Author Topic: Myers Stirling Stove Fan  (Read 1778 times)

Offline bent

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Myers Stirling Stove Fan
« on: June 20, 2019, 08:45:57 PM »
So, some time ago I added the subject casting kit (from myersengines.com) to a Christmas list...then pretty sure I deleted it as a) we no longer have a wood stove, and b) it's pretty big, too big for most of the required machining to be done on my mini-mill.  Also, it's been a busy year what with getting the youngest through school and all his concerts and shows and...well anyhow, it's been busy.

The youngest and I also have been planning a canoe trip, one last big outing for ourselves before he goes off to college -- something I did with his 3 brothers as they got older.  Part of that was finding all the camping gear and getting it in working order.  The old Coleman single-mantle gas lantern needed a new globe, so off to Amazon to order one...which of course was the wrong size. :Doh:

Meanwhile SWMBO apparently thinks I spend too much time behind a screen  :stickpoke: and dug the Stove Fan kit up off that old list and ordered me one.  So, on Father's day, I opened up the kit (see photo below) and was properly "thankful".  Now it's sitting in the office at work, while I contemplate the steps necessary to get it working.  At least one thing is going "right" - the wrong size lantern globe is the right size to use in this kit.    :shrug:

Hopefully I can get it built and working, and can test it out on the bbq or the wife's gas stovetop.  Then find somebody to gift it to...wish me luck!

Offline Ye-Ole Steam Dude

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Re: Myers Stirling Stove Fan
« Reply #1 on: June 20, 2019, 08:53:51 PM »
Hello Bent,

That is some good looking castings, are they aluminum or cast iron.

Have a great day,
Thomas

Offline Jo

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Re: Myers Stirling Stove Fan
« Reply #2 on: June 20, 2019, 09:33:39 PM »
That looks a very desirable set of castings   :)

Jo
Enjoyment is more important than achievement.

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #3 on: June 20, 2019, 11:13:35 PM »
Hi Thomas, they are aluminum.  Should be straightforward machining, but I need to think through the steps, how to clamp them, etc.

Jo, thanks.  A bit spendy, but it was the wife's money...ha ha.

Offline b.lindsey

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Re: Myers Stirling Stove Fan
« Reply #4 on: June 21, 2019, 02:01:48 AM »
Nice Bent. Myers usually does a pretty good job on their kits. Just study the drawings closely. I have found a few errors in other kits, though have no experience with the fan itself.

Bill

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #5 on: June 21, 2019, 05:43:39 PM »
So far the drawings seem fairly straightforward, though the tolerances aren't given, so it will be a matter of figuring out what is critical and what ain't.  Castings (I'm checking the big pieces first) seem to be good, i.e. there is enough metal to cut back and form the necessary features.  I've got to figure out how to hold some of these things, without distorting the parts too much, and that's got me slowed down a bit...along with the fact that work and things like that continue to get in the way.  Maybe I should push up my retirement date, but do you think they'd let me still come in and borrow time on the drill-mill and rockwell lathe?  ::)

Offline b.lindsey

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Re: Myers Stirling Stove Fan
« Reply #6 on: June 21, 2019, 06:10:07 PM »
As for retirement, I love it but have had less shop time for numerous reasons. Hope that will change here shortly!!

Bill

Offline Dave Otto

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Re: Myers Stirling Stove Fan
« Reply #7 on: June 21, 2019, 07:18:51 PM »
I built the Essex fan from Myers casting a number of years ago. I didn't like the fact that it had an aluminum bore, so I sleeved it with a cast iron sleeve. I also sent the piston to High Performance Coatings and had them coat it with their SDF moly graphite coating.
https://hpcoatings.co.nz/services/advanced-engine-coatings/#sdf

It has always been a great runner. Looking forward to seeing progress on your fan.

Dave

Offline Ye-Ole Steam Dude

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Re: Myers Stirling Stove Fan
« Reply #8 on: June 21, 2019, 07:45:05 PM »
 Maybe I should push up my retirement date, but do you think they'd let me still come in and borrow time on the drill-mill and rockwell lathe?  ::)

Hello Bent,

Sure they will, just tell them that you are doing all of this work for FREE :ROFL:

Have a great day,
Thomas

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #9 on: June 24, 2019, 04:55:49 PM »
I was thinking of charging them a consultant's fee Thomas!  :D

Dave, this version of the fan has a DOM steel tube cylinder liner (to be press fit to the aluminum casting), and is mated to an aluminum piston.  I'm a little worried about differential expansion causing binding...but we'll see.  Can always go back and build a steel or stainless steel piston if it is an issue.

