Author Topic: Elmer Engine Number 14 - Wobble Plate  (Read 31997 times)

Offline propforward

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Elmer Engine Number 14 - Wobble Plate
« on: January 24, 2013, 02:35:22 AM »
OK folks, here goes. This is my second engine build log. I have no idea how long this will take, so bear with me.

For my second engine, I have chosen Elmer number 14 - the wobble plate. Here is a drawing of it, taken from Elmers plans.



I chose this engine, because it incorporates a valve mechanism - therefore increasing the number of moving parts and complexity compared to the wobbler I just built - but at the same time the mechanism is an ingeniously simple one. As you can see, the valve mechanism is a simple rod with a machined groove, that slides across the inlet and exhaust. The valve is actuated by a lever, which is driven by a simple angled plate on the crankshaft.

Now, I am posting this in the CNC section, because, well, I intend to use a CNC machine on this.

Here it is:



I came by this when my company discarded it at the end of an R and D project. (it is perhaps fortunate that the person responsible for deciding what to do with the leftover gear happened to be yours truly, but I digress).

It's not a heavy duty machine, but I have hopes to use this for making fancy spoked flywheels at some point, so this will be a nice project to get familiar with it. I am going to use it to cut out and drill at least pilot holes in the two main side plates, and base plate.

But tonight I started with some more traditional work - to wit, the bronze bearings for the crankshaft.

The plans call for bronze - I think brass would be fine, but it just so happens I had a short piece of 1/2" dia bronze, so since I have never machined that before, I thought it would be a bit of fun. I used a regular knife type cutting tool, with brass type spindle speeds, and that seems to work well.

Here is the first cut, starting to turn down to 3/8 OD for the flange.



Turned down to 5/16 for pressing into the frames, and with hole drilled and reamed:



And after parting off and clean up:



I was happy enough with it, so I made another one. This is a rotten old blurred photo, but I am not a photographer, so never mind.



And that's it so far. Not much - but it's a start. Sometimes, you just have to pick an engine and a component, and start. Then you get into a groove and get going.

This bronze is funny soft stuff, looks like a very sharp tool is important. It burrs up very easily.



« Last Edit: January 24, 2013, 02:21:07 PM by propforward »
Stuart

Forging ahead regardless.

Offline b.lindsey

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #1 on: January 24, 2013, 02:42:39 AM »
Nice start prop. That is one of my favorites of Elmers and is a good slow runner. Great choice for a second engine.

Bill

Offline propforward

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #2 on: January 24, 2013, 02:48:06 AM »
Thanks Bill. I wanted to try something that included a valve mechanism, without going super complex. This fits the bill very nicely.

Actually I just went and checked my old orders, that is a piece of leaded naval brass, apparently - not bronze. I ordered it in 2008. Damn my memory.  :facepalm2:

I think it will work just fine though.
« Last Edit: January 24, 2013, 03:08:45 AM by propforward »
Stuart

Forging ahead regardless.

Offline swilliams

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #3 on: January 24, 2013, 08:02:25 AM »
Was just checking out the plans for the #14 Prop. Looks like a fun engine all right.
I think you'll be ok with the naval brass too. Not such a big disaster if you have to replace them later anyway.

Cheers
Steve

Offline b.lindsey

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #4 on: January 24, 2013, 11:21:31 AM »
It should be fine Prop...I think even brass would be ok, there isn't much stress on those bushings.  For the benefit of those that may not be familiar with the engine, you may wish to post a picture or cut-away view showing how it works.  Elmer was so good at coming up with different ways to actuate a valve mechanism. Maybe that's why i like this one so much.

