Flatten a plastic backflash

Advice and guidance on repair and restoration techniques.
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gameswat
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Re: Flatten a plastic backflash

Post by gameswat »

...As for the backflash, that's a very nice original so not sure why you would want to replace it? A repro is never going to better it. Because the plastic has shrunken over time you need to release the tension where any pins or screws attach through it and are locking those parts in place while other areas can stretch, which then causes the buckling. I just elongate the holes slightly with a Dremel or re-drill new ones in bad cases, just enough to leave a little bit of wiggle room for any further shrinkage. Looks like you have one bad split on the top lhd, which should be easy to fix by releasing that corner piece and bringing the joint back together. The plastic goes well under the side wood spacers giving you a lot to play with. I've sometimes had to use tiny brass nails to hold down cracks like that if they keep wanting to lift up and stop the ball. But I've also used a clear layer of polycarb over the top of badly warped ones to help keep them flat too.
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yaksplat
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Re: Flatten a plastic backflash

Post by yaksplat »

I removed the backflash as it was so warped and cleaned up the playfield an all of the parts. The backflash is much nicer with the layer of dirt removed. I may have to put a layer of plexiglass on it as Gameswat suggested.
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yaksplat
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Re: Flatten a plastic backflash

Post by yaksplat »

Looking better already. It took quite a bit of heat to flatten out the backflash. 300ºF in the oven. I started at 170ºF and increased at 20º increments until it would be soft enough to flatten. The paint on the backside is very delicate, so I lost a few flakes around the existing holes. I had to drill new holes through the backflash for all of the pins and screws as everything had shifted by a few millimetres.
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coppinpr
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Re: Flatten a plastic backflash

Post by coppinpr »

Looks great. Did you try touching up the paint from the back of the backflash? This can work well on small areas, but always add a top coat of matt white.
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yaksplat
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Re: Flatten a plastic backflash

Post by yaksplat »

I thought about doing some painting on the back, but for the few small areas, it won't really be worth it to acquire the paint, match the colors and then get it perfect. If I leave it at is, there's some paint flecks missing and that's because it's old. If I paint it and it doesn't match perfectly, that will annoy the crap out of me. If it does start to bother me, I can always do it later.
13rebel
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Re: Flatten a plastic backflash

Post by 13rebel »

Brave of you to use the oven method but by including the method it may encourage others to be equally brave. The idea of leaving the paintwork on the back as it is in case you can't match it I think is good too. Best to see if you can live with the aged look.
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badpenny
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Re: Flatten a plastic backflash

Post by badpenny »

I think that apart from the temperature that you found necessary to bake it at, what is equally important is approximately how long before it was pliant.
And, did you place it in the oven paint up or down?
What process did you employ to even it out? Was heat and gravity enough or did you put something heavy on it?

I ask as I could imagine getting any of those steps wrong could easily nause it all up in spectacular fashion.
I think you were very brave and thank you for bearing the mantle of guinea pig on behalf of the hobby.

BP !WORSHIPFULL!
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yaksplat
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Re: Flatten a plastic backflash

Post by yaksplat »

So, as you can see in the earlier photographs, there was one corner that was cracked off and it was a pretty decent size and it was extremely warped. First thing I did was place down on a piece of paper, held it flat and traced it. At that point I had the original size. I had feared that the heat would potentially make the plastic shrink, which would be a complete disaster. I kept putting this piece back in the oven for about 10 minutes, which was long enough for the plastic to reach the temperature of the oven. Then I'd take it out and I'd lay it on the piece of paper and sandwich the piece between the counter top and a cutting board, putting my weight on it. The temperature would drop quickly and then I'd check the piece for size against the outline I took, and deformity. The size never changed, which was great. But it was still warped for many iterations. I kept doing this, over and over, while increasing the temperature until the piece was relatively flat. Once I determined that 300 was the temperature, I threw the whole thing in, left it for 10 minutes and then attempted flattening. It wasn't perfect, but worked well enough that it no longer looks deformed. All of the nail and pin holes were completely flat.

If I was to do it over again, I'd probably keep going higher and use two pieces of glass to sandwich the backflash. I'd place a 30 pound weight on the glass once I pulled it from the oven and then let it cool slower between the panes of glass. I'd suspect that it would flatten quite well in that scenario.

At one point I couldn't find my corner piece. It had fallen off of the rack in the oven and was sitting against the back wall, touching the bottom of the oven. I'm not sure how it didn't completely melt. But that could have been disastrous.
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coppinpr
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Re: Flatten a plastic backflash

Post by coppinpr »

Somewhere on this forum, years ago, we looked at the method of flattening warped 78rpm records without affecting the grooves. If I remember correctly this was much like your "next time I do it" using glass on both sides (although I guess the temp would have been less).
Really well done, a ground breaking repair !THUMBS!
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