Author Topic: Wobbler Air Engine project for CCBCMD machine tools class CMM112  (Read 14525 times)

Offline PStechPaul

  • Full Member
  • ****
  • Posts: 688
  • Cockeysville, MD 21030
Wobbler Air Engine project for CCBCMD machine tools class CMM112
« on: February 10, 2015, 01:36:05 AM »
I started the second semester of Machine Tools class at the CCBCMD Community College in Catonsville, MD, and our shop project will be a wobbler air engine. Here are the plans:




















I have PDFs and other material for the class here.

Has anyone seen or built an engine similar to this? About the closest I could find is this:

<a href="https://www.youtube.com/watch?v=ootr4HGAg-8" target="_blank">http://www.youtube.com/watch?v=ootr4HGAg-8</a>

Some questions I have, that I will also discuss with the instructor, are:

1. Would it be better to make the cylinder from steel, to match the material of the piston and manifold/valve?

2. Similarly, perhaps the crankshaft should be steel, or perhaps brass. I think steel would be best, to match the thermal expansion of the steel dowel pins.

3. The flywheel is aluminum, but I think it would be better if made from steel, for greater inertia. Actually, I think it would look nice made from brass, and I have a 6" piece of 2" 360 Brass stock I could use. The aluminum was probably chosen for cost reasons.


Offline philjoe5

  • Full Member
  • ****
  • Posts: 1012
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #1 on: February 10, 2015, 02:54:43 AM »
Hi Paul,

I recently documented my building of a Wobbler here:

http://www.modelenginemaker.com/index.php?topic=4652.0

My build is related to your project, though I think my engine is simpler than yours.  I built mine to act as a standard project for our local Makers Group.  It would be an introduction to making a machine that requires some precision and accuracy.

As far as materials go, just avoid having identical materials in contact that will be moving at high velocities.  These engines won't normally see a load applied to them so an aluminum cylinder with a brass piston will provide hundreds of hours of running time.

A steel crankshaft is probably best but I built one of these with a brass one and it chugging along quite nicely.  The more mass in a flywheel, the better, so I'd use brass, steel, cast iron for that.

Good luck with your project.  I'm interested to see how yours turns out

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13860
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #2 on: February 10, 2015, 03:52:56 AM »
That should be a good project Paul. I agree with Phil, alum. cylinder, brass piston, steel crankshaft, and brass flywheel.

Bill

Offline Ian S C

  • Full Member
  • ****
  • Posts: 1080
  • Stirling Engine Maker Darfield Canterbury N Z
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #3 on: February 10, 2015, 12:30:22 PM »
The little wobblers that I have built, I used brass, or one with bronze for the cylinder, and stainless steel for the piston.  steel for the crankshaft and pin, brass for the crank web, brass for the bearing, flywheel, and bearing. Here's the smallest one, 1/8" bore, 1/4" stroke.
Ian S C

Offline ChipMaker

  • Full Member
  • ****
  • Posts: 37
  • Warren, MI USA
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #4 on: February 11, 2015, 12:35:28 AM »
What a great school project!  Students get to learn how to read drawings, identify various materials, and get to use some really neat shop machines!  I hope that they know just how lucky they are, and the will end up with a engine they built themselves and can share with others, that may lead to a career.  Great!  Regards, Karl, CM

Offline ausdier

  • Full Member
  • ****
  • Posts: 161
  • Burpengary, Australia.
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #5 on: February 11, 2015, 02:32:01 PM »
Here is a 3D PDF of the parts as drawn with a little licence on some parts that weren’t there and a couple of washers on the crankshaft.
Hope this is ok.

Offline PStechPaul

  • Full Member
  • ****
  • Posts: 688
  • Cockeysville, MD 21030
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #6 on: February 11, 2015, 06:33:30 PM »
That's a very good rendering. Do you have this in a CAD format that I could import to TurboCAD? I think the instructor uses Solidworks for the drawings, and I can import at least some of those models, although I don't know if I can edit them. I had thought about drawing the parts in TurboCAD but that would take some time, and if you have already done so, no sense re-doing it.

I see that this PDF is a 3-D view which can be rotated, but I can't take a snapshot or extract the image. I was able to take a screenshot:



I have a tendency to analyze a design and look for better, or more unique, ways to build it, but I think the instructor has designed it this way as an exercise to learn and gauge various techniques and skills. It seems to me that the large mating surfaces of the cylinder and manifold would be a source of a lot of friction, and may require lubrication, so perhaps something like a Teflon or silicone gasket might be beneficial.

Thanks!
« Last Edit: February 11, 2015, 06:51:15 PM by PStechPaul »

Offline philjoe5

  • Full Member
  • ****
  • Posts: 1012
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #7 on: February 11, 2015, 08:40:43 PM »
Paul,
It would seem that there is a lot of friction between those 2 flat surfaces.  I thought that as well before putting mine together.  If the spring pressure pulling the cylinder against the manifold is set right, the counter effect of air pressure pushing the cylinder away presents a nice equilibrium.  Now add a film of oil between those 2 surfaces and you've got a pretty smooth motion.  Of course, the bearing surfaces of the cylinder and manifold should be highly polished.  I used a flycutter on mine followed by successive polishing up to #800 grit.  Then I got lazy and quit.

