straightening warped plastic underframes Options

[cjbrock]

I'm looking for anything you guys have tried. I opened a Walthers 89' flat and the body was bowed like a banana - yellow like one too.

I straightened it by taping it to a steel 2" square tube, then glued the weight to the bottom and added the underframe. I hoped all that would pull it in, but no go. I am thinking about taping or clamping it back to the steel tube and then heating it in the oven to about 180 degrees for 10 minutes. Anyone else have a good temperature and time? Other ideas?

[k9wrangler]

I'm looking for anything you guys have tried. I opened a Walthers 89' flat and the body was bowed like a banana - yellow like one too.

I straightened it by taping it to a steel 2" square tube, then glued the weight to the bottom and added the underframe. I hoped all that would pull it in, but no go. I am thinking about taping or clamping it back to the steel tube and then heating it in the oven to about 180 degrees for 10 minutes. Anyone else have a good temperature and time? Other ideas?

Never done anything like that, 10 minutes sounds a tad bit long. Have heard of folks straightening out resin building walls with a little heat but don't remember the details.

Any chance of getting it replaced?

[IMhauler]

John,

I suggest asking Walthers for a replacement. Once they tell you they'll ship one to you, then try some experiments on the current one. I'm not sure how those go together, but if you could sandwich the underframe between the weight and a piece of plate steel/brass, hold it in place with C clamps, then try 150 degree heat for 5 minutes and see if that helps. If not, try an additional 5 minutes and check again. Better to try a low temp and longer cook time.

Knowing a replacement is on the way will put your mind at ease and free up the current one for martyrdom in fixing any future occurrences.

At any rate, that's how I would do it personally.

[cjbrock]

I hadn't even thought of asking them for a replacement, the kit is probably 15 years old - seems like the statute of limitations has probably expired on it (although I did buy it new at the lhs, I don't have the receipt ).

[IMhauler]

the kit is probably 15 years old

Ah, that might change the dynamics. Ok, a few years ago a Model Railroader Magazine had an article on making curved structure turrets with brick embossed styrene. I don't remember the issue # or month/year but it talked about the temperature and time used to heat the styrene sheet enough to keep the curved shape without over-heating it.
I seem to recall he had it in for 10 minutes, but I don't know if it was 150 degrees or what. Someone here might remember the issue #. I loaned mine out and never got it back.
I still think 5 minutes at 150 temp would be a good test combo, and leave it in longer if it needs it.

[cjbrock]

I'll go with the 5@150 and report back. Worst case, I've got more shelf space on the 'to be assembled' shelf. Intermediate case, the road into ol' Farmer Jones place will get a new bridge...

[Spikre]

John,
those cars arnt supposed to be flat,they had a reverse camber that
shows in pics of new cars.the Center should be higher due to the camber.
but one kit here had the center Sagging,is that Negative Camber ??
havent built it yet,but think that slightly bending the Wieght before glueing
it may help ??
are You building this as a New car or an old warrior that is getting near the
40 year old Rule ??
Spikre


This post has been edited by Spikre: Feb 20 2010, 11:06 AM

[cjbrock]

Bob, I wish I had taken a picture of this before I started straightening things. Maybe it will go back to its original bow when I pull it apart to cook it. The bend is the opposite of what it would be for a pre-load, the middle of this thing was saggin' so far the trucks were just wheelie bars on the end of the rocker.

[tomfassett]

I think Paul is on the right track here. Slow and steady is generally the best. It would be even better if you could add some side support to keep it from warping that way as it straightens back out. Something like a metal ruler (without a cork base), a framer's square or a couple of aluminum bars should work. Be sure it is restricted firmly on both sides so it bends straight down as it straightens out. I have been playing with styrene for the past year and the stuff really develops a mind of its own. Good even heat over the entire surface is much better than "spot" heat like you might get from a heat gun or hair blower. Keep in mind that styrene usually melts at 400 degrees and stays pretty rigid darn near up to that point. I swear 10 degrees can be the difference. I'd say you are more than safe up to 200+ degrees but like I said, I think Paul's suggestion of trying it in stages is a sound one.

Tom F

[cjbrock]

Ok, that's good advice Tom, I hadn't thought about the sides. I could mill a piece of channel with a few strategic cutouts for the brakestand etc and make sort of a U-shaped sandwich with the square tube. At some point it becomes ridiculous trying to save a $15 kit, but it's the learning experience, right?