Moriya Fan Variant - Double Sized


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I recently completed a variation of Dr. Jim Senft's Moriya Stirling fan, and learned an awful lot about building a Stirling engine that actually runs. Not wanting to let the lessons learned and the thrill of a running engine escape, I decided I'd like to do it again. Sooner, not later. It didn't make a lot of sense to make the same project again - I had my eye on something bigger - Orrin Iseminger's 2X Moriya. I emailed Orrin and he offered great encouragement and lessons that he had learned to get me motivated. Time to get started



When you double the size of the cylinder dimensions, you don't get double the displacement, you get eight times the displacement. I have questioned the need to double these dimensions but Orrin related a conversation he had with the late Jerry Howell who didn't mix words about the issue and essentially said "just double everything." So, that's what I'm doing.

I was fortunate to have a big slab of 1 inch thick aluminum - "fortunate" being a mixed blessing when you have to rough cut it to size and then machine that big blob into something usable on a little Sherline CNC mill.


I like to print the Cad file and, with a little spray mount adhesive, glue it to my work piece. I like having all of those reference points sitting there to look at. They remind me what needs to be done and help guide the order of the operations.


 To ease the burden on the mill, I cut out the majority of the displacer hole with a hole saw and cut the outside lines as close to final as possible.


Cutting down through 1 inch aluminum is no small job on such a small machine. I would typically cut down to about .250" or .350" in each operation, let everything rest and cool off for a bit ( maybe a cold beer and dinner ), and then resume.


The outline was particularly problematic. Normally, I would just cut the work piece oversize, clamp it down, and mill it out. But, this piece was so big that, even cut way down in size, it barely fit on my clamping table. This one called for some thinking.

What I did was to create four separate exterior segments - one for each side. One side of each of these virtual segments was the border of the work piece. This way a huge job could be broken down into four more manageable jobs. And each in turn was cut about .350" down at a time. This picture shows the bottom segment cut down to about .650" and cover the angled corners. The top is done the same way; the ends will be small rectangles. When the ends are milled, that end's clamps will have to be removed and a clamp place down through the displacer hole. With light cuts, this has been working fine.


I got a bit ahead of myself when I first started this project. Here's a sneak preview of a bonus add-on.

It's a mini fan to help keep the displacer cylinder cool. I don't know if it will work or not but it should add some visual and mechanical interest to the project. It will be driven by another pulley on the crankshaft.


"Mission Control"


Base is all cut out and first sub-assembly mounted.

Somewhere inside that miserable big lump of aluminum sits a lovely finned 3.50" finned cylinder

Cold end in progress


Reaching the finish line seldom feels so rewarding.


The posts will connect the crank brackets to the base while passing through the cold end cap and hold the whole thing together.

The original Moriya has a square cold end but I didn't have any square material that big and have seen more than one suggestion against using it due to the difficulties of cutting the fins of square stock in the lathe.

I'm not sure that I like the posts yet - they created the connection from the cap to the base to fasten it down. Or the oversized cap, but I have left myself a few back doors in the parts that I've made in case I decide to change it later. I'll wait until all of the parts are in place and see how it looks overall before I decide. Maybe a round cap but leave the posts to mount the crank brackets ?


This is the start of the power cylinder.

It's not easy finding pieces of 2" diameter brass in the scrap yard but I found this one a few years ago knowing that I would find a use for it. 2.25" would have been better, but it'll do. It's not big enough to have a wide enough base to screw down to the base so I'll make a bracket to hold it in place.


The diameter of the power cylinder base would have been way too big to scale it 2:1 and I didn't have a piece of brass that large. So, the base will be just 1/4" in diameter larger and it'll be held in place by this retainer. Here, it's still on the mill

Nearly finished power cylinder retainer in place.

It was a tough decision, but after cutter the square top down into a round tip, I'm happy it's done. It'll likely stay slightly over-sized though.

First of the crankshaft supports, with bearing, in place.

Second crankshaft support, without bearing cut. Both still need some finishing work.

The displacer connecting rod in progress

Displacer connecting rod, off the mill but still in need of a bit more work.

Power connecting rod now complete... mostly.

After all that time making the displacer connecting rod, I decided that it was going to be too heavy. I made another one but this one is a match to the power piston connecting rod.

Drilling the mounting holes in the cold end cylinder


Power cylinder almost complete. I still need to hone & polish the bore


The crankshaft lobes took a fair bit of time on the lathe and mill to get just right. The width of the spacers on either side of the connecting rod are within .0005" of each other to ensure that the rod runs perfectly centered.

The connecting rod pin will be locked in the hole with red Loctite sleeve retaining compound and a machine screw. 

If the lobes turn out to be too heavy, I'll machine some decorative holes or something in them.


Crank lobes and rod assembly


In their final resting place


Bearing retainers for the crankshaft.


Web to hold the fan blades.


The drive pulley finished. This will connect to the fan pulley below to turn the cooling fan to keep the displacer cylinder as cool as possible. ( The shaft shown is is temporary. )
Here you you can see the drive and fan pulleys. They will be connected with an O-ring belt.


The blade assembly felt like it was a little heavy with just three blades attached and I was a bit concerned about adding two more. So, I redesigned the web for three blades ( which also made the web lighter. )

And now you know what happens to old parking signs.

The new & improved three bladed model. It still needs a twist applied to each blade attachment point.
And a profile shot.

Blade web twisted, hub and cooling fan drive pulley in place.


Legs made and mounted along with a plate which I hope will deflect some of the heat away 
from the upper part of the displacer cylinder. Below that is the platform for the alcohol lamp.


For purposes of understanding how big this fan is, compare it to a standard sized Moriya ( variant ). If that doesn't mean much to you, a bottle of IPA may.

Power cylinder crank arm and connecting rod now complete.


Turning, boring and cutting off the hot cap and milling its retainer plate to hold it to the base.


For all outward appearance, it's finished. 
But, it still needs pistons and connecting components as well as a bit of other minor touches.


While waiting for some materials to finish this project, I got a start on the next project.
A half sized Moriya. More about his project later.


Power connecting rod - Piston connector


Cold end cylinder hold down tabs

 

 



Alcohol Lamp mounted below the hot cap with appropriately sized funnel
 
Updated: August 04, 2014