Re: Warpage of Resin Castings (was Virtual RPM Meet?)


Andy Carlson
 

Though JP's post seems to be a BCC to this group, resin casting warpage is certainly a common problem among STMFC'ers. For less drastic warpage than JP describes, I have a simple method of straitening warped castings.

I have a large aluminum stock pan with a very flat bottom which when heated over a low flame on the range top is hot enough to allow relaxing of the resin parts. I simply press the resin parts down gently with my finger tips, which removes the warp and leaves the parts flat. Not a lot of heat is necessary, as you are not trying to sear a pork chop.

I remove the pan from the heat and upon cooling remove the now warp-free casting. I believe that this action also contributes to heat curing and the part is now more warp-resistant than before.
-Andy Carlson
Ojai, CA


From: "'JP Barger' bargerjp@... [STMFC]"
To: resinfreightcarsW@...; STMFC@...
Sent: Tuesday, July 28, 2015 8:22 AM
Subject: [STMFC] Warpage of Resin Castings (was Virtual RPM Meet?)

 
 
Rich & Tony et al,
Your description of resin castings flattening (dewarping) when heated and rewarping when cooled reminded me of my own similar observations when I began with early resin castings. But as both of you probably figured out, if you restrain the castings while they are cooling, the will remain in their intended configuration. This is easily accomplished by carefully putting one or more castings between two smooth surfaced flat  heavy pieces of metal. A resin sandwich, so to speak. The pieces of metal and castings are put on a shallow aluminum baking tray with a rim and placed on an oven shelf. The oven can be preheated. A little experimentation with a scrap piece or two of the SAME resin material can determine the hottest setting for your particular oven, and the time needed to straighten your kit parts. When your parts have straightened, take the baking tray out of the oven and put it on a cooling pad (oven mitt or two or equivalent).Wait until you can touch or handle the metal pieces or a little longer and then uncover the castings They should be back in their “as cast” configuration. If not, recycle them with the same process.
 
Where to get the requisite pieces of metal? All machine shops, especially those focused on milling, have cutoff end pieces that they sell to used metal dealers. Make friends with your local machine shop superintendent: he’ll sell you a couple of pieces at scrap price or a little more, or perhaps even contribute them to more accurate resin models.
 
Another way to get these pieces of metal. Go to your local used tool dealer. These good folks often have cutoff pieces coming from defunct machine shops whose assets they purchased to get the hand and small power tools for resale. ThatR! 17;s how mine appeared. They’re  steel, about a half inch thick and about three by seven inches in the other dimensions. It’s as if they were designed for the job!
 
I considered not writing this little piece, Tony and Rich, because with you two, I’m probably sending coal to Newcastle. I’m reasonably sure you both already know how to straighten resin castings. But then I thought there must be some new folks doing this, so it would make sense to suggest a way to successful flattening to them.
 
Keep up  the GOOD WORK!     JP


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