Author Topic: Essex Hot Air Engine  (Read 13783 times)

Offline Dave Otto

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Essex Hot Air Engine
« on: October 26, 2020, 05:39:40 PM »
Hi everyone.

Here is a little fill in project that I have been playing around with as time allows. I still have at least a couple longer term projects in the works that I’m not ready share yet; but what the heck sometimes a guy just needs to make some chips!

This engine was designed by Henry Essex and was patented in 1902 US 723,660
The engines were on sale around 1905 and were advertised as suitable for running fans, window displays, model machinery, peanut roasters and sewing machines.
Some models had a fan to cool the cold end of the cylinder driven from the engine flywheel; others had a water tank at the cold end. A twin cylinder version was also available.
The engine works on the Stirling cycle principle but is unusual in that the heat is applied to the centre of the engine rather than at one end.
Essex claimed greater efficiency was achieved with this layout.

I built a full sized replica of an Essex hot air fan a number of years ago from Myers castings. I have always desired owing an engine too but the originals are scarce and quite expensive when found. When I discovered that castings were available from David Abbott in England I decided to go ahead and snag a set.  I think that he actually pours them to order. They arrived in reasonable time and are nicely made.


Here is a picture of a completed engine from David’s web site AKA Myford Boy. My engine will have a wood base which I believe is more true to the original anyway. I guess shipping the cast base is cost prohibitive.


Here is a picture of the castings as received.


I also decided to purchase the castings for the turntable that goes with the engine.


I decided to start with the Crankshaft Bearing casting. Sorry I got carried away and didn’t take any early on pictures of the machining. This pretty much was chuck it in the lathe and bore the hole for the crank bushings. This will be used to reference most of the remaining machine work. As you can see from the picture of the raw casting there is lots of extra material that needs to be removed; some manually i.e. hacksaw. I mounted the casting in an indexer which allowed me to access multiple sides without changing my setup. After establishing the height of the mounting flange from the crank centerline the screw holes and flange profile were carefully laid out. I needed to establish the piston center line as everything else is measured from that. Once the center was established the profile was machined and the mounting holes drilled using the CNC.
You can also see here that I had previously machined the mounting foot and it is being used to stabilize the casting by clamping to an angle plate.


Next the casting is rotated 180 and the mounting lugs are brought to thickness and also machined back far enough to allow the round head mounting screws to seat properly. This is not called out on the print you just need to make it happen. Here you can see that even after removing quite a bit of material that there is still plenty to go to bring it to the proper shape.


The casting is set in the vice and the round chucking lug is brought to length. This dimension is from the center line of cylinder bore. The previously machined surface was set on the parallel and back figured from that surface.


Using the same set up the CNC was used to machine the opening. No dimensions for this feature on the drawing, you just need to make it look good. Notice the steel slug placed in the bore to keep from crushing the bore.


The next step was to drill and counter sink the hole. There are two bronze bushings that leave a gap in the middle for an oil reservoir.


The bushings were turned and installed, I had to do some figuring to establish the stick out of the bushing on the crank side, this needs to place the crank shaft so the throw is centered in the cylinder bore. This dimension is not on in the drawings, but there is enough information to figure it out.

Except for the mounting screw hole here is the Crank Bearing pretty much complete.

There is a whole series of videos on building this engine which are great! And I think this is the reason there are some missing dimensions on the prints. By watching the videos some of this will become clear.
Do to different equipment sets and working styles everyone does things differently, so while I have watched and enjoyed all the videos I will most likely change the way I go about doing things on some of parts; I guess that I already have. :Lol:

More to follow,
Dave

« Last Edit: October 26, 2020, 07:08:51 PM by Dave Otto »

Online Kim

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Re: Essex Hot Air Engine
« Reply #1 on: October 26, 2020, 09:11:09 PM »
Dave,
That looks like a really intriguing engine you have going there!  And you've made an excellent start on it, but then, what else can one expect coming from a master craftsman like you.

Looking forward to seeing more of this build!

