How to cut a hole in a globe without breaking it?

Question

Together with my fiancée, we bought a globe very similar to the one below (same brand).

Now we want to cut a clean, rectangular hole (roughly 8 cm x 1-2 cm) in it in order to put envelopes in it but, of course, we don't want to break it. The plastic is ~ 1-2 mm thick. What is the best way to achieve our goal?

The globe is rather frail and we fear that putting to much pressure on it with a cutter will break it.

How is this possible without breaking the globe?

This is what we've thought about:

• start by burning a small hole, then expand it using heat, then when the hole is big enough to hold a cutter blade, switch to the cutter to make hole the size we want.
• use a cutter, but starting very superficially and going over and over again until the whole plastic layer is cut.

There are very likely other ways so what is the best way to cut this globe without breaking it?

Answer 1

I think you might be close to a solution by using heat, but consider to combine a source of heat with a cutter blade. This will allow you to use the tip of the blade to have a minimal impact on the surface, while providing the means to puncture the surface. You may find that you can re-heat the blade for each cut and use this method for the entire opening.

Your idea of repeat cuts is also good if you combine it with heat. This will minimize the damage to the surrounding area, while "gently" imposing the blade into the plastic surface.

The size you reference should be small enough to allow the rest of the sphere to maintain its shape. If an edge of the cut is snagged by an envelope, it may buckle inside, but the overall small size should allow it to pop back out.

With Henry Taylor's implied permission and recommendation, I am incorporating some of his support material below:

Manually heating the blade is absolutely an option, but there is also a specialty tool called a "hot knife" which is just a soldering-iron with an xacto-blade as the tip. I find that using a hot knife to "scratch" at sheet plastic slowly with very low pressure and going over the line a dozen or more times usually provides the best results. Practice on less precious objects of similar material before hand.

As for cutting the straight lines of a rectangular opening, set up a guide for your blade using layers of blue painters tape carefully applied around the outer edge of your cutting lines. Slide the blade along the tape wall with the tip resting against plastic at the cut point. Then once your hole is done, wet the tape to loosen its glue and peal off VERY CAREFULLY starting at the edge of the tape furthest from the hole with force perpendicular to the cut. Remember that you have seriously compromised the plastic's integrity by cutting it, so treat it like an empty egg shell... delicately.

Answer 2

Oscillating tool

I would think using an oscillating tool would work really well for this.

I'm not suggesting a brand, store, or anything, this is just a handy, random image from Google:

This will allow you to cut the rectangle in a relatively short time as well as avoid putting any real pressure on the globe. You just have to follow the normal tool usage guideline of: let the tool do the work.

There are a wide variety of cutting attachments for this, so you might find a blade that would work better than the one in this image. As a bonus, these tools are really handy for a lot of different projects, so it's not just a "one project" tool. You will find other uses for it, once you have it.

Rotary tool

You can also try a rotary tool, like a Dremel tool with a cutting disk. These disks can be fragile and hard to keep cutting in a straight line, so not my first choice for something like this.

Hot knife

With any tool when working with plastics, you want to avoid excessive heat. The heat can warp or discolor the plastic, especially when it's thin plastic. A globe like this is probably injection molded from a thermoplastic, which is usually very sensitive to heat. This is why I would avoid using a "hot knife" method.

Even if you are using a retail version of a hot knife, they tend to cool down below the melting temperature of the material you're trying to cut quickly, so it's always a race to finish your cut before it cools down too far, and the knife is stuck in your piece.

Also, these tend to leave a lip of plastic around the edge of your cut, leaving you to trim it away when it's cool, as well as avoid while it's still hot. Hot plastic and skin contact is very, very, extremely unpleasant most of the time, since they tend to stick to each other.