Author Topic: Ridder's Stirling Bobber  (Read 3430 times)

Online zeeprogrammer

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Re: Ridder's Stirling Bobber
« Reply #15 on: May 07, 2018, 11:06:22 PM »
"Grr" - a more polite way of saying 'crap' in my world.  ;D

It would be tough to see both sides of the flywheel at the same time. Looks good to me.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline b.lindsey

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Re: Ridder's Stirling Bobber
« Reply #16 on: May 07, 2018, 11:11:02 PM »
The flywheel came out very well. You have to be happy about that!!

Bill

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #17 on: May 08, 2018, 05:36:54 AM »
Yeah, happy with the flywheel.  Like Brian, I really liked how the cast iron took a polish with just a few passes with different grit sandpapers.  And found some brass chunks from an old valve stem that will suffice for the cylinder and caps, and got my steel for the die holders cut on the bandsaw.  So, Monday was a good day.  Sunday...well, that was a planning day and we'll leave it at that.  But if anybody know a good source for a quality small die set besides McMaster?

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #18 on: May 09, 2018, 06:57:41 PM »
Another evening at home, so got a bit more done.  Machined the cylinder, cutting fins with parting tool and then drilled and finish bored to 10mm. [pic #1] 

I had cut the pyrex test tube to length over the weekend with dremel diamond saw blade and drip can, same setup used as for the glass cylinder flame eater.  Getting pretty good at this, though the length of the test tube meant I had to make a couple of cuts, the test tube bumps against the dremel body on any cut over about an inch and a half.  So, a picture of the two parts, looks like it fits! [pic #2].

OD of my stock was on the thin side, so I tweaked the bolt circle inwards a bit.   Hopefully the #3 screws will still fit, if not I may turn some studs and nuts out of brass.  May take that approach just to get the odd lengths needed, and just to try it.  But dialing in the bolt circle was easy - zero on the center bore, then step off the x-y coordinates for the bolt pattern with the DRO's.  That is so slick.  Did also find out one way to make the DRO's read funky - step on the power cord and jostle the AC adapter, and hey, the readings are off.  :facepalm2:  Oh well, at least I've isolated a probable cause.  May need to get a power strip and fasten to the sides of the mill stand to keep things out of the way of my two left feet.  Pic #3 is finishing tapping the last hole on the cylinder side, then flipped and did the opposite end.  Now what to do next...hmm. :thinking:



 

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #19 on: May 14, 2018, 11:45:38 PM »
More progress.  Bored the cylinder heads for #3 clearance holes, 0.950" bolt circle (clamped together in the machine vise, might as well screw up two parts at once, no? :) - Pic #1.

Then set up and drilled/tapped #3 holes for the cylinder pivots.  Aligned as best as possible by making marks with the mill head centered on the part, then rotating horizontally to give Mk 1 eyeball alignment. Pic #2

Then back to the rod side cylinder head - a 6-hole pattern of 0.040" holes to provide breathers for the backside of the piston.  Not much room for error, about .008" wall thickness on either side.  So, spot drill with smallest center drill (just the tip, after watching Stephen's video) [Pic #3] then carefully peck drilling, one hand on the drill feed and one resting atop the quill to "feel" the advancing drill.  [Pic #4] Shows the last hole just before drilling it. 

Then the piston.  [Pic #5] Made this one from some crappy cold-rolled hardware store bar stock.  It machines horribly, and this time, drilling out and tapping the centerline for #6-32 I swear I could feel all the piping (sulfides and other debris from the cast bar) trying to snap my drill and taps.  But got the skinny side finished, then bored the fat end, and mucked it up (.005" undersized relative to the cylinder bore) somehow.  Sigh.  Will have to redo it.  This time, with some nice clean stainless scavenged from the scrap bin at work.

Set down tools and spent Sunday morning (after Mum's day breakfast) cooking up a new batch of IPA instead of making more scrap metal.

More good news is I found a good local supplier (they will replace if defective) for some HSS dies, #2 thru #6 plus #8, about $5 to $7 each.  Should last awhile and all are one o.d. size, so should be able to make just one die holder for the lathe.  Also put some various fastenings, along with some hex stock, on order from McMaster. 

Offline Ian S C

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Re: Ridder's Stirling Bobber
« Reply #20 on: May 15, 2018, 03:28:51 AM »
If for some daft reason you have to make piston #3, try and get some cast iron.
Ian S C

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #21 on: May 15, 2018, 05:47:33 PM »
Yup, will need to make another (3rd) attempt. :facepalm2:

Next time with sharp taps (the old ones got really dull trying to tap the crappy steel, and one snapped in the stainless bar).  Have some 12L14 rod on the way.  But cast iron...hmm.  Good idea, thanks Ian!

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #22 on: May 15, 2018, 06:05:25 PM »
Strange.  Cast grey iron bars running about 2x to 3x higher than 12L14 steel bars at McMaster.  Perhaps due to difficulty shipping (brittle iron breaks more often)?

