Essex Hot Air Engine

[Dave Otto]

Thank you for all the nice comments everyone, I appreciate them.

Jo, you are correct there are some interesting challenges in this engine.

Jason, not much work at all, just a little work with a needle file where the upper and lower tool paths meet and around the edges where rod will fit. I used a 1/8" ball end mill with a .005" step over. If you look closely you can see the tool marks in the part. If you are curious I have attached a screen shot of the surface tool path for one side. I used a 3D pocket to rough out the bulk of the material and then a surfacing tool path to finish. This was programed with Master CAM and run on my Haas VM-2 at work. Nice when work allows you to play with the cool toys.
I noticed that the picture is kind of wonky where the lines crest over the top of the pin boss, they don't make that funny zigzag. Some sort of resolution issue I guess.

Dave

[crueby]

Neat to see how it works. That funny business with the lines in the image is caused by 'aliasing', usually introduced when scaling an image down. Depending on the algorithm, it will be picking pixels to use as is every nth one, or blending a couple every few. Could go on for a long time about it (I used to do digital image processing algorithms in my paying life) but I'll spare you the snooze!   

 

[Dave Otto]

Thanks Chris

I have also run into this printing vintage line art of antique engines, even the high end laser printers that we make do it. But the Indigo digital printing presses don't.
We have a small Indigo lab at our facility with a few presses that they do development work on; so I'm able to get some real nice prints done there. Pictures like the one attached, but much nicer than this shrunk down one. 

Dave

[crueby]

I love those old pictures of machines. Even that one shows aliasing in places, as you say. Same thing happens on TV when someone is wearing a narrow striped tie, you can see the pattern waving back and forth. Looking through a window screen can do it too, even better stack two screens and move one around, all sorts of fun Moire patterns appear.

[Jasonb]

Thanks for the details Dave. A smaller stepover than I have used with mine usually being 0.33-0.25mm 13 -10 thou. I'm sure the Haas also has a bit less backlash than my machine particularly in Z as well as being able to move faster that keeps the runtime down.

[Dave Otto]

Hi guys

Continuing work on the Power Piston assembly, the next part is the piston extension.
The print called for 26 gauge stainless steel for the tube, I had some .02” 301 half hard SS sheet so I thought that I would give it a try. The half hard material is quite springy and I wasn’t able to roll it small enough as it would just spring open when removed from the slip rolls. I did some research and found that it can be annealed by soaking at 2000 degrees for the proper amount of time and water quench. I thought well, I might as well give it a try.


After removing from the furnace and quenching, it kind of resembled a potato chip. But at least it was soft now.


I rolled a scrap piece to see if I was able get it to the correct size, which I was able to. The rolling process tended to remove the warping.


After carefully removing the scale I rolled a piece for both the power piston extension and the displacer piston. The displacer tube is slightly longer and shown pictured here. The sheet metal tube was wired tightly to an aluminum core that had been turned to the proper diameter; then holes for rivets drilled on the overlap.


Enough stainless steel rivets were turned for both pistons.


I didn’t take any pictures but the tube seam was silver soldered first, and then cleaned up.
The end cap was turned from 304 Stainless sheet and has a .03” shoulder to locate in the tube. Everything was cleaned and fluxed and some small bits of solder were placed around the inside at the joint. Then the cap was soldered on by heating from underneath. Some solder was also added from the outside. The cap was left oversized to make it easier to solder and will be trimmed back later. The tube was also weighted down during the soldering.


It was pretty much rinse and repeat for the End Cap. I used 3ea 2-56 bolts threaded into the holes to set the assembly on. Again a weight was set on top and the cap soldered on.


Here is a shot of the Piston Extension after trimming and cleaning. Considering how thin it is I’m pretty happy with how it turned out.


The Piston was assembled to the Piston Extension with a solid gasket between. The whole assembly was submerged in a container of hot water to check for leaks. I was pleased to find none.


Here is a family shot of the Power Piston parts.


All the parts assembled.


And a view from the end, showing the Small End Bearing.

Thanks for checking in, more to follow.

Dave

[Kim]

Wow, very nice work making the stainless steel tube, Dave.

So, is the far end of the piston closed?   It looks like I can see the table through the tube here and I was thinking it would be closed off by the cap you soldered on.

Kim

[Bear]

Impressive, Dave. 

[90LX_Notch]

Nice!  Definitely storing that one away Dave.  Well done.

-Bob

[Dave Otto]

Thanks for the comments guys, they are always appreciated.
Kim, the piston extension does have a cap, it is not seen clearly in the photos. What you are seeing is the back side of the cap. The piston has to be air tight so the cap is an important part.

Dave

[Kim]

Kim, the piston extension does have a cap, it is not seen clearly in the photos. What you are seeing is the back side of the cap. The piston has to be air tight so the cap is an important part.

OK, that's what I thought, but it sure looked like I could see wood grain from the table through the tube in that last picture.  But clearly, it's just a figment of my overactive imagination!
Thanks Dave,
Kim

[Dave Otto]

Hi guys

Continuing work on the Power Piston assembly, the next part is the Connecting Rod.

I have seen in photos of original engines that the rod was made from cast iron or bronze. I decided to go for the bronze option. I did deviate from the plans slightly here. The plans call for the rod to have a straight profile, but pictures clearly show that the rod has a fish belly shape. I also added draft to each end to make it look more like a casting.


I started out with a piece of 7/8” diameter 660 bronze, machining two parallel sides and a flat to establish the top surface.


The first operation was to machine the basic shape then drill and ream the ends. I reamed both ends .001” under size so I could lap them to a nice running fit on the pins.


After the first side was complete the rod was flipped over and decked to the finished thickness.


A fixture was made to hold the rod to machine the second side. The pins position the rod, and a couple flat head screws only serve to hold it down.


Here the rod is assembled on the fixture ready for the second side machining.


Like the first side the second side has been machined. A ¼” carbide 3 flute bull end mill with a .03” corner radius was used to machine both sides of the rod.


The rod is set up on a couple of pins so I could center on each bore to drill and counter sink the oil holes. Each pin was slid out of the way to drill the holes.


The cutter marks have been removed and the rod polished up a bit.


To finish turning the piston to size and add the oil grooves a snug fitting mandrel was turned for a scrap piece of Acetal (Delrin) plastic.

<a href="https://www.youtube.com/watch?v=bkMfmSqDVTk" target="_blank">http://www.youtube.com/watch?v=bkMfmSqDVTk</a>
Here is a short video showing how the parts fit and some round and round action.

Thanks for checking in, more to follow.

Dave

[RReid]

VERY nice!

[Bear]

Very nicely done.

[Kim]

Wow!  That's frighteningly smooth, Dave! 
Kim