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Forum Index : Windmills : Cheap Mold-Release Agent
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Crew For those of you building epoxy stators and the like, I've come up with a dandy mold-release agent that's almost a no-brainer. What I did was overlay the mold with plastic sandwich wrap, then slop in the goop and when it went off, everything came out of the mold just lickety-split. Here are a couple of pictures of my latest endeavor. I'm building a magnetite-filled solid stator ring, which will be machined (once I figure out all this casting business) to hold coil windings much the same as an F&P does with laminates. Magnetite has no hysteresis and is free (magnetic beach sand); the perfect match. 
This shows the stator core already popped out of the mold. The plastic wrap sticks to the resin (I used polyester resin here), but it peels off without difficulty. The first rotor I made got stuck in the mold, so I came up with a better "release" agent -- plastic wrap. That first rotor didn't have enough catalyst in it and took about 2 days to harden up. This latest one went off in about 20 minutes; I doubled the catalyst amount. It's a learning curve! 
I still have to pay more attention to the area where the plastic tucks up against the corners and edges of the mold. As you can see, I missed it a bit on this one; again -- learning curve. This iron-filled donut gets machined, but unfortunately the inside (where I boogered it up) is already nearly to size and has to pop out of the mold not needing machining. I think on future castings, I'll smear Vaseline petroleum jelly on things before I flop in the plastic wrap. That way, I can use a sponge or Q-tip to get the corners and edges tight before I pour in the resin. Sooner or later, I'll throw up a post showing the whole process, but I thought I'd share now what I've learned so far. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Good tip Mac The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Update I figured out a way to make the corners square. I manufactured a 3-piece mold out of red oak that clamps together. Here's the contraption from the top: 
I used three 1/4-20 "Closet Bolts" (these usually hold down toilets), which both align and lock the halves together. The center cylinder, which becomes the inside of the stator is a bit smaller than I need, to allow for slight machining to make a close "air gap" between stator and rotor. Here's the bottom side: 
I counter-sunk all the bolt ends so the rig sits flat on the table while the resin mixture goes off. The basic premise here is as follows: First, I overlay the bottom chunk with plastic film, poking the threaded studs through the film, which holds it in place while I position both the top outside and inside mold pieces. The center core is first wrapped in film from the bottom up and the ends are taped in place, holding the film tightly against the central spindle. I plan on using cellophane tape against the inside of the larger circle, so when the resin cures, it'll just pop out (I hope!) and all the critical edges will be square and the right size. Once the film is in place, I clamp the pieces together using the wing nuts. I still plan on "facing" at least the top side, as the resin sometimes gets a little surface ripple when it goes off. Machining magnetite-filled resin is a little like working with cast iron. It's very granular and sounds similar as it peels off as it's dragged past the cutting tool in the lathe. I'll pour yet another test stator (3rd one) tomorrow and if it comes out like I want (perfect), I'll come back with some photos. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Mack When you use the sand does it increase the inductance of the stator? with the magnetic sand I think it may cause inductive losses and heating in the stator, I awaite your results to find out if it does cause losses. All the best Bob Foolin Around |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Bob Yes, the magnetite has no hysteresis and that's why I chose it. It increases the inductance, but has no memory, so can change back and forth as fast as I can throw magnets at it and not care a bit. I don't have any results yet, because the first stator cracked in half when I had to pry it out of the mold. The second one (shown in the pictures) didn't have good enough corners to be of much use, so I practiced facing it by attaching it to my face plate with screws from behind. It cuts like cast iron. Tomorrow, I'll pour another one and likely do a progressive "build" photo sheet as I do so. When it cures, I'll face it and then machine in the coil posts, wind a coil and see what happens. My original design had eight magnets, but it's just too hard to machine, so I'm thinking of dropping back to 6. I know six is not ideal (for that matter neither is eight), but then again, it's not a perfect world either, so I'll just try it and go from there. After the test coil tells me the turns per volt, I intend winding the stator using alternating right-hand, then left-hand windings in series for 9 coils. This is not unlike the modified "air core" alternator HERE shown on page 27. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
A tip on using polyester resin and the hardner. Rule of thumb.......weigh your resin, and add 2% hardner. How i do this is place the kitchen scales in a plastic bag (saves a sticky mess). Weigh the resin and for every 100 grams of resin add 2ml of hardner. Perfect every time. Pete. Sometimes it just works |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Downwind Thanks for the tip, Pete. "ml" that would stand for megaliter, right? 
Actually, these things are only 5" across and I'm using about 2 liquid ounces of resin to which I've discovered 25 drops of hardener works just right. The instructions are for mixing the whole can of resin and painting it on a surfboard, so I kinda had to improvise. I have an electronic "micro" scale that won't weigh anything over 5 pounds and has a metric scale to boot. I'll see if I can utilize your measurements using it. Thanks again. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Hi Mac, Here is a simple, small (24.4kb) metric converter calculator for you to download. It should help translate plain English (metric) into American jargon. 
