I like using Sephora sharpeners. The one I got was $2 and it works like a charm to sharpen UD pencils. It sharpens so smoothly too. Like with any sharpener, be careful with the amount of pressure you apply because we all know how easily UD 24/7 pencil tips fall off.

I have the UD sharpener, but, find it helps to put the pencil in the frig about 5 minutes or so first.

It probably is the sharpener. I would invest it a good sharpener if you can because there is nothing worse that ruining your pencils (I've done it plenty of times and hate it every time).  The Ulta Sharpener got great reviews from Total Beauty Readers.  You can read the review here.  

well, i personally like elf sharpeners so maybe it is the pencil.

The urban Decay 24/7 pencils are super creamy so they are very hard to sharpen...Make sure the sharpener is super clean and do it very slow...I love the @4/7 Pencils! They ROCK!

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Urban Decay's Grind Box is the best for sharpening their eye pencils and shadow pencils. I tried a drugstore brand sharpener on them first and it just made a mess. I'm pretty sure the grind box is less than $10 and it does a great job on non-UD pencils too.

Try Covergirl Sharpener. I dont know the exact name. It is navy blue and has 2 holes, and a attachment that you can pull off for an even bigger hole. I love this!

Have you tried a small pencil sharpener? I use that on eyeliner with no problem. It's also a lot cheaper.

I've used my little Sephora sharpener, my Benefit sharpener and my Urban Decay sharpener to sharpen my UD 24/7 pencils, and haven't had problems with any of them. Or maybe your pencil is old and dry, and so the "lead" is cracking?