Comber Rotary Engine

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Gordon

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I have built a Comber Rotary Engine and I am having a problem getting it to run. It seems to hang up when the cylinder is about 30° past vertical. This happens on both ends of the cylinder. The piston/rod does not seem to be binding up in the cylinder and the rod forks do not seem to be binding on the cam but something is binding up at approximately the same position. This is not happening on every revolution. Sometimes it will do two revolutions and then bind up. It does not seem to be just a tight spot but it is really hard to get past that point. I actually have about 1/32 clearance between the cam roller and the cam. I have even put a plastic busing in the bearing mount but that did not help. I am sure that I am missing something obvious but I certainly am not finding it.

Anyone who has built this have any ideas? I am starting to feel stupid because I cannot isolate the problem.
 
the cam is not truly circular...
When the piston rod is vertical, it passes through the diameter of the circle.
When the rod is horizontal, it is below the diameter, so you need to widen it a trifle (1.14 mm for 66.7 in dia) to avoid jamming.
And obviously widening is progressive between the vertical and horizontal positions.

this can be calculated with precision if you wish...
https://ti1ca.com/e06u3c9i-comber-tab2-comber_tab2.xls.html
 
It is quite possibly not a physical tight spot that is making it hang up but possibly you are getting air/steam to both ends of the cylinder at a particular point so look carefully at the ports. The intermittant nature could be that when it has enough momentum it carries itself over the point in the valve timing but if running slower it gets stopped.

You can get similar with a slide valve engine if the timing is off and the piston will just get held at one end of it's travel
 
It is quite possibly not a physical tight spot that is making it hang up but possibly you are getting air/steam to both ends of the cylinder at a particular point so look carefully at the ports. The intermittant nature could be that when it has enough momentum it carries itself over the point in the valve timing but if running slower it gets stopped.

You can get similar with a slide valve engine if the timing is off and the piston will just get held at one end of it's travel
I think that you may be right. I have drawn the engine in Alibre hoping to see the rotation but that will not show rotation because it will not constrain the cam follower to cam. It is not binding in the cam because I actually have about 1/32 clearance between the cam and the follower. What I do not understand is why it is not consistent. I made the cam using the spread sheet so I am fairly sure that it is correct. I will keep trying. Thanks.
 
I think that you may be right. I have drawn the engine in Alibre hoping to see the rotation but that will not show rotation because it will not constrain the cam follower to cam. It is not binding in the cam because I actually have about 1/32 clearance between the cam and the follower. What I do not understand is why it is not consistent. I made the cam using the spread sheet so I am fairly sure that it is correct. I will keep trying. Thanks.
Ah, so you used Alibre. You have overcome the problems you were having with it. Yeah, I had probs with it too but kept trying till I got it. So how do you like it now?
 
Ah, so you used Alibre. You have overcome the problems you were having with it. Yeah, I had probs with it too but kept trying till I got it. So how do you like it now?
I have mostly figured it out but I am using Atom which has some very real limitations but I am not going to pay $400 for Design. Atom seems to be deliberately crippled and is missing some features which should just be part of any cad program. I could use Free CAD now since a lot of the methods are the same but I do not want a web based program which can change or be discontinued at any point. I do not want any program which lives in the cloud instead of on my computer. For me the main advantage of Alibre is that I can use it forever and it is mine, not some cloud genie in the sky. For a lot of stuff I end up using my old 2D program.
 
I have mostly figured it out but I am using Atom which has some very real limitations but I am not going to pay $400 for Design. Atom seems to be deliberately crippled and is missing some features which should just be part of any cad program. I could use Free CAD now since a lot of the methods are the same but I do not want a web based program which can change or be discontinued at any point. I do not want any program which lives in the cloud instead of on my computer. For me the main advantage of Alibre is that I can use it forever and it is mine, not some cloud genie in the sky. For a lot of stuff I end up using my old 2D program.
out of curiosity, just what are the limitations? I use Atom almost exclusively now and have little complaint. Anything that is in a magazine or book, I can generally draw.
 
out of curiosity, just what are the limitations? I use Atom almost exclusively now and have little complaint. Anything that is in a magazine or book, I can generally draw.
The last thing I found was reference points and reference lines. In drawing the cam for this engine the center of the shaft was Y=-.25" and that is where most of the dimensions were referenced from. Also I needed reference lines at 15° from that point. That is not available with Atom. I had to first enter the points and the lines and then change them to reference figures. Actually one of the things I most dislike about Alibre is the dimensioning on the drawings. It is difficult to place the text and the lines where I want them. The program thinks that it knows better than I do what I want. That is probably also true on other 3D programs. Another frustration is when making a sketch part I end up placing dimensions all over the place trying to find which dimension I am missing to fully define the sketch.
 
