Wobbler Air Engine project for CCBCMD machine tools class CMM112

[philjoe5]

Good progress Paul.  Be sure to bring it to CF.  Hope to see you there

Cheers,
Phil

[BadSpellar]

Why is the crank shafts designed the way it is. I don't think I have ever seen one with the heavy side on the connecting rod side. Won't that really mess up the balance?

[vascon2196]

I have my students each build a small wobbler out of clear acrylic, aluminum, brass, and steel.

At the end of the 10-week quarter they have learned blueprint reading, setup/layout, measuring, mill & lathe basics, tolerancing, and assembly/fasteners.

Air engines are perfect for those types of students.

I'm happy to see you doing this...it is extremely important that this generation of students know how to apply what they are learning.

Great job!

[philjoe5]

I'm setting up a workshop for the Local Makers group, Make717, so anyone age 12 and up can make one of these simple but quite robust engines.  I'm with Chris, not many young folks at model engineering shows but I think it's from lack of exposure not lack of interest.

Besides, who am I going to sell my tools to when I get (more?) senile?

Cheers,
Phil

[PStechPaul]

I may be the oldest student at 65, but many others are 40-60, and only a few of typical college age (18-25). A few of them may have home shops, but AFAIK I am the only one doing any work at home. This week it will be warmer (above freezing) so I may be able to do more work in my unheated shop.
 
I made a document listing my proposed steps for making each of the pieces:
 
http://enginuitysystems.com/files/CAMM112/CCBCMD_CAMM112_Air_Motor_Project.pdf
 
http://enginuitysystems.com/files/CAMM112/CCBCMD_CAMM112_Air_Motor_Project.odt
 
I sent copies to the instructor. If you have any suggestions or better ways to perform these operations, please let me know.

[PStechPaul]

I've made more progress on the engine. At school we took an hour to go over stuff that will be on our mid-term exam this Thursday, and then we went to the shop. We got a demo of knurling, and then one other guy and I got ready to set up the cylinder in a special jig:
 

 

 

 
But there were problems getting it aligned, and I got on another machine to flycut the side of the cylinder:
 

 

 
I took a video clip of the flycutting operation:
http://enginuitysystems.com/files/CAMM112/Cylinder_Flycutting_1798.AVI
 
Next I set up the mill to locate and drill the 3/16" hole for the crankshaft pin. My part already had the 3/8" shaft installed so I tried to locate it from the edge. Without a DRO, I used an edge finder and the dials, but I made a mistake and located it about 0.14" too close to the center shaft. Then it was time to clean up and go home. Here is the crankshaft and some of the parts to complete the engine:
 

 
I never liked the idea of the aluminum crank. I was anxious to get the engine together and running, so I decided to make one from 1/4" steel in my home shop:
 

 

 
I used a piece of O-1 drill rod instead of the dowel pin. It's too long, because I copied a 1-1/2" dowel that was in the bag of parts, rather than the black 3/4" I should use. But I put it together, and after a bit of "running in" and 3-in-1 oil, it turns smoothly and should run if I connect the air hose.
 

 
 

 

 
 

[PStechPaul]

I got it running! I also attached a small 24 VDC electric motor with an O-ring that I spliced together with Cyanoacrylate (Super Glue), and I was able to run it as a pump by applying voltage (24 VDC and about 100 mA) to the motor. So that's 2.4 watts or 1/300 HP. Here are some raw video clips:
 
http://enginuitysystems.com/files/CAMM112/Air_Engine_DC_Motor_1839.AVI (23 MB)
http://enginuitysystems.com/files/CAMM112/Air_Engine_DC_Motor_1840.AVI (80 MB)
 
Ignore the TV noise in the background. 
 
Then I connected it to my newly repaired compressor (rebuilt the check valve about a year ago), and it runs pretty well. The monster steel flywheel lets it run fairly slow. I'll be adding a proximity sensor and the TigTac circuit to show the actual RPM. I connected an incandescent lamp (#47 6V @ 150mA) and it lights quite brightly when the motor is running at full tilt. Here are more raw video clips:
 
http://enginuitysystems.com/files/CAMM112/Air_Engine_Running_1837.AVI (42 MB) - Very first run - before adding motor.
http://enginuitysystems.com/files/CAMM112/Air_Engine_Running_1841.AVI (47 MB)
http://enginuitysystems.com/files/CAMM112/Air_Engine_Running_1842.AVI (42 MB)
http://enginuitysystems.com/files/CAMM112/Air_Engine_Running_1844.AVI (70 MB)
http://enginuitysystems.com/files/CAMM112/Air_Engine_Running_1845.AVI (20 MB)

[b.lindsey]

Its a runner for sure Paul, always satisfying seeing them tick over for the first time. So now what are you going to do for the rest of the semester

Bill

[PStechPaul]

Last evening's class was mid-term exams. I think I did pretty well. Most of the class left after they had finished, but four of us went into the shop about 6:30 to work on our projects. I decided to complete the cylinder, which needed the rounded profile cut on the special jig. First was to mill the rounded end with a straight end mill:
 

 

 
Then I used the round corner cutter to mill from the square end to the center of the hole, then using the rotary table turned the piece 180 degrees, and then continued the other side:
 

 
I had some problems with the rotary table so it seems it was not perfectly set at 180 degrees. On the final pass I fudged it a bit and ended up with a ridge, but it can be cleaned up by using the straight mill again:
 

 

 

[90LX_Notch]

Paul-

Congratulations on your first runner.