After dithering around thinking about milling the features on the base, I realized it would actually fit in the chuck on the Rockwell with the jaws reversed (photo #1).  That allowed me to bore all the internal features to size, and face the end of the part and the bolt pads (photo #2).  Then reversed (re-reversed? un-reversed?) the jaws and flipped the part over and clamping on the now machined i.d. surface, I very slowly (500 rpm or so) and carefully (light, .01-.02 deep cuts) machined the o.d. to size and made passes on the bottom face until it was cleaned up and nicely flat (photo #3).  All well and good, but the next operation was to machine the opposite face of the base flange, leaving a 0.300 flange width.  Flipped the part and chuck jaws again, and then shimmed behind the part to get the material exposure needed.  This setup felt a bit less secure than previous ones, so I put a live center in the tailstock and ran it down to secure the part a bit better (photo #4) and finish up the turning operations.  All that was left was to drill and tap 1/4-20 holes on the bolt pads...which is a good task for my mini-mill and its DRO's (someday we might put DRO's on the work machines... ::)).

Photo #5 is the base part fully turned, and sitting next to the next-biggest, and flimsier, skirting piece that fits atop the base.  May have a go at that today (Monday) if time and other tasks allow.  The skirt seems to be just a cosmetic feature, so if I bung it up, no harm?

Photo #6 is from Saturday, dialing in on the center of the i.d. bore with a center finder and the DRO.  Drilling and tapping was a snap (love the spiral flute tap for aluminum, photo #7) and the mill made short work of the bolt pattern - completed part in photo #8).  Even being interrupted halfway through by SWMBO (had a graduation party to go to), and losing the zero for the DRO's, it was still straightforward.

A satisfying day's work, spread over a couple of days.

Offline b.lindsey

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Re: Myers Stirling Stove Fan
« Reply #10 on: June 24, 2019, 10:34:07 PM »
Off to a great start Bent!! Looking good so far.

Bill

Offline Ian S C

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Re: Myers Stirling Stove Fan
« Reply #11 on: June 25, 2019, 03:52:53 AM »
Bent, the best material for a piston in a steel bore would be cast iron, steer clear of aluminium unless  it's got something like PTFE rings on it. What ever Stirling Engine you build you should always be on the look out for ways of reducing friction, happy is the day when you have to introduce some load to slow things down.
Ian S C

Offline b.lindsey

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Re: Myers Stirling Stove Fan
« Reply #12 on: June 25, 2019, 02:27:15 PM »
You might also consider a graphite piston if you can source the material....self lubricating and thermally stable.

Bill

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #13 on: June 25, 2019, 06:06:49 PM »
Thanks for the advice gentlemen.  Will probably try sourcing either grey iron bar or some graphite, if the piston proves any trouble.

Yesterday's efforts went towards the base skirt/shroud piece.  Once again chucked the part in the lathe (Photo #1), with the intention of scratching the i.d. opening on the surface of the casting, then cleaning it up on the mill.  But (being a lazy engineer at heart and in body) decided it was probably about the same amount of time to just take slow, small cuts on the lathe to clean up the chewed i.d. to form a smooth bore (photo #2).

With the i.d bored to size, reversed the part and found some shim washers to move the inside face out enough to make a skim cut and smooth it up (photo #3).  Then machined the face and end of the part, and cut a step to mate to the base piece made yesterday (photo #4 - trial fit, had to make a couple of adjustments from there...).  Took the part home last night to get the bolt pattern done, but we had a birthday dinner for one of the boys, so at home it sits.

Next...the tricky parts.  If I can figure out how to jig them up.

Offline Ye-Ole Steam Dude

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Re: Myers Stirling Stove Fan
« Reply #14 on: June 25, 2019, 06:47:40 PM »
Hello Bent,

Looking real good and some nice machine work.

Have a great day,
Thomas

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #15 on: June 25, 2019, 08:13:33 PM »
Thanks Thomas!

One thing I must say - these castings are of very good quality, both in the soundness/lack of material porosity (knock wood, haven't hit any yet) but also in the dimensional quality - faces are reasonably parallel across the parts (no pattern shift or float/tilt) and bores concentric.  There is one part coming up that has some weirdness, but in areas where it won't matter (they get machined away).  I do sit and stare at that part and wonder how the heck they made the core and pattern...will post photos of it when I get to that step.

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #16 on: October 08, 2019, 04:39:27 PM »
Man have I been busy...or lazy.  Quick update - took the time to locate the base cover on the mini mill at home, leaving enough room between clamps to "touch off" on the machined i.d. and find true center, then bored 9/32 thru, replaced drill with 1/2" endmill and spotfaced the holes (photo below).  It's so much easier to use DRO's for bolt patterns, I'm really glad I installed them.  Oh, and I need to invest in more 3/8" nuts, had to use some spare t-nuts to get the clamping done. :embarassed:

I've also ordered and received a nice little 2" boring head that will let me do some of the more complicated boring tasks at home...but in contemplating (fondling?) the castings realized that two of them need work done on the large lathe at work (because it has a larger chuck), and the drill/mill because it has the required headroom.  But work has been busy, with me being a machinist to make assembly jigs and tooling for a new product, and then doing some R+D...and more to do today...

So maybe later this week I can get some more done?  Will see.

Offline b.lindsey

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Re: Myers Stirling Stove Fan
« Reply #17 on: October 08, 2019, 08:05:30 PM »
You are making more progress than me lately and I don't have the excuse of W*** now. At least it's nice to have the machines at work when you need them though.

Bill

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #18 on: October 16, 2019, 07:46:55 PM »
A bit more done, once again using the work mill and lathe due to lack of headroom and/or swing on the home machines.  The upper piston housing needs to have the i.d. bored, so set it up on some blocks and used a 3" boring head to turn the i.d. (photo 1).  Had to use the side hole of the boring head to get to the 4.3" i.d., which means I couldn't clean up the bore all the way to the bottom.  Will either need to hand work this bit, or just adjust the displacer piston to fit, will decide that later.  After getting a reasonably square/true i.d. datum, I could chuck the part and turn the o.d. of the flange to remove the unsightly casting gate (photo 2 and 3).  Now that good datums have been established, this part will go back to the home mill to get a bolt pattern put in using the dro's, and then bore the power cylinder and displacer piston rod hole.

Photo 4 is just me contemplating the next tricky part - the piece that holds the fan and crankshaft.  Somehow I need to bore out all of the internal casting so the part will fit on top of the piston housing.  Not gonna fit on the lathe, so will need to dream up a jig and means of clamping for the drill-mill.  Hmm... :headscratch:


Offline crueby

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Re: Myers Stirling Stove Fan
« Reply #19 on: October 16, 2019, 08:05:54 PM »
Thats a pretty intricate part, looks more like the trim on an old Dusenberg or something!

 :popcorn: :popcorn: :popcorn:

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #20 on: October 16, 2019, 10:21:51 PM »
I know what you mean, Crueby!  Some days I just sit and look at it and marvel at the person who carved (?) the original pattern, then at the foundry man who figured out how to cast it.

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #21 on: October 17, 2019, 11:45:28 PM »
Well, I decided to jump in and get the fancy standard part started.  After thinking and kicking around ideas with a colleague, I decided to cut a piece of 4" steel pipe we had lying around at work, as it seems to make a fairly snug fit to the part's i.d.  Squared off the end with careful cuts on the lathe yesterday, and tested the fit (photo #1) .

Just needed a notch at the crank shaft end, right?  Yeah, no.  (photo 2).  The fins appear to have warped inwards as they cooled from the casting...or the i.d. of the part is actually tapered along the axis?  Ah, whatever.  Added a strip of polyethylene, and made a c-clamp shoe to fit over the external rib (and a pocket to center the c-clamp swivel end), and voila' (photo 3).  Kinda rickety looking, but it held up well to the shake test, and a couple of whacks with a bit of 2x4.

So, rough-planed the end where it will mate to the piston housing, then shimmed the part in its clamps to get it a bit more square and somewhat even around the rim (photo 4).  The other mickey mouse bit is shown in photo 5, an o-ring was used to stop the c-clamp handle from rattling around during the milling (annoying as all get out until I "fixed" it!).  Finally, in photo 6 you see I've made some marks for the flange and roughed out the center.  Next to bore through the flange with a boring head and make it more circular and sized to fit the piston housing...after finding the center of the rim with a mill with no dro's and really sloppy handwheels... :insane:


Offline bent

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Re: Myers Stirling Stove Fan
« Reply #22 on: October 23, 2019, 11:46:31 PM »
Okay, a bit further along.  After I finished boring out the i.d. of the standard piece flange, the next step was to bore an offset "notch" to allow clearance for the piston housing boss that the standard bolts onto.  Photo 1 below shows milling a R1.40 radius notch at about a 1.25 offset from center (dialed in by the handle markings on the drill mill, so those numbers are probably +/- .020 or so, but not critical.  Though I did need to open up the measurements after eyeball fitting the two pieces, and realizing the castings run out a bit more than the drawings show (drawing calls for R1.15 at 1.18 offset, a fair bit of difference. 

The fit was checked by eye (photo 2), which wasn't exactly the best method...the center part of the flange interferes with the cast "fin" running down the back side of the piston boss and the parts can't be mated flange-to-flange until that gets cut out (photo 3). 

But the drawing has a note about removing that material should wait "until all other machining is finished".  Hmph.  No way to clamp the parts and transfer punch the bolt hole pattern until the cut is made, and I can't dial in the bolt pattern very reliably with the dials on the drill mill (and part won't fit on the mini mill with its DROs at home).  Phooey, 4 drilled holes and then the rest of the machining at the opposite end of the part which will require a completely different workholding setup, so off to the bandsaw and zipped out the interfering piece.  (photo 4)

Tomorrow, perhaps I will get the bolt holes set up and do a bit more pondering on how to finish the displacer piston bore...I'm thinking I need a fly cutter to be able to mill the bore down flush to the cast bottom...or else come up with a 1/2" boring bar with a 1/2" or so offset.  Probably about time for a family shot then as well, once all the parts go home again.

« Last Edit: October 23, 2019, 11:52:14 PM by bent »

Offline b.lindsey

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Re: Myers Stirling Stove Fan
« Reply #23 on: October 24, 2019, 01:08:20 AM »
Nice work on that very tricky standard Bent. You are making nice progress on this project :ThumbsUp:

Bill

Offline Dave Otto

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Re: Myers Stirling Stove Fan
« Reply #24 on: October 24, 2019, 01:08:51 AM »
Lots of tedious work in that part, its coming along nicely though!

Dave

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #25 on: October 24, 2019, 04:55:49 PM »
Thanks Bill.  Dave: Tedious, yes.  One of the more puzzling things I've tried to machine.

But that's the fun, too, figuring out the 3d puzzle of how to get a working end product.  I did realize yesterday that, after getting the machining on the flimsy pieces all done, I might be able to bolt the two parts together, and then turn the o.d. of the standard to better match the piston housing (it's overhanging the housing right now about 50 or 60 thou and really rough looking).  We'll see.

Off to do some more R+D and a hydrotest on a new production casting, so probably a couple more days before any new progress gets made.  I also need to do some shopping for bearings and a piece of cast iron for the piston.  The drawings call for double-shielded bearings (to keep the dust out I suppose?), but I worry those will have a lot of friction drag (and be packed full of sticky grease) and hurt the performance.  If I soak them in solvent and then in a light machine oil, will they do ok, or should I opt for unshielded bearings that are either ungreased or lightly oiled?

Offline Dave Otto

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Re: Myers Stirling Stove Fan
« Reply #26 on: October 24, 2019, 05:33:49 PM »
I would go with the unshielded bearings and light oil.
I will post some pictures later today of how I did the bearings on my Essex; which I'm pretty sure is the same design as the stove fan. What I did is not to the plans but I'm pleased with how it worked out.

Dave

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #27 on: October 24, 2019, 10:36:45 PM »
Thanks Dave, I'll probably go with unshielded bearings too.

Offline Dave Otto

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Re: Myers Stirling Stove Fan
« Reply #28 on: October 24, 2019, 11:58:36 PM »
Hi Bent, Attached are a few pictures.

I had forgotten that the bearing shields were part of the original plans; I thought that I had added them; you can see one of them in the picture of the unpainted fan.
What I did add was the front bearing shield and the oil holes. The front shield is captured between the fan hub and inner race of the bearing, it spins along with the crank and fan hub.
In the picture of the original fan you can just make out the oil holes in the bearing housings. On the back end, the crank disk is so close the casting I didn't bother with a shield there.

Dave

Offline bent

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Re: Myers Stirling Stove Fan
« Reply #29 on: October 25, 2019, 04:38:11 PM »
That seems a pretty good solution, Dave, and I was thinking the same thing (externally mounted shields).  The oil holes are a good thought too.  Did you just make a weep groove for the oil to wash down to the bearings, or does the outer bearing race have an oil passage?

Offline Dave Otto

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Re: Myers Stirling Stove Fan
« Reply #30 on: October 25, 2019, 04:48:11 PM »
I think that put a small groove so the oil could flow around the bearing race; that was 15 years ago when I built it. :) The oil tends to collect in the outer race and gets spread around when the fan runs.
I only add a few drops once in a while, usually when running all day at a show.

Dave