a Jerry Howell "duplex vacuum" stirling engine build

[madjackghengis]

Hi lads, thanks much for the complements, and comments, I'm enjoying this build ever more, as I see the many other projects going together at the same time.  I reckon I'll have to live another hundred years to finish all my projects on my list   I've got a bit more done, having roughed out the outside of the hot cap, I cut it off, surprizingly easily, with a cutoff tool, glad the cut was right at the chuck jaws, and put the chuck on my dividing head, the hot cap in the chuck, to mill the "fins" to collect the heat.



This is after several cuts, taking care with a sharp 3/16ths mill as the carbide end mill I was using snapped off as it broke out of the first cut, it being a long cutter, and catching the brand new edge on the edge of the end of the cut, hate stainless.



This is among the last cuts, I went .250 deep twice at 90 degrees, and .125 in deep at 90 degrees, offset by forty five, making lots of little points to absorb heat from the flame, and retain a thick cap end.



of course after milling the slots, I put it back in the lathe and turned the part right behind the recess for the seal, down to about fifteen thousandths thickness to minimize heat conduction directly.



here's a shot of the whole mess lying on its side



lying on its side with a spare seal, turned out of a scrap of delrin I think, picked up off the floor waiting to be thrown away and ecstatic at being put to use again.

Of course, having lapped the cylinder, made the hot cap and seal, and fitted everything, I had to turn a piston, so a 1 in bar of graphite was centered in a four jaw, about five minutes taken to produce a teaspoon of black dust, and a perfect on size piston turned, with a touch of the finest file I have, just to take a quarter of a thousandth off, using a real micrometer instead of the all important calipers.



Here is the assembly, standing on the hot cap, with the piston floating on air in the very top of the cylinder.  Of course there was another hour of lapping, as measuring for a fit is a different story from fitting a plug into the actual hole.  Next, I will be machining the rough piston to take the aluminum piece which will hold the gudeon pins, and the bronze guide for the displacer rod, which runs vertically through the power piston.  With a bit of luck, I can get a crankshaft assembled as well, it's hard to have all these pieces and not have a shaft to turn with the fingers and watch things move as they should.  I am seriously challenged by that video of the Gold Blend engine running so sweetly with such a small flame.  Ta ta for now,  Cheers, mad jack

[sbwhart]

This engine is begining to look like an art work 

Excelent work jack 

Stew

[Dean W]

You're making good progress, Jack. 
If you have any trouble with that delrin seal, let me know.  I have some ceramic sheeting left over from mine.
Plenty of it, if you need some.

[doubleboost]

Nice very nice 
John

[Stilldrillin]

That's coming together very nicely Jack! 

David D

[madjackghengis]

You're making good progress, Jack. 
If you have any trouble with that delrin seal, let me know.  I have some ceramic sheeting left over from mine.
Plenty of it, if you need some.

Hi Dean, is that sheeting what Jerry suggests the use of for the hot cap?  I hadn't bothered to look it up yet, I tend to get caught up in the machining, and let somethings go to the end.  Thanks for the offer, and I think I will take you up on it when I get to a point where I've got a dimension for what I need.  What a web site , imagine all those other people who go to such things to exchange make-up ideas and other such foolishness.     Engines R us   Cheers, mad jack

[AndyB]

Hi Jack,

I have not been too keen on the idea of building these as they look too much like toys....until now!

Your build using whatever is to hand, and making it look easy and interesting, is fabulous!

You have given me an interest!! Looks like another project to line up!

I am definitely following

Andy

[Dean W]

Hi Dean, is that sheeting what Jerry suggests the use of for the hot cap? 

Jack, yes, for the insulator that goes between the hot cap and the bottom of the power cylinder.  It's a ceramic fiber stuff. 
I got it from a place in Seattle that uses it for insulating kilns.   Jerry Howell called it fiberfrax. 
You know from the prints that it only needs a few square inches, but I had to buy two sq. feet, so I have a little extra.  ; )
Send me a PM with your address and I'll shoot a piece your way.

Dean

[madjackghengis]

Well, boys, I got a bit more done since the last post, too much work and having to adjust some figures to the different sizes I used makes my brain hurt sometimes.



I'm using a .965 bore instead of the .750 bore, and chose to increase the stroke from 3/4 in to 7/8ths in, so I took some safety wire and wrapped it around the crankpin, cut it off a bit long, to test and see if the connecting rod would clear the bore.



another shot of the test piece





the jig with the wire showed plenty of room, so I soldered a couple pieces of flat brass together to make the split con rod out of.



the pieces are about half an inch wide, and a bit of 2.5 long, they will be soldered into a bushing on the big end, and each small end will be on either side of the displace rod bushing, which goes up through the middle of the power piston, necessitating this two piece rod.



I put the pieces in the vise and milled one edge to get parallel, then put the pieces on a parallel, and pulled the vise up tight on the edges.



touching off on the edge of the vise with a wiggler, centered the spindle, then found the end and moved the table to position the spindle where the big end hole needs to be.



starting with a center drill, I'll step drill up and end with a .250 reamer.



one step drill



another step taking it to about .012 under, and then reaming it out in a slow and easy pass.



and the reamer, taking its light cut.



drilling the little end, #1 center drill, then a sixteenth, and an .082 ready for the reaming.



final reaming the wrist pin holes at .093, because that was my smallest reamer.



and here is the pair of connecting rod blanks, which will remain soldered together until their outline is cut and filed to final shape and profile.  Once the actual limits of the power piston travel are observed, I will be able to jump into the making of the displacer piston, knowing how long it will be, and the length of its rod, after changing the other dimensions so fitting the power piston is next.  Cheers,    mad jack

[NickG]

Beautifully crafted that Jack    they do look really nice designs Howell's.

Nick

[madjackghengis]

You're making good progress, Jack. 
If you have any trouble with that delrin seal, let me know.  I have some ceramic sheeting left over from mine.
Plenty of it, if you need some.

Hi Dean, is that sheeting what Jerry suggests the use of for the hot cap?  I hadn't bothered to look it up yet, I tend to get caught up in the machining, and let somethings go to the end.  Thanks for the offer, and I think I will take you up on it when I get to a point where I've got a dimension for what I need.  What a web site , imagine all those other people who go to such things to exchange make-up ideas and other such foolishness.     Engines R us   Cheers, mad jack

Hi Dean, I just got the piece of insulation in the mail, thanks much, you'll see it in application soon I hope.  I'd email you but my email's down for the moment, not sure why but it happens pretty often, I guess those buggers know how angry and flustered I get with computer language.

[Dean W]

Glad you got it, Jack.