New Compressed Air Hit n Miss Engine

[cfellows]

I've begun work on a new, hit n miss engine that will run on compressed air.    It has a 1" x 1.5" bore and stroke with a 7" flywheel.  Two to one cam gearing is incorporated to run in 4 stroke mode like the old engines.  This engine is an inverted type, a design which allows the builder to use a much simpler, end-mounted crankshaft and a single, large flywheel.  It should be an easy engine to build. 

I'm using a new, quick release valve that will allow the engine to run in true hit n miss mode and should sound very much like it's larger, internal combustion counterparts, as in loud!  Even tho the engine is pretty large for compressed air, it will be run at full compressor pressure and should only "hit" about every 8-10 revolutions not requiring much air.

Here is a picture of the mostly finished design.  Still have some details to add like the governor assembly and the innerworkings of the valve.



I am designing this engine for others to build as well, so I'll provide drawings when they are finished.

Chuck

[saw]

This engine looks very intressting. I will be follow this project with great intresst. 

[Rob.Wilson]

Interesting  design  Chuck   

Looking forward to seeing the engine take shape 


Rob

[NickG]

Love the vertical configuration Chuck - will be an interesting build this 

[cfellows]

Thanks for the kind words, folks.  I do appreciate the interest and the comments.

Got started on the build this weekend.  The uprights are formed from 3" x 3/8" thick hot rolled steel, each 6" tall.  Most of the work was done with my metal cutting bandsaw and vertical belt grinder.   I did use the milling maching to clean up the edges and form the inside radiuses at the top and the bottom.  I've included pictures with two different flywheels.  I'll probably use the larger, 7" cast iron fly wheel that I had originally planned for but also kind of like the smaller, 6" brass flywheel that I had milled from solid several years ago.  I guess I'll keep the option open until I get further along.









Chuck

[cfellows]

One more picture, I forgot that I had finished the cylinder several days ago.  The lump of aluminum the cylinder is sitting on is just to show how it will look with the cylinder head.



Chuck

[Brass_Machine]

I always look forward to your engine builds Chuck.  great designs and great reading. Have you considered writing a book with your designs... 

Eric

[sbwhart]

Looking forward to seeing this engine grow and that brass fly wheel looks real nice. 


Stew

[saw]

Looking good

[Dean W]

It ought to be another winner with one of your valve designs, Chuck.  I like the "old-time" style.  Either of the
flywheels look good, too.

[cfellows]

Thanks again, folks for all the encouragement and positive comments.

I decided to do the base a little differently than in the original picture.  I had planned to use quarter sections of steel pipe to create a cove moulding like I did with the radial.  Instead, I'm using 3/8" thick angle iron.  I picked up a piece of 2" x 2" by 26" at my local metal yard, brought it home, and cut it down to the size I needed, 1.375" x .625".  The bandsaw made this job easier, but it was still a bit tedious to rip it down, not to mention a little hard on my arm muscles keeping the pressure on the feed.  Next the piece will be cut down to the proper lengths with 45 degree angles to form miter joints on the ends.  The 5/8" leg will be on the bottom, with the cut edge out to form a kind of cove.  The base will have 1/4" thick steel plate welded on the top so the total height of the base will be 1.625"

Here's a picture of the base pieces



And here's a drawing with the governor and the new base



Chuck

[cfellows]

Here's some more pictures of the base taking shape.  These are probably not interesting to all of you, but thought I'd show them anyway.  So far I have about 5 hours into the base alone.

This is just a pic of me using an indexable cutter to smooth the bandsawed edges.



This is just two views of the lashup on my bandsaw to cut the 45 degee mitre on the first end.  The angle iron is mounted upside down with a spacer indexed against the back of the built in vice.  Another spacer is used underneath to raise the workpiece high enough that the clamps could find purchase on a flat spot on the back of the vise.  C-Clamps are used to hold the work rather than the adjustable portion of the built in vice.





These are pictures where I'm cutting the 45 degree miter on the other end.  Here, the angle is right side up.





Getting the pieces cut to exactly the right length was very challenging since it was hard to project where the blade would intersect the base of the cut.  Exact length wasn't really important anyway, but getting the opposing sides the same length is important if you want a square base with tight mitre corners.  So, I used a stop block clamped to the back of the fixed vice jaw to make sure the matching pieces were the same length.



Here's a few shots of the frame assembled but not yet welded.  Outside dimensions measured around the bottom of the base is 5.75" x 6.75".  The height of this part is 1.375". The thickness of the angle iron is 3/8".







Now I can cut out the plate that will form the top of the base.

[saw]

It's just beutifull nice work 

[millwright]

Those bandsawn mitres look to have come out very good. watching the post with interest. have enjoyed your previous projects.
John

[cfellows]

Thanks again, for the comments and encouragement.  Here's a couple more pictures.

The first picture is the base dry fitted with the top.  The top is made from 1/4" thick cold rolled steel, 5.5" x 6.5"



And, here is the first of 2 pictures of the parts I finished so far, dry fitted.



And, a second picture with the soda can for scale.



