worry about your method of machining the eccentrics with the packer in the 3- jaw.  I made my eccentrics  using the same method  but not so particular as you, there is a 3/32" lift  on the eccentric and I used a piece of steel  as a packer and the engine runs very well and at 30 p.s.i. I can't stall the engine by holding on to the shaft without burning my fingers.

Many years ago a well known academic engineer ( Tubal Cain ) published a formula for doing the packing size method. ( great guy now deceased )
In one of my engine builds ( Stuart D10 ) I was picked up by another older member that I could land in trouble which never occured and I have used this method on several of my engine builds .
To prove a point I used the formula, but can't remember the final dimension and then used my method which proved that mine was about .007" out.
When you consider the amount of points that can effect the lift  i.e. Clearance on the main shaft bearings + clearance of the Sheaves on the eccentrics + the pivot pins on the quadrant + the connection of the valve rod + the clearance on the valve nut and the valve which has to be floating all of this has no effect whatsoever in the running and power output on such a small engine, so it's my opinion that your method and mine  id O.K.

I would point out a few things on the build progression.

When you get to the milling of the steam inlet ports which are shown as 3/64" there is no such thing available as a 3/64" milling cutter so I used  1/16" cutter to no ill effect on the performance, just make sure that the valve covers both inlet ports before marching the valves to size.

Another point to take in is the Valve rod which is threaded 7 b.a. for the valve nut I always make the valve nut with a thro' hole and leave out the threading , put a 2mm socket grub into the nut which saves so much trouble dismantling the reverse gear to adjust the valve ( pic enclosed )

Another point which I am to late to tell you is that I always bore the main shaft at the flywheel end 3/16" dia x 7/16" deep  to allow a coupling to the drive shaft which are usually bored 3/16"

Hope this helps.

George.
Your never too old to learn.

Online Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #31 on: September 11, 2018, 05:00:22 PM »
Thanks Zephyrin for your comment. At first I thought I have done something very wrong, but luckily we got an answer from George who has done the same thing with boring the offset in 3 jaw without any problem. It may be that this method is not the most accurate one, but as George reassured us it doesn't matter with this kind of an engine because there are so many other floppies in the mechanism.

Considering milling the steam ports, living in a metric country we have the possibility to get 1 mm milling cutters, with which it is possible to mill those 1,2 mm (3/64") ports. So I will try to make them according to drawing. But being so tiny, there is always a danger to break the cutter, so I have to be very very careful.

And thanks for the idea about the valve nut adjustment. I understand it is much easier to set with a grub screw than with a threaded valve rod. But does it hold it's position and not move when running the engine?

Offline Admiral_dk

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Re: Marcher, a twin cylinder marine steam engine
« Reply #32 on: September 11, 2018, 10:21:20 PM »
Hey Moxie

We have some very nice Titanium Nitride Coated Carbide End Mill from China in 0.8mm, 0.9mm, 1.0mm, 1.1mm and 1.2mm at work.
You can get more sizes all in 0.1mm steps and they are cheap on Aliexpress.

I will have to admit that I have only used them on PCB material and not metal so far - but the glassfiber usually ruins HSS in minutes and these last for many hours.

Best wishes

Per

Offline K.B.C

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Re: Marcher, a twin cylinder marine steam engine
« Reply #33 on: September 11, 2018, 11:26:30 PM »
Hi Moxis.

Your question.

  {And thanks for the idea about the valve nut adjustment. I understand it is much easier to set with a grub screw than with a threaded valve rod. But does it hold it's position and not move when running the engine?}


I have used this method on several engines with no slippage and have never suffered any problems, it sure cuts out the tedious dismantling of the revers linkage. Just make sure that the valve is floating as it's steam pressure that holds it on the face, all that is needed is a little clearance from the bottom of the valve nut.

George.
Your never too old to learn.

Online Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #34 on: September 12, 2018, 05:04:42 AM »
Thanks Per, I have also those very small carbide milling cutters intended for pcb work. I have tried them for metal, but unfortunately they are very brittle and break very very easily. From Aliexpress I have bought small milling cutters intended for metal, they last a bit longer, but you have to be very careful also with them.

#George, thanks again for answer. For sure I will use your method when I get to machine those parts.