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #23 on: May 23, 2018, 07:06:30 PM »
A bit more progress this last week, between the youngest's band concerts and other outside activities.  Got the 12L14 bar stock, and whipped out a new piston, much better machining than the last go with low quality steel.  The piston fits snugly enough to fall slowly (5 or 6 seconds) out of the cylinder, with thumb over the end, so that's sorted.  No pictures, as I'd left the camera at work that day.

Also machined down the gears to fit in the assembly and to get a decent round section to place #4-40 set screws (Pic's 1 and 2).  The white (delrin?) gear machined easily, but other gear (black nylon?) kept fighting back, slipping in the lathe chuck.  I managed to get a 4mm hole bored through, so that I could stuff a bit of 4mm shafting in, and then it clamped a bit more securely, at least enough that with light (.010 in) cuts, I could finish it up. 

Then bolted the tilting vise down on the mill bed and machined the set screw hole (at about a 15 degree angle) for the flywheel (Pic 3).  Also noted a bit of surface rust on the exposed iron faces of the wheel, so spent a little time polishing that off with some 1500 grit wet/dry paper, then wiped some corrosion-inhibiting oil on the surface.  May need to think about waxing it, or clear coating?

Also got some #3 socket head cap screws for the cylinder caps.  The #3 tap I have is so long on the tip, that the threads on the finned end of the cylinder did not fully form before the end of the tap hit the next fin (couldn't get the screws to go all the way through the fin).  So, I re-cut the end of the tap, by chucking it in the lathe and then very slowly hand-grinding the tip with a diamond wheel in the Dremel tool.  Pic #4 shows the result, something much closer to a plug tap.  Also used the Dremel/diamond wheel to shorten one set of four screws to fit the skinny end of the cylinder, where the tapped holes go through the first cooling fin.  Also found during this assembly of the cylinder, that the silicone o-ring Jan uses to hold the glass test tube in place does not provide very secure grip on the tube - the glass tube can slide/rock within the machined sleeve and slowly works loose.  I will probably fix that problem by wrapping a bit of teflon tape around the test tube, to give a bit tighter fit between the cylinder cap and the glass.  Or, if that fails, use some epoxy to fill the gap, as Jan suggests in his build notes.

Waiting on a set of HSS thread dies from local supplier, should be in today, and can then make up a die holder for the lathe tailstock, which will help in making the the cylinder pivots with #3 threaded ends.  Also make up a piston guide bushing (planning to use a bit of the graphite rod I have for that), and then should be mostly done - cut some 4mm axles, and spot the set screws, grind flats...assemble and test.  Then fix the mistakes, re-assemble, re-test, tweak, find the camera, etc. :Lol:

Offline Ian S C

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Re: Ridder's Stirling Bobber
« Reply #24 on: May 24, 2018, 03:45:41 AM »
Don't laugh, I use old window weights for making cast iron pistons, you have to be a bit picky, the skinny ones tend to have a higher chance of being clilled. I have only had one failure, that was down to me trying to get the skirt too thin, and it broke off at one of the labrynth grooves(there were 4 on the skirt).
Ian S C

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #25 on: May 24, 2018, 03:40:23 PM »
Not laughing.  But I haven't seen sash weights since I left my Mom & Dad's home some number of years ago, everything uses multi-pane aluminum-frame sliding windows now it seems.  That said, my sister just finished renovating the old family farmhouse to put it up for sale, can't remember if she said they replaced some windows?  If so, did she happen to keep the weights?  Hmm. :noidea:

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #26 on: May 24, 2018, 03:58:07 PM »
Hmm.  Still like your cast iron idea, though Ian, but finding some at reasonable prices.  I think I need to keep my eyes open for returned valves.  When I first started at my current job, all of the valve cases were cast grey iron in big, heavy sections (my first designs were converting them to ductile iron).  If one of those comes back thru, it may need to make a trip past the bandsaw for, um, engineering samples.  ;) 

Offline Tennessee Whiskey

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Re: Ridder's Stirling Bobber
« Reply #27 on: May 24, 2018, 07:32:14 PM »
If you live anywhere near an agricultural area, another good source of cast iron is old tractor weights. The ones in usable condition usually bring a $1/lb and they are usually 50 pounds and up, however, the ones with the attaching structure damaged, bring a good bit less. The grain structure is usually very good and at these weights, chilling isnít usually an issue. Just a top tip from here in Springbucket.

Cletus

Offline Ian S C

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Re: Ridder's Stirling Bobber
« Reply #28 on: May 25, 2018, 02:52:38 AM »
In NZ we have what are known here as Demo yards where demolition firms sell the remains of demolished buildings, and thats the place to look.  My last lot had been used as counter weights on sliding doors in my brother in laws' piggery.  The trouble with cast iron is that it is cast to shape using the minimum amount of metal and its some times hard to hang on to to cut a bit out the right shape and size.
Ian S C

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #29 on: May 25, 2018, 05:50:05 PM »
If I stick with this much longer (there are so many engine designs!) I will just have to suck it up and buy some bar stock.  Or use up all my aluminum swarf for mixing thermite. :Lol: