Another Elmer's OCR

[cfellows]

Success!

I made another crankshaft out of a piece of 1/4" drill rod that was just a hair thicker than the first one. I also shortened the slave valve spring in the head by about 1/8". Runs pretty good now. Gotta put stops on the reverse lever and maybe twiddle with the spring some more. I'm also thinking about grooving the crankshaft on each end and fitting an o-ring to see if I can cut down on the air loss.

But for now, I'm happy! ;D

[ame=http://www.youtube.com/watch?v=BfsX2juV9O8]http://www.youtube.com/watch?v=BfsX2juV9O8[/ame]

 

[GailInNM]

Congratulations Chuck :bow:
We all knew you would beat it into submission.
Gail in NM,USA

 

[Maryak]

Chuck,

Pure Genius, (10% inspiration - 90% perspiration). :bow:

Winners are Grinners. :bow: :bow:

Congratulations. :bow: :bow: :bow:

Best Regards
Bob

 

[90LX_Notch]

Very nicely done.

 

[kvom]

love the sound!

 

[Metal Butcher]

Hurray! :big: Hurray! :big: Hurray! :big:

Glad you got things sorted out! :bow:

I don't think I could have handled another day of suspense!

-MB

 

[bearcar1]

Sounds like you threw a rod at the end. ;D :big:

Nicely done.

 

[rake60]

Congratulation Chuck!
Looks and sounds great! Thm:

Rick

 

[Shopguy]

Two thumbs up! Success with a very interesting design.
Ernie J

 

[PhillyVa]

Good job :bow: Chuck :bow: and it looks cool too.

Regards Thm:

Philly

 

[SignalFailure]

I'm having trouble with my build of this engine....

http://www.homemodelenginemachinist.com/index.php?topic=4819.0

Most of my dimensions (although metric conversions) match those above but it won't quite go on around 5 psi

The vertical air passage meets the bore right at the top as do the two horizontal passages.

The inlet tube is threaded 3mm on the outside with a 1.5mm (1/16") hole - I wonder if that's the problem?

I made a new shaft slightly tigher fit with shallower flats (around 0.75mm deep rather than the 1.25 ish on the original0 but still no joy

Any suggestions please before it goes to the scrap box? :'(

 

[Metal Butcher]

I'm having trouble with my build of this engine....

http://www.homemodelenginemachinist.com/index.php?topic=4819.0

Most of my dimensions (although metric conversions) match those above but it won't quite go on around 5 psi

The vertical air passage meets the bore right at the top as do the two horizontal passages.

The inlet tube is threaded 3mm on the outside with a 1.5mm (1/16") hole - I wonder if that's the problem?

I made a new shaft slightly tigher fit with shallower flats (around 0.75mm deep rather than the 1.25 ish on the original0 but still no joy

Any suggestions please before it goes to the scrap box? :'(

Oh no, don't put it in the scrap box. Tighter fits are good provided that the parts are free and smooth. The shallower flats will give you a shorter air intake timing. That may not admit enough pressure to cycle a full stroke. Check to make sure your flats are lining up with the valve ports. Check that the crank flats don't have excessive overlap at the upper port that leads to the cylinder piping. All of your port and passages openings should be at-or-above the specified size. Your piston to bore fit should be a smooth .001 clearance. Try to lap the piston and crank with a fine lapping compound. Metal polish or a abrasive tooth paste will work. Also check that the timing is correct. Check that you milled the flat for the crank disc set screw accurately in relation to the intake and exhaust flat angles.

I can't tell you how many times I came very close to giving up. My desire to succeed was so strong that when a part went wrong I thought I was going to cry. Other times its a good thing that my shop is in a basement, so no one can hear what I need to say to release stress when things go wrong. I'm not a person that easily shrugs off loosing the better part of a day making a useless part. Its a struggle to overcome this human trait, and I'm probably not alone.

Don't give up!

You will find the answer, its just a matter of time.

-MB

 

[SignalFailure]

Thanks for the encouragement - I only threatened it with the scrap box to try to make it work!