For interest i punched in 2Fld Oz and it gives me 59.14ml or 0.125pt or 0.0625qt..... I think you might find it a hand tool to have around. Pete. 2010-08-23_030442_MetricConv.zip Sometimes it just works |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Pete My! You're up late. According to my "Time In Tasmania" link in my tool bar, it's like 3 a.m. over your way! Chocolate chip cookies and milk makes me sleepy after a dozen or more and a couple glasses; try it maybe, eh? Could it be that's why some of my friends refer to me as "Big" Mac?
. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Bingo! I made a new mold and now have a new stator that looks very promising. I'll run through the steps here in case there's anyone else wishing to travel this path: 
First off, I covered the face of the red oak wood mold with blue plastic sandwich wrap and taped it to the back, smoothing out the wrinkles: 
Here's that back side. I used blue film and blue tape so folks could see things better. You can use any color or no color. 
From the back side, I then jammed all the bolts that clamp the thing together through their respective holes. 
This is what they look like as they come poking through the top side. 
Next, I fitted the top half of the mold over the pegs and cinched all the wing nuts tight. 
I then wrapped the center spindle with film and taped it closed at the top after getting as many of the wrinkles out first. I think I'll use wax paper on future builds as the film is too thin and it was hard to remove the plug after the resin cured. 
The center plug was then slid down over its hold-down post and the nut was tightened over a washer to make things good & tight. That reminds me of a joke: What is the German word for virgin? Gootundtight!
Next up, I cut a strip of wax paper the same width as the thickness of the mold's top half and taped it in position with blue tape. Future builds will use two layers of wax paper, as this first casting took a little more than "friendly" persuasion to get it out of the mold! 
Next, I draped another sheet of sandwich film over everything and tucked it into the corners with a Q-tip and pencil eraser. This is to allow me to pour in magnetite powder until it's full, so I have enough and the casting doesn't come up short. 
This is my jar of magnetite. It's a plastic quart jar intended for peanuts, but I use it for magnetite. It weighs in at around 35 pounds when full. Even though this stuff is "free" at the beach, it took me about 10 hours of trapping and refining to get it pure enough to use in a stator. I built a contraption that holds a large ceramic magnet under a stream of sand that pours down through two slots of an 8" x 16" wood funnel into which I pour dry beach sand. The thing stands on 4 little adjustable legs. 
Here's a picture of it from the side. That big square black thing is a flat ceramic magnet that catches magnetic sand on each side as it pours past, mixed with the blond sand. 
Here's a view from the top. The "funnel" is divided into two halves, separated by the magnet hanging at the apex (bottom). As the sand makes its way by gravity to the opening, half falls on one face of the magnet, while the other half falls past the magnet's opposite side. The magnetite has no hysteresis, so it sticks equally well to either side. When you shove it from a north face to a south face, it doesn't care. 
Here's a shot of that over-laid sheet of film holding enough dry magnetite to fill the space. 
The pre-measured amount of magnetite was then poured into a small plastic mixing container. If you look closely, you'll see where I've marked the outside of the container at the top level of the magnetite. Next time I build a stator, all I have to do is fill the container to the line and I can forego the over-laid film step.
I added enough liquid polyester sanding resin to make the mixture the consistency of brownie mix, then added more until it was like cake mix, then a little bit more to make it barely "runny". I then added 26 drops of catalyst. I was going only for 25, but an extra one dropped in at the last second. I didn't take any pictures of the mixing phase, cause I didn't want to take time, fearing the mixture might decide to "go off" before I was ready. So, anyway, this is a picture of the mixing cup and plastic stir rod after I had poured the mix into the mold: 
And here's the mold holding the magnetite-resin mix sitting in the warm sunshine curing. 
After about a 3-4 hour cure in the sunlight, here's what popped out. I should explain that in actuality, it didn't exactly "pop" out. Next time I'm doubling up on the wax paper and lining the center plug with two layers of wax paper too. This time I had to bang on my creation to get it out of the mold. Kinda like spanking the hell out of a newborn! 
Notice the crisp, clean, straight right-angle sides. This is exactly what I was after. That inside hole is a bit too small for my magnets, which allows me room to zero in on it with my lathe. By cutting this to its final size, I can assure the smallest air gap possible. 