Offline Zephyrin

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Re: Marcher, a twin cylinder marine steam engine
« Reply #35 on: September 12, 2018, 09:17:45 AM »
It was not my proposal to criticize your work, I actually spend most of my own efforts on the way to get an accurate steam distribution, (or the most precise one can get with these tiny engines !).  I use a valve gear software (the Charlie Dockstader package) to check and adjust rod sizes and pivot positions for the most efficient steam distribution with the oval diagram.

As regard milling the port on the cylinder face, these tiny cutters flexes a lot, and it is difficult to get a straight line. I now use a home shop made mill bit to mill the 3 ports in one shot by "gang milling", once the steam passages are drilled.

Offline Admiral_dk

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Re: Marcher, a twin cylinder marine steam engine
« Reply #36 on: September 12, 2018, 12:30:03 PM »
I run the mill bits at over 25000 RPM's as they should in those sizes, but they do admittedly still flex a bit - running them slower results in more flex ….

In those sizes we should probably use single flute (aka D-Bits) as mills in metal as they usually are much stiffer and true running.

Online Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #37 on: September 12, 2018, 06:42:55 PM »
Thanks for the tip Zephyrin to use home made milling cutters. Very effective to get all the ports made at the same time. From which material do you make those cutters?

Admiral_dk, unfortunately the max speed of my milling machine spindle is only 3000 rpm, far from enough. That might be the reason why I have not succeeded very well with those tiny cutters. It might be better to use Zephyrin's way: To use self made milling cutters.

Offline Zephyrin

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Re: Marcher, a twin cylinder marine steam engine
« Reply #38 on: September 12, 2018, 08:21:41 PM »
Cutters are made of carbon steel, silver steel, or 100C6 steel, milled and/or filled or "Dremel-ized", hardened and tempered. Teeth are lightly sharpened with a stone before use.
The point is that the stem must long enough to reach the centre of the cylinder face, and without flexing...
The external dimensions of the cutter are easy to measure, corrected with grindstone on a dremel if required, and therefore, the ports are precisely cut, with sharp edges.
 I learned this method while reading the paper of JP Bertinat in the "Model Engineer" ,on Marcher precisely,  ages ago...


Online Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #39 on: September 13, 2018, 06:00:12 AM »
Very clever indeed Zephyrin! I might try that too. I wonder if you have still that article.

Online Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #40 on: September 14, 2018, 07:10:38 AM »
Slowly progressing. This time working with cylinder block. It was first milled into outer dimensions. Then marked the ports, holes for columns and cylinder centers. Holes for columns drilled. And finally attached on the columns with M3 model nuts. Next I have to consider, should I bore the cylinders in the lathe using faceplate, or in the milling machine, using boring head. What would you suggest?

Offline Zephyrin

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Re: Marcher, a twin cylinder marine steam engine
« Reply #41 on: September 14, 2018, 08:47:42 AM »
As long as the bores are truly perpendicular with the bottom face, it depends on the confidence you have with your machine tools; on the lathe you may give a shaving of the bottom face for the cylinder cover on the same setting used for the bore. milling marks with bronze can be annoying.

PS I send you a PM with the link for the Marcher article...

Online Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #42 on: September 14, 2018, 02:35:22 PM »
Good point Zephyrin. I am not quite sure if the spindle of my milling machine is absolutely perpendicular to the table. So in the lathe it will be.

But first big enough holes must be drilled to get the boring bar into the hole, and to fasten the block easier to the faceplate. So in the first photo I am boring the cylinders roughly, and in the second one light shavings are taken in the lathe with a boring bar.

Online Moxis

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Re: Marcher, a twin cylinder marine steam engine
« Reply #43 on: September 16, 2018, 04:35:55 PM »
Cylinder covers were made next. There are 4 pcs nice castings provided, two for top and two below the cylinder block. Simple turning work, but you have to think in which order to turn them.

After everything has been turned, the piece is fastened into rotating table and four holes for M2 screws were drilled. And finally holes for the screws were marked on cylinder block, using cylinder cover to locate them, then drilled with 1,7 mm drill bit and M2 threads were cut.

Offline K.B.C

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Re: Marcher, a twin cylinder marine steam engine
« Reply #44 on: September 16, 2018, 07:14:03 PM »
Hi Moxis,
Your workmanship and finish is to be admired, it's when I see the finishes that most of you guys produce makes me try harder to get a better finish to mine.

Well done .
George.
Your never too old to learn.