Ringbom 1: Tim's Ringbom Stirling Engine Build

[tvoght]

A few days ago I showed a video of my Ringbom Stirling engine "Ringbom 1" running. I thought then that I might not do a build log, but I have reconsidered. I have a lot of build photos for some parts, but I imagine some parts will have little or no photos. I'll do the best I can.

Before you make any comments about how fast the build is going, remember the engine was essentially complete 3 years ago. I'll put this photo here as a reminder:



I'm going to attach a .pdf drawing with the log of each part.
Here we go!


--Tim

[tvoght]

The power cylinder and cylinder head were made first. They are of cast iron. The horizontal bandsaw was used to slice off pieces to arrive at stock closer to the finished shape.
The various slabs went into the junk box for future projects.




The larger piece just above the part numbered 1 was to become the cylinder head. Here it's shown in the 4-jaw having a boss turned which will extend into the cylinder bore.



Then excess was sawed off creating more scrap box fodder. Focus!


The flange portion was then milled to thickness.


Now with the main cylinder stock placed in the mill vice, the mating flange to the cooler was cut. Since the sides being clamped are not parallel after the sawing operation, A sheet of paper was folded into multiple layers and placed between the movable jaw and the part to take up slack.



With the broad milled side as starting reference, The other surfaces of the cylinder block were milled.





The cylinder block then went to the lathe for drilling and boring.
It seems there is no documentary evidence of the boring.


Back at the mill, the head was temporarily super-glued to the cylinder for placement of mounting holes.



The head flange and cylinder werre drilled to depth with a 4-40 tapping drill, then only through the head flange for clearance. Finally the cylinder was tapped with the head still in place since the tap cleared the clearance holes in the head. A screw was placed before proceeding, and the remaining holes were done in a similar way.




The cooler mounting face previously cut for reference was then cut to final dimension with a face mill for a decent sealing finish.



Mounting holes for the cooler were drilled through, and then the port hole cooler-to-cylinder was drilled through to the bore.



The next cuts are decorative to give the cylinder some character.




And that's about it for the cylinder and head (until the bore is lapped).

[crueby]

Not seeing any pictures here...

[RReid]

I'm seeing the pictures.

[tvoght]

Picture are seen on Firefox browser and not Chrome. I just checked an old build of mine and the pictures aren't showing there either. Something has changed.   --Tim

[crueby]

Yup, I am using Chrome on my tablet, not seeing them. Will check with firefox on the pc. All the browsers have changed thier rules on linked content, its really hard to diagnose. Usually something to do with whether all content, or none, is a secure link, https, or not. Mixing them causes lots of odd behavior lately.

[tvoght]

The chrome debugger revealed the problem. MEM is now https, but my self-hosted pictures are on an http server. It's not immediately obvious how I can fix this. I may not be doing this build log     --Tim


P.S. For interested techies:    https://love2dev.com/blog/chrome-mixed-content/


The only solution is probably to switch the server I'm using to https. I'll have to check into it.

[MJM460]

Hi Tim, all the pictures are showing here on iPad plus Safari.

I do hope that you will be able to continue somehow.  Perhaps. The standard attachment method will work.  It would be a pity to not be able to proceed.

Thanks for the pictures so far.

MJM460

 

[PJPickard]

Yeah I hope you continue as well. I have one of these on my eventual list. I have Senft's book, but I like the design of yours better.

[tvoght]

First, thanks crueby for your help in troubleshooting this.My solution will be to transition my server to https. This could take a couple of days, and it's unclear to me whether I will need to change all the links in my prior builds so that they can be seen with Chrome also.

MJM460, it's likely that this is only a problem with recent versions of Chrome, but it's probably only a matter of time before other browsers take this measure. The standard attachment method will not remedy my existing builds here which have the same problem, and I don't like the text first, then pictures format.
PJPickard, I have built Senft's "Tapper" as well, and I also like mine better .  I stole some of Senft's design ideas, though. I am attaching drawings as I go, and will eventually place them in a .zip in our plans section.

