Jan Ridders Horizontal Stirling ‘Bas’

[HowiParticipant @howi]

Posted by pgk pgk on 15/02/2016 19:53:25:

There's no obstruction in the channel between the two cylinders. it's just that if the displacer is supposed to move warm/cold air cyclically between the two then i expected some detectable flow…

NO! That is not it's job either, it is not moving hot or cold air to the power piston. The displacer piston is just moving air around in the displacer cylinder – it is the action of Boyles law that causes the power piston to move.

I

[pgk pgkParticipant @pgkpgk17461]

OK I see what you're getting at.. whilst the altyernation of hot/cold air necessarily creates a flow through the connecting tube it's a function of expansion and contraction of that air and may remain still if no heat is applied to the displacer cyclinder

[HowiParticipant @howi]

Posted by pgk pgk on 16/02/2016 12:00:12:

OK I see what you're getting at.. whilst the altyernation of hot/cold air necessarily creates a flow through the connecting tube it's a function of expansion and contraction of that air and may remain still if no heat is applied to the displacer cyclinder

Think of it this way, remove the displacer piston all together. Apply a lot of heat quickly to the displacer cylinder and the power piston will be pushed one way, remove the heat and quickly cool the displacer cylinder and the power piston will be sucked back in the opposite direction ( negative pressure from Boyles law).

The displacer cylinder in this case has a heat source applied to one end (the hot end), at the other end is a large lump of finned brass which is going to suck all the heat out (the cold end), the displacer piston merely facilitates this heating cooling cycle.

It is the temperature differential that provides the work energy to drive the engine. More air volume and more temp diff means more power.

Edited By Howi on 16/02/2016 17:10:38

[pgk pgkParticipant @pgkpgk17461]

Thanks.

I've identified a couple of issues..where i'd made the fixing plug into the back of the displacer to the drawn size it's slightly less than the od of the glass..and potentially snags on inadequately deburred passage through to the cold side. Deburring improved and polished and the displacer spun up and glass to ally blended in with a diamond file. A new displacer rod from silver steel (only 'cos it's ground accuratly for the reamed channel).. and then polished in situ wth brasso for a smooth passage.

I'l make a new carbon power piston next but time short today: finally had home field dry enough to plough my veggie patch and had to go collect more animal feed.

[pgk pgkParticipant @pgkpgk17461]

A new carbon piston today.. with a thumb over one end of the tube it falls only slowly. I also dismantlet and checked all parts, repolsihed the flywheel axle to make it easier to insert, eased the flywheel bearing holders and replaced the bearings while seated on the axle to confirm their alignment. I also discovered that the flywheel spins longer when horizontal and identified an imbalance – rebalanced temporarily with a screw taped to a spoke.

The only soud when spun by hand s the displacer rod going through it's phosB bush.. oiled that and dried it as any dark residues came out of the bush (?old brasso) until it was clean and dry of oil.

Put it all together with a thin film of new silicone between all cylinder parts.

And it still won't run. I even tried adding extra heat from a blowlamp and checked the cold side stayed cool.

I'm out of ideas short of rebuilding the flywheel support arms with a better design to aid concentricity of the two bearing holders.. or opening them right up and then using a slow set bond and ceramic bearings so they can self align… but I don't think they're out of alignment.

The only other option (reluctantly) might be to rebuild/redesign the whole thing with a bigger hot and cold chamber.. as in longer glass cylinder, longer crank throw and extend the cold side with an insert…

Frustrated although it does look pretty.

[Ian S CParticipant @iansc]

I hope you have not contaminated the graphite piston with oil or the silicon sealer. I'd tend to lay off the blow lamp, one chap on another forum was complaining about over heating, he was using meths because it makes it go faster.

The arms that support the flywheel, are they just attached with one screw each, is that all that keeps them alined?

Ian S C

[pgk pgkParticipant @pgkpgk17461]

Posted by Ian S C on 18/02/2016 12:34:20:

I hope you have not contaminated the graphite piston with oil or the silicon sealer. I'd tend to lay off the blow lamp, one chap on another forum was complaining about over heating, he was using meths because it makes it go faster.

The arms that support the flywheel, are they just attached with one screw each, is that all that keeps them alined?

Ian S C

No silicone contamination but i did try oil on the graphite when nothing else was working.. nowt to lose and can always make another.

