Warpage of Resin Castings (was Virtual RPM Meet?)


JP Barger
 

 

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. That’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


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



mwbauers
 

Once the warpage is corrected and after the model has been built....... Do some models warp eventually again???

Mike Bauers

On Jul 28, 2015, at 10:39 AM, "Andy Carlson wrote:

Though JP's post seems to be a BCC to this group, resin casting warpage is certainly a common problem among STMFC'ers.


tyesac@...
 

Mike,
 
I've only built around 150 - 200 of them, and so far, I haven't seen that warpage problem reappear.  That includes some of the early resin kits made from the metal filled dark grey resin and a few cast in the early yeloowish aluminite resin.
 
 
Tom Casey
 
 

-----Original Message-----
From: Mike Bauers mwbauers55@... [STMFC]
To: STMFC
Sent: Thu, Jul 30, 2015 9:43 am
Subject: Re: [STMFC] Warpage of Resin Castings (was Virtual RPM Meet?)

 
Once the warpage is corrected and after the model has been built....... Do some models warp eventually again???

Mike Bauers


> On Jul 28, 2015, at 10:39 AM, "Andy Carlson wrote:
>
> Though JP's post seems to be a BCC to this group, resin casting warpage is certainly a common problem among STMFC'ers.


mwbauers
 

Thank you,

I have some rather warped kits I’ve not built and this possible later warping was a concern.

Best to ya,
Mike Bauers
Milwaukee, Wi

On Jul 30, 2015, at 10:30 AM, tyesac wrote:


Mike,
 
I've only built around 150 - 200 of them, and so far, I haven't seen that warpage problem reappear.  That includes some of the early resin kits made from the metal filled dark grey resin and a few cast in the early yeloowish aluminite resin.
 
 
Tom Casey


Pierre Oliver
 

For the most part, no. But in some cases, yes.
In my experience,(almost 2000 models built), flat cast kits that warped and were then flattened tend to stay flat if assembled straight away. With one major caveat, there are some cast sides out there that have cupped or dished. They can be very challenging to flatten and will return to the undesired shape. It seems to be an issue with the type of resin used.
There are a few one piece body castings out there that will never be able to be corrected. They are a certain vintage of passenger body� castings and flat car castings. There seems to be a stability issue with the thin sides and very thick roofs or floors. Again , I believe it's an issue of the material used for the casting.
Pierre Oliver
www.elgincarshops.com
www.yarmouthmodelworks.com
On 7/30/15 10:16 AM, Mike Bauers mwbauers55@... [STMFC] wrote:

�

Once the warpage is corrected and after the model has been built....... Do some models warp eventually again???

Mike Bauers


> On Jul 28, 2015, at 10:39 AM, "Andy Carlson wrote:
>
> Though JP's post seems to be a BCC to this group, resin casting warpage is certainly a common problem among STMFC'ers.



WaltGCox@...
 

For what it's worth I have an unbuilt caboose with a rather thin warped floor that I was planning to stiffen by laminating a styrene sheet to the floor to fit inside the ends and sides. Walt
 
In a message dated 7/30/2015 5:49:55 P.M. Eastern Daylight Time, STMFC@... writes:

 

Thank you,


I have some rather warped kits I’ve not built and this possible later warping was a concern.

Best to ya,
Mike Bauers
Milwaukee, Wi

On Jul 30, 2015, at 10:30 AM, tyesac wrote:


Mike,
 
I've only built around 150 - 200 of them, and so far, I haven't seen that warpage problem reappear.  That includes some of the early resin kits made from the metal filled dark grey resin and a few cast in the early yeloowish aluminite resin.
 
 
Tom Casey


Allen Cain
 

I agree that MOST once glued solid will stay flat, maybe even if not flattened prior to assembly.  However, as stated by another, if the sides are “cupped” along the long centerline assembly may not correct the problem.  However, if the assembly process pulls the part straight AND you clamp it while glued AND you leave a filet of glue to create a REALLY STRONG bond, you should be okay.  Now if you want to be even more comfortable, glue a scrap piece of resin along the seam on the inside to strengthen the joint.

 

Just my 2 cents.

 

Allen Cain

 

 


Anspach Denny <danspachmd@...>
 

Like the experiences of others, I have never had a piece of  warped resin -once straightened- re-warp.   However, if the piece is otherwise unsupported, I do strengthen it commonly with model basswood, or even balsa, secured with Barge Cement,  the grain running 90º to the warp. The wood has more tensile strength than most styrene size for size. I usually do not seal the wood . BTW, balsa is pretty soft, but it has relatively surprising stiffness- and it is cheap and easily found in craft departments.. 

Pierre’s comments on the warped one piece car bodies gets my attention (!@#$%^&*).  These I bring into shape by forcing carefully  a forest of carefully measured struts of balsa wood between the sides (usually pre=warmed). Friction alone secures them in place, and only God will ever know that they are there.

Denny 

 
Denny S. Anspach MD
Sacramento





Tony Thompson
 

Anspach Denny wrote:

 

Pierre’s comments on the warped one piece car bodies gets my attention (!@#$%^&*).  These I bring into shape by forcing carefully  a forest of carefully measured struts of balsa wood between the sides (usually pre=warmed). Friction alone secures them in place, and only God will ever know that they are there.


   But Denny, now we ALL know .        

Tony Thompson             Editor, Signature Press, Berkeley, CA
2906 Forest Ave., Berkeley, CA 94705         www.signaturepress.com
(510) 540-6538; fax, (510) 540-1937; e-mail, tony@...
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