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Author Topic: Got Milk (jugs)?  (Read 45211 times)

johnm

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Got Milk (jugs)?
« on: May 29, 2010, 08:56:38 PM »

You may never look at a milk jug the same way again. ;)

I'd been thinking about using milk jugs as a source of cheap plastic for learning about injection molding and making some plastic tops which might be less likely to break on our hard surface play areas.   After harvesting a large piece of aluminum from some scrapped equipment (aerospace engineering has really large experimental equipment), I designed a two part spintop and the molds to inject them based on the size of the aluminum stock.  I had planned to do the machining myself but could not pass on the offer of one of the shop guys to make a piece here and there during slow times.  About two or so weeks ago, the final components of the molds were completed.  Since I haven't finalized the design of the injector and I couldn't stand letting the molds go unused, I tried casting with them in an oven by simply melting the plastic directly in the lower part of the mold and pressing the upper part into the melt and letting the assembly cool.  Although there are some problems, it works well enough to make some very playable tops.

Here's a pic of the molds and some of the milk jug tops.  The molds are open to show the assembly on the bottom with the additional mold-half stacked above with a formed part installed for demonstration.  On the right is one spinning top assembled with tape and its string with milk jug lid button.

One of the problems is the shrinkage of the plastic upon cooling.  I knew it would shrink but had no idea about how to design that into the mold so I just designed it to my intended shape.  For the cap in the mold on the right you can easily see the gap between the mold and plastic.  Another problem is air that gets trapped when the bits of plastic melt.  These air pockets can leave blemishes (hard to see in the picture) on the cooled surface and can leave major hidden voids which affect the balance.  Because of voids and variable squeeze out the weight is not very consistent between tops but a cap and base are around 60 grams and a milk jug with the paper label cut out is also about 60 grams so 1 jug = 1 top. :)

The blow molded HDPE (high density polyethylene) of the milk jugs doesn't melt together really well but what works better is injection molded HDPE such as that found in milk crates and 5 gallon pails.  These have the added advantage of coming in lots of different colors as demonstrated by some of the tops cast from 2 liter bottle crates, bread crates, pails, and pallets (basically anything with a recycle number 2).


For a size comparison here from left to right are
1. turned HDPE from a melted pail, 2. Spintastics Trompo Grande, 3. Cast HDPE, 4. Duncan Ripcord, 5. Spintastics Gladiator, 6.Mexican 5 Estrellas Atomo


Currently, the tops with the tips in the middle pic are the ones we've been beating around the halls and have had no casualties.  Even Aaron the top-destroyer hasn't broken any while learning suns, so you know they've been launched and slammed into concrete walls, pipes, hard floors, and steel door jambs.
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robtsou

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Re: Got Milk (jugs)?
« Reply #1 on: May 29, 2010, 09:57:42 PM »

That's pretty awesome!  How are you melting all of that plastic?

Rob
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lincolnrick

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Re: Got Milk (jugs)?
« Reply #2 on: May 29, 2010, 10:08:06 PM »

I am impressed.  In the last pic, the shape reminds of a Gates.
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poptop

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Re: Got Milk (jugs)?
« Reply #3 on: May 29, 2010, 10:21:54 PM »

Wow! On to something new and exciting and awesome; wow.

I totally dig the solid red & solid blue ones...

I finally tried to turn a few tops over the past week, but still working it out...
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Erratic Wobbler

ta0

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Re: Got Milk (jugs)?
« Reply #4 on: May 29, 2010, 10:22:34 PM »

My kind of recycling!
I am speechless! Amazing work, John!
« Last Edit: May 30, 2010, 01:00:56 AM by ta0 »
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Neff

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Re: Got Milk (jugs)?
« Reply #5 on: May 30, 2010, 12:25:11 AM »

SO COOL!!!  I love the multi-color.  I may start warehousing #2 plastic.  I am a customer should some become available!
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SpinQueen

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Re: Got Milk (jugs)?
« Reply #6 on: May 30, 2010, 12:51:32 AM »

Holy Lactating Spin-Tops!! ...I mean WOW!!!  These are freakin awesome!!!  Love the ingenuity, colors, shapes, the fact that the two halves tape together evenly  (unlike snap together tops).....and I love the matching milk cap button :)  Reminds me of when Pedro's came out with tire levers and water bottle cages made from recycled milk jugs.  Mucho Props!  I'm your biggest fan :)
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Java

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Re: Got Milk (jugs)?
« Reply #7 on: May 30, 2010, 08:15:57 AM »

Wow, John, those are seriously cool! I love the shape. I'm with Chris, I've got a check here with your name on it if/when you're ready to part with a few.