Bill
« Last Edit: January 24, 2013, 02:25:46 PM by b.lindsey »

Offline Terryd

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #5 on: January 24, 2013, 02:04:31 PM »
Hi Prop,

It looks like an unusual and interesting engine to build.  The brass bushes should be ok, it's not as if you are going to use the engine to drive a generator 24/7   ;).  The bushes look like nice work, but I have just one reservation.  It is good engineering practice to drill/bore holes before making the parts which fit into them.  This is because holes are usually made with fixed size tools such as drills or reamers and the holes produced are not always exactly to size.  By boring/drilling the holes first you can then make the bushes to fit.

This may not be a problem on this project but it is a thought to keep in mind for future ones.  In volume production systems very careful 'limits and fits' are observed and quality control systems ensure that these are adhered to.  This is not always possible in what is effectively a prototype workshop where parts are made to fit.  An illuminating read is John 'Bogstandard's' paddleduck build notes here http://www.machinistblog.com/bogstandards-paddleduck-engine-plans/ - worth reading even if you don't intend to make one yourself.

But good progress so far, let's have lots of pictures and don't worry about them being a bit out of focus - it is still possible to see the quality of your work.

Best regards

Terry

Offline propforward

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #6 on: January 24, 2013, 02:22:53 PM »
For the benefit of those that may not be familiar with the engine, you may wish to post a picture or cut-away view showing how it works.

Good point. I added a diagram and short explanation in the first post.
Stuart

Forging ahead regardless.

Offline propforward

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #7 on: January 24, 2013, 02:28:03 PM »
It is good engineering practice to drill/bore holes before making the parts which fit into them. 

Fair point Terry, thanks. I made this very mistake on the wobbler, and ended up having to remake the brass bearing for that because the first one was too loose in the hole. This time I have tried to leave these bearings to the correct dimension for pressing into the frame.

And if I have to remake them, well, that will highlight the truth of your words very much. But I certainly shall not make the piston until the cylinder assembly is complete.
Stuart

Forging ahead regardless.

Offline propforward

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #8 on: January 26, 2013, 04:19:27 AM »
I managed to get a little bit more time in the shop today, so I made some progress.

The first part of the day was just spent turning and facing brass, and better understanding tool grind details, spindle speeds and feeds, and how they relate to finish.

After a little practice / playing about, I decided to tackle the wobble plate and collar.

These are two simple parts - a 1" diameter disc, which sits at an angle on a simple brass collar. Per Elmers guidance, I made the plate first, and then made the collar to suit.

I had some 1 1/8 brass in stock, so I faced off and turned the OD first.



With that done, I drilled the through hole.



I didn't worry overly about what hole diameter I ended up with, since I knew I was going to turn the OD of the mating part to suit. All I mean there is that I did not feel the need to set up and bore the hole to a close tolerance.

I parted the disc off, and must say I was happy with the finish on side 1 (which I faced earlier).



Oh dear - but not so happy with the finish of the parted side.



I suspect that if I had ground a better relief angle on the parting tool, I could have parted it to the right width, and got a decent finish too. Lesson learned.

Anyway, I decided to try and save the part, since it was on the thick side. I made a simple expanding collet from a piece of leftover brass. It is simply a piece of brass, with a shoulder turned on it to match the ID of the disc. Then, I drilled through and tapped M6 (because that was the size of countersunk screw I had handy), then counterbored, and then countersunk the ID. I then cut (with a hacksaw - quick and easy, but it did the job) 2 slots, to allow the part to expand when the screw was tightened.



Of course, I had to dress the shoulder up to true it, so I'd have been better off not machining the shoulder until this point, but no matter.

The result is this fairly brutal fixture. I had to turn the OD of the screw slightly so that it would fit through the collar hole. No big deal.

With that done, I could mount the wobble plate.



The fixture worked a treat. Admittedly, this is somewhat making  mountain out of a molehill, but I saved the part, and learned some stuff. It's all good. I turned the plate to the right thickness, and all was well with the world.



It is a pretty ugly, tarshled screw. I usually throw those out - I'm surprised it was in my odds and ends screw jar, but it did the job.

