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dgoddard

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Well
A.-- It looks like a lot of fun
B.-- I am a mechanical engineer
C.-- I am an hobby machinist.
-- a.-- Lagun FTV2 10x50 knee mill
-- b.-- Harbor Freight 12x36 lathe (seems to be better than many are reputed to have been made)
-- c.-- Horizontal Band Saw
-- d.-- bench grinder
-- e.-- tool grinder with diamond wheel for carbde
-- f.-- Hobart "Handler 187" MIG welder
-- g.-- etc. too numerous to list
D.-- I need to make a hot air engine as a gift for someone going into politics (The multitude of humility reminding attributes should be obvious).

Now I suppose that I will find many interesting models to build of all manner of things but just at the moment, I think I have come to the fellowship of those far more expert in the craft than myself. So my current need has given the final push for me to appear before you of the more accomplished in this matter.

So........

Does anyone here know where I can get plans (preferably free but definitely downloadable) for a Flame-Licker / Fire-Breather / Atmospheric-Engine that is
-- Fairly quick to gather material for
-- Readily fabricated
-- Easy to adjust
-- runs well
-- sits easily on a desk or book shelf
I would like to make one in the next 2 to 3 weeks.

A kit with castings might be considered if it is likely to produce a superior result but I believe I have all the necessary metal stock and could obtain bearings readily.


 

Tin Falcon

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Mr goddard; Welcome to our wacky world of model engineering. I split your post off from the original thread so we can give it the attention it deserves.
thank you for the intro. sounds like you have a well equipped shop.
as for your question. check out Jan ridders web site. http://heetgasmodelbouw.ridders.nu/ his plans are free upon email request .
just tell him what plan set or sets you want and he will send them to you via e-mail. Limit 2 per request. and personalty I would limit requests to one a month.
my favorite for a gift to a politician would be a low delta t sterling. yes he has those plans as well.

The above engines have a reputation for being difficult to get running . fit and finish of mating parts is very important.
we generally recommend a simple wobbler for a first build.
I do know what it feel like to need to build a gift for someone and you get a vision of it . and you are up against a deadline ...
There is as least one guy here that did a complete low delta Stirling build in a long(3day) weekend.
there is also a nice article /post here on pointers of building such engines . this is written by a guy who builds them for sale. It is well written.
so have fun.
we are here to help and answer questions.
Tin
 

b.lindsey

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Welcome to the site. I can't add anything to the advice already given above, the Phillip Diclos was my first flame eater eingine but don't think those plans are free or downloadable so no help there. Tin is right, they can be a bear to get running but with your background and equipment that shouldn't be a problem.If you run itno any issues, I am sure the members here can help out too!!

Bill
 

Omnimill

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As mentioned, have a look at Jan Ridders site. Plenty of engines of all different types on there and Jans plans are second to none IMO.

Vic.
 

dgoddard

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?1
A type of labyrinth seal can be achieved by grooving the outside diameter of a piston that runs in a smooth cylinder. This works with compressible fluids (e.g. hot air) because of the flow losses as the gas goes through multiple expansions and contractions as it passes by a land into a groove and then by the next land etc. The flow losses from the multiple expansions and contractions of the fluid serve to make an effective seal with little leakage. It would seem that this would be a useful trick in model engines because it allows for very low friction between the cylinder and piston. It allows a less precise fit while still controlling blow by. It is like a piston grooved to accept rings but there are no piston rings. Do any engines use this trick?

?2
All of the designs that I have seen so far have been simple "slider crank" mechanisms (i.e. the centerline of the bore intersects with the axis of the flywheel & crank) If the axis of the crank were raised above or lowered below the the centerline of the cylinder bore the mechanism would become an "offset slider crank". This can result in improved torque on the power stroke, and can be used to give different lengths of time for the "down" stroke vs the "up" stroke. It does give a preferential direction of rotation to the engine. Do any of the model engine designs make use of this technique?
 

dgoddard

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Ok, so what I am building is an atmospheric (AKA flame Licker) engine. The one I have chosen to make is shown at:
http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_happer_inw_schuif/inw_schuif_frameset.htm
(be sure to click on "English" when you get there)
But what is unclear to me is what sort of graphite one ought to use for the pistons So far I have identified that there is fine and medium and EDM electrode versions as well as Isostatic pressed and extruded, (and maybe other varients, so I am wondering what grade of graphite I ought to be using
 

Chriske

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Hi,

You could use bronze for that piston, works just the same.
one of our pupils made this one, piston made out of bronze.

[ame]http://www.youtube.com/watch?v=UZhygoq5Yps[/ame]

Chris
 

dgoddard

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Anybody got a good source for those tiny ball bearings 16x8x4 (ODXIDX t) and especially that 8x3x3 Connecting Rod Bearing?
 

dgoddard

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16x8x4 .... tiny...???
Well my last bearing job was rebuilding the drive head on my 3hp 3phase 10x54 2800 lb vertical mill. It is all relative.:D
And what would you call this one..?
Miniscule;)

But back to the issue for me:, Is there any source for the bearings I need that can provide quick service from here in the U.S.?

And of course I have not solved the problem of the proper graphite grade for material to make the piston & valve.
 

GailInNM

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dgoddard,
The last few years I have been using bearings from Avid RC that they sell for radio control cars. They have always shipped the same day if the order is in before noon and the prices are hard to beat. Fair shipping costs also. I know they are inexpensive import bearings, but I have been quite happy with them. I have them in 6 Gauge 1 locomotives and 9 hit-n-miss engines.