I was careful re heating with blowlamp but again nothing much to lose. Ina worst case the glass cylinder would have slumped down and I'm classy at cutting glassy now…

Flywheel support arms were made as a glued together pair. the drawng has them held by one bolt and soldered. I decded on using epoxy steel as being more controllable. But it is a weal point in the design.. with the benfit of hindsight the bearing holes could have been made once the arms were assembled and with a spacing tube to be sure of boring them in alignment. the base the arms attach to is only 4mm thick and really that isn;t enough to guarantee parallelism and no twist. Yet another option woudl be to remake that base part thicker at that end (either a three layer sandwich or a thicker block and sculpt it pretty and mill the thickened sides true. From just ebing able to force the graphite into the glass cylinder (press fit) and then using a bit of grey scotchbrite was a reduction of 1.5 microns.

I used a very very light oil to see if it would improve tht seal..if anything it made the graphite slippier.

And to add to woes the vaccuum cleaner decided itwas too full and let my lathe get covered in graphite.. so more cleaning.

If/when i get back to it then the lazy wy forward will be a new graphite, loosen up the flywheel bearing holders for a sloppyish fit and sit the bearings on a thin layer epoxy while paired on a close fitting axle and balance the flywheel with some lead strips (lead was in the barn in the dark yesterday)

if that fails then it's redesign the flywheel arms and base and ceramic bearings. The arms are 4mm thick so it should be possible to make clamp holders and with the flywheel hub beng thicker than the rim then the arms could be made with an inner stiffening spine along part length or milled out of one piece…..?

[Ian S CParticipant @iansc]

When making the new piston, get it to a size where it just about goes in the cylinder, then with it spinning in the lathe use a strip of paper (copier paper will do fine), in the same way you would use emery cloth on steel. I'm just sorry that I can't give you info on working graphite first hand.

Ian S C

[Ian S CParticipant @iansc]

Back again, you can use isopropyl alcohol to clean the oil of the glass and the piston. The recomendation is to handle the piston like eggs, finger pressure can distort it. Try to handle as little as possible (grease on fingers), although you think it may feel slipperier with oil, the oil is viscose, and causes drag.

I was looking at the Air Pot web site, and if you contact them it is possible to get a free sample of a glass cylinder, with matching graphite piston.

I also looked at one of Jan Ridders' sites about a 4 stroke IC engine with a glass cylinder, using a glass medical syringe, and graphite piston, his comment about glass tube was that until he used the syringe, he couldn't get tube round enough. When he used other tube, he used a brass piston with a thin O-ring with a diameter .02 mm bigger than the bore.

Ian S C

[pgk pgkParticipant @pgkpgk17461]

Thanks for that.

Interestingly looks like one can buy glass syringes still on ebay.. they will be thicker walled but that's not an issue. Not like the old glass cyinder in a steel housing but a chep one-piece which necessarily would have to have an accurate bore….Or since its for the power piston which wont get very warm one might even use a plastic syringe and use a sliver of the silicone plunger as a sealing ring. So lots more ideas to try.

I'l work at improvng the flywheel bearing alignments first and probbaly make my own designed bearing fork..

Edit.. the only reason to suggest plastic syringes is that I've got a bagful of the darned things sitting around somewhere

Edited By pgk pgk on 19/02/2016 14:05:47

[pgk pgkParticipant @pgkpgk17461]

I had another fiddle and made another power piston and had it sized to be tight then progressively rubbed it with paper trying to create a taper since the glass tube has an internal one. i got it so it was atd loose one end of travel and a tad tight the other end..little point in fiddling more until some glass syringes arrive (ordered) hopefully with a more consistent bore. I;m not confident on my abilities to hone glass parallel bored. that or I make a brass one.

I also fiddled with the flywheel forks.. and one side epoxy steeled has come loose to a sl rock. it's noteworthy that a decent fick and I can get over 60 revs tensioned one way and 36 revs tensioned the opposite..so looks like i have to redesign and make new forks out of a solid bar to ensure they're aligned with each other. i just don't see a reliable way of doing it with the design as is. I'm planning on making the new forks out of ally just because it's a lot of mill work and it'll be easier/quicker than steel to slot out and make some internal ribs to stiffen it more than the original design but keep the aesthetic. I'll also change the 11mm od bearings to 10mm od 'os i have a 10mm reamer and have the bearings in stock too.