Here's a tight shot of the outside edge. That wax paper will peel right off. The outside doesn't matter much except maybe for looks. It's the inside where it matters. I'll wait until tomorrow before I machine in the wire lands, allowing things to cure for another day. It smells pretty strongly of polyester resin still and may be soft in the middle (like me!). When I get some more done on this project, I'll be back with more pictures and more show-'n-tell. My original design used eight stacks of magnets on a steel base, but it is too hard to align things, so I'm going to go to a 6-sided piece of steel to use as the magnetic-flux-return junction, which will also be attached to the windmill's shaft with set screws. The windmill will spin the "spokes" of stacked magnets as closely as possible to nine "posts" or "lands" carved out of the stator material and wrapped with wire. I'll do a test coil and if I remember, will take some pictures, then wind the whole stator and see what we've got. Until then, hang in there. Edit: I added a couple pictures of the magnetic-sand gathering tool I built. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Im a little lost with what you are doing here, as you call it a stator but have no coils in it. Another tip is to use alfoil as it is easy to shape and will also peel away after its set. I have used it to take a 1/2 mold off things like a dremel tool, by wrapping it in alfoil and glassing over it. works well. Pete. Sometimes it just works |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Downwind Patience my boy, patience. I'm getting to that part, but I have to make sure I let the thing cure enough so it doesn't fly apart when I machine in the hubs where the wires will wrap. I have to cut 9 crescent-shaped "lands" around the inside circle as well as machine the inside diameter to match up to my rotor magnets to create an air gap that is open enough to allow things to spin freely, but closed enough to keep the whirring magnets close to the coil pick-ups. I'll maybe do that tomorrow and be back with more show-'n-tell pictures. That's a great idea using the aluminum foil. I'll have to try that. I can see right away it might be the answer to covering the inside of the outer diameter of the thing instead of using wax paper. I'll have to make sure there are no little wrinkles in it though, cause wrinkles act as anchors when it's time to pop things out of the mold. I'm pretty satisfied with the way it's turned out so far. The plastic film is so thin, even the grain of the wood shows up in the casting that was poured against the wood backing plate. I imagine aluminum foil would just be smooth, which is also fine. When I yanked the mold apart, the sheet of plastic on the bottom of the pour remained in tact and didn't even tear, so I know it's a good "release" agent, which was after all the premise for this whole thing. Thanks again for that good tip. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Mack I see what you are up to now, just a thought on the bobbin, could you have cast the grove into the bobbin using a split mould for the center with a sloght taper on it to release easier. All the best Bob Foolin Around |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
VK4AYQ Hi Bob. Actually, the center spool is already split. I thought it might be a bit of a tug getting it out, because I thought the resin mixture might expand a little and act like a brake. If you look closely at the pictures, you'll see that its about twice the height of the core thickness. I grabbed it with a pair of channel locks and twisted half of it out first, then tapped the other half out the back side. Future pours will see two layers of wax paper around this thing, which should allow both enough room for expansion (if any) as well as a small interface between the wax paper layers. That should afford me enough slippage to get it apart more easily. I purposely made the center spindle smaller than the final inside diameter so I could machine it to fit the magnet rotor. As for molding in all the little notches where the windings will go, I thought it easier to use a fortner bit and cut them on the drill press after first having marked their position off a drawing I constructed with my compass (second favorite tool I own) after dividing a circle into 9 equal parts. In case anyone is wondering how I did that, it's easy. 360* divided by 9 equals 40*. Someone more clever than I took the sin of half that and came up with .342 and I multiplied the diameter of my core (on a paper drawing) by .342 to get the length of one side. Next, I used my digital calipers and set them to the answer, which in my case was 1.92375 (rounded to 1.92) and set my compass to that reading. Next I marked out lines along the outside edge of my stator's circle, placing the point of my compass on the drawing starting at an arbitrary point making 9 equally-spaced lines crossing the circumference and then drew a line from each of those points to the center. Bingo! Nine equally-spaced lines to center. I marked the distance from the center of the fortner bit to intersect the correct position on one line, then spun a circle on the plan using that point and the center to make a circle intersecting all the other lines and thus marking each drill center position so I get all the holes in the core at the correct position. Easy, really. So, the next step will be to drill out all 9 places where windings will go leaving 9 little open spaces and creating an actual stator. I'm using 9 coils and swinging 6 magnets, hoping the odd combination will offset it cogging somewhat. If it cogs, I'll just add two more cores and offset them from the first, then run three individually-rectified circuits down the pole. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Update I've made a few changes to things. I figured out a way to make the center "plug" mold out of rubber mat, so when things cure, all I have to do is pull it away from the edges. Being flexible, it just comes out of the mold making the mold ready for a new pour. Future molds will be constructed from all-rubber sheets laminated together. There will be one mold for the outside and another for the inside. The two halves will fit together. Magnetite-filled resin will be poured in between the two molds, so when things go off, the two mold pieces will simply get peeled away from the finished product. Make any sense? I've heard it said a picture's worth a thousand words: 
Ta-da! This is the latest to pop out of the mold. The little spokes will get wrapped with enameled copper wire and become coils, which the magnets will whir past. Future cores will be made so there is a dimple where I'll drill the mounting holes. Those holes will serve to both hold the core to my lathe's face plate so I can machine the central hole to the correct size, creating the thinest air gap possible, as well as hold it to the actual windmill when it gets that far. Also, I've cut down the coil count from nine to six in hopes to better-accommodate the 6 magnets on the spinning central shaft. There will ultimately be three coil cores, each off-set from the other by 1/18th of a circle, so as one set of magnets is on top of its respective coils, another set is just arriving and yet another is just leaving its coils. This is an attempt to counter the cogging effect. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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