Sometimes, you just gotta make chips! :)
Kim

Offline Ramon Wilson

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Re: Essex Hot Air Engine
« Reply #2 on: October 26, 2020, 10:32:56 PM »
Coo! There are some lovely pieces of casting work there Dave and particularly so in that last component - very impressive.

And an impressive set up for machining too  :ThumbsUp: :ThumbsUp:

Bet you'll enjoy this one - nothing beats machining good cast ali  ;)

Regards - tug





"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline Dave Otto

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Re: Essex Hot Air Engine
« Reply #3 on: October 27, 2020, 06:29:32 PM »
Kim & Tug

Thanks for stopping by and the nice comments.  :)
Yes the ali is nice to machine, it can be a little gummy though, with some WD40 for lube and sharp tools good finishes can be obtained.

Dave

Offline Bear

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Re: Essex Hot Air Engine
« Reply #4 on: October 27, 2020, 09:38:02 PM »
Very nice. I will be following this thread with interest, Idaho neighbor  :).

Offline Dave Otto

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Re: Essex Hot Air Engine
« Reply #5 on: November 04, 2020, 12:56:54 AM »
Hi Bear, thanks for following along and the nice comments.

Work continues with the cylinder castings, both castings are the same to start with but each get finished differently.


Machining the cylinder castings is pretty straight forward lathe work; it involves getting the end flanges the same thickness and keeping things parallel and concentric. Here the power cylinder has been machined.


The displacer cylinder is in process in this photo. The extended boss will hold the bronze bush for the displacer rod.


After the turning operations were complete the cylinders were moved over to the mill to have the mounting feet machined and the holes drilled and tapped. Here the bore is being dialed in on one of the castings.


Working from the center of the bore the mounting foot is machined to the proper height.


Each cylinder casting gets a hole pattern on each end, so once one end is done the machined foot was used to square the casting to the table and the next set of holes drilled and tapped.


These are the mounting holes for the water jacket.


A piece of cast iron bar stock is used to make the power cylinder liner.


After turning the OD the ID is bored and then parted off.


Here are the parts so far, the liner has been installed in the casting. I still need to do some fettling, drill the holes for the mounting screws, and hone the cylinder.
More later,
Dave

Online Kim

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Re: Essex Hot Air Engine
« Reply #6 on: November 04, 2020, 05:40:47 AM »
Very pretty work, Dave!
Kim

Offline Dave Otto

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Re: Essex Hot Air Engine
« Reply #7 on: November 04, 2020, 07:33:00 PM »
Thanks Kim!

Dave

Offline Dave Otto

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Re: Essex Hot Air Engine
« Reply #8 on: November 13, 2020, 11:30:31 PM »
Hi everyone

The next item to be worked on is the engine frame casting. This casting like the crank shaft bearing casting came with lots of extra material that needed to be removed. Not wanting to saw and file this to shape I needed to come up with a way to machine it. The following photos will show how I decided to proceed.


Here is the casting as received; after smoothing the bottom with a file to get it to sit flat, I measured the height of each end. Notice the X on the right hand side, this is the low side. It will be shimmed so the right and left hand sides end up at the same height.


Here is another shot showing the casting from the bottom side.


The casting was aligned and clamped down to the mill table; notice the shim on the right hand side? This was to bring the low end up to level. Each end was machined moving the outside clamps to accommodate this; the center clamp was not disturbed to maintain part alignment. This operation brought the casting to proper length with both ends parallel to each other.


After the last operation the casting is now able be clamped in the vise. Here the chimney opening is opened up to size and a very light skim cut is also taken off of the top surface. That skim cut will be used later to level the casting for subsequent operations.


Next, the two openings on each side of the chimney were opened up.


I decided to add the patent information like the original engines had. Working from photographs I created text that closely matches the original. The two tapped holes are to hold the furnace assembly on to the engine frame; and just like on the original, the holes are drilled through the text.


Here is another view of the engraving that was done using the CNC.