It'll keep me occupied whie the syringes arrive from china.. then a question whether their dimensions fit the cylinder cap or not…..

[pgk pgkParticipant @pgkpgk17461]

Some changes to the plan. I rebonded the flywheel forks with a careful alignment setup. Today when testing it I get nearly 70 revs with a gentle flick while there's no cranks attached. So fairly confident that the flywheel is as free moving as it can be.

I also had a go at making a new guide bush using the idea of a toolmakers reamer from the same s/s as the crank guide. frankly there's as much 'rock' in that as before. it's 20mm long bush. I'm going to have to rethink that..perhaps the crank guide got polished down or my reamer action was incorrect (I used it unhardened, took of any side burs, off hand ground and then stoned and burs stoned and used in the tailstock etc)

Out of interest while waitng for glass syringes i made a brass power cyclinder out of a piece of tubing polished inside with brasso (I need to make laps) and rinsed out with carb cleaner and made a new carbon piston. Interestingly the piston was a tight fir until the brass tube comes up to body temp.. then it's loose. Jeez that's a tolerance nightmare…

It still won't run with everything sealed with silicone but I get the impression it's thinking about it..

I need to improve the seal on the hot cylinder glass and fiddle more with the guide bushing/rod and wait for this glass syring

[pgk pgkParticipant @pgkpgk17461]

Interesting…

Just came into a cold shed (lit fire etc). this engine so stiff it wouldn't turn and no play on the displacer rod which also would hardly move. Showed my temp brass power cylinder a flame (just to hand temperature) and everything freed up. Heated the displacer cylinder, wouldn't run but the displacer rod quickly started getting loose in it's PB guide bush. It can't be more than 20C difference in temp to cause enough expansion to move from stiff to sloppy.

I do all my work at t shirt only temps .. can get too hot in here sometimes which doesn't make sense for this top have reamed too loose..unless I remake and deliberatly heat the part before reaming for a closer fit? it makes me wonder if there's an element of lottery for those guys who get them working having made their parts at the right ambient……..

[Ian S CParticipant @iansc]

I think the friction in a plastic syringe would be fairly high. Some of the metal syringes take a glass cartridge with a rubber plug in each end, needle end gets pierced by a needle, the other end becomes the plunger, the glass tube is about 1/4" dia. Called a dental syringe, although I think dentists all use plastic disposable these days.

I think you and Brian are nearly there, the difference between going and not going is so small that it will take you by surprise when it does go.

Ian S C

[pgk pgkParticipant @pgkpgk17461]

the cartridges for those dental syringes are too small diameter fr tis purpose.

I'm guessing Brian gets away with his brass power cylinder due to it's mass taking longer to warm up than the brass tube I tried as a temporary measure.. amazing how that little expansion makes a huge difference.

I was also geting slackness around the displacer outer glass and sealed it with silicone.. but when i showed it a way stronger flame that loosened again. It's going to need a shim washer behind the O ring to compress it more. really it's all on hold waiting for the glass syringes ordered although i may play with lapping the testube glass with diamond paste I bought a while back..if only 'cos liek brian i want this finished and move on.

Also considering changing the displacer rod bush to a carbon one.

[Ian S CParticipant @iansc]

I,v tried brass, bronze, cast iron, and carbon impregnated Teflon, they all work, and I don't really know if one is better than another.

The O-ring needs to be lightly nipped in place, the distance between the bottom of the groove to the outside of the test tube should be a few thou less than the thickness of the ring.

Ian S C

[AjohnwParticipant @ajohnw51620]

Has anyone managed to get some info on the bore of typical glass syringes. One ebay seller mentions them for a range of sizes but if the volume they can deliver is worked out using the figure they don't work out at all.

Best bet so far is a Chinese seller who posts big shots and over all length so they could be scaled.

John

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[pgk pgkParticipant @pgkpgk17461]

It's a reasonable guess that the chinese glass syringes will have similar dimensions to plastic ones.. albeit possibly with a thicker wall..otherwise things would get very clumsy. With plastic syringes then 5 or 10mm capacity will be the practical options and i have both on order.

