# Hypocycloidal Engine



## Ken I (Aug 13, 2020)

The Hypocycloidal design always intrigued me as I could not see any valid reason for going to such extremes when a simple crank would suffice – that was until I discovered that this was to work around various patents that had been lodged covering the crankshaft.

(Edit) I started this post calling it an "Epicyclic" - I had this wrong and have corrected it to its proper name of "hypercycloidal".

So I decided to design and build one - this is the GA







I will post a full set of plans and build notes when completed - hopefully successfully.

I have started on the cylinder assembly.

Regards,
               Ken I


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## vederstein (Aug 13, 2020)

Do you plan on purchasing or making the ring gear?  If it's making, I'd like to see that process.

...Ved.


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## Ken I (Aug 13, 2020)

Ved,
       I have made plenty of pinion and spur wheels (even from my own hobs) but I'm afraid a decent annulus is a bit much for my machinery so I'm having a friend wire cut EDM the set from my developed database.




I posted a piece on developing profiles under Tips & Tricks because of this - I know there are packages that can do this but most won't bend or break the rules - so I thought I would do a posting as it may be of some interest to fellow members.

If you have a home brew solution to an annulus I'd like to see that.

Regards, Ken


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## Richard Carlstedt (Aug 13, 2020)

Matthew Murray of Leeds is the originator of the Hypocycloidal Steam Engine
He did it mostly to bypass Watt's patent on  Parallel Motion on Beam Engines. 
It eliminated the need for a Beam which was a huge weight and cost savings.
Murray also invented the short stroke "D" valve which we use today .


			Leeds Engine © MMXXIII
		


James Watt feared this man and his capabilities.  I have a copy of a letter from Watt's son to his dad telling him of their efforts to infiltrate Murray's foundry/factory with 3 industrial spies ( espionage ! ) in 1803 .Watt bought all the land around Murray's foundry so he could not expand..
I look forward to your build .
Rich


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## Jasonb (Aug 13, 2020)

It's not to hard to cut your own internal gears, basically grind a single tooth cutter to match the drawn profile and then mount it in a holder in your mill and use the quill as a manual slotting head.

I started describing making one for an epicyclic gearbox in this thread and carry on down that page with teh finished item on the next.






						A Robinson from rejects.
					

A Robinson from rejects.



					www.modelenginemaker.com


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## Steamchick (Aug 14, 2020)

A simple ring-gear, made by another member of my local club, used a MyFord change-wheel as a pattern to cast the ring - using Mayzac zinc alloy from scrapped car and domestic appliances.... Low melting point, durable and casts well.
K


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## Ken I (Aug 14, 2020)

Richard - thanks for the history - steam age espionage - whodathunkit ?
JasonB - I have used a Bridgeport to broach with but my home minimill won't cut it (no pun intended).
Steamchick - now that's a clever idea - start with the ring gear and design around that - but a negative gear shape is quite a bit off an annulus - but I suppose you can compensate with the pinion - I'll give that a whirl on CAD. - I have cast parts in Mazak alloy for jukebox restoration projects.
Regards all - Ken


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## Jasonb (Aug 14, 2020)

That's how Alyn Founry used to do the cast gear that they supplied, although the profile is not correct when casting from a Spur gear if you use a fairly large tooth size and allow for some running in they work OK.

Photo is a bit dark but top right shows the mould with the spur gear just visible and the resulting cast zinc rich alloy ring gear below.

You can also plane the teeth in the lathe if that is a bit heavier than your mill or even just use the slotting method to put the final profile on a cast gear.





						A Robinson from rejects.
					

A Robinson from rejects.



					www.modelenginemaker.com


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## Ken I (Aug 14, 2020)

Just to follow up of the cast gear idea....illustration for a 16T / 32T M1.5 gearset.




Top Centre = Normal and Cast overlay
Bottom Left = Normal Annulus (blue) and Pinion (Magenta)
Bottom Right =Annulus (cast from a spur gear) Green    &    Pinion generated to suit (Red)

Casting an annulus from a spur gear will have the spur "clearance" extend into the pinion - which means you have to generate an undersized pinion - both those factors combined with the "pinched closed" profile of the cast annulus introduce massive undercutting into the pinion.
(After casting you could bore away the extra annulus tooth height (created by the clearance on the spur) - which will help a bit - but even then you must at least truncate the pinion to get clearance - however slight.)
This will give rise to a very strange tooth form where only the addendum will do any useful work the dedendum has to be cut away to clear the interference. As you can see below....




But yes it can be made to work - a neat idea in a pinch.

Regards - Ken


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## JCSteam (Aug 14, 2020)

Ken my head hurts after reading that lol. Very informative response that I think I'll have to read again without the kids yapping in the background to digest.
Jon


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## Shelton (Aug 14, 2020)

Testing to see if this will show in New Posts


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## Ken I (Aug 17, 2020)

*Making The Cylinder & Cylinder Heads.*

I chose to make all three parts from one piece of stock – as much as possible in the same setup - this process will ensure all three parts align perfectly.
I started by blocking up a piece of brass 33.5mm x 26mm x 100mm – which I then mounted vertically to drill and ream the Ø5 bore of the gland end cylinder head – as datum.





Photo above:
Left = drilling the Ø2.5 hole (long series drill) after the Ø5 reamed hole (datum) & the 4 x Ø3.2 bolt clearance holes deep enough for both heads – followed by the 2.5 (M3 tap size) into the cylinder.
Top Right = Mount to lathe – clocking from Ø5 datum.
Middle Right = M8 thread added + parting / forming
Bottom Right = using the part-off to turn Ø20 location boss on the backside – to ensure concentricity and save on having to set up second operation work.




Top Left = Finish & part-off blind end cylinder head – note: Ø3.2 holes continue through this piece but stop short in the part off gap (plan ahead – depth drilling diagram in the drawing). The Ø2.5 holes continue into the cylinder for the M3 threads.
Top Right = Finish boring the Ø20 cylinder bore.
Bottom Left = Finished cylinder and heads assemble perfectly.
Bottom Middle = Loose Parts
Bottom Right = End view – porting and gallery holes drilled.

The cluster of 9 Ø1.5 holes in the cylinder are the cross holes drilled into the gallery holes and the central exhaust port.
The “D” valve slides over these holes commutating pressure from the steam chest into the cylinder
and directing the exhaust from the cylinder to the exhaust.

The steam chest is bolted down to this face by the 4 x M2 screw holes around the ports.

Obviously care must be taken drilling all these holes to avoid inter gallery or cylinder breakthrough. Follow the drilling depths indicated in the drawing.

To be perfectly honest – the three holes side by side abreast for each gallery is excessive – you can get quite enough air through a single Ø1.5 hole to suit a running model – so it’s O.K. by me if you drill just the middle one or just the two outer ones – instead of all three. The inlet and exhaust ports are single Ø1.5 holes in any case.

 Now for the steam chest and "D" valve.
Regards, Ken


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## Ken I (Aug 23, 2020)

*Making Steam Chest & Inlet Cover.*

A picture is worth 1000 words – should be self-explanatory.




Final filing is easier mounted back in the lathe chuck prior to finishing off the rear end and parting off.




The steam chest cover also has the inlet nipple which accepts a Festo KD-M5 quick coupler which I use for all my models – you can make it anything you please – also as an option in the drawing is an M3 inlet port into the side of the steam chest – you will also need an access hole through the Faux Wood Barrel to access it.
Bottom Right – I always mark the #1 Chuck Jaw position – when you return to the lathe you more or less retain your concentricity (typically within 0.1mm TIR) good enough for most second operations or parting off.

*Making The “D” Valve.*
I made the square cavity by center drilling the corners and working inwards with increasing diameter slot drills to depth before cleaning up.




Something of a fiddly bit to make.
To make the “U” slot (which the valve pin fits into) I first drilled the 1.5 hole and then sawed the remainder of the slot.




Below – assembled onto valve stem and assembled into the steam chest.




*Cylinder Assmbly Completed.*




Next step the Faux Wooden Barrel & Hoops.
 Regards - Ken.


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## ACHiPo (Aug 23, 2020)

Wow.  I know my articulation can be overwhelming.

Really nice work!


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## deeferdog (Aug 24, 2020)

Nice work Ken, looking forward to the plans. Cheers, Peter


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## Ken I (Aug 24, 2020)

Deeferdog - the plans are finished - but I don't want to post them until the build is finished.
I found one small problem and it was an easy fix - but..... when it runs I'll post the plans.
Build notes are progressing with the build - should be finished within the next two weeks.
Thanks for your interest - Regards, Ken.


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## Richard Hed (Aug 24, 2020)

Richard Carlstedt said:


> Matthew Murray of Leeds is the originator of the Hypocycloidal Steam Engine
> He did it mostly to bypass Watt's patent on  Parallel Motion on Beam Engines.
> It eliminated the need for a Beam which was a huge weight and cost savings.
> Murray also invented the short stroke "D" valve which we use today .
> ...


