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Author Topic: Educational size rotational molding machine  (Read 49770 times)

Neff

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Re: Educational size rotational molding machine
« Reply #60 on: December 20, 2014, 06:52:32 PM »

YAAAAAYYY!
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ta0

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Re: Educational size rotational molding machine
« Reply #61 on: December 20, 2014, 08:07:40 PM »

This is wonderful! I am very excited!

Don did not want to charge any packing expenses, so the total amount I sent him was $350.
There are still about $48 on the paypal account. I will send John a check to pay for supplies.

Thanks to everybody who contributed to this project and specially to Don and John for making it possible!
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the Earl of Whirl

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Re: Educational size rotational molding machine
« Reply #62 on: December 20, 2014, 08:08:08 PM »

Merry Christmas, johnm.  And Merry Christmas to the rest of the top spinning world.  I think we all may have just received a top gift!!!
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jim in paris

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Re: Educational size rotational molding machine
« Reply #63 on: December 21, 2014, 02:46:08 PM »

YIPPEE!!

I image a night at the physics lab

close up on
FranKenJohn busy and pausing on molecular tea
slow pan on
the Roto Molder in full action
low angle shot
the were-tops suddenly getting back to life
blurred view of
more coffee mugs waiting for re-incarnation

.....................////////////////////////cut


jim :-X
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silvertop

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Re: Educational size rotational molding machine
« Reply #64 on: December 23, 2014, 10:51:07 PM »

So glad it arrived safe and sound.... have you plugged it in yet?  Be sure to call if you have any questions.  As I recall, it takes a bit of creativity to get the top mold between the plates.  I had it made as big as I possibly could could fit.  My less expensive trucker took a while to get a run to Ohio, but once he picked it up it was there in under 12 hours!
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Don Olney
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johnm

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Re: Educational size rotational molding machine
« Reply #65 on: December 24, 2014, 09:25:33 PM »

Here is an update on the rotomolder at its new home in Cincinnati.

On Saturday afternoon (it arrived around 10:00 am), I did give the electricals a once over and was comfortable giving it a test run.  The motor worked fine and without the motor on I tested the heating elements to map out the control range of the thermostat.  It seems the original dial type thermometer had long since disappeared so I stuck a thermocouple sensor into the chamber through the port with the thermostat sensor.  The control temperature range for the system is from roughly 125 C to about or slightly above 190 C so it is designed for polyethylene plastic as suspected.  I say about or above because at that temperature the evolving smoke got a bit worrisome so I stopped testing and opened the oven door next to the fume hood.   Turns out someone had been following the instructions to lubricate once a day all the bearings inside the chamber with light oil (printed on the aluminum casting of the rotational arm and again on a decal on the control panel) so there was oil on most surfaces.  Additionally there was a lot of plastic residue on most surfaces as well.  This is not surprising since static electricity it a real problem when dealing with these powders, and the mold flanges have sizable gaps when together  (not to mention a vent hole) so a lot of powder can fall out (and perhaps be thrown around as the mold is spun) before it melts.  So with all this contamination and the smoke issue, I thought it prudent to take everything apart and clean it up before proceeding.  With a lot of hand scraping, glass bead blasting, and some sanding everything cleaned up pretty well.  I also spent some time flattening the mold flanges to get a better joint but it is not close enough to seal so it will get used with a gasket in place to seal that joint.  I also modified the mount in the rotary assembly somewhat to more conveniently hold the mold.  Here are a couple before/after cleaning photos of the oven and the removed rotary parts.





I finished the last of the first round of modifications today and this evening had the initial test run with plastic in the mold.  As source plastic, I’m using lathe swarf from making HDPE tops.  Starting out this is a stringy mess but a little time with a scissor/shear it becomes fairly small flakes and 4 or 5 times the mess.   I was pleased to see the effort was not a complete failure, but it is not a total success either.  The vent tube is stuck in the top so I’ll be redoing the whole capping plug differently for the next run.  The surface of the top is not particularly smooth.   The small flakes have not bonded completely at the surface so it is a bit fuzzy and there are small voids plus one significant void at the flat where the tip goes.  Perhaps with a bit higher temperature and maybe a bit more time at melt temperatures these surface conditions could improve.  The void at the tip is likely going to be hit or miss because the size of the flakes may prevent material from getting to that narrow section before it melts and forms a dam, but I can probably patch that after the fact.   Anyway the exercise served its purpose of testing the machine and pointing out some needed design modifications to make using it a little easier.  Again a sort of before and after with a top body that Don had cut in half and the first attempt from UC.
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ta0

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Re: Educational size rotational molding machine
« Reply #66 on: December 25, 2014, 01:34:44 AM »

On the after photo the mold looks brand new!  :o

It could not be in better hands!
Great things will come from this machine!
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johnm

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Re: Educational size rotational molding machine
« Reply #67 on: December 25, 2014, 09:42:12 AM »

The top mold is spun copper?