The last thing I found was reference points and reference lines. In drawing the cam for this engine the center of the shaft was Y=-.25" and that is where most of the dimensions were referenced from. Also I needed reference lines at 15° from that point. That is not available with Atom. I had to first enter the points and the lines and then change them to reference figures. Actually one of the things I most dislike about Alibre is the dimensioning on the drawings. It is difficult to place the text and the lines where I want them. The program thinks that it knows better than I do what I want. That is probably also true on other 3D programs. Another frustration is when making a sketch part I end up placing dimensions all over the place trying to find which dimension I am missing to fully define the sketch.
Ah, I know what the problem is with Atom: There are a couple possible solutions to the angle problem, (of course, I don't really know for sure what problem you're having), the first and most important would be to make a new drawing plane at an angle usually at 90deg to the part you want to draw. Do you use that ability, to make planes at angles and offsets?

Your other problem is one I encounter when I need to make a sweep, either building something like a curved pipe or cutting something in an odd shape. That's one that I have a difficult time with as the reference line which the sweep follows has to be perfectly lined up with the object to sweep. I doubt that your problem is exactly what I am talking about.

Anyway, about the dimensioning. In Atom there is an automatic dimming and one in which you place each dim manually. Turn off the automatic one, don't use it. It is not very good. When dimming by hand, I come up against one dimming prob in atom, and that is I cannot, in all cases, place the arrow line left or right of the arrow==it's always one but never the other. The "other" is my choice. It's minor but still irritating. I'm sure your prob is not the same as mine,. and in that case, I am not a liscenced therapist, and you will have to go to your own shrink ;)o_O

P.S. You do know there are built in reference lines and circles? I use them all the time. For instance, If I need a bolt hole at a certain distance and angle from a point, I will use the ref circle for the distance from the point and then draw a ref line at the angle which automatically tells the angle and distance of the ref line being drawn.
 
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I thought the ref line worked the same in all versions. start your line at the -0.25 point and then hit tab, you can then enterer the angle. Then do a circular pattern of that line to get your 24 points
 
I thought the ref line worked the same in all versions. start your line at the -0.25 point and then hit tab, you can then enterer the angle. Then do a circular pattern of that line to get your 24 points
I just tried that. It gives the LENGth not angle. Must be another way.

Ah, got it. click on the starting point, "enter", add the length, tab, add the angle!

Thanx, this will help a lot, won't have to put in a circle to acheive the same thing
 
I must be missing something on this engine. I do not seem to be getting any appreciable rotary action on this thing in any position. In the position shown below the air pressure is coming in from the right and pushing the top of the piston down which generates almost no radial action. Even at 40 PSI there is almost no rotary action. What am I not seeing? Others seem to have this thing running on very low pressure.
1722961019544.png
 
I must be missing something on this engine. I do not seem to be getting any appreciable rotary action on this thing in any position. In the position shown below the air pressure is coming in from the right and pushing the top of the piston down which generates almost no radial action. Even at 40 PSI there is almost no rotary action. What am I not seeing? Others seem to have this thing running on very low pressure.
View attachment 158742
can you show a photo of your actual motor?
 
I would have thought that at the position shown the steam/air should still be going to the lower side of the piston or have just about shut as it is near to it's full travel.

The passage to the side where the piston rod is sticking out the most should be about to open to air and the passage to the half that is now full of air should be about to open to exhaust.

You don't say what direction you have it rotating in but if anti clockwise I would expect air to be entering from the LEFT as that is just about to be shut off

can you post an image square on that is sectione dthrough the inlet/exhaust pipe and say what rotation direction.

I assume you have plugged the two holes in the outer face of the valve?
 
Jason: Tried to do a section but did not figure it out so that it shows what I want but this shows the pressure port on the right pushing down on the piston for clockwise rotation. The more I play around with this thing the more confused I get. I have tried both right and left intake and rotating clockwise and counter clockwise. I have looked at several other builds and I am not the only one who has this problem. Some folks have increased the bore and increased the port into the cylinder.


1722971383467.png
 
I think that I have found the problem or at least a problem. Elmer calls for the inlet/exhaust port into the cylinder at a 15° angle which makes a portion of the bore open so a part of the stroke is able to leak past the piston. Others have noted this and have drilled straight down with a horizontal relief at the top of the cylinder. That is going to involve making a new cylinder so at the same time I will probably increase the 3/8" bore to 7/16" bore and increase the ports from 1/16" to 3/32"

1723043396096.png
 

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could you bore it out and sleeve it?
 
I think that I have found the problem or at least a problem. Elmer calls for the inlet/exhaust port into the cylinder at a 15° angle which makes a portion of the bore open so a part of the stroke is able to leak past the piston. Others have noted this and have drilled straight down with a horizontal relief at the top of the cylinder. That is going to involve making a new cylinder so at the same time I will probably increase the 3/8" bore to 7/16" bore and increase the ports from 1/16" to 3/32"

View attachment 158769
I went into my files to look for the Coomber but I cannot find it. I thot I had ALL of Elmer's engines but apparently not., I wanted to look at the drawings so I could understand what it is supposed to look like. I swear I have redrawn it somewhere, but we all know how files can become mixed up when there are such huge numbers of files.

However, I have all my Elmers files filed under "Elmers" where all the engines should be. I thot maybe there was an identical one under "John-Tom"s but cannot find it. What a shame 'cause I intended to attempt to build one eventually. There are so many good sites that have disappeared that it is now difficult to find. Anyone know where Elmer's is on the net now? I tried looking for it but goggle doesn't find it anymore. (or am I mistaken?)
 

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