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Step 6Casting and more gluing
Here's where we cast a piston. I've tried nearly everything under the sun I could find. Nothing. Without machining something, you're left with very FEW options of what to use for a piston. Now, if you don't want to worry about this, you could go to www.airpot.com and buy a piston/cylinder (or a dashpot w/ some slight modifications) and use that. They've got excellent machined graphite pistons running in Pyrex tubes...
But, if you're just the average person who doesn't feel like ordering anything, we'll just cast one.
So, break out the epoxy (this is the non-nonshrink stuff)
1- cut around one inch of copper pipe with a hacksaw. (sorry about the pictures, I used a huge piece, I meant to use an inch of pipe)
2- using the utility knife, trim the inside edge of the pipe. DO NOT USE SANDPAPER. this is to smooth it for when we push the cast piston out.
3- clean out the inside of the pipe until it's nice and shiny. Use Windex to help.
4- wrap the base of the piece with plastic film (saran wrap)
5- oil the inside of the pipe, regular spray on cooking oil is fine.
6- warm up your epoxy, we want it nice and runny.
7- mix enough to fill a half inch of the pipe or so.
8- wait
9- once cured, remove the saran wrap and the cast piston should push right out. It may need some force, but it'll come.
10- take some wire (about an inch) and bend the end into a hook like seen in picture nine
11- drill a hole in the piston and glue the wire piece in.
While you're waiting for the piston to cure, pull out the JB weld or kwik and glue the plastic piece of the CD tower you cut to the bottom aluminum plate. This is the one that hasn't been drilled into.
*for more advanced builders* you might want to try using a glass cutter and cutting a pyrex cylinder from a test tube instead of a copper pipe.
***WARNING*** I'd like to note that for the BEST piston results:
1- do not mix the epoxy in the cylinder. The oil seems to contaminate the mix and keep it from hardening. mix on wax paper or saran wrap.
2- Do NOT use 1 minute epoxy. Avoid 5 minute epoxy as well. I tried one minute epoxy and it got really hot in the tube. The problem comes when it cools then severely contracts, leaving TOO much of a gap. It's thermal expansion, plain and simple. This needs to be avoided. Warm should be ok. Hot is not.
But, if you're just the average person who doesn't feel like ordering anything, we'll just cast one.
So, break out the epoxy (this is the non-nonshrink stuff)
1- cut around one inch of copper pipe with a hacksaw. (sorry about the pictures, I used a huge piece, I meant to use an inch of pipe)
2- using the utility knife, trim the inside edge of the pipe. DO NOT USE SANDPAPER. this is to smooth it for when we push the cast piston out.
3- clean out the inside of the pipe until it's nice and shiny. Use Windex to help.
4- wrap the base of the piece with plastic film (saran wrap)
5- oil the inside of the pipe, regular spray on cooking oil is fine.
6- warm up your epoxy, we want it nice and runny.
7- mix enough to fill a half inch of the pipe or so.
8- wait
9- once cured, remove the saran wrap and the cast piston should push right out. It may need some force, but it'll come.
10- take some wire (about an inch) and bend the end into a hook like seen in picture nine
11- drill a hole in the piston and glue the wire piece in.
While you're waiting for the piston to cure, pull out the JB weld or kwik and glue the plastic piece of the CD tower you cut to the bottom aluminum plate. This is the one that hasn't been drilled into.
*for more advanced builders* you might want to try using a glass cutter and cutting a pyrex cylinder from a test tube instead of a copper pipe.
***WARNING*** I'd like to note that for the BEST piston results:
1- do not mix the epoxy in the cylinder. The oil seems to contaminate the mix and keep it from hardening. mix on wax paper or saran wrap.
2- Do NOT use 1 minute epoxy. Avoid 5 minute epoxy as well. I tried one minute epoxy and it got really hot in the tube. The problem comes when it cools then severely contracts, leaving TOO much of a gap. It's thermal expansion, plain and simple. This needs to be avoided. Warm should be ok. Hot is not.
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what should i do?
http://www.loctiteproducts.com/p/13/6/epxy_qset_s/overview/Loctite-Epoxy-Quick-Set.htm
I realize you said not to use the 5 minute kind, but I did not see any thermal contraction issues when it was setting. On the contrary the epoxy seemed to bond to the copper. Is this because I did not put a sufficient coating of oil on the pipe? I used wd-40. I also pre-mixed it before pouring it in.
If you did You need to run a file around the inside to stop the edges catching.
I mixed all of it and packed it into the plastic tube it came in, it does not stick to the plastic and is easy cut out once it hardens.
The hardened epoxy bar reads 25.1mm on the calipers or 63 / 64 in old money.
I have just bought a mini lathe and the first project I intend to do is a Stirling built from scavenged PC parts.
the first time, i did finish but the small piston is no smooth so it did not work. the small piston with the hole has to have the small space or not.
However, both should be as light as possible. If one or the other is very heavy, it'll mess up the engine.
The 'Hard to move' part worries me though. Does your piston slide smoothly? the engine should NOT be hard to move at all! It should turn easily.
If there's a specific part of the rotation that it sticks, or becomes hard to move at, check that out. There is likely a problem there. Either the piston isn't smooth at that point, the displacer is hitting the top or bottom, or a shaft is rubbing.
i done it by using glass to do piston but it does not work. so can you tell me why and what should i do.thanks
Glass piston? I'm not sure I understand, did you grind the glass? or have a glass test tube? or what?
If you have a picture that'd be great!
It can't be perfectly secure, because the pipe isn't perfect, and small defects would catch it. However, too loose and it won't run.
i cant find any different epoxy other than the ones i have...
http://www.amainhobbies.com/product_info.php/products_id/37084/n/Bob-Smith-Industries-MID-CURE-15-Minute-Epoxy-9oz?utm_source=Google-Base&utm_medium=cpc&utm_campaign=Product-Feeds&source=google_ext
Anyways, give it a try! The main point of this instructable is to use what you've got!
Here's the deal, if it does shrink too much, you could try putting something in the middle of the epoxy (ie a smaller solid cylinder) to reduce the overall shrinkage.