--Tim

[tvoght]

The cooler (in 6061 aluminum) came next. A chunk of 2 inch square stock was cut slightly over-length and centered in the 4-jaw, then a hole was drilled and reamed clear through for the displacer rod bushing. That hole can be seen at the bottom of the larger displacer cavity that had been bored to depth here.
The hole was bored ever slightly deeper than required and then the end was faced to establish the design depth.



A recess was bored to accept a flange on the hot cap.



This shows that a form tool was made to cut a groove for a sealing o-ring at the bottom of this recess. Ultimately, a wider square-section o-ring was used here and the groove serves no function.



The cooler was clamped in the CNC mill for a fin-cutting operation. The clamps to the sides served to ensure no lateral movement.



A 3/32" saw was used with a CNC program to cut the fins. A slow operation compared to cutting these in the lathe, but good luck has been had with the method, and some frustrating bad luck trying to do it with a lathe.
Also -as you'll see- some of the fins do not extend entirely around the cooler, so a lathe operation would not have worked for those anyway.



In the lathe, the cooler was centered on the hole that had been previously reamed for the displacer rod bushing. A boss was then turned, No photo is shown of that operation.



Here in the mill vice you can see the boss that was turned, and that holes have been drilled and tapped to match up with those previously made on the mating face of the cylinder. The hole in the middle provides direct connection from the cylinder bore to the displacer bore in the cooler. Plenty of cleanup still needed.



A corner was rounded off to build character for this part. It was decided to use a coarse step in the round off to give this scalloped effect. An observer at a show asked in a surly tone why in the heck it was like that. To each his own.
You'll also see the adjacent corner was truncated for appearance.



This photo shows a now-favorite tool, this edge-finding device. It is mounted in a dedicated tool holder and then adjusted to eliminate runout. It is a very accurate tool. Here It's being used to find the middle of that bore using the Osborne maneuver. What's not shown is why: holes were drilled surrounding the hot cap flange recess. Those will be for a clamping ring which will hold the hot cap.



That's all the existing photos of cooler operations, but one more step taken was to mill each of the 4 flat sides with a face mill just to cleanup the extruded faces and any clamping marks.

[crueby]

No pictures yet in chrome. 

[tvoght]

I'm sorry to anyone who's looking. All that I succeeded in doing is partially fixing this for Chrome, and completely breaking it for other browsers. I've at least restored it to work with other browsers, but I won't be posting anymore until I get this figured out (if ever).
If I have bad days on my day job, it is quite often because I'm dealing with browser compatibility issues (but I get paid for that). Meanwhile I have far too much day job work to do to spend so much time on this.
--Tim

[crueby]

Yeah, just checked in Firefox, no pics there again either.   

[RReid]

Using a laptop running Windows 10 I see the pictures in Firefox, but not in Chrome.

[Admiral_dk]

Nice work Tim 

I can't see the pictures at work on a Win 10 with Chrome - but here @ Home on a Win 7 with Chrome -> no problem 

I'm sure that the reason, is that here Chrome is in http format and af work it's in https .....

Per

[tvoght]

The photos should be viewable now in all browsers. A lot of back-and-forth effort between myself and my web host provider. I'll be posting some more build material after I get some other duties knocked out.
--Tim

[crueby]

YES!  Pictures now show for me in both Firefox on pc and chrome on tablet!      The fins look great!   

[fumopuc]

The photos should be viewable now in all browsers. A lot of back-and-forth effort between myself and my web host provider. I'll be posting some more build material after I get some other duties knocked out.
--Tim

Hi Tim, my Opera does show it now too.

[Admiral_dk]

Total succes - I can see them on Win 10 now too 

[tvoght]

All of the Stirling machines I have built use displacers of very thin-walled stainless steel. I machine these parts from solid bar stock. I have made a number of them, each time refining my technique. This is my latest refinement.

First, a mandrel was made starting with a length of 1" cold-rolled steel in a collet. The extended part was turned to the inside diameter of the displacer shell. The end was faced.



The mandrel was then reversed in the collet and drilled for a center.