After cleaning it is easy to recognize how the mold halves were made.

The body is a 1/8 inch thick brass ring flange silver soldered to a 0.040 inch thick brass sheet rolled into a cone which has been silver soldered at the seam.  If you look carefully at about the 4 to 5 o'clock position in the picture you can see a solder line from the ring to the small opening on top where the cone was butt joined to itself.



The cap is a 1/8 inch thick brass ring flange silver soldered to a 0.040 inch thick brass sheet metal-spun into its shape (like the Trompos Space Mercurio and Neptuno top bodies are metal spun).


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lincolnrick

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Re: Educational size rotational molding machine
« Reply #68 on: December 25, 2014, 11:32:12 AM »

You're doing such great work with this machine.  The before/after shots are amazing.  Just reading what you've done and what your ideas are for upgrading the workings of the machine make me believe that indeed, great things could be coming.  Thank you for preserving this piece of technology.
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the Earl of Whirl

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Re: Educational size rotational molding machine
« Reply #69 on: December 25, 2014, 10:41:43 PM »

Wow!  Like lincolnrick said, those before and after shots are stunning.  Very very nice work johnm.

Thanks for sharing your progress.  It is fun to hear.  Good luck as you continue on with this project!

This is certainly another wonderful Christmas message along with Daveid's superglue/string tops.  What a great finish to a great day.
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Dick Stohr

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Re: Educational size rotational molding machine
« Reply #70 on: December 25, 2014, 11:42:17 PM »

Ditto from me too! WOW !!!!
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johnm

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Re: Educational size rotational molding machine
« Reply #71 on: December 26, 2014, 08:15:41 PM »

The second round of modifications is finished.  I've replaced the threaded rods and nuts frame work for the inner rotational frame with aluminum standoffs/spacers to make things a little more rigid and easier to get parallel and now the installation/removal of the mold requires just moving 4 wing nuts before pulling the spider and upper clamping plate.  The new capping plug has an alignment hub which fits into the upper clamping plate so the form is now fully confined and aligned by the two plates when installed.  The plug also has a 1/4-20 screw extending into the top body instead of the venting tube thus eliminating the venting feature which I think is not necessary.  The threaded hole left behind in the plastic may or may not be used for mounting the tip.



I didn't notice before the previous update but upon pulling the vent tube from the first top and shaking the top it is obvious there is un-melted plastic remaining inside.  With a slight increase in the thermostat set point and doubling the time at the set point to one hour (the built in timer is only for 30 minutes which is I why I tried that time first) several issues have cleared up.  All the plastic melted and the surface quality is greatly improved.  There was still a bit of a void where the tip installs but I'm not sure there will be a fix for that, so I'll try again with these parameters to check the reproducibility of the result.  I had weighed out about 220 grams of raw materials but the top is about 200 grams so I suppose during the filling process I had lost more than I realized in spillage.  The material was packed in rather tightly so I'm not sure the extra 20 would have fit.  For reference the body that Don sent along is 120 grams--anyone else have a weight for a top body without a tip?



If I get some consistent results with the new parameters and the tip region is reproducible, I'll begin thinking about the tip design.  I'm not sure what material the tip will be.  The top is on the light side in my opinion, so I don't want to over weight the tip end with a really heavy tip.  Some possibilities include steel, aluminum, or a hybrid based on HDPE melted onto a piece of steel all-thread.
« Last Edit: December 26, 2014, 08:20:51 PM by johnm »
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the Earl of Whirl

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Re: Educational size rotational molding machine
« Reply #72 on: December 26, 2014, 10:22:02 PM »

Wow!  So cool.  I do have a top like that without a tip.  I do not have a scale nearby, though.  I will have to look around.

Thanks for all your work johnm.  Thanks, also, for all your reporting.  After a long day of trying to catch up, I found it very relaxing to see your post!
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ta0

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Re: Educational size rotational molding machine
« Reply #73 on: December 26, 2014, 11:16:03 PM »

Those sound like great updates to the machine.

I wonder if by closing up the venting hole there would be a partial vacuum inside the top when it cools down.

I weighed one of Don's tops without the tip and it measured exactly 130 grams.
Do you think he used less material or lighter plastic? On the one he cut the walls look pretty thick.
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jim in paris

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Re: Educational size rotational molding machine
« Reply #74 on: December 27, 2014, 01:55:32 AM »

thank you very much for the report , John !
beautiful work, i'm elated ...
and the prototype came out really nice
does is smell a lot ? do you wear a protection during the cooking time ?
about the tip : the " HDPE melted onto a piece of steel all-thread" works really well on your other tops : on mine, the plastic at the tip is barely scratched after a year of use

wishing you the best for the next steps ;)

jim

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