Between two pieces of playfield glass in the sun on a hot summer day will help flatten them out.

Heat gun and they will flatten out once you heat them up gently push on them use a glove or something not to burn yourself

Do some reading. While I have not done this I would worry about different era plastics and mixing heat with pressure. I would rather let low heat flatten than putting something pressing on top and leaving marks.

Place in a 200° oven for five or six minutes. Just keep an eye on them while they are in there. Definitely make sure you use a flat cookie sheet. Let cool completely before handling.

What year is the game? In the 1940s and 1950s, the plastic formulations would warp a lot. That era of plastic also tends to be very brittle. DO NOT try to flex that type of plastic to straighten it without heating it, as that will almost certainly fracture it.

More modern plastics (mid-1960s and later) seem to be an improved formula that is both less susceptible to warping, and more forgiving if you flex it while it is at room temperature.

For either type of plastic, if you have two thick pieces of glass (3/16" or thicker), you can place the plastic onto one glass with the printed side down, heat the plastic for a couple of minutes with a heat gun, and then place the second piece of glass on it. Then you need to immediately put some heavy weights on the top glass to keep the plastic flat. Give the plastic 5 minutes or more to cool down, then remove the weight and top glass and the plastic should be flatter. If it's still too warped, you can repeat this process.

WARNING: It takes some practice to flatten a plastic with an artificial heat source (either heat gun or oven) and have it come out looking better than it went in. As others have already noted, artificial heating is not a safe way to flatten plastics. Some plastics will develop pimples over the top surface when heated, and these pimples will remain and will be visible. Also, if you over-heat a plastic, you can blister it and that will ruin it. It can be difficult to judge when you've got a plastic hot enough to flatten it, but not so hot that one of these unpleasant side-effects occur.

I've heard that putting a plastic in a glass sandwich, and leaving it in the sun for a while is safest way to flatten it. I have not tried this technique, so I don't know how long "a while" is.

- TimMe

Heat gun with a steady back and forth motion. and a heavy book on a flat clean surface like concrete in your garage. Hairdryer does not have enough heat. Never lost a plastic yet and they come out fantastic. It should be noted that I have only done this technique with 60's and 70's plastics, unknown what it will do to 50's and before era.

When you heat them up with the heat gun just go slow and easy. You will see the plastic begin to rise and initially will look like it's getting worse... then it will "relax" and go flat. At that point use a good weight to keep it flat till it cools.

I've done it using a medium heat clothes iron and parchment paper over the top. Just ironed them right flat.

All the other methods will work too. I have used the iron because it allows me to keep a close eye on the progress. The glass in the sun process, you have no control over the heat.

I put some plastics in the oven at the lowest temp 140-160 and I fell asleep ..... The wife woke me up three hours later asking what was in the oven??? ... I was sure they were ruined ... Nope not at all
Took em out laid a heavy glass dish on top and they came out perfect!!!!

Ditto. Recently did several plastics from a "Bowling Queen". They had the same type of warp that yours shown above has. I sprayed a little silicone on a rag and wiped it on top of my clothes dryer. Then I placed the plastic ink side down and used a heat gun to apply heat, keeping it constantly moving, about six inches above the plastic. When it softened a bit, I put a heavy book on it. Waited a minute or two, removed the book, and voila; nice flat plastic.

I prefer out in the sun method when possible, but when using heat gun be sure to use something super smooth as the inner weighted layers. You don't want a bumpy book texture to leave impressions in your flat plastic.

No amount of religion or untraining can make a bent plastic not bent.

That's really profound!

This thread is cracking me up two peices of bent plastic is like some serious rocket science

So many good ways described here!
I have a good method...and no patients, so...
I have a couple pieces of granite counter top.
1. place one in the oven smooth side up at about 200-220 for 15 mins. gets it nice and warm.
2. place the plastic right side up on the warm granite, heat for 15 mins.
3. place a second piece of granite on top of the plastic, smooth side down, heat for 15 mins.
4. remove both pieces of granite together, and let cool.
5. remove top piece of granite, and enjoy your nice flat plastics.
I guess what ever works for you.

I've used this method myself with excellent results.

Had bent plastic on a 1971 4 Square and a 1974(?) Fun Fest. Used a hair dryer rather than heat gun and two pieces of parchment paper with a stack of hard hack books on top of my workbench. Worked well. Not being experienced with a heat gun, didn't want to take a chance on ending up with a puddle of plastic.

I tried the heat gun method this morning. Worked perfect. I thought about the oven but mine doesn't go below 225.

I have used a heat gun bunches, but not on pinball plastics.
what I find, is if you heat too much, you get a shrinking effect on the top layer, then, goo...or char.
I guess any method that produces the desired result, is just fine.

You have to keep the heat gun moving and watch carefully. I've seen plastics curl wickedly under a heatgun, then drop back down perfectly flat. I looks like a disaster, then suddenly the plastic relaxes perfectly flat.

I'm doing some tonight. I bake mine between two sheets of glass in the oven at 250F (oven thermostat and internal thermometer agree) for 15 minutes. After I remove them I place jugs of water on top for weight and allow them to cool. Works great for me. I tried 200F and 225F but even after 1/2 hour in the oven they still didn't want to bend. I'm working with 60s and 70s plastics.

I think the oven is more controlled than a heat gun since the heat gun is sending out air at 750F or so, easier to get overzealous and start to burn something.

I can bake cookies with my heat gun!

Did 3 more with the heat gun last night with excellent results. Just keep it a 4-5 inches away and keep it moving and no problems. Heat it, set a book on it and some weight and let cool. These were f14 plastics.

I have a project space mission to do next. Those plastics are way worse.

This is how you flatten plastics with a low stress low heat approach.

I've used this approach for years now on mostly 60's and 70's Gottlieb plastics with great success. I've found 90's Williams/Bally game plastics to be more sensitive so shorter time under the heat is recommended until you get a feel for what works.

Take two pieces of playfield glass, four or 6 quick clamps, and an articulated arm lamp with 60 watt incandescent bulb.

Clamp plastic between two pieces of playfield glass. Place lamp shade right over plastic to be flattened, heat for 45 minutes, let cool for 30 minutes, and remove your flat plastic. I put it in and turn it on and set the alarm on my phone so I don't over do it.

Larger plastics will take longer as the shade on this lamp is maybe 6-7 inches in diameter. So after 45 minutes move the lamp position to the next adjacent spot on the plastic. Repeat until the whole plastic has been flattened.

For very bowed plastics it can take longer and the clamps need to be re-tightened as the plastic flattens. If you don't get the full flatness you are looking for just reheat it again making sure the clamps are tight.

I just flattened a complete set of original plastics for an El Dorado, including the long one at the top, and they all came out great.

What I like about this arrangement is that, as long as I don't leave the plastics in there too long, there is never a concern that I will over-stress the plastic. Also, it is always available. The disadvantage is that it does take time and probably more patience than some of the other methods suggested here.

Here is the rig preparing to flatten a plastic and then in process of flattening a plastic.

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IMG_4214 (resized).JPG

That is just too perfect..."Dr of style" has "no patients"

Or did ya actually mean your office is empty, so you had time to explain?

Yeah, I wuz on break! got a few mins in to talk...???...type.