Building an Oscillating Engine for my first engine

[malofix]

I'm using the plan i found at LittleMachineShop. Plan looked simple so i started turning the piston to the size. So after i took my supposed last cut i measured the diameter with both a caliper and a micrometer (25mm-0.01mm precision) with caliper it showed slightly(from a few 0.01 to a few 0.10mm)different each time i took measurement so i tried the micrometer,it was better. Then i checked different sections and to my surprise it was showing slightly different diameters at different sections? Am i not taking measurements correctly? Or is it caused by not locking the carriage, although when i tried to move it by hand it doesnt move?

 

[kvom]

Different pressures with a micrometer can cause different readings unless yours has the ratchet mechanism.

But very small variations won't matter.

It's easier to get a fit by boring the cylinder first and turning the piston to fit.

 

[malofix]

Different pressures with a micrometer can cause different readings unless yours has the ratchet mechanism.

But very small variations won't matter.

It's easier to get a fit by boring the cylinder first and turning the piston to fit.

I think i have that ratchet mechanism, gotta try. I Also noticed that work piece gets so hot when doing large cuts so it is probably better to take the last cut after it cooled down, that way i don't take wrong measurements.

Is there any other part that can cause me problems with measuring? or they can all be made to fit?

Edit: Hmm it looks like my work piece isnt still centered despite i removed close to 20mm.Checked with a TIR and indeed there was a small swing. When i check with micrometer from different angles it is showing different values even at the same section. I'm using a three-jaw chuck, is this even possible?

 

[vederstein]

These simple oscillators are very forgiving. That's why they're beginner engines. If it leaks a little, it'll still run. At this point in the hobby, strive for accuracy, but don't get discouraged by it.

Steam (at least compressed air) is far more forgiving than internal combustion.

Even though my current steam engine designs are far more complex than a simpler wobbler, I still remember the thrill I had when my first, very badly built engine ran on compressed air.

Today I just expect them to run and much of the excitement is gone.

(If I can ever get an IC engine to run for me, the thrill would probably come back).

...Ved.

 

[malofix]

These simple oscillators are very forgiving. That's why they're beginner engines. If it leaks a little, it'll still run. At this point in the hobby, strive for accuracy, but don't get discouraged by it.

Steam (at least compressed air) is far more forgiving than internal combustion.

Even though my current steam engine designs are far more complex than a simpler wobbler, I still remember the thrill I had when my first, very badly built engine ran on compressed air.

Today I just expect them to run and much of the excitement is gone.

(If I can ever get an IC engine to run for me, the thrill would probably come back).

...Ved.

Do you know how much can i stray from tolerances till the part loses its function in such oscillating engines ?

 

[vederstein]

I no longer have my first engine, but my cylinder was probably 0.002-0.005 under and the thing still ran. I'll grant is leaked huge amounts of air, but hell it was my first engine.

...Ved.

 

[malofix]

Sizes like the piston rod is not that critical i take. Like if the rod turns out to be 0.4inch instead of 0.313 it wouldnt be much of a difference since it doesnt have to fit some where ? Maybe it would add some weight.

 

[ag1985]

Hi malofix, I got this engine running for the first time this Saturday. It is the first “real” machine project I ever completed. And let me tell you it is rough, but runs. I even accidentally drilled the the pivot screw hole all the way into the cylinder. Re-made the cylinder and did it again. I figured whatever, I’ll just continue on and let it rip and the engine worked. If something didn’t work after assembly I would worry about remaking it then.

 

[methuselah1]

Oscillators are serious engines, and were used in full sized ships such as Brunel's SS Great Eastern. This used screws powered by "conventional" horizontal engines, but the paddlewheels were powered by oscillators. It was the largest ship ever built (1854), only surpassed in size, forty-one years later in 1899.

So oscillators are not quite "Mickey mouse"!

They're attractive for beginners in single acting form 'cos you can get them made quick, and there are only two critical aspects- piston/cylinder fit, and port positioning.

Now I looked at the design before writing, and it strikes me it is a compressed air model; as such the barrel is best done first, with the piston machined afterward to a "pop" fit. "Nominal" diameters are not critical here, it's the fit that does the work. The ports on this engine are 1/8", so it will need a major error to stop the engine from running; if you centre punch the location of the pivot on both the upright and the cylinders with dividers (set at 5/8") you can forget about the 0.402" given dimension, as the scribed arc on the standard will be exacty correct when intersected.

One further thought, though - if you bore the cylinder right through, then loctite a top-hat plug in the top afterward, it may make machining easier; i.e. you can ream right through, or nor worry about boring a square bottomed hole blind.

Enjoy!

-Andrew

 

[methuselah1]

On the subject of calipers vs. micrometers, the caliper is a good guide, but it is the micrometer, used only with the ratchet, that is absolute.

Caliper readings can be aided by supporting with the right hand, whilst drawing the jaws together across the work with your left thumb and fingers. I know that there's a thumb grip on the moving jaw, but this will give rise to false readings if the jib adjustment is out in any way.

It's also important to check your mic for zero error every so often. Close it on a piece of thin card, then pull it out to make sure that the anvils are clean first.

Also, be aware that reamers, when new, often cut a trifle oversize.

-Andrew

 

[malofix]

I completed the piston today, it roughly matches the dimensions on the plan. I'm thinking next the cylinder but i'm wondering how will i do the boring with a 3 jaw chuck, with this square piece?

 

[methuselah1]

You haven't said what lathe you are using... Does it have a tee slotted cross slide?

 

[malofix]

I think not. I'm using this lathe.

 

[methuselah1]

Are you sure you've sent the right link? Why not secure the workpiece (your cylinder) to the cross slide with tee bolts and packing, and drill/ream from the headstock? That's what those tee slots are generally for... After securing a toolpost, that is. Horizontal boring.

 

[kvom]

For turning rectangular stock a 4-jaw chuck is preferable. If you are serious about machining your lathe needs one.

 

[malofix]

Are you sure you've sent the right link? Why not secure the workpiece (your cylinder) to the cross slide with tee bolts and packing, and drill/ream from the headstock? That's what those tee slots are generally for... After securing a toolpost, that is. Horizontal boring.

Yes this is my lathe. How can i secure it with tee bolts? Woulnd't it be hard to center the cylider for boring?

How do i do the cavity on the flywheel? with a boring tool or with a cuttin tool?

 

[ShopShoe]

malofix,

You asked: "Woulnd't it be hard to center the cylider for boring?"

Compared to other approaches, probably. The location of your hole in the horizontal plane is easy , using the cross-slide hand wheel. The location in the vertical plane will have to be set by putting blocks and shims under the piece as you clamp it down.

You will need to remove your toolpost from the cross slide. Note how the toolpost bolts on. You most likely will find that there is a T-nut in one of the cross-slide slots. You will need some more T-nuts and apppropriate bolts and hardware to anchor your workpiece. T-bolts are just bolts with heads to fit your slots. You can use either T-nuts or T-bolts.

You can make T-nuts or bolts by copying what you have that anchors your toolpost. You should be able to make them with a hacksaw and files. You may also be able to buy them in the size you need.

This link from Grizzly provides an EXAMPLE of T-nuts. Those particular ones WILL NOT FIT YOUR LATHE. But, If you look in the upper left corner of that page, you will find a key to the critical measurements you need to pay attention to when measuring or making T-nuts or T-bolt heads.:

https://www.grizzly.com/products/grizzly-t-slot-nuts-pk-of-4-5-8-slot-1-2-13/g9515.

--

I'm not sure what you mean by "the cavity on the flywheel." Can you illustrate the feature for us?

--ShopShoe

 

[malofix]

malofix,

You asked: "Woulnd't it be hard to center the cylider for boring?"

Compared to other approaches, probably. The location of your hole in the horizontal plane is easy , using the cross-slide hand wheel. The location in the vertical plane will have to be set by putting blocks and shims under the piece as you clamp it down.

You will need to remove your toolpost from the cross slide. Note how the toolpost bolts on. You most likely will find that there is a T-nut in one of the cross-slide slots. You will need some more T-nuts and apppropriate bolts and hardware to anchor your workpiece. T-bolts are just bolts with heads to fit your slots. You can use either T-nuts or T-bolts.

You can make T-nuts or bolts by copying what you have that anchors your toolpost. You should be able to make them with a hacksaw and files. You may also be able to buy them in the size you need.

This link from Grizzly provides an EXAMPLE of T-nuts. Those particular ones WILL NOT FIT YOUR LATHE. But, If you look in the upper left corner of that page, you will find a key to the critical measurements you need to pay attention to when measuring or making T-nuts or T-bolt heads.:

https://www.grizzly.com/products/grizzly-t-slot-nuts-pk-of-4-5-8-slot-1-2-13/g9515.

--

I'm not sure what you mean by "the cavity on the flywheel." Can you illustrate the feature for us?

--ShopShoe

Thanks for the information. If i were to make the t-nuts is it okay to make them from aluminum?

For the flywheel question. I was asking how to do the part highlighted below.

 

[methuselah1]

Ideally this detail would be done using a trepanning tool- one that is made to part into the face of the work. These thing are ground like left hand grooving tools but presented as you would a boring tool; with extra clearance ground to allow them to clear the inside of the radius they are expected to cut.

This is not the average turner's favourite operation, and on a lathe like yours, the chatter may shake your fillings out! To mitigate this, turn the tool upside down, and machine *on the other side of the lathe Z axis*.

Option 2. Make the flywheel from brass, *drill and ream the size of the boss o/d*, bore as normal, make the boss as a separate piece, undrilled, and secure it with solder. Then hold by the flywheel rim and drill/ream then tap the boss to make sure everything remains concentric.

You may be able to use the same procedure with aluminium, as per the drawing specifications, but using one of the more virulent types of loctite, like 638.

-Andrew

 

[ShopShoe]

malofix,

For the flywheel, methuselah1 explains it above. You could try using a standard cutter to cut a shallow dish to start, then use boring tools to sharpen the corners. You will have to alternate between the three tools and gradually work up to the shape on the drawing.

You will find that the flywheel near the outside rim needs to run at a slower speed because the circumference is longer and more metal goes past the cutter in a given period of time. You will be able to run faster nearer the center. This constant juggling of speeds and feeds and cutters is, as is said above, a challenge on a small machine.

A useful alternative might be to consider modifying the design of the flywheel to make it easier to make. this is just one of the things all of us have to face from time to time.

--

When you were asking about setting up your shop, one of the things that wasn't really mentioned was the part where you might want a grinder to make toolbits to solve your own problems. In my case, thus in my own opinion, learning to grind tools is part of the skillset. I think that is also where you learn the relationship between the shape of the cutter and the job it is required to do, or vice-versa. It is also true that the cost of plain square toolbits is quite low and you can do a lot of experimenting with a bunch of them (At least in my area, your situation may be different.)

--

Yes, you could probably make T-nuts from aluminum. You would want a high-quality, high-strength aluminum, something like what is called 7075 ("aircraft aluminum") in my part of the world.

--ShopShoe