Author Topic: Stupid Mistake 111: When Things Get Routine  (Read 1029 times)

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pnolan48

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Stupid Mistake 111: When Things Get Routine
« on: August 18, 2013, 10:00:34 PM »
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It's not boredom, it's inattention that causes problems.

I had my casting routine for the Edna G hull down pat. Place the mold slightly to my left. Select one 10 oz.plastic cup, two 3 oz. dixie cups, one popsicle stick stirrer. All of them new and clean, lest there be some residue. Set the egg timer to 0:00.

Shake Part A of casting material thoroughly and pour about 2.7 oz. into one dixie cup. Wipe the lip of the bottle with a waste towel, and move it from my right side to my left side. Move the dixie cup toward the center of the table so I won't tip it in the next step.

Do exactly the same with Part B. There's all sorts of flowers and stems on the dixie cups to measure how high to pour. Besides, if I'm 98:100 in volume, it really won't make much of a difference.

The intent is to pour the two dixie cups into the larger plastic cup, side by side so the components start to mix immediately, then mix for about ten seconds with the stick, then pour slowly into the mold, with other molds for small stuff at the side for any excess material.

OK, go do something else for a minute or two while the bubbles at the surface of the dixie cups subside a bit. I never knew whether this helped or not, as a 6 oz. pour into a hull mold usually results in one huge bubble somewhere but no smaller ones. When you are my age, going away to do something may mean you don't come back to exactly where you thought you would be. So--

Ready to go. Hit the timer. I have about 2:45 to pour the mixture very slowly into the hull mold, which has lots of undercuts and thin strakes. If I do it slowly enough, there's few problems with bubbles. If I rush it, there will be two or three voids in the strakes--not a big problem, but easier to avoid by mixing quickly and pouring as slowly as possible, before the resin starts setting.

So, pick up the two dixie cups and start to pour them . . . into the mold, instead of the mixing cup!

OMG! Panic sets in, and clear or even muddled thinking stops. I drain the mold into the mixing cup, spilling the mixtures all over the table, thus creating another mess in a few minutes, when it sets (or doesn't set, which is worse). I mix whatever is now in the big cup frantically, and pour it back into the mold, figuring any residue left in the mold would mix with it. I vibrate the mold vigorously.

Right.

Of course this did not work. I should have just stopped, thrown the casting materials out, tried to clean out the mold, and started over. Hindsight is always correct.

When I pulled the mess from the mold, I had--well--a mess. Gooey unset casting materials in the deepest parts of the mold tore out critical parts, making the mold unusable. This was a Smooth-On OOMOO mold, with little tear strength, and I have lots of OOMOO to do another mold, so it's not a disaster, especially since OOMOO is kind to masters. The mold is only about 12 oz., so it's not expensive to replace.

But I got only 15 casts before my mistake, and probably could have got 25 or more. I have to make a new molding box, modify the master for thicker rails, and start again. But that is the subject of Stupid Mistake 112.
« Last Edit: August 18, 2013, 10:07:55 PM by pnolan48 »

Ed Kapuscinski

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Re: Stupid Mistake 111: When Things Get Routine
« Reply #1 on: August 21, 2013, 09:55:07 AM »
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I think it'd be awesome if there was a "modeling whoopses" blog somewhere.

Sorry to hear this pete!

Bob Bufkin

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Re: Stupid Mistake 111: When Things Get Routine
« Reply #2 on: August 21, 2013, 10:14:39 AM »
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There was a thread here a few years back on big whoops, f-ups, etc. 

pnolan48

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Re: Stupid Mistake 111: When Things Get Routine
« Reply #3 on: September 19, 2013, 05:29:09 PM »
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I did my Stupid Mistakes thread over on Trainboard for about 100 episodes.