A Beginner's First Engine (Single-acting Oscillator)

[gary.a.ayres]

Thanks Gentlemen.

@ Peter - the test belts in the picture do seem a bit hard, but perhaps longer ones would soften up with a bit of handling and provide some grip. If not, there are options as you suggest.

@ Chris - thanks.

@ Bill - I hope so too. It'll be bleak if the bores are knackered. However, I think they are probably ok. In fact, thinking it through, after the screwup I cut what I thought was an undamaged part of the shaft (it was behind the ER-32 collet when it happened), put the wheels on and just nipped up the grub screws and it seemed to be running true again. I then took the wheels off, milled flats on the shaft for the grubscrews, reassembled, and it seemed to be only after that that it wobbled. I admit I was perhaps a bit overenthusiastic in milling the flats - each one down 1mm, on opposite sides of the shaft. More like notches really. I'm now wondering if this distorted the bar by creating or relieving stresses in the steel (or even just mechanically bent the bar by taking too-heavy cuts). It didn't happen the first time, but still...

I hope that new 6mm bar arrives tomorrow!

[steamer]

Hey Gary

My very first crank...turned on a AA109...I was on the last cut, and I fouled the tool...BANG!   Instant pretzel....I was gutted....

I took it to work, and I showed one of my machinist friends in the prototype shop...."Think we can straighten it?
"
He picks up a babbit hammer and gives it a mighty WACK!..........     I say hmmm    Looks good!....I put it between centers   0.003" run out.....I called it done!!

 

If you have issues after this when the new shaft comes in...post it up ...we'll talk ya through it.

Dave

[Jasonb]

It's coming along well Gary

You may want to think about swapping the pulley around so the forces from the belt are not as far from the bearing, as you only have a single bearing any pull from a belt will tend to make the bearings bind. Also diameter could be another issue, smaller the pulley the more mechanical advantage the poor little engine will have - think of a Mamod with the pully groove cut into the flywheel's hub.

[gary.a.ayres]

@ Dave - yes - it's that horrible moment of realization, when you hope you just imagined it but really know that you didn't.
I could try whacking mine with a hammer but I don't have the Jedi touch that your friend does. I'd be at it for 10,000 years and still it wouldn't be straight.

@Jason - thanks. I'd be a fool to ignore your advice. I'll reverse the pulley and reduce the diameter (perhaps not to Mamod-like dimension but a bit less chunky than it is now).

This morning when I woke up, I suddenly remembered what probably caused the runout after the initial mishap. Having shortened the bent shaft and re-chucked the assembly, it ran true. However, after I had milled the flats it didn't. It came into my mind that while the shaft was held horizontally in the rotary table chuck for milling, I was changing chucks in the mill and I accidentally dinged the shaft with one of them. That's probably what did it, though I convinced myself at the time that it wasn't hard enough (the power of denial!). Fortunately the pulley and flywheel were lying on the bench at the time so the bores *should* be ok... 

Strange, the way that memory works (or doesn't, as the case may be...).

[gary.a.ayres]

Today's endeavours:

The new silver steel didn't arrive but I found an undamaged offcut from the original piece. Flats (shallower than last time) were milled for the grub screws and the flywheel and pulley were mounted on the shaft, with the pulley the other way round as per Jason's advice. A very fine skim cut saw the flywheel running true, and the diameter of the pulley was significantly reduced (again as suggested by Jason):



Then, moving on, I marked out a piece of French walnut which in due course will become a sub-base for the engine. This was from a tree at my place in France that sadly I had to have cut down as it was too near the house and threatening to do damage. The upside was that I now have a supply of walnut that will last me for years. Never thought any of it would end up supporting a steam engine though:



Next, I broke out the yummilishious red layout dye ( DO NOT !!!) and did some initial measuring and marking out on the standard. Ramon advised me that a brass cylinder oscillating against an aluminium port block is not ideal, and suggested that I make a brass wear plate. It appears in situ (but not attached) in this photo:



The plate is cut from thin brass sheet and it was much easier to shape than I thought it would be (pair of snips and a small drum sander in the drill press). After shaping it was a bit bent, but responded well to a small planishing hammer applied to the reverse side on the anvil of the vice. Now it is in the vice, being squeezed mightily for a couple of days between two flat pieces of wood (which at the very least will do no harm). The plan is to fix it to the frame with epoxy and tiny cap head screws, but as you can see it will first require some fine sanding and polishing to achieve the appropriate surface quality:



Finally, the story so far:



Many thanks to all you guys for your support with this simple build. Even though your skills are way beyond the level of single-acting oscillators, so many of you have checked in to this thread with encouragement and sound advice. I truly appreciate it.

gary

[b.lindsey]

Looking great Gary. The wear plate should work well no more that the engine will run. The main thing is lubrication between the cylinder and wear plate, that will help as much as anything. Love the walnut btw.

Bill

[crueby]

Fine progress Gary!

One thing I like to do on mating surfaces like your cylinder and plate is to lap them on a diamond stone to be dead flat and no bumps. I have a couple different grits that I bought for sharpening chisels and plane blades, they are flat steel plates with the surface covered with diamond grit. You can do the same thing with a sheet of fine emery paper taped to a glass plate, or use diamond lapping paste on the sole of a wood plane (have one I use for that which is no longer used for wood work).
 

[gary.a.ayres]

Many thanks both. 

@ Chris - is this the kind of thing you mean? :



If so, I have one for sharpening wood chisels. Should I use it with water for the port face and wear plate?

[Gas_mantle]

Taking shape nicely 

I can see the thinking behind the wear plate but my only concern is if it allows leakage between the plate and the aluminium upright. I guess with air it wont be noticable but it you want to run it on your boiler I think you'd need to solder some sort of intake tube (and probably exhaust) to penetrate into the aluminium with a leak proof seal.

[gary.a.ayres]

Ah... the plot thickens!   

Peter, I will be running it on steam. After Tug suggested the wear plate my thought was just to give it a good thick coat of epoxy, stick it on, clamp it until it sets, put screws in for good measure (and appearance), then drill the ports and pivot hole through the brass, epoxy and ali in a oner. In other words with the epoxy forming a seal.

Wouldn't that work? Or would the wet steam mess with the epoxy? And if so, I wonder if there's an alternative adhesive / sealant as the soldering idea sounds a bit fiddly...

[crueby]

The lapping plates I have are solid blocks, about 3/16" thick so no flexing. Not sure how rigid the one you showed is. If it can flex its no good, you would wind up with a curved plate. I use mine with oil to float off the metal dust.

[gary.a.ayres]

Chris -

Under the steel it's hard plastic so I think it's pretty rigid, but I will check.

Thanks again,

gary

[Gas_mantle]

I appreciate that the steam wont be of high pressure but knowing how steam highlights even the tiniest of leaks I think you'll get leakage around the plate, on a little engine like this it isn't really going to affect performance but as you've taken care to make it attractive looking I think steam leakages may detract. The problem may be worsened if you apply load to the engine.

The thing to do is try it and see what happens 

Soldering shouldn't be a problem, I'm not sure where you intend to mount the intake but if it is on the back the same soldered tube could be the intake pipe.

[gary.a.ayres]

The thing to do is try it and see what happens 

I'll probably do that in the first instance Peter, but if there are leaks I'll be wanting to fix them so could consider the solder then.

I presume we're talking soft solder here if I go down that road?

 I'm waiting for some pipe-to-thread connectors to tap in as steam supply and exhaust. I'll see what they're like before deciding where to put them but straight in the back for them both would be my preference so as not to detract from the outline of the engine's shape.

Cheers   

[Gas_mantle]

It's got to be worth trying with your original intention, you haven't anything to lose.

I'm not sure how far the ports are apart (4mm?) but unless the epoxy holds up well it will be easy for the inlet steam to start finding it's way into the exhaust. Mind you that may give it a great V8 sound 

I can't say I know a lot about epoxy but if it softens under heat could it block the ports ?