Back in the day when they were steel ends bonded to glass barrels they were unweildy enough to use.. and often leaked around the plunger from the inevitable wear. I can remmeber boiling them up on a gas ring between customers and testing fitting the right plunger to barrel option – often followed by a mouthful of bitter barbiturate as the thing discharged from the worng end… how we learned to keep our mouths shut during certain procedures. And definately those involving the excreting end of the patient..

[pgk pgkParticipant @pgkpgk17461]

My second lap was functional.. I mis-guessed the taper effect for sizing the first time but beggared if I could find my diamond powders..looked everywhere and now wondering whether I actually bought them or thought I would..Doh! Doubtless they'll turn up next week.

So I thought I'd have a go at lapping the glass tube using fine car grinding paste. I was quite suprised to find it actually working. After rinsing I only had a choice of brasso for a finer lap and that's when i got too enthusiastic and overtightened the lap…the 'tic' sound as the glass cracked was the ominous giveaway..

Nevertheless there is potential there. One can see the ground glass effect on parts of the bore and my snap gauge felt pretty consistent throughout and measured 0.05mm wider diameter than before.

I do have another couple of test tubes..

[AjohnwParticipant @ajohnw51620]

When telescope mirrors are ground a whole series of grit sizes are used down to really fine before polishing with cerium oxide on pitch. The finest grades of grit is usually aluminium oxide and some people have been known to speed up polishing by using toothpaste for an extra final grit.

I'd guess you would want 400 and 600 silicone carbide and 1000 or finer in that or aluminium oxide. On ebay I would guess that is the facial scrub powder also listed as very fine. Then glass polish / cerium oxide. A lapidary supplier should state the grades. 400 might be too coarse. Paper laps have been used for polishing

I did some sums on glass syringes from photo's. 2ml 9mm bore, 5ml 13.4mm bore, 10ml 16.4 and 20ml 21mm bore. Be interesting to see how accurate those are. I have a 2 and 5 on the way. Maybe some people have them around. For stirling engines all sizes are of interest really.

John

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[pgk pgkParticipant @pgkpgk17461]

I have a vague (very these days) recollection of an article on telescope lnses where they finished with just pitch laps (no grit) on the grounds that the glass moves anyway as a thick liquid?

If fine valve grinding paste is around 280 grit?? then perhaps i should have started even coarser 'cos when really cleaning up after it had cracked i could still see some longitudinal streaks in the test tube barrel that weren't ground. it may have been technique or a reflection of how out of round they are. It was also a pain tryng to clean the lap.. the grit had embedded in the ally and kept coming out after several washes.

The timesaver stuff sounds ideal..

[Ian S CParticipant @iansc]

It could be worth visiting Koichi Hirata's site Let's build model Stirling Engines, there is even a section in that on how to cut glass syringes, and another on where to buy them, plus a number of plans for building. I have one based on one of his designs, it works well as a motor in a boat, although the boat is a bit too big.

Ian S C

[AjohnwParticipant @ajohnw51620]

Ceri rouge was used on the pitch lap for polishing – iron oxide. It gets all over the place so these days it's cerium oxide. There has been some debate about pitch polishing concerning something going on at a molecular level on the glass as it can be polished to tiny fractions of a light wave – really tiny ones.

Paper laps are much quicker but can't achieve the same level of perfection.

The higher the grit number the finer it is. The grades I mentioned come into the range of what is usually called fine grinding – finessing the shape in other words. Some of the grits used are mainly to remove the scratches from the previous one.

John

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Edited By Ajohnw on 26/02/2016 14:26:02

[Ian S CParticipant @iansc]

I remember using tooth paste when I was at school to lap steel and cast iron specimens for microscopic inspection.

I have used tooth paste for the final polish when lapping a cylinder, the tooth paste was from one of those little tubes the airlines supply, I found it cut almost too quick, and I nearly went to far bringing the piston to size.

Ian S C

[AjohnwParticipant @ajohnw51620]

The syringes arrived today. Very rapid from the uk ebay seller that does a range. I just paid extra for 1st class postage on one and they sent the lot first class without me mentioning it.

5ml 10.28mm bore, 10ml 12.37mm, 20ml 21.43mm. Last one for if I fancy something bigger. Mit digital callipers so a close approx – so much for scaling from photo's

John

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