Yes, James Watt, like t edison, was a bustard, took advantage of his employees, stole their ideas, etc. etc.


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## johnmcc69 (Aug 25, 2020)

Great progress Ken!

 John


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## Ken I (Aug 26, 2020)

*Making The Faux Barrel.*
In a fit of design exuberance, I designed an elliptical barrel – which is a PITB to make but looks nice.




The slot down the side clears the steamchest and valvegear, the two holes in the underside are for the cylinder mounts to go through.

At this stage, I had forgotten the exhaust hole in the top side and added it later.

I had a piece of Namibian “Kameeldoring” = Camelthorn: used for making barbeque fires (makes great coals).
However it has a very attractive crown grain and red colour – it is also very dense and as hard as a whore’s heart. It sinks in water – its bone dry density is 1.06g/cc (I measured it).

Turns out it machines nicely as well.




Top Left: Block up and machine interior, drill dowel holes for assembly alignment – the Ø2 dowels are cut from bicycle spokes.
Top Right: Glue together. Make sure it fits your cylinder assembly before this step.
Bottom Left: Mounting blocks machined from MDF to mount it accurately on an M14 threaded rod mandrel in a collet chuck. Hole is a tight fit on the bar – it is not threaded.

I used the (non-preferred) M14 as it is the largest thread that will fit through my MT2 rotary table.

In the end it didn’t need to go all the way through and I could just as easily used M16 or M20





Top Left: Assembled (but not tightened) to collet – note turned down nut at rear.
Top Right: Collet tightened onto M14 rod and locknut tightened.
Bottom Left: Rough turning to Ø54.5 = 0.5 over finished major diameter of ellipse.

Remove from lathe to Rotary Table – which has an ER42 adaptor flange – makes moving between turning and milling operations nice and easy.





Top Left: Setting the job level at zero degrees on the RT – I didn’t want to use the RT to level and end up with some arbitrary numbers.
Top Right – The flange “floats” slightly and can be clocked dead true – in this case clocking wood with a micrometer clock might just be considered “anal”.
Bottom Left: Co-ordinate milling the ellipse with a R6 cutter – in retrospect a flat face or side of the cutter would have been better – I have provided co-ordinates in the drawing for either option.
(Above photo) Bottom Right: Rough machining completed.





Note the “Near Miss” indications – the mounting MDF block gave me a visible warning that I’d made a mistake. With hindsight it would have been just as well to attach a printed self adhesive label of the outline onto the MDF to act as a guide. Since the OD is only cosmetic you could use this form of “marking out” to eyeball the cuts.

Again the drawing has co-ordinates for using the corner of a milling cutter to produce fake “joints” approximating equal 8mm “planks” all round. Since the outside is still “rough” cutting the grooves is an act of faith in the data.
Back to the lathe for a quick linish to remove all the high points – and my faith in my co-ordinates was justified.





*Barrel Assembled To Cylinder* - unfinished and without hoops.




Not bad for a piece of firewood.

Next machining the hoops.

Regards, Ken


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## Steamchick (Aug 26, 2020)

Lovely finish! But I first saw this type of solid lagging on engines my Father had made in the 1980s~90s. He only made cylindrical lagging though. I think your elliptical engineering deserves to be a chapter in a text book!
I have usually fabricate lagging from Balsa strips - quite thick usually - as I want "easy" lagging. (I have lagged 4 boilers with 1/2" thick balsa as it has a low thermal conductivity, and boilers need that!). I use 5mm wide x 0.5 thick brass strip to make straps. The joints and different colours and grains of the balsa planks indicate the planking without the "scribed joints" you have - and it looks guite good, but not as pretty as yours. Incidentally, I think I recall my Father making the "joints" by simply marking the wood surface with a sharp tool (perhaps a thread tool?) turned side-ways on to face the chuck, then simply marking a couple of thou deep grooves with the lathe main-shaft stationary and simply traversing the main carriage from tail to head. This is how he also marked indications on a micrometer barrel, and gauge rings when he made them for other tooling. He used a dog engaging with  a gear on the main-shaft to hold it stationary and to index uniformly around the barrel. He also broached key-ways with a suitable tool and manually traversing the carriage - with a locked main-shaft.
Also. when making the deck of a boat, I used a single piece of 2mm plywood, then marked the planking simply "by eye" and a ruler, using a scriber, very carefully. When finished, the dye/varnish had developed the lines thicker where the grooves were scribed, so it looked like planking! Much easier than doing it with strips stuck on a base. Adhesive in joints seems to make the lines look wrong so must be avoided. (On Naval ships the deck-planking joints are black (Tarred), decks unvarnished, so a black fine ball pen marks those planks on my models. I know from hours of scrubbing decks!).
Hope these tips help someone? Any better ideas?
Well done and thankyou for the lesson in elliptical engineering!
K


