Re: Epoxy-filled toroids

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org> 

Indeed, the epoxy used WAS for model building.  The Society of Physics 
Students used this epoxy to build cedar strip canoes in the past few 
years.  I don't know the age of the stuff I used, but suspect it had been 
sitting on the shelf for a few years.  The pump spigots were leaking air, 
especially on the resin pump.  So I ended up "guessing" how much actually 
went in, and actually thought that I had not added enough hardener within 
20 minutes of pouring.  I had set the lathe on "medium" to try to prevent 
much movement of the stuff inside the toroid, and the autopsy showed that a 
fairly good coverage with about a 2" wide band around the circumference of 
the toroid.

I had considered using fiberglass and epoxy to cover the outside, but this 
seemed to me to be far too much work with all the sanding and dust and 
elbow grease.

Thanks for the feedback!

Mark Broker
Chief Engineer, The Geek Group


On Tue, 13 Jan 2004 19:02:26 -0700, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: brent meyer <res095fx-at-verizon-dot-net> The more disparate the 
>mix ratios on an epoxy, the softer it usually it ends
>up curing.  You need to use an epoxy rated for application in thick films if
>you want complete hardening in something with this much volume.  Table top
>(decoupage) epoxies are somewhat aerobic, and need airflow to cure properly.
>Use a resin rated for mold building, and you will get better results, though
>be aware of the fact that motion will sometimes inhibit the formation of
>polymeric bonds, and you will end up with a lump filled with voids.  Better
>to use a high density (20-30lb/ cu ft) buildup foam instead of the epoxy.
>Look for a supplier who sells fiberglassing/ composite materials.
>
>  > From: "Tesla list" <tesla-at-pupman-dot-com>
>  > Date: Mon, 12 Jan 2004 07:32:12 -0700
>  > To: tesla-at-pupman-dot-com
>  > Subject: Epoxy-filled toroids
>  > Resent-From: tesla-at-pupman-dot-com
>  > Resent-Date: Mon, 12 Jan 2004 07:58:26 -0700
>  >
>  > Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org>
>  >
>  > Well, I was able to make a "prototype" this weekend as I had hoped.  My
>  > results weren't spectacular but show promise.
>  >
>  > I mounted the 4x18" aluminum drier duct toroid off the end of an old metal
>  > lathe and added about 3-4 cups of two-part "System Three" (I don't 
> recall a
>  > manuf.) epoxy through a hole in the inside of the toroid.  It was a little
>  > messy since I made the hole too small and ended up with a bit dribbling
>  > down the side.
>  >
>  > I set the lathe to spin on its lowest speed - about 60RPM I think.  I let
>  > it run for about an hour, then turned it up a bit to about 300RPM.  I did
>  > add a band of 1" masking tape to the major diameter of the toroid to
>  > prevent it from flying apart from centrifugal force.  I let it run on
>  > "medium" for about 1.5 hours or so, at which point I had to shut it off to
>  > leave the shop.  The epoxy in the bowl hadn't set yet, but was in the 
> "very
>  > thick and gooy" stage.  There was still a heavy spot under the
>  > "fill  hole," so I rotated that to the top of the toroid.
>  >
>  > When I came back in the next afternoon, the epoxy was set, but pretty soft
>  > and pliable.  But the heavy spot was now at the bottom.  It was too
>  > lopsided IMO to keep, so I decided to do an autopsy.
>  >
>  > Indeed there was a huge puddly of epoxy on the "bottom" with a several 
> inch
>  > wide band of epoxy around the major diameter.  However, I found that even
>  > the "sides" of the toroid had a very thin coating, which seemed to add
>  > significantly to the dent-resistance.
>  >
>  > So I think I've demonstrated that it's possible, but needs some more
>  > investigation.  I think that I ran it too fast to begin with - something
>  > closer along the line of 5RPM probably would have spread the stuff 
> around a
>  > little better.  I also definately used too much epoxy for the 4x18" toroid
>  > - half the amount I used would have sufficed.  Next time I get back to
>  > Platteville I'll try again.
>  >
>  > Again, the only thing I wanted this to do was to add to the 
> dent-resistance
>  > of aluminum drier duct toroids.
>  >
>  >
>  > Regards,
>  >
>  > Mark Broker
>  > Chief Engineer, The Geek Group
>  >
>  >
>  > On Sat, 10 Jan 2004 12:18:34 -0700, Tesla list <tesla-at-pupman-dot-com> wrote:
>  >
>  >> Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org> Ian, and others:
>  >>
>  >> I wasn't planning to fill the toroid, actually, and really wasn't too
>  >> interested in other types of foams.  I only want to "partially fill"
>  >> it.  For instance I just made a standard 4" drier duct toroid last night
>  >> (4x16.5")  I was thinking that I could mount the toroid vertically
>  >> (horizontal axis) in a lathe (or some motor).  I could pour some epoxy
>  >> through a smallish hole on the inside of the toroid by using a funnel.  I
>  >> would only add about 3 inches worth of epoxy.  I could then turn the 
> lathe
>  >> on "highish" to spin the epoxy to the outside via centrifugal force until
>  >> the epoxy sets (perhaps an hour or two)  When the epoxy hardens, it has
>  >> filled the big crevices in the periphery of the aluminum drier duct,
>  >> preventing damage where it is most likely to occur.
>  >>
>  >> I bought an extra 4" duct to experiment with and have another back in the
>  >> shop at my alma mater with the rest of my TC in progress.  If the Society
>  >> of Physics Students left the epoxy from their canoe-making around, I'll
>  >> try this and maybe a variation, and report back on Monday.
>  >>
>  >> TTYL
>  >>
>  >> Mark Broker
>  >> Chief Engineer, The Geek Group
>  >
>  >
>  >