A 5 year old... Play-Doh and Progress...

[Cedge]

Ok... you won't see it in any machinist manual. It's even a little hair brained and probably worth a good laugh, but a 5 year old just might have saved my bacon with Pla-doh. Yup... that brightly colored, smelly, dough like concoction that gets on everything within a hundred feet when they play with it.

As I've mentioned before, the Elbow engine has been defying all efforts to eliminate a persistent stiff spot . With 10 piston ends, 10 cylinders and 10 decorative balls that potentially limit adjustability, there are quite a few possible combinations to try when looking for a bummed piston set. Add in the fact that they all look alike and... well you get the picture. It's easy to lose track of what you've done in a real hurry.

My 5 year old grandson was over for the weekend and, as is his habit, he broke out the Play-doh. While he played with it, he pressed a number of objects into the goo, over and over. I wandered into the play room this morning and saw he had once again left some out of the container and it had dried to a solid imprint of his efforts. I was about to throw the small dried pancake away when a bell went off in my head.

I swiped a bit of the stuff, pushed it into a plastic container lid, put this into a plastic bag and rolled it out smooth with a water glass. I then located a piston set that seemed to be performing well and pressed it into the Play-Doh. When removed, it had made a perfect impression of the piece.

I then carefully laid each piston set into the imprint for comparison and immediately noticed a variance of about .020 in. with one end of the set. Each set showed the same variance. When checked with a depth gauge, the piston ends were all evenly matched in length. It took a couple of minutes to digest what I was seeing.

I compared the pieces again, but this time I placed the set in the mould and then reversed them for a second test fit. The variance was definitely present in each set, but it was uniform across the group. I began looking for a reason for this oddity. It was found in the bend of the elbow. I apparently missed the center point when I built the bending jig I used. It was ever so slight a miss, but enough to add .020 in to one end of the piston sets.

For the heck of it, I arranged the pistons on the work table so that I knew which end was a little short and began replacing them into the cylinders. I chose to place the long end in the upper drum. Since my adjustment point is the lower drum, I can easily move the pistons in and out to make the required adjustments.

Things feel much better and I'll be putting air to the little devil again this evening. Wish me luck.

I think I'll be keeping a bit of Play-Doh or modeling clay around the shop....LOL.


Steve

 

[Bogstandard]

Hi Steve,
What are you keeping the play-doh for? Making this elbow engine isn't reverting you back is it?
There is in fact a very easy way of checking for correct length, using the engine itself.
Take off the bottom cylinder but leave the valve in place. Turn the top cylinder so one of the holes is at the bottom. Put a piston in the bottom hole and measure the distance from the bottom valve block to the bottom of the hanging down piston, this will also show if any pistons are too long and liable to hit the valve block. This method can also be used for the other valve block by resting the engine on its end and carrying out the same procedure but taking off the vertical piston block and flywheel.
Sorry, but I forgot to mention this to you before, I didn't do it on purpose, even though I am a black hearted soul.

John

 

[Cedge]

John
Heck... you have to have given up on a first childhood to bother with reverting ...LOL. Actually the Playdoh idea mdde for an easy way to get a quick visual of what was proving to be difficult to measure. I've gone through the process you mention, but since the piston ends themselves are of identical measure, it didnt show up during the check.

The variance was due to an off centered bend which, when mixed in opposing positions, was causing a difference in the way the cylinder was supporting the piston. Once all were of the same "polarity" the flex equalized quite a bit. Tough one to spot. For some reason it caused some sets to be free while others wanted to bind. Adjust for one group and the other would be displaced.

I guess the bottom line is that the center line of the bend is apparently a fairly critical point. I'm pretty sure this little problem is solvable, but it was certainly an unexpected one.

Steve

 

[1Kenny]

Wow Steve,

You can get Playdoh! All I can get here is Claytoon. :lol: I like the orange or the yellow for engine work.

 

[Bogstandard]

This is where we differed Steve,
My bends aren't in the centre, because I did everything by eye, but that didn't cause any problems.
I have just done a very quick sketch to show how I did my pistons.
I took the outside edges as datum faces, then when in the miller they were all dropped onto the parallel and machined, so they were all the same length, no matter where the bend was. Wacked them in any way and it was then fine tuned to run.

Now thats what I call a rough sketch.

John

 

[Cedge]

John
Just another example of there being any number of cat skinning techniques...(grin). I tend to work more on the lathe, so I turned the centers of the pistons after doing a mark up using the caliper trick I shared in tips and tricks. A final check before cutting off confirmed all was as it should be. I then moved to the jig shown below and bent each piston to the witness marks by eye.

This proved to be a little bit inaccuarate, but after using a 1-2-3 block as a square, the pistons were tweaked into square. I repeated this step several times and finally got zero light gap between each piston and the block.

