Does t-molding shrink over time?

JohnnyNickel

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I've just gotten my first game (Atari Gravitar). The t-molding in all inner curves is pulled away from the cabinet, as shown in the photo. It's as though the t-molding shrank and pulled out of its channel. Does vintage t-molding have a tendency to shrink, or does it appear that the molding was installed improperly at the factory or by a previous owner? I don't have enough history with these games to know.

Thanks...
 

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Plastics tend to shrink, I've seen the same thing. When you install new, it's helpful to use a little wood glue in those inside curves to help lock it in.
 
Maybe it went for a swim in a cold pool.

I haven't tried wood glue, but I've used a hot melt glue gun on several of my cabs, and it's worked wonders. I bought a gun with a very thin metal nozzle, that lets you get it right down into the groove. Works great, and it also isn't so permanent that it can't be removed, if need be.
 
Depending on the type of plastic a variety of things can happen (not all plastics are the same), but shrinking and cracking are two examples.
Sulphur is used in the vulcanization process for many early plastics.
Depending on how much or how little sulphur is used it reacts differently over time.
The more sulphur that is added to the plastic, the harder it becomes.
The less sulphur, the softer the plastic.

Sulphur in the chemical world is what is referred to as a sublime element.
That means that it goes from a solid state to a gas state without ever becoming a liquid.
Effectively the sulphur will leave or escape from the plastic over time.
Things like heat or exposure to elements will accelerate this process.
This is what causes shrinkage, cracking and yellowing (foxing).
 
Also cutting lines in the t molding helps it bend and release tension and stay in place better.

Lines for a bend like that, cut triangles out for a bend around a corner.
 
Also cutting lines in the t molding helps it bend and release tension and stay in place better.

Lines for a bend like that, cut triangles out for a bend around a corner.


Careful with this, you may get lines or creases in your corners if you don't do it correctly.

I like to lay a small strip of duct tape on the areas that don't tack in very well. Tapping the molding in with tape laid across the channel seems to do a good job holding it in too.
 
My Pole Position still has the original T-molding, but the cabinet sides are about a single millimeter wider and larger than the T-molding. The width of the cabinet sides measured the appropriate thickness, so swelling wasn't the main reason.
 
My Pole Position still has the original T-molding, but the cabinet sides are about a single millimeter wider and larger than the T-molding. The width of the cabinet sides measured the appropriate thickness, so swelling wasn't the main reason.

Just curious, instead of shrinking of the plastic, could it be expanding of the wood from people's sweaty oily hands?
 
Just curious, instead of shrinking of the plastic, could it be expanding of the wood from people's sweaty oily hands?

No, even on cabinets that get wet and expand the cabinet will get thicker to where you have a millimeters two of extra wood on the sides where it expanded like a sponge but the T-molding still fits.
 
Sorry to revive an old post but I just got my first cab and have the exact same issue: it shrinked and got pulled away in the curves.
It has been left for over 30 years in an under roof storage space and it surely got a huge amount of heat there.
Any hope I can heat up the t-molding and be able to extend it enough to get back into position ?
It's a black 19 mm t-molding with chromed double stripes, so far I only found single chrome stripe ones for potential replacement.
 
I doubt you'll stretch it. If it's t-molding you can buy, then replace it. I always add some wood glue in the inside curves when I apply t-molding to help prevent this.
 
The question is does it shrink.

Yes, it does shrink, very slowly.

When it does, one of two things happens:
1. The material pulls out of inside bends (due to tension)
2. The material cracks on outside radius bends (due to tension)

What can you do?

Replace it once it happens.

Gluing it, stress relieving with cuts / triangles won't stop this process.
 
Was the older t-molding a different plastic then what is used today? I pulled some off of my bowling cab and its seemed more like rubber than plastic.
 
Was the older t-molding a different plastic then what is used today? I pulled some off of my bowling cab and its seemed more like rubber than plastic.
That's a really good question. I don't know the answer.

What I do know is all plastics contain some volatile organic compounds, or VOCs. They are what keeps it flexible over time.

As the VOCs (gives off that "plastic smell") evaporate out of the compounds, it gets harder and less pliable.

So the volatiles may have changed, but the effect is fundamentally the same.
 
If you can't get a replacement you're happy with, you can pull it all the way off and then start where you want it visible (top, or bottom) and do it over again, when you get to the end you'll be slightly too short but it'll look better than sticking out all over the place.
 
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