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## a41capt (Aug 27, 2020)

Ken I said:


> *Making Steam Chest & Inlet Cover.*
> 
> A picture is worth 1000 words – should be self-explanatory.
> View attachment 118805
> ...


Spectacular work Ken, and way beyond my current means!!!

Thanks again for sharing,
John


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## Ken I (Aug 27, 2020)

*The Barrel Hoops.*

Thanks John  & Steamchick for your comments.

I was thinking much along the lines that Steamchick suggested - making brass hoops with rivets but I experimented on a scrap piece of Aluminium just to see how sizes worked out and was quite happy with the final result – so Aluminium it is.

The “Hoops” were made by pre-parting down to 0.80mm deep (using a 1mm wide grooving tool) – the finished rings being only 0.5mm thick – so when you take your final 0.5mm cut with a boring bar (1.0 on diameter) to finished size – the rings are parted off by the boring bar. The burr twists off with pliers.

Don’t try to part off 0.5mm wall tube, it will end in tears .





The theoretical circumference equals an inner diameter of 49.124 – I measured the wooden barrel by wrapping a strip of paper around, marking and measuring it which gave me a theoretical diameter of 49.5 – so I made my first ring 50.0 and surprise – it was a bit loose. The next ring was 49.5 and fitted perfectly. So you can trust the paper strip measurement.

Final ring positions set with a Vernier and lacquered into position.

*Cylinder & Barrel Assembly.*





The M2 & M3 Hex bolts are made by silver soldering nuts onto threaded rod or cut off cap screw shanks and then cleaned up.

Next job the gearset.


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## Steamchick (Aug 29, 2020)

I'm lazy - I but the bolts. Or if an odd size, make from hex bar. But I enjoy your endeavour! If you want a comment of the "rivet counter" type, you have missed following the grooves (plank joints) across the ends of the cladding, but I only mention it because a "rivet counter" pointed it out on one of my models! The decision is whether "real" plank joints would be effectively radial, or rectangular in geometry! Hope you are enjoying this as much as we are enjoying your posts..!
Thanks,
K


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## Ken I (Aug 29, 2020)

Ah ! The "tyranny of the rivet counters" is oft heard in my other hobby - Slotcar racing.
I too would but the bolts (I also frequently mis-hit the t instead of the y key) but you can't get M3 or smaller in Hex - and cap screws don't do it for me.

Regards - Ken


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## Ken I (Aug 31, 2020)

*Making The Gears.*

Firstly I developed the tooth profiles on AutoCad vis:-





See my post on generating your own gear profiles :-

Home Machinist Gear Cutting

Basically a Module 1.5 gear profile with a 32T annulus and a 16T pinion. The resultant Ø48mm pitch circle of the annulus is therefore the stroke of the cylinder – I left an additional 1mm clearance at either end between the piston and cylinder heads at TDC & BDC.
I generated the pinion tooth form from a rack (black lines a’La Maag shaper) then used that tooth form to generate the annulus (cyan lines a’La Fellows shaper).
I found the standard 20° pressure angle a bit too “coggy” for my liking and changed to 25° as shown above. (I 3D printed an ABS prototype.)
The root radius and clearance is non-standard – I developed this with the intention of water jet cutting the gear and M1.5 is the smallest module you can accomplish with a waterjet’s Ø1.2mm kerf.
My friend’s waterjet machine had problems with precision geometry and I ended up getting them wire cut on another friend’s EDM.
The nice thing about generating your own profiles is you can play with it to your heart’s content and then use the database to cut it (or make cutters). Both the 20° and 25° profiles are in the drawing.
I have in the past laser cut gears - it works quite well in stainless - which laser cuts beautifully. Its probably the cheapest way of getting it done.




Both Annulus gear and footplate bolted together for common alignment of bores, mounting surfaces etc. Both plates drilled and bored to their smaller bore sizes for subsequent independent machining – to facilitate clocking.
Tapping the M2 threads through 6mm stainless was a bit nerve-racking.

Finally (bottom right) wire cutting both annulus and pinion (I have turned the scrap over – different patina – shows up better.

Next step the crank assembly.


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## Ken I (Sep 3, 2020)

*The Crank & Pinion Assembly.*
Since the purpose of this engine was to work around crankshaft patents – I would imagine the use of the term “crank” would have been studiously avoided.




Above all the bits that make up the crank and pinion assembly.
All the bits assembled below (with flywheel).




*Making The Cranks.*
I had a small piece of brass stock but too little extra length to work it so I reamed the Ø5 hole and soldered it onto a smaller shank – after finishing the machining operations I parted it off (whilst simultaneously cleaning away the solder at the backside) – heated it up to push out the remaining piece of Ø5 brass – and then re-reamed the hole to clean up.




Note: the valvegear eccentric – in the above photo the part is off centre in the 4 Jaw for this operation – the other diameters were previously turned concentric to the (soldered on) shank / bore.

I set up the offset by mounting my dial gauge on the cross slide and using the gauge as a zero marker, measured the "throw" with the cross-slide scale.

The drawing calls for silver soldering or riveting of the axle pins to the cranks.
I like riveting joints vis :-




Top Left – Machining the pinion crank – a piece of Ø30 mounted 2.5mm off-center was used – the 4-Jaw then transferred to the mill which retains the off-center alignment (same with crank).
Top center – using the pinion as a holding fixture to counterbore the holes.
Bottom Left – riveting tooling – the lower snap (held/supported in vice) is a drilled out bolt shank.
Bottom Centre – Riveting using a flat face pin punch (a hollow snap would be better).
Top Right – Cleaning away the excess after riveting.
Bottom Right – the cleaned up riveting of the crank to its main axle.

Note: The Ø5 holes are flared at the riveted end (60° x 1mm deep) – completely filled by the riveting – those axles are going nowhere.





The pins have 0.8mm extra length for riveting.




You have to choose which way you want the motor to rotate by the eccentric offset when you make the crank.
I went for antclockwise - and I am still pondering if I can somehow incorporate a reversing set up.

Only the baseplate and presentation base still to do.

Regards, Ken


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## ACHiPo (Sep 3, 2020)

Wow this is incredible!


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## deeferdog (Sep 3, 2020)

Your post is as professional as your work Ken, thanks for all the effort you have gone to. Cheers,Peter.


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## Ken I (Sep 4, 2020)

*Making The Baseplate.*

Nothing much to show here other than the circular (machine) polishing :-




Use a machined wooden dowel faced with a 3mm thick leather pad – glued on.
Choose a convenient size and pitch and work to a pattern.
In this case Ø16 @ 9mm pitch (my minimill’s leadscrew is 1.5mm) – I first ran down the middle – then offset 9mm from row to row and 4.5mm offset of the pitching on each following row – starting each row from the same end – repeat until your arm falls off. Then work outward on the other side mirror image.

I used coarse valve grinding paste, keep it wetted – using oil or water depending on what your paste base is - this is water based – but it tends to dry if you press hard – so I think oil based might be better here. A few seconds of moderate pressure per whorl is all it takes.

I've done this before and tried sandpaper disks, plain wooden dobs, rubber faces etc. etc. - the leather disk and grinding paste works the best.

*Assembly & Fit Up.*

Loosely assemble all the crank and gear parts.
Next assemble onto the base with the pinion gear correctly engaged – rotate crank, the big end pin should cycle horizontally in a straight line.




First go - the pinion was tight at the bottom and had lash at the top - clearly the two halves were out of line - I slackened off the nuts and re-tightened whilst rotating the gear - eventually rotated perfectly with practically zero lash.
Before fitting the cylinder assembly – check the centerline height of the big-end pin – it should be parallel to the base.
If it’s miles out then you probably don’t have the gear correctly aligned (like a tooth out).
It is possible, due to small angular errors in the orientation of the Annulus Gear (Detail -4-) or the Pinion  Crank (Detail -12-) that the locus of motion is not parallel to the base - this will cause binding.
This can be corrected by shimming the Standoff Spacers (Detail -25-) to correct this with respect to the base or by adjusting the length of the Upright Spacers (Detail -26-) to set the cylinder to align with the locus of motion of the big-end pin. Or a combination of both.

My assembly ran true to the base and ran fine with the cylinder attached.

I had a tight spot near the end of the cylinder stroke which was cured by a little more honing of the cylinder bore at that end.

Other than that it ran first try – with no sealant on any of the joints or gland packing – so quite a bit of leakage.

The gland packing is PTFE plumbers tape twisted into a cord (use a drill) and then wound around the shaft and compressed to fit and seal by the gland nut.

Once happy with the running and fit up I assembled all the metal to metal surfaces with Loctite acid free silicone gasket maker (Loctite SI 5699 Grey).
Assembling the steam chest under the barrel hoops was a PITB but otherwise fine.
I then ran the engine at about 100 rpm for 4 hours – lubricating with ATF (automatic transmission fluid) – at the gears, conrod ends, valve stem and piston rod glands – stopping periodically to open the quick coupler and inject oil directly into the steam chest – to oil the piston internals and “D” valve.
It ticks over beautifully at slow speed and low pressure – being Ø20 x 48mm stroke it’s actually quite a powerful little engine.

I'll make a video once the presentation base is finished and post a link to the YouTube video of it running.

*Presentation Base.*
Finally a base :-




Chunk of wood cut from an ugly old plank of (what I think is) Kiaat.
Top Right – Use self adhesive printed sticker for “marking out” (my printer is more accurate than I am).
Mid Right – Drilling for M8 holddown Hex bolts.
Bottom Right – Milling the pocket.

Not shown – milling the moulding using router bits.




I used no stain and finished it with a polyurethane lacquer.
Still needs one more sand & another coat of lacquer.
I should have it finished & mounted and the video posted by Monday - then I'll post the plans.
Regards - Ken


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## Peter Twissell (Sep 4, 2020)

There is another name for this crank gear: Hypocycloidal.


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## Ken I (Sep 5, 2020)

Pete & JasonB - you are correct - I've been calling it by the wrong name all along - so I have changed the title and all references of Epicyclic have been corrected to Hypocycloid.
That's twice on this build the error of my ways has been pointed out to me.


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## Peter Twissell (Sep 5, 2020)

You didn't need to go to such lengths. It's your engine and you can call it what you like!
Your work is excellent and I am looking forward to seeing video of the engine running.


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## Ken I (Sep 7, 2020)

O.K. All finished....




And a clip of it running



I have posted the drawings under downloads. 

https://www.homemodelenginemachinist.com/threads/hypocycloid-engine.32466/

As ACAD.DWG or DXF (zipped) or an A0 PDF.

Regards, Ken


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## ACHiPo (Sep 7, 2020)

Stunning.  Quite the curiosity, and beautiful as well.


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## johnmcc69 (Sep 7, 2020)

Excellent Ken!

 John


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## Richard Hed (Sep 7, 2020)

Ken I said:


> O.K. All finished....
> View attachment 119154
> 
> And a clip of it running
> ...



LOVE THE MUSIC, TOO


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## Cogsy (Sep 7, 2020)

Beautiful and very well made.


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## minh-thanh (Sep 8, 2020)

Beautiful !
I love it..


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## werowance (Sep 8, 2020)

that's amazing.  by chance do you have any pictures of making the flywheel?  looks like you used dowels in it?


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## Ken I (Sep 8, 2020)

Werowance - I repurposed that flywheel from an earlier (failed) project - no photos.
However - I machined the boss with 5 spotfaces and M3 female threads - the Ø6 spokes were made with M3 female threads - at one end and a screwdriver slot at the other - the rim had 5 reamed holes so once all the axles were screwed in the rim was concentrically positioned - with the screwdriver slots proud of the rims' outer diameter.
So the threads screwed together with a short length of M3 threaded rod and locktite - and the spokes were turned 0.2mm undersize to a depth of 4mm (into the rim) and once assembled were soft soldered. The outer diameter was then machined (with the hub mounted on a stub shaft turned in the lathe) to clean up and remove the protruding screwdriver slotted spoke heads - _et viola._
Since you can't machine the inside of the rim after soldering - mount the assembly in a lathe and clock it up - it should run true - but you can always beat some sense into it with a hammer if it doesn't - before soldering - of course.
_


_
You can see the 0.10mm annulus - filled with solder in the photo above - so it can never come apart. -
Also note that the material of the spoke has developed a different patina to the rim. This is about two years old - polished you cannot see the annulus - so I'm going to repolish it and clear lacquer finish it - as I have done for all the other brightwork.
The details are in the drawing under downloads.
Not 1000 words - but hopefully as good as a picture.

Regards, Ken


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## a41capt (Sep 8, 2020)

Most excellent!  Wonderful work, thanks so much for sharing with us!
John


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