Author Topic: PMR Coke Bottle Engine  (Read 8379 times)

Offline rleete

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PMR Coke Bottle Engine
« on: December 23, 2008, 04:34:57 PM »
Okay, so I've goaded Bernd into trying to get these engines made.  We both have the kits, but his appears to be mostly brass/bronze while mine has the major structural elements (like the frame) made of cast iron.  I refer you to Bernd's website for a pic: http://www.kingstonemodeleng.com/EngineShop/Model5b/5b.htm

So the question is, where to start?

The frame is, naturally, cast in the coke bottle shape.  [Hint: it's the tall thing in the center of the picture].  There are no straight lines on it.  The top and bottom are uneven, having a casting line through the center, and draft on both sides.  If it is clamped into a vise to square off the ends, and it is not perfectly done, the thing will sit off kilter.  Maybe only a little, but being so small (6" or so), the slightest variation will show up as the whole thing leaning like that famous tower in Italy.

Do I clamp it up, trying to use the fairly thick casting/parting line to get it square?  If, after machining, it appears to be off, to try and shim it and cut again?  This trail and error method (mostly error in my case) seems a bit crude.  I'd mount a shaft in the vise and use that to line it up, but the bore is also cast, and may or may not be perpendicular to the base.  It's also not very round.

So, help a newbie out and let me know where to start.
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bogstandard

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Re: PMR Coke Bottle Engine
« Reply #1 on: December 23, 2008, 06:06:59 PM »
This is where making from bar stock is more preferable for a beginner than making from castings. You can easily get a datum face with stock, rather difficult with a casting.

But that doesn't solve your problem. Finding a datum face to work to.

Without a datum, you will be working totally blind and stabbing at it, hoping everything will line up afterwards. I will tell you now, that way just doesn't work.

Not having the castings to handle, it is difficult to imagine the best way to machine them, but by looking at the picture I can only suggest a way to go.

Looking at the main bottle casting, I personally would go for one of two ways.

The first one is the rim around the top.

Holding the square base in the four jaw, get the casting running as true as possible, you can see how it wobbles about when run up. By eye, get the main bottle shape running as true as possible by moving the jaws and tapping with a soft hammer, and hope that it is nearly symetrical. Then using super fine cuts, turn the end rim on it's outside edge until it has just cleaned up all round (do not take it down to size, that can come later), followed by a very fine skim across the end face. These first two operations have to be carried out very tenderly, as any heavy handling will knock it off centre. Once that is done, you will have a good datum.

If you have soft jaws you would bore them out until you can fit the datum into the recess, but if you don't, put your outside jaws into the 3 jaw self centring chuck, and mount the newly cut datum part of the casting into those. By gently tapping and seating the casting into the back of the jaws, the bottle shape should run true, or very close. Now another very fine cutting exercise, face off across the bottom of the base.

That was the first way.

The second way goes like this.

Using outside jaws, mount the casting by holding the rim in the nipped up jaws, and tap the casting until it is running true by looking at the bottle shape of the casting. Fully tighten up the jaws and recheck it is still running true. Very gently tap to straighten it up.  You might need to shim the rim to get the neck part running true as well.
The better you can get it trued up, all following machining operations become easier.

Machine very gently across the casting foot. This will ensure that at least the casting is looking upright when sitting on the foot.
Mount the casting onto your faceplate using the now datum foot, and tap everything straight, bottle shape running true. Now you can machine the rim and it's face, plus maybe the hole in the end as well.

If you can get those two datum faces made, you will most probably find you can mount it onto a faceplate using the base datum, and a mandrel to go into the end hole for mounting the other way.

There is another way, by making a mandrel and fitting it into the core hole in the end, but it all depends on how accurately that core has been placed prior to casting.

Castings have to be machined initially by eye, to get your datum faces. Only then can other machining be carried out.

I hope this has helped a little and not confused you too much.

John

Offline rleete

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Re: PMR Coke Bottle Engine
« Reply #2 on: December 23, 2008, 07:28:30 PM »
Yes, this has helped.  I kinda worked it out myself the same, but was hoping there was a simpler way, or something I'd missed.