I think everything you suggest is in order although I'd need to check the overlap of the flats.

I was reluctant to open out any of the passages as if it didn't work the main part of the engine would be ruined and with no milling facilities that was by far the most labour intensive part! I'll open them out with just the next or next but one number drill size if all else fails.

Incidentally I deliberately didn't make a flat for the crank disc screw as it would allow me a little more leeway when setting the timing (it'd also mean filing a third flat exactly perpendiculr to the two flats...not easy!). In fact I've yet to come up with a foolproof way to get the flats exactly 180 degrees apart as it is.

Thanks again, more tweaking to follow...

 

[Metal Butcher]

Elmer has the timing correct, and its very critical! On my modified build I milled the flats accurately. On one occasion after I took it apart for cleaning the motor would not cycle a full stroke. Upon close examination I found the set screw slightly off and not perpendicular to the flat. Its THAT critical!

With no other way to get accurate flats, lock a shaft in a square block using a brass screw. Clamp the block in a vise and file or mill the flat. rotate (index) the block in the vise and file the other flat(s).

Here's a link to my up sized version of elmers #3 O.C.R. If you haven't seen it.
http://www.homemodelenginemachinist.com/index.php?topic=4412.0

Best of luck.

-MB

 

[bearcar1]

Hi Pul, Would it be feasible to file the leading edge of that flat in order to obtain some 'degree-ing' of the valve opening? The same could be done to the lagging edge as well if required. A very shallow angle and very fine cuts, followed up by a stone would seem to be the order of the day. You'll get it, I have the faith in your determination and can not wait to see this one fire off!

BC1

 

[cfellows]

Paul, what kind of compressed air source are you using?

Chuck

 

[SignalFailure]

With no other way to get accurate flats, lock a shaft in a square block using a brass screw. Clamp the block in a vise and file or mill the flat. rotate (index) the block in the vise and file the other flat(s)

Doh! Why didn't I think of that?

Bearcar1, I'll open up the airways a tad first and see if that helps but a little 'lead' would seem to be a good idea.

Chuck, it's an aquarium pump that probably outputs about 5psi (it's rated at 10psi but I doubt it's accurate). I can get the engine to turn over with a car tyre footpump so maybe I'm expecting too much from this little air pump?

 

[cfellows]

Paul,

With compressed air engines, the volume of air is as important as the pressure. You can have a lot of PSI, with very little volume and it might not be enought to run your engine. You need a combination of both to get adequate power.

Using an electrical analogy, PSI is like voltage and volume of air is like amps.

Chuck

 

[Metal Butcher]

I would think that a diaphragm type aquarium air pump would not be sufficient.

If you have a piston type aquarium air pump it would probably be sufficient on a small engine.

I have a diaphragm type on my wish list as a way to do demonstration runs away from the mess and chaos of my shop. I don't think it will produce the pressure to run a single acting engine and especially one like #3 O.C.R. that uses a single cylinder port for both intake and exhaust. That's a bit of a problem as far as I'm concerned. I have a few motors that can run for short bursts on lung power alone. I tried this a few times and nearly passed out. The guests found it entertaining, but I did not!

I'm sure Chuck will be along shortly to shed some light on this subject.

Edit. This design of motor would run better at very low speeds in an inverted position. Gravity would benefit the up stroke (down stroke when inverted). Maybe I should consider mounting mine to the ceiling? Now that would be entertaining! ;D

-MB

 

[mklotz]

Aquarium pumps are indeed low volume. Just look at the feeble bubbles they produce in an aquarium.

For on-the-go demonstrations, you can't beat an air brush compressor, e.g.,

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93657

All (~12) of my versions of Elmer's engines and others of similar size run nicely with this compressor. It's very quiet too. You can hold a conversation with it sitting on the bench next to you.

If the air brush compressor exceeds your budget, consider getting a refillable air pig, e.g.,

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41712

although you'll need access to a conventional compressor to fill it.