To make the displacer shell, a solid rod of 1.125" 303 stainless was chucked in the 4-jaw. The first operation would be to drill it to depth at .938" diameter, and then bore it to slip onto the mandrel.
I know many like to "step drill" with a number of progressively larger drills when drilling a large diameter hole. Here, just two steps were taken.

First, the width of the .938 drill's "web" was measured.



Then a small drill was selected just a hair larger than the large drill's web, and a starter hole was drilled to depth.



The large .938" drill was then used in a second drilling. I got this technique from a book and it works for me.



An endmill just slightly smaller in diameter than the drilled hole was then used to flatten the bottom of the hole.



The hole was then bored for an easy (but not loose) fit on the mandrel. No photo is shown of the boring operation.
The mandrel was then loctited into the still-chucked stock. A dead center was brought up to the center drilled in the mandrel.



With that setup, the outside could be turned to achieve the desired .01 inch (.25mm) wall thickness. Look carefully to see the transition from displacer shell to mandrel.



The displacer shell was parted off just beyond the depth of the hole, leaving plenty of end material, then the mandrel went back into the collet, and the end of the displacer shell was faced to desired thickness. .01 inch end wall thickness was the target here too, but it's a little scary since any slight miscalculation could result in an open ended tube.



 Later, propane heat was used to break the loctite and remove the part from the mandrel.

The surface finish is not pretty, but on an engine of this type, the displacer's outside surface serves a regenerative function in the engine. The rough surface should actually enhance that.

[Kim]

Thanks for taking the time and effort to figure out the issue with the pictures.  I've just read all your posts and am finding your build very interesting.  I really like the step by step on how you did the thin wall displacer!  Fascinating!   

Kim

[tvoght]

Thanks Kim! And thanks to everyone who provided moral support during that pictures snafu.

The displacer cap was to be made of 6061 aluminum. 1 inch rod stock was placed in a collet and a boss turned.



A short section was turned on the outer diameter that will fit the inside diameter of the shell. A small carbide-tipped boring tool was used to remove material between the boss and the outside flange. Weight reduction in the displacer of a Ringbom engine is critical.



A check to verify the fit of the shell onto the short shoulder section.



More work was done with the boring bar to thin the outer wall of the cap, and the outer diameter beyond the shoulder was turned to match the outer diameter of the stainless stell shell.



The cap was parted off and then the boss was placed in a collet. The part was faced to length.



A blind hole to accept the displacer rod was drilled, bored, and reamed.



A shot of the displacer shell with cap test fitted.



And a trial fit of the rod. The shell, cap, and rod will be epoxied together with JB Weld at a later stage



The displacer rod itself is made from purchased precision stainless tubing. Lacking the availibility of this, it might have been machined from solid stock.

[tvoght]

The bearing block attaches to the engine frame and holds 2 ball bearings for the crankshaft to run in. As with all the parts I'm building, there's a drawing attached to this log entry.
Since in many cases there aren't a lot of photos, I'm hoping the drawings will help to fill the gaps.

1" 303 stainless stock is put in a collet and drilled past the length of the part with a drill size that will allow finishing with a boring bar.



Then the hole is bored to fit the outside diameter of the flanged ball bearing.



The shoulder portion will fit within a bore in the frame. It's turned to diameter, and the design plan also intended for the shoulder to fit within a collet on hand, so that the other end of the part can be machined. A sharp tool is used to remove any inside radius at the should transition.



A recess for the bearing flange is turned using a small boring tool.



A bearing is test fit.



The part is cut off with length to spare, and then the shoulder end is put in
a 7/16 collet. A recess is also bored here for a bearing flange.



Another test fit.



At the mill, I use my "3d taster" to locate the center of the bored hole



And then center and drill for 4-40 tapped holes equidistant on a .688" circle.



The holes are tapped.  The DRO's bolt hole circle function makes it so easy to return exactly to each hole
location for center drilling, drilling, and tapping.



The part is complete.

[tvoght]

The frame is a pretty simple affair. There is a drawing attached.

