coffee cup stirling

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coffee cup stirling

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vtsteam:
It may take a lot of heat if the bearings friction is great. They usually use super light weight components to reduce bearing friction in low tempereature differential engines.

If your dispacer is heat resistant you can increase the temperature over a foam displacer, if you find it doesn't work at low temps. Balsa can go higher than foam.

bertie_bassett:
got a bit more progress done.

first I cleaned up the flywheel with some heat and an ally scraper, also persuaded it to be somewhat flat.

that was followed by turning up a center bush and soft soldering it in place

once cool (ish) it was out in the lathe and using the outer edge as a reference I cleaned up the center and drilled it out to 4mm to fit the crank shaft

made a small cock up when turning the larger boss on the backside, was supposed to mirror the other side but forgot to direction or the auto travers and ran into the work :doh:

set it on the shaft and it runs nicely, seems a bit un-balanced but that may work to my advantage when it come to balancing everything else.

i then moved onto the con rods decided to use the mill a bit more and made up these

worked out the required lengths on autocad, so im hoping they are right

also made up the pins for both power piston and displacer

and heres how its looking

tonight's job is to work out where everything is going to sit on the crank, then it can be glued together

Steenkamp:
Hi Bertie, nice looking stirling. They are absolutey fascinating engines.I have also built a few of the Jan Ridders ltd's and if done right they will run reliably forever as long as there is a large enough temperature difference between the top and bottom plates.

One thing that is a killer on these engines is friction. I have used computer harddrive bearings and needle point bearings in my engines. Both without any oil. The viscocity of even the lightest oil in a ball bearing creates enough friction to make the motor a non starter.
Coupled with reducing friction is reducing weight. I have made my displacer rod out of brass tube running in graphite bushing and sealed at both ends with ally "plugs" light press fitted with locktite. These plugs would also serve as displacer holder and displacer conrod clevis.
Pistons were made with graphite running in brass tube as i could not get hold of truly cylindrical test tubes. Final "cuts on the graphite parts were made with copier paper as i just "sanded" them to size, leaves a very smooth finish. Balancing is another issue and should be done with the bottom plate off.
To check for any air leaks i "pressure test" the engine by leaving it in the freezer for an hour or so. Once a nice white frost condensates on the engine as you take it out and submerge it in warm water. I normally use a clear salad bowl when swambo isnt looking. Thus heating up the air inside the displacer it expands and make bubbles where you have air leaks. Do not leave it in the water too long as theengine will heat up sufficiently to start drawing the water in. Bad news!!
I hope this can help you to get the stirling going

bertie_bassett:
well as usual its all starting to go wrong! 1 step forward and 4 steps back :bang:

started to put the crank together yesterday. thought id use a nice bit of 4mm steel rod that fits the gears perfectly, but couldn't work out how to fix the brass cranks to it. so I switched to 4mm brass rod. problem was the 4mm rod was actually 4.2! so after a lot of work with sandpaper I got it down to a size where the bearings would fit on it nicely (after breaking 2) so I assembled said shaft in one piece with bearings and con rods installed and warmd it up to solder it together, all went to plan - sort of

then carefully cut out the bits I didn't need and gave it a test fit, it did spin - honest

looking ok, but a bit bent and conrod bearings have got a bit warm, should be ok I think to myself.

so today I started trimming up the excess and cleaning the crank up with the aim of straightening it. unfortunately I found one of the conrod bearings to feel 'gritty' and as I moved it about , the balls fell out! :Doh:

so now iv got a crank all solderd together with con rods attached, but with buggerd bearings.

also iv noticed I need to redo the displacer shaft seal again, as the hole still isn't right :doh:

soo Iv now given up and am going to get a large whiskey, if anyones got any good ideas on how to do this crank pleas let me know. its got me rather annoyed at the moment.

awemawson:
Bad luck Bertie : I think 1 step forwards and 4 back is just about par for projects like this. It's all good character forming stuff that will stand you in excellent stead for the MK2 version :thumbup:

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