Gail in NM

http://www.avidrc.com/

http://www.avidrc.com/product/1/bearings/227/3x8x3-Metal-MR83ZZ-bearings.html

http://www.avidrc.com/product/1/bearings/374/8x16x4-Metal-688ZZ/B4-bearings.html
 

dgoddard

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I figured getting the cylinder right would probably be one of the harder tasks that I was ready to do so I started there. Ridders' website talks of stainless for the cylinder but his plans call for aluminum, and since I had that on hand I chose aluminum. However I did alter the cooling fin design by using a 0.051" parting tool to cut 9 grooves in the same space. (image #1)

I then chose to alter the flywheel design and rather than using 14mm thick brass I used 1/2" (12.7mm) 1018 CR steel plate. I calculated the mass moment of inertia for the brass design and then adjusted the inner radius of the rim to give the same value to the steel flywheel. I rough sawed an octagon and bored the center hole to 8mm

I made a steel mandrel (image #2) from some 1.5 inch turned stock with a 3/8 in x 8mm stub turned concentric. The photo shows a step washer that fits the 8mm bore and has an OD equal to the hub diameter as a guide to aid cutting the hub The 1.5 inch face of the mandrel is made concave to maximize the torque that the work piece can stand while turning.

The photo (image #3) of the turned face of the fily shows the lathe set up with the boring bar to make the cut. Cutting the hub did require running the spindle in reverse.

The next image (image #4) shows the result. With the tooling available I had difficulty with chattering. The tolerance and the surface finish were acceptable but less than fully satisfactory. I discovered too late that I had erred in using 1.5 inch stock for the mandrel because this was smaller than the ID of the rim and would not provide driving friction at a large enough diameter to cut the second side.

Rather than make an adapter or new mandrel I decided to mill the second face of the flywheel using a rotary table (Image #5). The set up was involved:
a) getting the rotary table on the mill table,
b) mounting the chuck to the rotary table,
c) centering the table under the spindle,
d) mounting the flywheel and precisely
e) dialing it in concentric to the rotary table axis.

But once that was done the the mill was plunged to the proper depth and the face was milled in 3 quick passes:
(1) remove most of the material with a pass at the mean diameter between the Hub Od and the rim id,
(2) move outward to finish cut the id of the rim,
(3) move inward to finish cut the OD of the hub.
This time the surface finish and tolerances were excellent. (Image #6)

This post would have been easier to read if I could have figured out how to intersperse the photos, placing them "in line" with the text but I have not figure that out yet on this web site software.
--------------------------------
I still could use some advice on what grade of graphite to buy and where it is cheapest. Do any of you more experienced guys (or gals?) have any suggestions?

12072601_Cylinder+Legs.jpg


12072701_Fly_Wheel_mandrel.jpg


12072702_Turning_Flywheel.jpg


12072703_Flywheel_Turned_Side.jpg


12072901_Milling_Flywheel.jpg


12072902_Flywheel_Milled_Side.jpg
 

dgoddard

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While I appreciate the asthetics of Jan Ridders' brass flywheel supports, practicality and available materials and concerns about allignment of the bearings prompted me to make a design modification. My design is a single assembly of aluminum and allows for the bearing seats and bearing caps to be bored aligned to size in a single setup. This should reduce a risk of bearing friction from misaligned bearings and also accommodate variations in the shaft design (which I may consider). My flywheel support should work with the rest of Ridders' parts provided his base plate is tapped for two M4x.7holes in lieu of his four M3x.5 holes for his bearing supports. I have included my drawing with both metric and inch values should anyone be interested.

12080102_Flywheel_Support.jpg


Flywheel_Support.jpg
 

dgoddard

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Because I lack silver soldering capacity, I decided to make my crankshaft differently. First, I made a special screw (#1) that has a shank below the head which is a snug fit in the bore of the flanged ball bearing (#2). The screw has a washer face under the head that will bear directly only against the inner race of the bearing and not interfere elsewhere. The screw will clamp the bearing inner race firmly to the spacer (#3) so that all accomodation of rotation of the connecting rod is provided by the ball bearing. The spacer (#3) will be soldered in place on the crank arm and then tapped M3x.5 for the crank-pin / screw. By making the crank-arm / counterweight (#4) and crank shaft (#5) out of brass soldering should be very easy and the parts are keyed together for accurate location. The crank-arm / counterweight looks a little crude at this point as it will not be final turned to diameter until after soldering the assembly.

When welding or brazing I prefer to use self locating features on the parts rather than rely on fixturing. I have better luck getting accurate assemblies this way. Also having the parts "keyed" together as shown assures a stronger assembly.

The light knurl on the shaft provides a way to get a very precise fit between the bearings and the shaft as the first bearing pressed on will smooth the knurling to precise bearing bore size and also accommodates the grip of loctite should I choose that as an additional form of retention on the assembly.

12080501_Crankshaft_Pieces_Numbered.jpg
 

dgoddard

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And now for my Newby question of the day. Most of these small engines I see seem to have unshielded bearings. The bearings I have are shielded and pre-lubed. Is it recommended to remove the shields and replace the grease with light oil in order to minimize friction?
 

rhitee93

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And now for my Newby question of the day. Most of these small engines I see seem to have unshielded bearings. The bearings I have are shielded and pre-lubed. Is it recommended to remove the shields and replace the grease with light oil in order to minimize friction?
I'm not an expert on this, but these external combustion engines need very low frictional losses, so I would think this is a good idea.
 

skyline1

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16x8x4 .... tiny...???
And what would you call this one..?



Chris
Wow that is tiny It's only about 1/8" O.D. I thought the bearings on my steam turbine were small (1/8" Shaft) these would fit inside 'em !
 
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