Stirling '60'

Discussion in 'HMEM Forum Support & Suggestions' started by Clockman, Jul 22, 2018.

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  1. Jul 22, 2018 #1

    Clockman

    Clockman

    Clockman

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    Hi - I'm new to HMEM so I hope that I'm doing this right.
    Since retiring, my hobby has been making clocks - proper ones with weights, mainsprings, pendulums etc. For a change I thought that I would try to make a Stirling engine and found the drawings for the Stirling '60' by J.Jonkman on the internet. Thanks to HMEM I was able to get the drawing page that was missing from the original internet download. Also, I found some useful information in earlier threads from people who had made the Stirling '60'.
    The machining appears to be rather more complex than with clock making - there is little blind boring, for instance, in clock making so it is going to be an interesting challenge.
    Two things concern me and I hope that someone who has made the Stirling '60' may be able to give me some advice. Firstly, the displacer piston is hollow with a domed end. Whilst thin-walled brass tubing is readily available, how do you form the domed end?
    Secondly, I assume that the test tube has to be heat resistant glass such as borosilicate? If so, how do you cut it to length?
    Any advice about constructing this engine (and the potential pitfalls) would be very welcome.
    Many thanks.
     
  2. Jul 22, 2018 #2

    fcheslop

    fcheslop

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    Hi, for the displacer internal rad I simply ground one side of a twist drill to a rough rad the other side ground slightly further back and made it from bar stock in alloy. The external rad was done with a file .Not very technical but it works
    To cut the glass I made a simple glass cutter along the lines of the one Jan Ridders shows on his site prior to that I used a diamond file in the lathe a wee bit more risky
    There is loads of ways people cut these tubes but they never worked very well for me jjust to many scrappers until I made the simple cutter. I use a Dremil clone with a flexi shaft to power it
    I can do a wee pic if needed
    The engine is a good runner and I cannot remember any probs with the drawings although I broke a few tubes due to the O rings been slightly to tight
    Friction is a killer for these engines as are air leaks
    http://ridders.nu/index.htm
    http://ridders.nu/Webpaginas/pagina_glassnijder/glassnijder_frameset.htm
     
    Last edited: Jul 22, 2018
  3. Jul 23, 2018 #3

    minh-thanh

    minh-thanh

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    Hi !
    one more thing : with the power piston-power cylinder, displacer bearing-displacer rod must fit, but move lightly : Especially when it's hot
     
  4. Jul 23, 2018 #4

    Clockman

    Clockman

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    Thanks for the helpful replies. I like the idea of using my Dremel as a cutter and will follow this up. Friction is the enemy of clock making too but the point about changing clearances as the engine heats up is not something that I had thought of before. I feel that there is going to be some trial and error with this build.
     
  5. Jul 23, 2018 #5

    minh-thanh

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    \

    It's just my experience doing some stirling engines, because it's difficult to accurately determine clearance with small piston and cylinder when cold and hot for the best

    about ""some trial and error"" : I have a lot of trial and error before the first engine runs
    AND : You should ask questions in :
    https://www.homemodelenginemachinist.com/forums/general-engine-discussion.26/
    will have more answers.
     
  6. Jul 23, 2018 #6

    fcheslop

    fcheslop

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    As Minh Tanh mentions they often take a wee bit of suck it and see
    Have a look on Jans site under his hints and tips section and you will get a good idea for fits
    When fitting ball bearing dont make the seats a press fit just bore to size and glue them in also for the displacer shafts give them a slight polish along the length just to remove the grinding high spots or at least thats what I do and find the bushings last a lot longer. The spindles that run in the bearing I tend to polish just to reduce the tighness of the fit just so they slide with enough resistance to still rotate the inner race or if I go a bit to fat glue them in
    For the glue I just use super glue as it canbe released with a sharp tap or a bit of heat.I find loctite just to good at its job and have had problems when overhauling engines in the past.
    Despite what most say about washing the grease out of ball bearings I dont have not had a problem
    Good luck
     
  7. Jul 27, 2018 #7

    Clockman

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    Thanks for the tips about fit. In clock making fits are generally on the loose side. There is a saying "If it rattles then it will run" which works for clocks but probably not for the Stirling. I am having problems finding test tubes of the specified 13mm diameter. I presume it would be better to get larger tubes (rather than smaller) so that there is enough air to run the Engine?
     
  8. Jul 27, 2018 #8

    minh-thanh

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    Hi Clockman .
    With larger or longer tubes or both, it will be difficult for the engine to run or not run, because it will reduce the volume of air in the engine, resulting in reduced air expansion.
    The expansion of the air is the principle of the stirling engine
     
  9. Jul 27, 2018 #9

    fcheslop

    fcheslop

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    Cromwell tools used to sell the right size . I got my last ones from fleabay they are a bit thinner walled but have worked ok
    I just increased the displacor dia to give the right clearance . Bengs in Germany probably sell them
    https://www.bengs-modellbau.de/materialbausaetze/flammenfresser/flammenfresser-jarne
    You should be able to navigate to the spares shop from the link and yep its another future project
    As Minh Thanh mentions if you go larger the power piston dia will need adjusting as well to keep to the correct ratio .
    Remember one burn and you become an addict to these engines
    cheers
     
  10. Jul 28, 2018 #10

    Clockman

    Clockman

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    Thank you - that is very useful information. After much internet searching I think I have found 13mm dia. test tubes. But I will need to check the size when received as advertisers are not always that accurate.
    Best wishes, Clockman
     
  11. Jul 28, 2018 #11

    minh-thanh

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    Hi Clockman !
    The inner diameter of hot cap ( test tube... ) - the outer diameter of the displacer = about 1,5 to 1,8 mm with small stirling engine
    Do not let them touch each other when moving.
     
  12. Jul 28, 2018 #12

    fcheslop

    fcheslop

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    Test tubes are not very accuratly made and if there is a bead at the open end it tends to measure smaller that the actual tubes ID
    I only found this out the hard way when building Jan Ridders Thermo pulse engine and every tube has a slightly different ID not a problem on the Stirling60
    There is room for a bit of give and take around the size of the tube although you will need to tweak the O ring fit .I broke several tubes before getting it to go together .Make sure you assemble it dead square to the O rings and I ended up boring the grooves a few thou deeper than recommended as long as it seals it will be OK
    Good luck
     

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