I can only guess why matching the bends made such a noticable difference in things. I'm just happy to be at least a little further in the right direction...LOL. I was just informed of a social obligations so I'll not be playing in the shop tonight. Testing with air might be delayed until the weekend.

Steve

 

[Bogstandard]

Whats all this then, that little piccy most probably took more time to produce than the pistons themselves. Modern day wizz kids. :lol:
In the UK we call ours 'fag packet' drawings and convey the message straight away, then get in and do it. I don't just use paper, I use any flat area in the workshop and use a spirit based pen, then every so often go round with a spirit soaked cloth and wipe it all off.
I understand where you are coming from, and to make them as accurate as possible, but I think in this case, trying a little too hard. A++ for effort, B- for results.
Joking aside now, your little engine has me totally baffled, by all the laws of making this engine, by now it should run, if it turns freely both ways by rolling your hand along the flywheel then there is no reason this engine shouldn't turn under power.
I think you need to put it under the bench for a week, then come back with a clear mind. Make a quickie snow engine just to relieve the frustration. I release mine by teaching the cat new tricks, like doing somersaults down the garden after being shown a size 10 boot up his a**.
When I have a few spare days I will try to knock up another one of these engines just to see if mine was a fluke. That will be about number nine in the queue.

John

 

[Cedge]

ROFL.... John, I once had a shop foreman who was in the habit of scribbling his ideas on any available surface. He once even drew one in the dust on my car, which didn't set very well. I was forever having someone erase is drawings from machines, work tables etc. I finally broke him when I took an erasable pin to the shop and proceeded to do a such drawing as we talked... right on his tool boxes. From then on, with my point having been made, he carried a small pad of paper, although he still left drawings laying around everywhere.

The rendering was done more for those who might have a need. I work in 3D, quite a bit, so it feels natural to do it that way. That little program has been a godsend for trying things out before going for the metal.

Put it on a shelf?.... get thee to a nunnery, ye heathern. I've got her ready to go back again for air testing, now that she's pretty much decided where her sweet spot is. Whatever the effect of the imbalanced bend, matching the pistons so that they all were singing from the same page made a huge difference. I've enjoyed this challenge tremendously and I'm having way too much fun to stop now....LOL.

I've already got an idea for another very different version of the engine that is looking like it could work, but a bit more modeling will be needed to be sure.

Steve

 

[Bogstandard]

Steve,
I can really rub you up the wrong way, can't I?
BTW it is all done in jest.

What it is is jealousy, I just can't get my single brain cell around all these 'time' saving whatsits and thingies they keep coming out with. If I can't hear it, touch it, see it, taste it or smell it, it is not real.

I've enjoyed this challenge tremendously and I'm having way too much fun to stop now....LOL.

When it comes to getting this engine running it is such a fine line between having fun and masochism, maybe you just don't want it to run, it will extend your pleasure for as long as you want. :twisted:

Best of luck with the air trial.

John

 

[Cedge]

When it comes to getting this engine running it is such a fine line between having fun and masochism, maybe you just don't want it to run, it will extend your pleasure for as long as you want.

Now you're way too close to the truth....LOL. The fun is truly in the journey and the end always comes way too soon.

The experience of sharing the goofs and screw ups is a little unusual for me since, in the graphics community, no one ever sees anything I've done that hasn't already passed the smell test. I've just never been brave enough in the past to share the failures and the successes at the same time.

This has been somewhat akin to changing one's drawers in Macy's front window. I've shared the tricks, the tribulations and the advances so that my mistakes might help others , who are masochistic enough to want an Elbow engine....avoid them... LOL. The small dignity loss is worth the price, if it gives some other poor schlub a glimmer of a solution for his own devil and deep blue sea conundrum.... (grin)

John me boy...Can't say that you've ever managed to get my goat, but I'll admit that you're a worthy jousting partner...LOL Thanks for playing Abott to my Costello. I would surely miss the teasing and dry wit, were it to end.

Steve

 

[Bogstandard]

Hi Steve,
No joking on this post, time to be solemn.
What you have said has really struck a chord with me.
It is my belief that sharing information, no matter how trivial, just might help someone solve a related or even a totally unrelated problem.
My posts might seem a bit long winded with too much information contained in them, it is not for my gratification, I'm not showing off or anything like that. I am just trying to help by supplying as much information as possible, just as you are doing with this damned engine build of yours. One person helped along the way, justifies all your suffering, and boy are you finding the going tough.
So in that context, may your suffering be a long, drawn out and very painful affair. :twisted:

Abott John

 

[Lew Hartswick]

Just a suggestion: Please insure that a post dosent require a horizontal
scroll to view. When I come across one, like this one, I just ignore it.
I don't know how many others do but I'm sure a lot of "input" may be
missed due to the effect. :-(
...lew...

 

[Bogstandard]

My fault Lew, in such a rush forgot to resize it.
Size now fixed.

John