Have Fun,
Tom
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johnm

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Re: Got Milk (jugs)?
« Reply #8 on: May 30, 2010, 10:57:18 AM »

How are you melting all of that plastic?
For the molds, the plastic is all cut up with a tin snip (to avoid all the little fuzzies generated by band sawing) to bits about 1cm x 1cm and heated directly in the mold in an oven at about 180 Celsius.  When the initial charge of plastic melts together and creates some space, additional bits are added to ensure the form is overfilled.

For the larger turned tops, I have an old copper beaker which I wipe with some silicon grease as a release agent and fill with band sawed chunks (the fuzzies don't get in the way here) and refill as the stuff melts down.  I've only made two 'blocks' of the stuff and both times there was a single major void inside the piece.  The first time the block was unusable so is will be remelted.  The second one became the pictured top which still has a small portion of the void inside which contributes to some wobble.

I am a customer should some become available!
I've got a check here with your name on it if/when you're ready to part with a few.

Thanks for the interest.  Unfortunately, I don't have any intentions of selling these tops.  I play/make/think about tops strictly as a hobby for fun.  I know that if I start selling tops (plastic or wood), the fun will be replaced by stress and ruin the experience for me.  Besides that, my casting process isn't really reliable and the time it takes to make a single good top and tip (plastic prep, heat up, cool down, remove squeeze out, prepare for tip mounting, machine tip, etc.) would merit a crazy price for the simple toy it really is.  Maybe if the injector turns out to be a little more reliable, these could be souvenirs for visitors to the Cincinnati spinners who meet some minimum requirements like being a full member of this board, having visited the Hall of Fame, and having boomeranged Charlie Brown. ;)
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ta0

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Re: Got Milk (jugs)?
« Reply #9 on: May 30, 2010, 11:31:55 AM »

Maybe if the injector turns out to be a little more reliable, these could be souvenirs for visitors to the Cincinnati spinners who meet some minimum requirements like being a full member of this board, having visited the Hall of Fame, and having boomeranged Charlie Brown. ;)
Put my name on it!  ;D I'll try to swing it this year, if not next, I promise!  8)
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MatiasStuntMan

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Re: Got Milk (jugs)?
« Reply #10 on: May 30, 2010, 11:50:08 AM »

WOW Johnm, that is pretty cool defenetelly a GREEN top, that journey tru plastic injection is fascinating, thanks for sharing
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agentsac

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Re: Got Milk (jugs)?
« Reply #11 on: May 30, 2010, 12:45:41 PM »

neat.
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robtsou

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Re: Got Milk (jugs)?
« Reply #12 on: May 30, 2010, 12:59:38 PM »

What are you using as your heat source to melt the plastic? I'd totally want to try melting some plastic down and turning it. Maybe even make a mold if I could get the time together.

Rob
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johnm

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Re: Got Milk (jugs)?
« Reply #13 on: May 30, 2010, 03:10:29 PM »

What are you using as your heat source to melt the plastic? I'd totally want to try melting some plastic down and turning it. Maybe even make a mold if I could get the time together.

Rob
I've got access to a scientific research gravity oven, but 180 C = 360 F is well within range for a common household oven.  I have noticed a slight hot plastic smell (if you know what I mean) so use of the kitchen oven may be upsetting to other residents but I bet people are trying to give these things away for removal so a suitable 'garage' oven may be had for cheap.  (Perhaps an appliance dealer that sells 'with removal' or a thrift store would sell and deliver a used oven cheaply.)

HDPE turns nicely with sharp tools, but with a nice smooth cutting motion on the wood lathe, super long tough/strong shavings are made that sort of weave together which can then loop around the tool and your arm and instantly wind up around the spindle possibly pulling you or the tool with it.  I frequently stop to clean up before this happens but have had it wrap around the live center enough to lock it up.  It is great fun and a nice change from the dustiness of wood and the uniform density/consistency is easy on the arms.  If you slip (I have) it gouges easily :'( but it cuts so easily that catches are much less aggressive than with wood.
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the Earl of Whirl

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Re: Got Milk (jugs)?
« Reply #14 on: May 30, 2010, 03:29:01 PM »

I am away from the board for a few hours and look at what I miss!!!  Wow is right.  Now I need to figure out how to get down there before I go to San Antonio.
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Happiness runs in a circular motion!!!
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