Since most of the dimensions are taken off the base (or the foot, as you call it), and that sets the stage for everything being lined up vertically, I think method two is the one to use.  True up the bottom, and take everything off that as a datum.
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Offline Bernd

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Re: PMR Coke Bottle Engine
« Reply #3 on: December 23, 2008, 08:17:35 PM »
Bogs,

The place I worked in I used to have to work on rough castings. Of course they had fixtures that they fit in so you could do your maching. So I'm not new to maching rough castings. It's just I would hate to ruin this casting. You've mentioned using the lathe. How about the milling machine to a get some of the maching done? Just thinking outside the box here.

I have the casting sitting right in front of me right now. Looking at it sitting up, just like I have the pic on my web site. You could file the bottom of the frame to get the major burrs off. Just sitting here on the table it looks to sit pretty darn straight. Then you could mill the top off to clean up the casting. Once clean turn 180 and do the bottom same way, just a cleaning cut.

That was one reason I didn't go further on machining the engine. I had a hard time trying to figure out how to begin on the frame. Also remember seeing some were how somebody machined the frame. I did notice a note I had written on the print for the stean chest cover "done 9-30-03. So I haven't touch this kit for 5 years.

BTW, the casting are quite clean, very little flash on it. I'll take a couple of pics and post them.

Bernd
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Offline Bernd

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Re: PMR Coke Bottle Engine
« Reply #4 on: December 23, 2008, 08:23:30 PM »
rleete,

How much have you got done on your engine? I have both wheels semi-finished (at least that what I marked on the print) and the steam chest cover is milled flat both on the bosses and the back with the holes drilled in.

I'm going to hold off on the frame until the end. I want to do a bit of searching and see if I can find how to hold the frame for machining. Could be an off the wall idea. I also remember some place I saw how it was done. If I find it it would take the fun out of finding a solution of our own.

Bernd
You can't fix "STUPID".

Offline rleete

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Re: PMR Coke Bottle Engine
« Reply #5 on: December 23, 2008, 08:35:21 PM »
I've done almost nothing.  I ground the worst of the flash off the parting line on the bottom, but didn't do too much.  I also sanded the sides of the frame - nothing like starting on the finish work!

Frankly, I realized I was jumping in a bit over my head, and better get some experience before messing it all up.  I cut apart some of the iron castings with a hacksaw (my parts are mostly iron), but not much else.
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Offline Bernd

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Re: PMR Coke Bottle Engine
« Reply #6 on: December 23, 2008, 08:51:00 PM »
Might I suggest you give the fly wheel and belt wheel a go. That's what I did to build a little confindence on doing castings. The steam chest is also easy to do. In the mean time we can discuss how to do the frame. This will keep you enthusiasm going.

Odd that yours is mostly cast iron. I think I bought mine back in the late 90's early 2000. Their 2002 catalog has them either in bronze or aluminum.

Bernd
You can't fix "STUPID".

Offline Bernd

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Re: PMR Coke Bottle Engine
« Reply #7 on: December 23, 2008, 09:18:34 PM »
Ok Bogs, I've got 6 pics here for you to study.













It's even tough trying to come up with a way to machine it if you do have it in your hand. I won't worry about getting an answer right away since we're both a ways away from maching the frame.

Bernd
You can't fix "STUPID".

bogstandard

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Re: PMR Coke Bottle Engine
« Reply #8 on: December 23, 2008, 11:06:57 PM »
Bernd,

Now I can see the casting more closely, verfies that the second method is the way to go. The top boss looks rather substantial.

Normally, when build instructions come with a set of castings, they usually suggest you file by hand the first datum face, then after the second one is obtained go back and machine the first hand filed one. My first method eliminated the hand filing bit.

With a casting such as this, your pics verify that turning is the way to go as the first operation, by eyeballing the run of the casting to make it look truly vertical. It is very difficult to make sure it is vertical by doing the first op on the mill.

This casting is very similar in shape to a Stuart Turner standard casting, and I machined one many years ago by using the second method to get the base face true, by holding the standard's top boss, eyeballing to get it running true, and taking a skim across the base face. Everything turned out fine first hit, and ST castings are renowned for having no spare meat on the castings to get a second chance.

