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Pinball Rehab

pinball repair and restoration

Repairing Cracked Plastics Repairing Cracked Plastics Hot

Cracked plastics are a common problem on pinball games and the type of crack you're dealing with will determine the type of approach to use.  If the two plastic pieces have broken cleanly and fit perfectly back together, use a low viscosity super glue.  In other cases where you don't have a good fit and need to fill a gap you'll want to use a gel product (see references).

The first thing to do on any crack is to clean the area with a toothbrush and your preferred plastic cleaning product (Novus 1, Mean Green, etc.).  While there is no way to completely keep a crack from showing after repair we don't want to add to the problem by gluing dirt or grit inside the joint.

Cracked Plastic with Good Fit

Our first example is a cracked slingshot plastic which was most likely a result of over-tightening the mounting screw (see Image 1, lower right screw hole).  As is common with this type of crack the pressure from the screw has spread the two sides apart.

In this example there was a nice tight fit when the two pieces were pressed together, but since we're using instant glue we want the joint in place before applying the glue.  It's almost impossible to properly align two pieces of plastic by applying instant super glue to each side and then pressing them together.

Using a heat gun, set at 200 degrees, heat the plastic for a couple of minutes (until it's flexible) and press the two edges back together.  You'll have to hold the joint for a few minutes until the plastic cools (see Image 2).  Once it cools, squeeze the joint together and tape the top side (the one without the decal) using packaging tape (see Image 3).

Image Gallery

Repairing Cracked Plastics
Repairing Cracked Plastics
Repairing Cracked Plastics
Repairing Cracked Plastics
Repairing Cracked Plastics
Repairing Cracked Plastics
Repairing Cracked Plastics

The tape will hold our joint together and keep glue from seeping through and damaging the top of the plastic.

Squeeze the joint together and using a thin super glue place a drop on the bottom side of the crack.  Spread the glue across the crack using the tip of the applicator.  If you have a longer crack it may take more than one drop.  Hold the joint until the glue is hard.

If you use too much super glue do not wipe it off or it will haze the plastic.  Instead use the corner of a paper towel to wick up any excess.

You can see the finished product in Image 4.

Cracked Plastic with Poor Fit

If the two pieces of plastic do not have a good fit you have a couple of choices.  If possible use the technique above to glue as much of the crack together as possible.  This will hold everything together while using the thicker, slower drying gel.

If you don't have a good enough fit for this method, use clamps or hemostats (plastic ones work great) to securely hold the parts in place.  You also still want to use the packaging tape to protect the front of the plastic from damage.

Use the gel type super glue to fill any gaps and use tape to create a dam on each side of the plastic if necessary.  With a thick gap it can take overnight for the glue to completely harden so you can use a CA accelerator like Zip Kicker to speed up the process.

Cracked Plastic with Reinforcement

In Image 5 you can see a plastic from Bram Stoker's Dracula after gluing with the method above.  The crack was at the narrowest part of the plastic, which is less than 1/4" wide.  Since it was clearly not well designed it will most likely break again.

To prevent this I added a small piece of clear plastic to the bottom side (see Image 6) and attached it with super glue.  Make sure the thicker section of plastic will not interfere with installation before using this technique.

In some situations, like on a ramp where you want the repair to be as invisible as possible, you can reinforce the area with epoxy after gluing.  If possible apply the epoxy to the backside where it will be less visible and use a crystal clear product like Epoxy 330 (available through Amazon).  Also a smooth surface will minimize light refraction and make the repair less visible.

You could also use the Plastex product (see references) and their fiberglass reinforcement cloth for larger structural repairs.  It won't be pretty so only use this technique when the underside of the plastic is hidden.

Hairline or Star Cracks

In Image 7 you can see a star crack around a mounting screw hole on a ramp.  This is also common when the rivets holding ramp flaps have been over-tightened.  In this case, or that of a long hairline crack you want to use a very low viscosity glue like Plast-i-Weld from Flex-i-File that will seep into the crack (see super glue reference below).

If the crack goes all the way through the plastic place packing tape on the top side.  Lightly apply the glue along the crack line.  Flex-i-File makes an applicator for their product, and another for super glue, that allow small amounts of glue to be precisely applied (see super glue references).

If possible it's a good idea to drill a very small stop hole at the end of hairline cracks.  Just like a car windshield the crack will continue to spread due to vibration.

Plastic Replacement

Sometimes it's necessary to recreate a portion of a plastic piece, like a mounting tab on a ramp.  See this article for how to use the Plastex Repair Kit in this situation.  Be aware the Plastex product does have a slight yellow tint so it works best when used as a structural repair rather than cosmetic.

Reference 1