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  • LTD Stirling engine - build thread

    I've started building a low temperature differential Stirling engine, and will try to document how it goes here - hopefully I'll make some useful mistakes that people can learn from! I've not really done any machining since I left school (20+ years ago) and lost access to a machine shop. Recently I got myself a workshop, bought a lathe, and have been remembering what I used to love about it. A LTD Stirling engine is a slightly silly first proper project, but I've wanted to make one for ages (since making a high temperature one years ago), and I'm enjoying myself even if I can't get it running. I thought I'd follow some plans so that if it doesn't work I know it's because of the machining and not the design. I'm making this one: http://www.ridders.nu/Webpaginas/pag...g_frameset.htm

    First step was the top plate (made of aluminium). Faced off and turned to size, and then I discovered that I didn't have a parting tool long enough. Sawing it off wasn't fun and I've now bought a proper parting system, but lacked the patience to wait for it to arrive.
    Click image for larger version

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    I remounted it in the lathe to clean up my saw marks. I also needed to make a hole part way through this plate that takes the (16mm OD) glass power cylinder. This was my first go at mounting something a part off-centre in a 4-jaw chuck to drill and then bore this. I kept speeds low and cuts light in case of wobbles from the off centre mass, but it really didn't seem to mind.

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    And finally with the glass power cylinder (cut from a piece of glass measuring cylinder) inserted, along with the two supports for the flywheel threaded into it. The reason the supports look splayed out is camera distortion - they are actually vertical. The reason they look different at the base is because I was experimenting with grinding my own tool bits for one of them, and while I produced a tool bit that worked pretty nicely, it couldn't get into the corners properly. I make re-machine one to make them match, or just leave it as a document to my learning process.
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    I've got a bit further than this, but haven't taken pictures yet.

  • #2
    Looking good so far. Glad you decided to make a build thread.

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    • #3
      Yep, it's good to see stuff like this.

      I've see pictures of a few of these coffee cup Stirlings but not seen one that is this simple and direct. I like it! And I can see why then specified the cone bearings. I can also see that instead of the cone sockets where the smaller size mini ball bearings out there could be built into cups with threaded studs off the back of the cup. So very little change to the original plan.

      I think I'd also want a heavier sheet metal flywheel....

      You don't have any sort of bandsaw for metal? Plans to get one at all? I hug my cheezy and uber basic 4x6 inch saw that works in both the horizontal and vertical modes on at least a weekly basis thanks to how useful it is. It's a saw! It's a burly big parting tool! It's a slitting saw! It's so many things central to a machine work shop.
      Chilliwack BC, Canada

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      • #4
        I currently have a drill press, a lathe, and a bench grinder. I'd love to have a bandsaw and a mill and more tooling etc., but am trying to take purchases slowly while I work out what I need/would use the most. Hacksawing smaller stock isn't too bad, but that big chunk of aluminium was hard work!

        I'm planning to make it pretty much as designed to start with, and will then experiment with swapping bits out. Ball bearings and a metal flywheel should be fairly easy to add later.

        Comment


        • #5
          If you use ball bearings soak all the oil out of them and run them bone dry. Even the low viscosity of an oil will retard an LTD. The speed and duty cycle of an LTD are both low so bearing wear is not an issue.

          Another hint: Air leaks in the displacement chamber can be sealed with petroleum jelly or silicone grease. The pressure variations in the chamber are very low so this will work well.

          You can see a video of mine running on ice here:

          https://www.homemadetools.net/forum/...010#post168218
          Regards, Marv

          Home Shop Freeware - Tools for People Who Build Things
          http://www.myvirtualnetwork.com/mklotz

          Location: LA, CA, USA

          Comment


          • #6
            now there's an enthusiast.... sawing through a bar like that. I look forward to seeing the project progress
            in Toronto Ontario - where are you?

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            • #7
              This is an interesting project. I may even try one at some point. I will be following closely. Good job on sawing that off with a hacksaw. That is hard work!
              Kansas City area

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              • #8
                I built a coffee cup sterling a number of years ago. It was probably the first time I had worked with very small machine screws and parts. It ran quit well, but not for long. You had to get the coffee mug and water very hot to start with but it would cool down quite quickly and the engine would slow down and stop. I was in Lee Valley tools here in Canada and saw a sterling running on a mug of hot water that was sitting on top of a very small hot plate made for keeping your coffee warm. I found out they actually sold them so I bought one. The sterling will run as long as there is water in the mug now.
                Larry - west coast of Canada

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                • #9
                  Originally posted by hollo View Post
                  I currently have a drill press, a lathe, and a bench grinder. I'd love to have a bandsaw and a mill and more tooling etc., but am trying to take purchases slowly while I work out what I need/would use the most. Hacksawing smaller stock isn't too bad, but that big chunk of aluminium was hard work!

                  I'm planning to make it pretty much as designed to start with, and will then experiment with swapping bits out. Ball bearings and a metal flywheel should be fairly easy to add later.
                  It's such a nice simple design that it lends itself to doing it that way very nicely. And a good plan for how you'd proceed with changes I like the idea of being able to evaluate any changes you make as you go.

                  When you get the "machine fund piggy bank" up a little I think the big majority of us would recommend that the next step is a metal cutting band saw.

                  I bought my own 4x6 H/V saw about 30 years back even before I found a deal on the first mill drill. Despite being the smallest of the small in the bandsaw world for a floor mount tool it has been a key player in the shop for the amount of work it has saved me and for the greater sizes of stock I can reduce down to workable lumps.

                  For example I've recently done a couple of tool holders for my lathe's quick change post. And they worked out so nicely that I want to make a few more. This involved cutting off hunks of 1.5 x 3 inch mild steel bar stock. Thanks to the bandsaw I set up the cut and wandered off to do something else until I heard the piece hit the floor and the saw turn off. And then I cut three more to go with the first..... Your arm squirming in sympathy yet?

                  As I mentioned I also use mine a lot in the vertical mode for for actually shaping or "saw milling" parts and cutting slots for parts that will pinch clap and such. And especially for cutting plate parts roughly to shape it's a handy thing. As a result I use the vertical mode position probably 30 to 40% of the time. Some of the jobs could be done with a cutting disc in an angle grinder. But only with a lot more sparks, fumes and noise. The mild purr of the saw is far more pleasant. It's such a key player that if something happened to it reparis or replacement would become an immediate issue. It's just simply that important a tool for me.

                  Many times I've found myself thinking that I should get a better bandsaw. But the bigger/better ones don't come with this same horizontal and vertical mode option. So my cheap dry cutting H/V saw soldiers on as my ever faithful shop companion. And I really do think that for a smaller home shop it's a heck of a bang for the buck and for the room it takes up.



                  Chilliwack BC, Canada

                  Comment


                  • #10
                    Originally posted by Cuttings View Post
                    I built a coffee cup sterling a number of years ago. It was probably the first time I had worked with very small machine screws and parts. It ran quit well, but not for long. You had to get the coffee mug and water very hot to start with but it would cool down quite quickly and the engine would slow down and stop. I was in Lee Valley tools here in Canada and saw a sterling running on a mug of hot water that was sitting on top of a very small hot plate made for keeping your coffee warm. I found out they actually sold them so I bought one. The sterling will run as long as there is water in the mug now.
                    I wonder how much of it was the heat from the cup getting to the "cold side" plate? A variation I've seen of these engines is where the engine drives a fan which blows cool air over fins on the "cold plate" to aid with shedding the heat brought up by the displacer. If one can keep the cool side cooler then it keeps the heat difference between hot and cold greater and for a longer time.

                    Of course the point is that we are still only going to work for a short time anyway. After all, part of the function of the engine in this case is to move the heat out of the coffee to where we can drink it...
                    Chilliwack BC, Canada

                    Comment


                    • #11
                      Originally posted by mklotz View Post

                      You can see a video of mine running on ice here:

                      https://www.homemadetools.net/forum/...010#post168218
                      Marv,

                      I had not seen an ice engine, and yours is an inspiration. Now that Phoenix is in for almost five months of 100ºF (or hotter) days I wonder if this would be enough temperature differential to turn your flywheel as a fan, directing some chilled air to to cool one's head while contemplating the Second Law!
                      Allan Ostling

                      Phoenix, Arizona

                      Comment


                      • #12
                        Originally posted by aostling View Post

                        Marv,

                        I had not seen an ice engine, and yours is an inspiration. Now that Phoenix is in for almost five months of 100ºF (or hotter) days I wonder if this would be enough temperature differential to turn your flywheel as a fan, directing some chilled air to to cool one's head while contemplating the Second Law!
                        During the Raj the British in India had kerosene lamps fitted with small Stirling engines that drove a fan to provide a much-needed breeze. It always seemed counter-productive to me to burn a fuel to move air for the purpose of cooling.

                        I've never seen anyone attempt to use an LTD to do any useful work. The net output power is just too small. I think the drag of a fan would be too much to be overcome. But, hey, what do I know? Perhaps with a pressurized gas and cryogenic cooling it could be done but the cost would far outweigh the benefit.
                        Use a 12v computer fan run off a motorcycle battery with a photovoltaic recharger (Phoenix gets a lot of sun, too).

                        Regards, Marv

                        Home Shop Freeware - Tools for People Who Build Things
                        http://www.myvirtualnetwork.com/mklotz

                        Location: LA, CA, USA

                        Comment


                        • #13
                          Originally posted by BCRider View Post
                          I bought my own 4x6 H/V saw about 30 years back even before I found a deal on the first mill drill. Despite being the smallest of the small in the bandsaw world for a floor mount tool it has been a key player in the shop for the amount of work it has saved me and for the greater sizes of stock I can reduce down to workable lumps.
                          I'm very tempted by this to be honest, but have no experience with them - presumably you're talking about something a bit like this: https://www.machinemart.co.uk/p/cbs4...l-cutting-ban/ (first google hit - I'll research more carefully, and am just checking I'm on the right lines). Still wouldn't have fitted that 5" aluminium bar though!

                          mklotz - love the engine you've built. I've heard the trick about washing the oil out of the ball bearings with acetone or similar to reduce friction (presumably at the cost of increased wear which wouldn't be an issue here).

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                          • #14
                            It would have cut the 5" bar. It will cut to 6" wide. The 4.5" dimension is for a rectangular bar. The round bar doesn't have the corner on top. Plus, you can cut larger material by cutting part of the way, turn the stock, cut some more, etc. till you get through it.
                            Kansas City area

                            Comment


                            • #15
                              Originally posted by mklotz View Post
                              ............... It always seemed counter-productive to me to burn a fuel to move air for the purpose of cooling................
                              And yet, if you are typical, you do it all summer................
                              2730

                              Keep eye on ball.
                              Hashim Khan


                              It's just a box of rain, I don't know who put it there.

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