I know it can be very daunting when coming to machine expensive castings like this, but there are no hard and fast rules to doing it, it is just a matter of gritting your teeth and hope you make the right decision. Only take off as little that is needed to get your first datum, doing it that way gives you a good chance of a second hit if you don't get it quite right first time. Once you get a few more datums from the first one, you can always come back and trim it down to size.

Once you get done with the base face, then it can be mounted onto a small angle plate, or if small enough onto a 3-2-1 block. Then you can get it onto the mill for machining everthing square to each other.

Good advice on using non essential items to learn how to machine the castings, especially as rl's are cast iron. He can learn how to get under the tough outer skin, and grind up some tooling to achieve it.

John

Offline rleete

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Re: PMR Coke Bottle Engine
« Reply #9 on: December 23, 2008, 11:13:17 PM »
Odd that yours is mostly cast iron. I think I bought mine back in the late 90's early 2000. Their 2002 catalog has them either in bronze or aluminum.

Not really.  The parts that you often see painted are iron, the rest is still bronze.  Why make them of the more expensive material if they're going to be covered up anyway?  So, frame is iron, as are the main bearing caps and both head cover and valve chest cover.  The rest is bronze.  The part underneath the cylinder (bottom cap?) is bronze, too.  Go figure.

They no longer carry it in aluminum.  Apparently, there was a cheaper one and a better one (which you got), and they consolidated into one model - which I have.
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Offline rleete

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Re: PMR Coke Bottle Engine
« Reply #10 on: December 23, 2008, 11:17:45 PM »
Bogs,

I'm happy to see that I figured the best method out correctly on my own.  Shows I'm not a complete dunce at this, and may end up making an actual working engine.
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bogstandard

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Re: PMR Coke Bottle Engine
« Reply #11 on: December 23, 2008, 11:31:52 PM »
R,

You will be just fine, take it steady, think about it a lot, make a few notes, take small cuts to begin with, and all will turn out OK in the end.

It is just a matter of confidence and experience, and that comes with time.

Bogs

Offline sbwhart

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Re: PMR Coke Bottle Engine
« Reply #12 on: December 24, 2008, 04:47:04 AM »
Hi Chaps

It Looks like you'vr got the bottle sorted, castings can be a bit of a pig to get your head round, the first thing I always do with them is clean them up, take them in the house and sit and mull them over whilst watching TV,  :scratch: Getting the datumn right is the first place is the most important, when you've done this every thing else sort of drops in place.  : :thumbup: .

I like the idea of mounting it on a mandrel after you've got the base skimmed off, it can be a lose fit to get everything running true and you can put a centre in the end, this mandrel may be usefull for doing follow on machining, Tip:- try running through all the machining ops in your mind, working out as you go how and what you will need to do the job, you'd be suprized how often people get to the last op only to find that they can't hold the work :(



CrapOcad rules OK  :headbang:

When you come to the fly wheel  set it up so that the inside of the rim runs true, then skim the outside true that way you'l have a wheel that won't look wobbly.

Have Fun

 :wave:

Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

Offline Bernd

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Re: PMR Coke Bottle Engine
« Reply #13 on: December 24, 2008, 04:32:37 PM »
Bogs,

Did a scan of the print with the frame dimensions on it.



and



I'd like to call your attention to the number 4 with a circle around it on the second pic. The note associated with that states, "Cross head guide must be concentric and perpendicular to top of frame where cylinder mounts."

Just a bit more information I thought that might help.

Bernd
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Offline sbwhart

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Re: PMR Coke Bottle Engine
« Reply #14 on: December 26, 2008, 04:04:08 AM »
Hi Bernd

Now that you'e posted a drawing I can see thats it a dinky little engine, I thought that you Chaps over the pond always suppersized every thing, or is that just the Burgers  :lol:

It should make a real neat engine one that you can put on display the problem with big engines SWMBO kicks up a fus where to put it My beam engine tucked away on top of a book case.