Next I made the collar. It is a simple part - so not too many pictures here. Basically, the trick is to machine it close to the diameter of the ID of the wobble plate, and then take small finish cuts off the OD, test fitting the plate, until you can get the plate to sit firmly at the correct angle. I suppose I could have done the trigonometry to calculate the required diameter, or even laid it out on CAD (which I know would have met with disapproval), but in the end taking light cuts until the correct fit is achieved works perfectly well.

After that, I parted the collar to length, and added a threaded hole (4-40 rather than the 3-48 on the plans - because I have 4-40 grub screws in stock).



You can see the little remnants of blue that I used to help mark the hole position - that will clean off when I prep the parts for soldering.

Next up - the cylinder.

The plans show a plain brass cylinder, soldered to the cylinder head, of 0.5" OD and .375" ID.

I saw someone somewhere add some fins, just for aesthetics, and I thought that was a splendid idea, so I followed suit. I increased the OD to 0.625", and then cut some grooves, about 0.1" wide, leaving fins of 0.05". The fins should come flush against the side plate, I should not need to increase the length of the valve or the crankshaft to match it - although that is another valid option.

First cuts:



A little further...........



Most of the fins done



After the fins were all machines, and the edges lightly chamfered to remove burrs, I drilled and reamed the bore to 3/8. Then I cleaned up the end, and parted off the cylinder.



The cylinder just needs deburring at the parted end, and then a light face to length, and it is complete, and ready for soldering to the cylinder head once that is made.

Here are the parts so far:



Plenty to do yet, but I am 5 for 5 so far - no scrap on this project yet!  :whoohoo:

Tomorrow - perhaps the cylinder head and piston. I'll see how I feel.

Stuart

Forging ahead regardless.

Online Jo

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #9 on: January 26, 2013, 07:10:29 AM »
If the scoring was not too bad, you could have cleaned up the back of that disc by rubbing it on a piece of wet and dry :ThumbsUp:.

Jo
Enjoyment is more important than achievement.

Offline b.lindsey

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #10 on: January 26, 2013, 11:08:44 AM »
You are making some good progress there Prop. Still following along with enthusiasm here!!

Bill

Offline zeeprogrammer

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #11 on: January 26, 2013, 12:05:37 PM »
Sorry to be a late comer. Missed the start of this while I was sick.

I think I've only seen one other engine like this. It'll be a an interesting read.
I look forward to it.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline Tennessee Whiskey

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #12 on: January 26, 2013, 12:16:07 PM »
Prop, you are moving right on along. I gonna have a lotta catch'n up to do. Your surface finish does appear to be spot on. Keep up the good work and I'll be watching. Great pics too.

Eric

Offline propforward

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #13 on: January 26, 2013, 02:20:42 PM »
If the scoring was not too bad, you could have cleaned up the back of that disc by rubbing it on a piece of wet and dry :ThumbsUp:.

Jo

An excellent point. At the time, I really badly wanted a nice, smooth and machined finish both sides.

Of course, having achieved that, it dawns on me that I am going to solder this disc onto the collar later, and after that it will need some sort of clean up anyway, so in this case it would have been quicker and easier to just clean up on the wet and dry as you suggest.  :facepalm2:

It just goes to show how you have to think about making the part all the way through to the conclusion, including its integration with other parts, not just the next one or two steps. No big deal though, making the little collet wasn't a bad exercise and didn't waste a lot of time.

I'm quite enjoying this project, I should be able to get out in the shed for a bit today. Maybe tackle the cylinder head, piston and valve.
Stuart

Forging ahead regardless.

Offline Don1966

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Re: Elmer Engine Number 14 - Wobble Plate
« Reply #14 on: January 26, 2013, 04:13:19 PM »
You are making good progress Prop. I like what you did to the cylinder. Keep the photos coming, and I do like brass by the way. It's cuts easier and molds easier then steel. A little more expensive but perfect for first projects.

Don


 

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