The material is hot-rolled steel angle 3/16 inch thick with 2.5" legs.

Set up in the Bridgeport vise backed from below with a 1-2-3 block, a first
leg was cleaned up with a facemill. Then in a similar setup with that face against the fixed jaw, the other leg was cleaned up.



While still at the Bridgeport, all important holes were drilled, including the
large hole which will hold the bearing block. That hole was bored to size.
What is meant by important holes? All the holes which must have a precise locations.

Then to the CNC mill, where the part was clamped in the vise in a similar way.
The spindle was zeroed at the center of the bearing block hole for reference in the CNC program to be run. The program cut a profile in a series of progressively deeper cuts.



A separate program was used to cut some decorative slots.

[tvoght]

Next up is an overhung crank consisting of a web, a shaft, and a pin.
The web comes first. A drawing is attached.

1.25" 303 stainless stock is put in the 4-jaw and drilled .015" or so less than
the .25 inch intended shaft bore, and deeper than the final length of the part. The hole is then reamed to .25" for the shaft. A shoulder is turned to space the web off of the ball bearing it will butt against.



The part was cut off with extra length and taken to the mill. The center hole was accurately located and a hole drilled at the crankpin offset.



The web was milled to thickness, and then the crankpin hole was drilled and reamed.



At the CNC mill, a tooling plate was clamped down and drilled and tapped for
shoulder screws to clamp the part. A program cut the web outline a little
oversize in progressively deeper cuts.



Then another program cut to final outline at full depth. Notice that there was no margin of error for that smaller shoulder screw. I don't recall how I managed to prevent it from being unscrewed by the cutter. It's possible I used loctite on the threads.



The shaft is purchased 1/4" stainless ground rod. The only machining necessary was to cut it to length. A drawing is attached.

The crankpin is made of stainless and unfortunately there are no photos of the
build. A fairly straightforward collet job. See the drawing.

I don't seem to have any photos of the parts first asesmbled, but they were put together with loctite 609.

[tvoght]

A brass piston rod was made.

1/8" brass stock was setup in the Bridgeport vise. A hole for the big-end bearing (a ball bearing) is drilled, bored, and reamed.


]hr]


Then the hole for the gudgeon pin was drilled and reamed.



At the CNC mill. A tooling plate was drilled and tapped for two hold-down screws. Shoulder screws are usually used here, but with no correct sizes in stock, close-fitting bushings were made and used with ordinary cap screws.



A CNC program was unleashed.

[crueby]

 

[tvoght]

Thanks for looking, Chris!
The piston is in two parts: the piston, and a gudgeon insert.

To make the insert, a rod of aluminum was placed in a collet and the two diameters shown in the drawing were turned. A hole for a 2-56 thread through the depth of the part was drilled.



The collet was put in a square collet block and taken to the mill to make a hole for a gudgeon pin. A spot-face was made, a center-hole was drilled, and the part was drill through and reamed.






With the collet block upright in the vice, a slot for the piston rod was milled.



Back in the lathe, the insert was parted off.



The part was reversed in the collet. The clamping in the collet of that split boss seems a little tenuous, but light cuts were taken to arrive at the correct thickness of the base of the part which mates with the piston. Photos don't show that the edge of the part was deeply chamfered to clear any fillet left in the bore of the piston. Also in this setup, the previously drilled center hole was tapped.



This photo reminds me that on this day in the shop, two other parts were made: 1) the displacer stop, which fits on the displacer rod and limits the travel of the displacer. 2) the piston rod holder, which is essentially a washer that bears on the inner race of the big end bearing and accepts a screw into the crank pin.



There are no photos of the making of those small parts (I must have been "in the zone"), but drawings are attached.

All the complexity of the piston is in the insert, with the piston itself being quite simple. The one pictured is made of graphite, and that is a tried and proven material to use here, but in the process of troubleshooting a problem, another was later made of cast iron with the same dimensions. The cast iron version runs in the engine now.

A quick picture of the graphite piston in process...



The piston, piston insert, and rod with big-end bearing and gudgeon pin installed.



