Cutting off the top of a light bulb

Hello! I'm having a problem and have ruined quite a bit of incandescent light bulbs over it:
I need to open the thing just below the thread and I have no idea how. I've tried doing it with an X-acto knife, but it never breaks evenly, and usually, there are tiny cracks along the edge. Anybody out there have experience doing this and any words of wisdom?
Thanks in advance :)

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Kiteman5 years ago
I managed to "cut" glass tubes with a file, scoring round and round the tube and then snapping.

Because of the off shape, you might need to file into the glass quite deeply before snapping - be careful of the glass dust.
TashaDax (author)  Kiteman5 years ago
I did try that, though with a box cutter (I messed up my terms before, sorry about that) and at some point it just snaps off on its own, but I can't put it back on , because there are bits of glass missing...
I think any method will leave at least some glass missing.

If you cut real close to the thread, the seam should be easier to hide.
gmoon5 years ago
This question rattled an old memory. I'm looking at Mother's Energy Efficiency Book: Heat, Light, Power, published in 1983, pg. 28. It's a plan for an electric hot-wire glass cutter, used for cutting the ends off old florescent tube bulbs (which are then used for a solar water heater).

Pretty simple--a 12V car battery, with an old headlight dimmer switch and heavy wire. The dimmer switch is just on/off--a good knife blade switch would work well, too. The cutter is a large wooden dowel cut in half, and the "working end" is a 5 inch loop of 0.034" steel wire.

The cutting wire is anchored with a screw, inside a hollow square steel tube (solder would melt). From the pics, the cutting wire definitely get's hot enough to glow...

Pretty simple, but it might take an afternoon to build...
Goodhart5 years ago
Do you need to do this "with the threads intact"? Or attached? Sometimes one can slowly and carefully work the metal threads back and forth loosening them enough to remove them so you have more room to work.


From that point,  Kiteman's suggestion has merit, and as he mentions, there WILL be glass particles, so be careful of cuts or breathing it in.  

If you aren't careful enough, the bulb may even emplode and you'd have glass everywhere.   Make sure you have a face shield or at least safety glasses / goggles on while doing this.

With Warrengoff's  suggestion, definitly make sure you don't breath in the flying particles of glass sure to be flug at high speed from the tool . 
TashaDax (author)  Goodhart5 years ago
I did try that, though with a box cutter (I messed up my terms before, sorry about that) and at some point it just snaps off on its own, but I can't put it back on , because there are bits of glass missing...
batonas5 years ago
smooth it down with fine sandpaper
warrengoff5 years ago
Use a dremel mototool with the diamond wheel. This will cut smoothly and cleanly.