Ausdier,
Great job on the 3D rotatable drawing

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13860
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #8 on: February 11, 2015, 09:00:56 PM »
Ditto on Phil's comments..wobblers are intended to have that metal to metal fit but they do need to be smooth and with some oil for lubrication. I think an intermediate piece like Teflon film or any gasket arrangement would be more complicated than beneficial.

Bill

Offline ausdier

  • Full Member
  • ****
  • Posts: 161
  • Burpengary, Australia.
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #9 on: February 12, 2015, 09:28:47 AM »
Hey Paul.

Send me a PM with your email and I will send a few formats for you to try.

Cheers.

(Render done with Keyshot 5)

Offline PStechPaul

  • Full Member
  • ****
  • Posts: 688
  • Cockeysville, MD 21030
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #10 on: February 12, 2015, 10:03:52 AM »
[edit] Just noticed that it looks like the flywheel is not centered on the shaft. But it might be an illusion due to the mirror finish. Otherwise the rendering is really nice!

[from HSM] Last night I got started on the project by making the flywheel, but I used a piece of 2.062" diameter x 1.56" round 1117 steel. I turned it to 2.000" with a 0.875" neck. I made the neck slightly oversize and about 0.02" longer than specified, and I faced the opposite end so that the flywheel is about 1.50" long rather than 1.125" as specified. I figure that, for a flywheel, more (mass) is better, and this should be a bout 4 times that of the specified 6061 aluminum. Here are pictures and links to some videos:
 
 
 
 
 
 
 
 
 
 http://enginuitysystems.com/files/CA...wheel_1721.AVI
 
 http://enginuitysystems.com/files/CA...wheel_1723.AVI
« Last Edit: February 12, 2015, 10:25:49 AM by PStechPaul »

Offline PStechPaul

  • Full Member
  • ****
  • Posts: 688
  • Cockeysville, MD 21030
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #11 on: March 01, 2015, 12:17:46 AM »
I have made a few more parts, at least "partially". My problems with parting the piston is documented in another thread, but here is the (almost) finished result, with the repaired part:
 

 
Here is the crank, made of 6061 aluminum, surronded by a coil of swarf from a successful parting operation:

 
And with a 0.375" dowel pin inserted. It should be a press fit, but I was able to push it in by hand (further than as shown), so some Loc-Tite may be necessary:
 

 
I also bored the cylinder to 0.625" using a boring bar on the Clausing lathe toolpost at school:
 

The finish is a little rough because I bored it by hand rather than power feed, since the carriage stop clutch is not reliable. I could have used it and disengaged when it got close to the stop and finished by hand, but this should be good enough.

 
The bore might be 0.001 larger than tolerance, but the piston goes in smoothly with some air compression resistance, and it makes a nice "POP" when I pull it out quickly. A machined part's way of saying "Who's your Daddy!"  :naughty:

 
I may modify the flywheel something like this:
 

 
I made it thicker than specified on the drawing and from steel rather than aluminum, so it is quite heavy. This modification will make it much lighter while still maintaining considerable angular momentum. I would also like to machine a groove in the flywheel for a belt to connect to a DC motor as a generator, and it may also then be able to work in reverse as a pump. But I need to concentrate on getting these parts finished, and the other parts as well. I have all the materials I need, now, and I bought some reamers and other tooling so I can do much of it in my home shop.
 

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13860
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #12 on: March 01, 2015, 12:48:02 AM »
You are making some good progress Paul. I think the steel flywheel should serve you well. Looks like you should be finished long before the end of the semester :)

Bill

Offline PStechPaul

  • Full Member
  • ****
  • Posts: 688
  • Cockeysville, MD 21030
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #13 on: March 01, 2015, 01:07:24 AM »
I am hoping to get this finished and running in time for Cabin Fever, just six weeks away. The semester ends May 21. I'll be having cervical spine surgery on my neck April 16, so I won't be able to do much for awhile, although in a month I should be able to drive and resume somewhat normal activity in time to take the final exam. That's why I need to stay concentrated on this project, and do some work at home. It seems to take much longer in the school shop, finding the tools needed, getting set up, distractions, and leaving time for cleanup. About all I did last Thursday was cut a piece of 1" square steel for the manifold, and then bore the hole in the cylinder. We have about three hours in the shop, which seems like a lot, but time passes quickly, and I work slowly.
 
I was using only 200 RPM, and the instructor said I should use 1000. I also went slower because I forgot that the Clausing cross-slide is calibrated in diameter, rather than radius, and I was wondering why the hole didn't open up as I had expected. I thought it might be due to the backlash, and also I think I may have sometimes bumped the handwheel as I was moving the carriage. There is probably a way to lock the crossfeed, but it was not apparent, and I didn't want to mess around with adjusting the gibs or otherwise attempting to secure it better.
« Last Edit: March 01, 2015, 01:10:42 AM by PStechPaul »

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13860
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Wobbler Air Engine project for CCBCMD machine tools class CMM112
« Reply #14 on: March 01, 2015, 01:17:02 AM »
I know all too well about the school shop thing. Of course by the time the kids check their cell phones 50 times, ask questions (which is fine), and do a half baked job cleaning up after themselves, they don't manage to get a lot done. Then (back when I was managing the shop), come the end of the semester they wanted me to hang around till 6-7 PM so they could catch up. Adults are so much easier to work with  :lolb:

Bill

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal