Elmer's Tiny in 1/4 scale.

[ttrikalin]

More than a few months later, this morning I was able to finish all the parts of Elmer's tiny in 1/4 scale. On with assembling the parts...

I had to machnine the airducts. Because the engine is so small, I have to supply the air through the base.

These are 2 parts that will form the ascending airduct (My drill is a tad short, and I had to build the duct up from 2 parts). The part that is laying down is 0.285" long, with a stem of 0.044" diameter. The upright part is the lower portion of the ascending airduct, has an external diameter of 0.0531" and it's upper part has a hole at 0.0445" to receive the other

The two parts loctited together

And with the horizontal bridge that will connect to the main column of the engine.

This is how it fits the main column of the engine. If you were following the thread you may remember that my mill has had an extensive 6-7 thousands of backlash which I mistakenly did not account for when drilling the ports and holes, which ended upp 6 thousands off center. To correct the geometry I made an eccentric bushing for the crankshaft - eccentric by 6 thousands. :-*

Crankshaft in place, cylinder and piston assortment on the left.

They fit...

Note the long pivot pin -- it is meant to have a tiny spring to hold the cylinder in place... Instead of a spring I'll use another solution (thanks Bogs)...

Another view...

Another view...

With the flywheel...

Another angle...

Together with the 1/2 size of Elmer's tiny I made last year...

And together with the full size of the tiny...

Next week, perhaps, I'll implement Bogs' solution to replace the string... and test if it runs...

till then take care,

tom in MA

 

[NickG]

Wow! I'll have to look at the sizes again to get an idea of scale, it's deceptive! :bow:

 

[arnoldb]

Great job Tom - that really is a small little engine. I can't wait to see how you retain the cylinder - and to see it run!

Regards, Arnold

 

[ttrikalin]

Yes, it's been a trip... even if it does not run in the end, I couldn't care less. I learned so much, made new tools to make the parts, tuned my lathe and mill to watchmaker precision... I enjoy it. Next weekend I'll try to run and trouble shoot.

tom in MA

 

[mklotz]

Nicely done, Tom, but if you're going to show us such fine miniature work, flaunt it! Put some common object in your pictures that establishes the scale of your work.

I've built Tiny so I know just how difficult it would be to build it in quarter scale but others unfamiliar with the engine won't grasp just how small it is.

 

[kjk]

I'm trying to get my head around how small this is and having now looked at the plans for the original "Tiny", I am absolutely amazed.

a 5/32 diameter flywheel on a 1/64 inch axle. Wow! this thing is small.

 

[NickG]

Wow, those sizes really tell the story - if possible it'd be good to include something in the pic to give an idea of scale (picture is worth 1000 words!) e.g. an m&m or coin to name two items that have been used!

Well done again tom, as you say, even if it doesn't run it's still a great achievement.

Nick

 

[ttrikalin]

Ok then, perspective...

and a close up using a reference unit...

Regarding size, I would not be able to machine the parts without a stereomicroscope. It is a bit rough in manual rotation, the bore is most likely not smooth... damaged during fitting? :-[ I'll see next weekend... :-X


take care,
tom in MA

 

[kustomkb]

Amazing work Tom, very impressive. I hope you get it running.

Just a thought, when you shoot a video, try to leave no reference of scale in the frame and after it has run for a bit move in with your finger. They'll say "Bawaaa!?"

 

[BlakeMcKee]

Wow thats a tiny engine, nice job!

 

[NickG]

Wow - other than that I'm speechless!

 

[Maryak]

Tom,

I can barely see it let alone make it. That's amazing. :bow: :bow:

Best Regards
Bob

 

[Groomengineering]

I make swarf bigger than that... (but not as nice). Amazing work Tom!

Soooooo..... 1/8 scale next? ;D :hDe:

Cheers

Jeff

 

[ttrikalin]

We do not have a runner . Near the top dead center the piston stops as if it hits a ridge in the bore- you can turn it with force and it overcomes it... but I think that we need an overhaul :big: .

So tomorrow, I'll probably make a new cylinder out of steel. There is not enough meat on this one to rectify the bore (and it'd take too long to set up... longer than cutting a new one... another cylinder in the scrapbox.... all this material I throw away... Rof}).



till tomorrow then

tom

 

[NickG]

Nearly there Tom - what a waste of material though :big:

 

[ttrikalin]

OK, started machining the cylinder out of steel on the 4-jaw... manually this time, not CNCed. I want the pivot pin and the cylinder machined out of the solid. This will allow me to pursue a bigger bore, and increase the likelihood it'll run. If the cylinder and the pivot pin are not one piece, you need a thicker cylinder wall to press-fit or loctite the pin in it. If the assembly is one piece, you can afford a bigger bore.

Starting from a 0.250" piece of steel I machined the pivot pin, which is 0.0315" in diameter. It is eccentric to facilitate later setup.

Digging in the corner where the pin meets the face with a sharp cutoff tool. I undercut a bit, to ensure that the faced surface will be flush on the column when the cylinder is done.

I offset by 0.059" and drilled the port hole, using the tailstock adapter to center the drill.

And here is the drilled port hole 0.016", at a depth of 0.047".

tomorrow morning mill time.

take care,

tom in MA

 

[NickG]

That probably is the way to do it for this one Tom - what you've said makes sense, not easy though :bow:

 

[ttrikalin]

An update... Overhaul completed last weekend... A new one piece steel cylinder and pivot pin replaces the previous brass cylinder and steel pivot pin. I did not round the corners of the new cylinder. Also the bore is a bit bigger (0.055"). You'll see it in the next photos. Attempt to implement John's solution... Here is a piece of brass shim, flattened out...

and this is the shim holding the cylinder on the column. It will sit on the centerline of the pivot pin. Here it is approximately positioned.

Another view...

Another view...

It did not run, but I think I'll make it in the end.

1. The piston moves smoothly and with nice clearance. It may be a bit tight for this size, but the movement is smooth all around.
2. The geometry of the ports is correct. When I position the piston over the intake port and start the air, it moves to the bottom dead center, but the flywheel is small, stores too little energy and cannot self-start.
3. I will have to use an electric starter motor to turn the flywheel until the engine starts under air.. It is very small, I can not give it a flip with a finger nor a string.

take care,

tom in MA

 

[arnoldb]

Thanks for the update Tom - I get the cylinder retention method now :bow:

Regards, Arnold