Had a real good think about machining casting , see photo

1:- Hold in three jaw and skim up base. take small cuts

2:- Hold base in four jaw push base hard up against back of chuck or  a stop.  Get casting running true as posible, it may help to plug the bore with a piece of broom handle, we've got ral short brooms in our house, and mark centre. Face of and skim OD  drill or bore 0.75 dia to size, this  will make your datums.

3:- Make an arbour nice fit on the bore screwed both ends, you could also make a revereance washer again a nice fit on the 0.75 dia with a concentric OD that will clear the casting, you could use this to pick up off and find the centre.

4:- Mount casting on the Arbour on an angle plate or cube, mark it out bearing position slide face etc, you'd be suprised out usefull marking out can be if nothing else its a easy reference that you're machining is ok.

5:- Machine the base square to do this clean up one face losen mandrel set the clean face vertical to the table with a set square clean up second face etc etc:- if carfully done you should end up with a dead square base.

6:- Keeping the casting on this set up and using the square base you should be able to machine up the rest of the casting and everything will come out dead square a parralel to everything else.

I've added a few phtos of my set up for machining the sadle on a traction engine cylinder that uses this method you should get the idea.







Know get stuck in and make some swarf  :whip:  :whip:  :poke:  :poke:

Have Fun
 :wave:
Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

Offline Bernd

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Re: PMR Coke Bottle Engine
« Reply #15 on: December 26, 2008, 12:34:13 PM »
Hi Bernd

Now that you'e posted a drawing I can see thats it a dinky little engine, I thought that you Chaps over the pond always suppersized every thing, or is that just the Burgers  :lol:


Ya we do. You should see some of our suppersized women that eat those suppersized burgers. :jaw:


Thanks for the Crap-O-Cad. It's very helpful. I printed out the pic and 6 steps. I'll have to study that a while. But in the mean time I'm going to do some of the easier parts. I'm going to do as many as I can on the Sherline lathe and save the frame for the Logan.

On your step 2 you show using the four jaw. I'm thinking of maybe using the face plate to mount the "now flat bottom" of the frame to.

Needs some  :med: time so the brain can absorb all that info.

Thanks for the the time it took you to write and draw that up. Much appreciated.


Quote
Know get stuck in and make some swarf  :whip:  :whip:  :poke:  :poke:

Have Fun
 :wave:
Stew

I think the wife has more "whips & pokes" at me for finishing the pantry than you do to make swarf. But I think I'll be able to squeeze in some shop time.  :clap:

That second pick reminds me I need to get a boring head now that I have the Bridgeport.

Thanks again for the time you took to explain it all.

Bernd
You can't fix "STUPID".

Offline sbwhart

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Re: PMR Coke Bottle Engine
« Reply #16 on: December 28, 2008, 04:48:58 AM »
No Problem

I like those sort of things to mull over I find it kind of relaxing :med:, some people do crossword puzzles  :smart:, some people knit, some people read,  :coffee:

Have

Fun  :wave:

Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

Offline gilessim

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Re: PMR Coke Bottle Engine
« Reply #17 on: February 08, 2009, 05:47:51 AM »
Hi Bernd, just saw this post, I too have one of those kits that I got from ebay a couple of years ago, but my frame is cast iron (and full of hard spots!) instead of gun metal or bronze and I did have fun machining it :bang: to the point where it all got put to one side for some time!

how were you thinking of going about cutting the little square guides for the valve? :scratch:

Giles

Offline Bernd

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Re: PMR Coke Bottle Engine
« Reply #18 on: February 08, 2009, 10:14:42 AM »
Hi Giles,

This project is going to go in "spurts" (drips of water) as I get ideas of doing things. I was looking at doing some of the machining of the frame and just couldn't statisfy myself on a proper way of doing it, even with all the help I recived from the members. So I've put the engine aside for now so I can build some much needed tooling.

Quote
how were you thinking of going about cutting the little square guides for the valve?

I've looked at that part of the project and to honest I have no clue as to how I'm going to do this. Once I get back into working on the engine I'll be posting about it's build again. But for now it will sit on the shelve.

Regards,
Bernd
You can't fix "STUPID".