Trick for removing almost-ruined Phillips head screws

[ptpalpha]

Valve grinding compound trick works great!  Thanks for that one.
Now...how do you remove the 4-40 tap that just snapped after cutting about 4 threads??

[Springrrrr]

Do a good job of cleaning off the valve grinding compound.  I found it to be a bit corrosive and rusts the tip of a screwdriver.

[ZiaBeam]

Valve grinding compound trick works great!  Thanks for that one.
Now...how do you remove the 4-40 tap that just snapped after cutting about 4 threads??

Find a machine shop with a sinker EDM machine, which erodes the tap with electrical sparks.
With larger taps in tough steel parts I have taken a punch and hammer to shatter the tap, carefully picking out the fragments, shatter some more, until complete. It is scary as heck, and looks ugly, but each time I have used this method the end result always turned out much better than it seemed during the process, which was used out of desperation, yet yielded near flawless results. Sounds maniacal but believe it or not it can be done.

[stevemag]

i have these in my tool box, they work well.
http://www.sears.com/craftsman-3-pc-deck-out-screw-and-bolt/p-00952151000P

[Dirty Ern]

You might also try giving it a couple light taps in the direction of tightening with an impact driver, then some with the same tool in the loosening direction. It wouldn't let me post the link, look for it at Sears as Impact Driver. The bits that come in this kit are also handy because they are so strong, you can slip one into 1/4" nut driver or a 1/4" socket on a ratchet. I also believe that starting out with a Phillips screw driver that is in very good condition is important. Also important to keep a strong inward pressure while turning. I also lightly dress my Phillip points on the grinder if they start getting shabby. When each blade on the driver starts getting a knife edge on them they slip easily.