Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4812026.
I needed a flat top LED for a project. I didn't want to order a pile of them as I am already overflowing with dome style LEDs. I made this little jig to cut off the top of the dome with an exacto knife. One version has a recess for a flat washer to protect the plastic from the blade. I just used the closest washer I had on hand that had a hole bigger then 5mm. I believe it's a #10 imperial size.
I made a version without a washer recess in case you live in a more advanced country where metric is used. Should be easy enough to create a recess in Meshmixer.
The two pieces snap together and allow the knife blade to easily slip in the groove without twisting. Slight pressure cuts off the tip. Takes a little practice to get a perfect 90° cut. Even at a slight off angle it still produces a very nice flood light effect.
UPDATED: Version 2 cuts off a bit more of the bulb tip (1.5mm) as I found the original one was too close to the the tip making a more uneven and difficult cut. I also added a small hole to put a toothpick (or anything 1.6mm in diameter) between the leads and the base of the bulb to help hold the bulb in place as it tended to slip back while cutting. If the tip is still uneven a small micro file works really well to even it out.