The casting was flipped over and set on the previously machined rim of the chimney. Once indicated in using the chimney hole, the underside of the frame is machined to accept the furnace.
A light skim was taken off the bottom surface to help with laying out the ends of the frame.

More later.

Dave

Online Kim

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Re: Essex Hot Air Engine
« Reply #9 on: November 14, 2020, 05:44:21 AM »
That is meticulous work, Dave!
Thanks for the detailed setup info, I really appreciate that.  It helps me see how other people think about their setups and machining steps.

Beautiful work, as always.
Km

Offline Dave Otto

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Re: Essex Hot Air Engine
« Reply #10 on: November 14, 2020, 06:06:32 PM »
Thanks Kim!

Offline Dave Otto

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Re: Essex Hot Air Engine
« Reply #11 on: November 16, 2020, 11:33:41 PM »
Hi Everyone,

Continuing with the engine frame machining.


You can see in the picture of the raw casting, David Abbot had made his pattern to leave a cut line for the sides of the frame. Working with some known dimensions and a little messing around I came up with a tool path the followed these lines pretty close.

As this part is going to get pretty fragile I needed to come up with a way to fixture it. The casting was secured to a 123 block stack that is square to the vise jaws. The 123 blocks are locked down to the vise bed using a strap clamp. Parallels and shims were used to position the casting so that it would align with one of the tapped holes in the 123 block. Again the skim cut on the chimney top is being used for alignment. The rear vise jaw and the 123 block were used for my X and Y origins.

An open pocket, adaptive type tool path was used at full depth of cut. Using a ¼” 3 flute carbide end mill taking .02” step over at 40IPM it didn’t take long to turn that extra material into swarf.
In this photo the first side has been machined.


Here is a shot of the right hand side showing the 123 block fixture.


Next the casting is flipped over and the other side machined. With this set up very light vise clamping pressure is used to avoid crushing the part.

Next will be machining the end profiles and mounting holes.

Thanks for stopping by,
Dave

Offline Dave Otto

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Re: Essex Hot Air Engine
« Reply #12 on: November 21, 2020, 12:16:22 AM »
Hi everyone
Continuing with the engine frame machining.


Each end of the engine frame casting was carefully laid out to determine the center line of the engine as well as checking that the profile and hole patterns were going to work ok. Here a wiggler is being used to pick up the center line.
The engine frame is secured to an angle plate and supported for drilling. A hole was also drilled at the cylinder center line so the center could easily be picked up when the casting was removed and reinstalled in the mill. The machinist jack was used for support while drilling the holes.


The hole locations were drilled from coordinates based on the center line of the engine. The cross hairs were just part of the laying out process.


Some pieces parts were made to support the ends of the engine frame for milling. Here is a picture after these parts were installed. The center is being picked back up using a dial indicator.


Here is a shot of the lash up; two 3/8” rods were machined for a squeaky fit between the ends of the engine frame. As you can see they were tapped on one end and locked in place with a couple socket head cap screws. Each rod has a shaft collar the supports a piece of CRS flat bar. The flat bar is held down using a strap clamp which in turn also stabilizes the upper surface for machining.
After the profile was machined on one end the operation was repeated for the other end; this worked quite well. Sorry I didn’t take any pictures of the actual machining.


Here is the finished part after deburing and a light bead blast.


And the underside, I did do some blending with the Dremel tool, where the arms meet the end flanges



Just for fun here is a before and after shot of the casting.


Here is the family shot so far, you can get an idea of the size by the 12” ruler on the bench.

Thanks for checking in.
More later,
Dave

Online Kim

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Re: Essex Hot Air Engine
« Reply #13 on: November 21, 2020, 06:49:09 AM »
That's a very delicate piece when you're done with it - so much of it has been removed!

It's going to be pretty good sized when you've got it all together.    :popcorn: :popcorn:
Kim

Offline Dave Otto

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Re: Essex Hot Air Engine
« Reply #14 on: November 22, 2020, 04:15:22 PM »
Thanks Kim, I appreciate the comments.

Dave

 

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