Here is the piston attached to the insert with a screw. Looking back, you'll see that the cylinder head has a hole to clear this screw head.



Thanks for looking.

[tvoght]

The hot cap of the engine is the last part I have any real build photos of. After this, I'll post drawings of the few remaining parts with a brief description for each. Then I'll be essentially finished with the log.
The hot cap construction is similar to the displacer shell done earlier. The only real difference is the inclusion of a flange to clamp to the cooler.

It started as a solid hunk of 303 stainless. The original stock was in better focus.



Same approach to drilling as with the displacer. Selecting a drill for the pilot hole about the size of the large drill's web.




Drilling in two steps and flattening the hole bottom with and endmill.





Then boring to the final inside diameter. The endmill used to flatten the bottom was a little small, so some work with the boring bar was necessary to complete the square bottom.



Making the mandrel. A lesson was learned when making the displacer: it was tough to remove the mandrel because of suction. Here a pressure relief channel is cut to fix that issue.



After turning the outside diameter, leaving the flange. Cutoff just beyond the hole bottom would be the next step.

[Admiral_dk]

A nice detailed description so far - still following and enjoying your description 

Per

[tvoght]

Thanks for checking in Per.
As I said in my last post, the photos are exhausted, but I will attach drawings of the remaining parts and try to give descritptions of how these parts were made.

The next part is a graphite bushing for the displacer rod. It is epoxied (JB welded) into the cooler. It has a reduced diameter in the center of its length so that the JB Weld that bonds well to the aluminum will fill the reduced diameter portion and lock the bushing into place. This is because the epoxy will not bond to the graphite.

There is little to say about the machining of the part in the lathe except that graphite turns extremely easily, and there is danger of over-shooting the mark on intended dimensions. One strategy is to get near to dimension with lathe tools, and then finish up using ordinary printer paper as an abrasive.

A drawing is attached.

[Roger B]

Interesting      I am heading towards the cylinder and pistons for my rhombic hot air engine and due to the lack of suitable SS tube I was thinking about making them from bar stock. I have managed to core drill cast iron and aluminium but I am not sure it will work with SS

[tvoght]

Hi Roger, thanks for commenting. The latest iteration of my method really works quite well and allows for a really thin wall. The next time I do it, I will try an even thinner wall perhaps 1mm. I know there must be a practical limit, but the 2.5mm walls are not a challenge at all using this method.
When you speak of core drilling are you referring to using annular cutters? I saw a good video from Adam Savage (of Myth Buster TV show fame), advocating them for our kind of applications. While he is a bit prone to hyperbole, He said they have "changed his life". I went ahead and bought a small set and will experiment with them for this purpose.
I have experimented some with 304 stainless tubing, with the intent of hard soldering ends on, but in the end, I would want to thin the walls anyway.

--Tim
Adam Savage on annular cutters:
https://www.youtube.com/watch?v=-5zSadDZMhA

[tvoght]

I do have a couple of photos to show concerning the flywheel, but only of the operation I used to reduce waste of my cast iron stock. I had purchased some 3.5 inch stock at 1 inch length. The supplier sawed it off a bit more than an inch long. I really only needed the inch so that I could turn a hub on the wheel as planned. But I thought "how can I make the hub without so much waste?".

These photos show briefly how I got material for two viable flywheels from the stock.

Using a CNC program to outline the hub portion about halfway through the stock. A lathe operation would have worked with possibly a wider cut.



Cutting down to the hub groove. This took a few settings in the bandsaw to cut all around.




The rough parts. The one on the right to serve as stock for the flyweel on this engine, the other can be attached to a separate hub for a future engine.



A drawing of the flyweel to be made is attached. It was meant to be held to the shaft with a clamping collar. A vendor's drawing of the collar I used is also attached. I have to point out that the clamping method ultimately failed with cast iron, as the "tabs" were just too brittle, and one of them broke off under clamping pressure. I ended up drilling out the cast iron hub and replacing it with a more ductile steel hub. The same clamping method was used, and worked fine with steel.