-Bob

[Roger B]

Excellent work    The first runner is always good   

[philjoe5]

Nice runner Paul.   I like the generator setup.  Hopefully I can get some details about it at CF.

Cheers,
Phil

[PStechPaul]

Thanks, everyone. It is a good feeling to see a creation run for the first time. I will be adding a valve and pressure gauge so I can easily regulate the speed and see what it takes to run. I have 1/8" NPT fittings and some 1/4". I put this together, but I'll use shorter or close nipples, or I might even make my own fittings. I might even try my hand at making a valve, but I have other priorities and that would just be for the learning experience and perhaps "bragging rights". 
 

 

 

 
As for the generator, I'm using a 24 VDC "hobby motor" that I bought two of from SurplusShed for $0.75 each and 50% off that. They seem to be well made and little 24 volt motors are somewhat rare and very useful as generators. I will probably order maybe 10-20 more, hopefully if they have another sale, and I'll bring them to CF in case anyone wants one. It has a resistance of about 75 ohms so the maximum power at rated voltage would be into a 75 ohm load with 12V or 2 watts.
 
I happened to have a small pulley that fit the 2 mm motor shaft. I might order some drive belts like these, but they come from Asia and delivery is very slow. It may be better to order O-ring type belts from SDI. A 3/32" thick and 3" diameter (9.4" long) neoprene belt is only $0.85. It looks like the combination of a grooved pulley and the flat flywheel works quite well, and no additional groove is required. They don't seem to have pulleys small enough to use on a 2 mm shaft. But they should be easy to make.
 
I found some from a UK supplier:
http://www.ebay.com/itm/Qty-10-18mm-Miniature-Model-Belt-Pulley-Wheel-for-2mm-Motor-Shafts-/120894972581
http://www.ebay.com/itm/Qty-5-8mm-Diameter-Miniature-Model-Belt-Pulley-Wheel-for-2mm-Motor-Shaft-/120848374323
 
Here are some that are from a Chinese supplier:
http://www.ebay.com/itm/5pcs-Small-Orange-Belt-Fixed-Pulley-3mm-2mm-for-Toy-Robotic-Module-Car-Model-/391085408796
http://www.ebay.com/itm/10pcs-plastic-sheave-belt-pulley-6mm-white-small-2mm-hole-timing-pulley-for-DIY-/231374536151
 
You can get an O-ring splicing kit with five sizes for $26:
http://www.use-enco.com/CGI/INSRIT?PMAKA=505-3883&PMPXNO=948270&PARTPG=INSRHI
 
Here is 3mm Viton O-ring cord $7/meter:
http://www.ebay.com/itm/3mm-Diameter-Viton-O-ring-cord-75A-Max-temperature-260-c-price-for-1-meter-/330920156954
 
Probably easier and cheaper to get it from McMaster. They have Buna-N, Viton, silicone, neoprene, and EPDM. Ranges from $0.21/foot to $1.67/foot for 1/16". Various grades of hardness, chemical resistance, temperature, et.
http://www.mcmaster.com/#o-ring-cord-stock/=we8wgs
 

[PStechPaul]

Beautiful warm evening yesterday for our shop class. I decided to finish the base, which required cutting the edge profile with a 1/2" ball end mill, and then flycutting the top surface. The mill I chose to use did not have a working DRO, and I had some problem with backlash on the X and Y dials, and also I neglected to account for the edge finder radius when locating the back left corner from which I started. I used a depth of 0.230", leaving 20 thou for finishing, and also about 0.020" extra for the edges. It cut pretty well, conventional milling in all four directions, but it messed up a bit on the second cut left to right in the X axis. I did not have the Y axis locked and it may have shifted in about 20 thou. But then I got the "hang" of it and continued the rough cut and then got within about 5 thou using climb milling for a nice finish:
 

 

 
The corners look like they are cut correctly, although I think they need to be cut deeper, and cleaned up. The edges definitely need to be milled clean and bright, but I can do that in my home shop:
 

 

 
I especially like the finish obtained by flycutting. My first attempt with a cutter from the tool drawer had many fairly deep gouges, even when I went painfully slow with only about 5 thousandths DOC at about 250 RPM for a 3" diameter cutter. Looking carefully at the cutting edge, it was apparent that it was not correctly ground for this process. So I touched it up on the grinder and did it again, with much better results. Then the instructor recommended that I use the high speed setting with a light DOC and slow feed, which definitely produced a nice finish:
 

[Don1966]

Looks good Paul and doing the edges gives it a nice touch. 

Don