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Author Topic: Educational size rotational molding machine  (Read 49790 times)

poptop

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Re: Educational size rotational molding machine
« Reply #90 on: December 31, 2014, 02:23:18 PM »

Wow, fantastic work John!  Cant wait to see how you finish them out with tips.

Neffy must be just itching to poke a hole in that cap :)

Carry on man....and happy New Year!
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Erratic Wobbler

Dick Stohr

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Re: Educational size rotational molding machine
« Reply #91 on: December 31, 2014, 08:54:16 PM »

Those are supper looking and I can not wait to see one up close, and LOVE the mostly blue color. VERY WELL DONE JOHN!!!!!!!!!!
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silvertop

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Re: Educational size rotational molding machine
« Reply #92 on: January 01, 2015, 10:42:51 PM »

WOW!  I'm impressed, and very pleased that someone more knowledgeable that myself is now in charge of the machine!  All I ever did was fill one half of the mold, and then assemble it.  I did always add three or four small C clamps around the rim to better seal the connection point - not sure if I included the little C clamps when I sent the machine.  Not sure where I got the info, but my understanding was that the vent hole was necessary to vent the hot gas from the process, and needed to extend to the center of the mold to avoid powder getting into the tube.  I'm amazed at how good the parts of the machine look after whatever you did to clean them.  I pretty much just used the machine as it came to me, and I had no plastics experience or knowledge.  I know I used some bottles of very finely powdered plastic - I think supplied by the folks who made the machine???  Your attention to detail should give you much better balanced tops than I was ever able to achieve.  Hope I can get one of the tops when you get it all worked out!  Thanks to all who contributed to this project, and especially to John!
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Don Olney
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cecil

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Re: Educational size rotational molding machine
« Reply #93 on: January 02, 2015, 02:02:34 PM »

I have to do the same thing with the Koma, top that I got for Christmas. Put the hole I want in and make a new tip. I'm waiting for my son to go back to work then I have access to the machine shop. You have to know how to do this kind of work, and have the equipment to do it. You have to follow the rules PERPENTICULARITY AND TRUE POSITION AND CONCENTRICITY. And that makes it close to having a good top.
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Neff

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Re: Educational size rotational molding machine
« Reply #94 on: January 02, 2015, 11:46:49 PM »

poptop you are right, i want to see a hole... nevertheless, the closed crown does look pretty slick!

Awesome work as usual John, I wish I could witness first hand
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the Earl of Whirl

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Re: Educational size rotational molding machine
« Reply #95 on: January 03, 2015, 07:15:12 PM »

I was questioning johnm about hot air filler molding.

He wrote back "Since I'm just using hot air welding to fill voids, I want good localized control of the heat and am using a hot air soldering station we bought a long time ago when I had to do a lot of surface mounting of electronic components for one of the experiments.  I'm not sure if a hair dryer gets hot enough for melting HDPE but a heat gun like plumbers etc. might use would certainly have enough power."

I have been looking around and doing a little research.  Some are not that expensive.  I sure would like to get one and try it.  It would open up some more doors for me.

Thanks for your help, johnm!!!
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johnm

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Re: Educational size rotational molding machine
« Reply #96 on: January 05, 2015, 08:51:37 PM »

Your attention to detail should give you much better balanced tops than I was ever able to achieve. 

Don't sell yourself short Don.  The tops you made and the balance you achieved were at the limit of success for this technique.  My success ratio will not be better than yours.  Without complicated features for heat control at various places on the mold as Kirk suggested, the tumbling action of the material inside the mold provides only an approximately uniform distribution of material around the mold.  In reality there is no control over how the material contacts and bonds to other material during the melt cycle.  Vast differences in wall thickness are likely which in addition to providing unbalanced weight distribution, causes non-uniform shrinkage which can distort the shape and contribute to a poorly spinning top.

As Poptop and Neff suggest, these tops are begging to have the crowns opened up (the diet mod).  The novelty of the sealed hollow top is nice so any that are coincidentally balanced will not be opened, but those with poor balance will get the cap turned opened to allow the installation of balancing putty or perhaps even the removal of obviously misplaced plastic.

My attention to detail is most likely unnecessary and over kill.  Think about having a mile of highway to pick up litter and working with a toothbrush to clean up one foot. ::)

On Wednesday the molder displayed an issue with one of the chains that drives the rotation mechanism.  I took that as a sign to move on to the tips for a while.  I made a prototype tip from steel to check the play and decided that steel was the right choice.  The step at the joint between the top body and the tip will be filed flush with the tip before everything is complete.



To continue with the description of the construction, my approach to making a batch of tips for these top followed the sequence in these pictures of the tip evolution and the basic set up on the lathe.  For making one tip at a time I would machine the whole tip in one mounting on the lathe and machine it out of the bar of stock.  For a lot of them it is faster to cut a bunch of blanks from the stock, set up for each profile, and perform that profile cut on each blank before proceeding to the next profile.  My first set up was to machine the hub that fits into the top body and drill and tap a hole to accept a threaded stud.  Next was to cut the first sloped surface which will match the body angle of the top.  Third was to cut the second angle which defines the other side of the diabolo style neck.  Last was to machine the point.  The point was actually machined to a sharp which was filled to a round such that is felt good spinning in the hand.



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ta0

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Re: Educational size rotational molding machine
« Reply #97 on: January 06, 2015, 11:02:53 AM »

Those metal tips are nice! I was expecting plastic tips on these: you have worked hard! You should price them accordingly.

I prefer mine with a closed crown so next time I visit Jim I can use it near a body of water without fear ;D

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dazzlingdave

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Re: Educational size rotational molding machine
« Reply #98 on: January 06, 2015, 11:14:26 AM »

Awesome work!
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Larry D.

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Re: Educational size rotational molding machine
« Reply #99 on: January 06, 2015, 11:16:05 AM »

I prefer mine with a closed crown so next time I visit Jim I can use it near a body of water without fear ;D

Even though the top may float you should take a net along with you just in case. 
Unless of course you are willing to go for a swim in the Seine river.  ???
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Sabaspin

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Re: Educational size rotational molding machine
« Reply #100 on: January 07, 2015, 03:37:11 PM »

WoW.
This is an awesome thread!
Really enjoy reading about the process.
Thanks for posting.
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johnm

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Re: Educational size rotational molding machine
« Reply #101 on: January 13, 2015, 07:54:13 PM »

I have depleted my swarf supply and done a performance cull based on balance in the hand and on string.  Although most of the tops made are quite playable, these pictured are the ones with a balance that I'm comfortable sending out to project contributors.  Many have surprisingly good balance and the remainder have a noticeable vibration in the hand but not upsetting (to me at least).  I will point out (or warn depending on your perspective) that many of them have an interesting wobble to the motion of the volume of the top as it spins but minimal vibration suggesting the distribution of mass is quite different from that which the shape implies.  This visual wobble does not seem to interfere with play but could be distracting to some players. 







I'm waiting for some cord that I hope will be appropriate for these tops.  In the next few days I'll be sending a personal message (PM) to the contributors with more details about how thing will likely proceed.  Thanks for following along.
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the Earl of Whirl

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Re: Educational size rotational molding machine
« Reply #102 on: January 13, 2015, 08:35:29 PM »

So cool.  Or, as I have learned on the Spanish forum, muy chulo!!!

Thanks for that great display and the great pics.
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ta0

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Re: Educational size rotational molding machine
« Reply #103 on: January 13, 2015, 08:48:10 PM »

What a gorgeous group of tops!
You should be very proud of your work John!
Thanks for taking over this project and rescuing this part of spintop history (and in the process writing a new chapter)!
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Sabaspin

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Re: Educational size rotational molding machine
« Reply #104 on: January 13, 2015, 09:00:34 PM »

Incredible work Johnm!
Beautiful tops.
Many thanks for your dedication to this project.
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