Chuck

[KB3RLJ]

That's looking great. Keep it coming.

[NickG]

Nice work Chuck, really  nice looking design and maybe even simple enough for me! 

[Rob.Wilson]

looking great Chuck 

i sure like the way you are constructing the base     ,,,,,,,,,,,,,,


Rob

[raynerd]

Fantastic workmanship - the base is just great, really smart design..and the brass fly wheel 

All the best
Chris

[cfellows]

Thanks for the comments, folks... always appreciated!

Here is the magic that will make the engine operate pretty realistically (I hope).  It's a quick release valve that I discovered in an airgun book.  It uses air pressure from the air source to quickly open the valve when the cam rotates to the cutout.  In the airgun world, the trigger mechanism releases the valve.  Either way, the 100PSI air source should exert a pressure of about 5 pounds on the air valve, more than enough to open it quickly.  This first picture shows how it all works in a drawing with description.



And here are the pieces that I've made.  The valve body is made from 3/4" brass rod and the valve is 1/4" drill rod.



And this picture shows where the valve body sits on the engine base



Chuck

[NickG]

Chuck,

thanks for explaining the valve mechanism clearly. What sort of pressure do you think this would work down to? I can see that it's partly due to the strength of the spring on the ball and I realise that you want it to behave as much like an i.c. engine as possible hence the high pressure but was just wondering. I guess it wouldn't sound much like an i.c. at the lower pressures but should still work? It won't take much pressure to lift the valve off its seat. I initially thought by looking at your cam you were getting the pressure to act in a short sharp burst but looking again it looks like the valve can be open for about 90 deg on the cam? = a full stroke? I guess you could play tunes with that too but the way you have it will give the most power.

Anyway, brilliant stuff 

Nick

[cfellows]

Chuck,

thanks for explaining the valve mechanism clearly. What sort of pressure do you think this would work down to? I can see that it's partly due to the strength of the spring on the ball and I realise that you want it to behave as much like an i.c. engine as possible hence the high pressure but was just wondering. I guess it wouldn't sound much like an i.c. at the lower pressures but should still work? It won't take much pressure to lift the valve off its seat. I initially thought by looking at your cam you were getting the pressure to act in a short sharp burst but looking again it looks like the valve can be open for about 90 deg on the cam? = a full stroke? I guess you could play tunes with that too but the way you have it will give the most power.

Anyway, brilliant stuff 

Nick

Hey Nick, thanks for the input.  There are a number of variables that determine how these air engines operate.   I'm in new territory with this quick release inlet valve but I do have some experience now with the ball slave valve.  With a lighter spring, the engines will run on lower pressure but they won't rev as high.  Most of my engines are slow runners and I use a light duty spring, about 5/32" OD, 3/4" long, wire size of .012" - .015".  They will run well on about 40 PSI, maybe less.

For this engine to sound as realistic as possible, I want it to free-wheel for as many revs as possible, then hit really hard when it fires.  The idea is to control the speed with the governor, not the air pressure.

I finished up the valve last night to a point where I could test it.  With the valve closed, there was no leakage, and the air pressed hard on the valve stem.  However, I was able to hold it with my thumb and forefinger.  I think this valve is going to work well, although I might have to rebuild the valve body for a smaller, 3/16" valve stem... 1/4" may exert too much pressure on the cam assembly.

Chuck

[cfellows]

I'm into the fiddley bits now so progress will probably be slower and not very exciting.  I had decided to use 3-48 SHCS to fasten the two halves of the valve body assembly to the base.  However, after I drilled and tapped the holes, I found that my screws were too short.  So, I made some brass screws from a piece of hex rod I had on hand.  Screws turned out nice:



But, when I tried to tighten them down, I promptly twisted one off.  Guess brass was a bad idea in these small sizes.  So I drilled out the holes and tapped them to 4-40.  Had the right size screws on hand and screwed the valve assembly to the base:





Next I started on the timing gears.  The small gear is made from two pieces, the gear and the hub.  After the gear teeth are cut, the gear will be bored out, then loctited or hard soldered to the hub / collar.  Here I've turned the gear blank and the hub at the same time from a piece of 1" 12L14.



Next I'm parting off the hub:



Here's a picture of all the gear blanks.  The large timing gear was turned from cast iron and will have a pitch diameter of 1.5".  The small gear is mounted on a mandrel, ready to have the teeth cut:



Today's work will include cutting the teeth on the gears and getting the smaller, primary gear assembled into one piece.  Then, it's on to the cam.

Chuck

[cfellows]

Here's a couple of pictures of the gears.  The first picture shows the primary gear set before assembly.



And here's a picture showing the large timing gear and 2 copies of the small timing gear with hub.  The one on the left shows a pitiful attempt at silver soldering.  I used too much solder and got the assembly too hot.  This resulted in solder flowing into the valleys between the teeth.  I tried to dig the solder out but no luck.  Now I know why they call it hard solder!  The assembly to the right is put together with loctite 620.  It will probably hold alright... at least I've not had it fail on any of my applications yet.



Chuck

[cfellows]

One last picture for today.  Got the cam finished and attached to the large timing gear.