These screws are countersunk into an aluminum block, and are flush across the surface of the block. They're Allen drive, so are removed by inserting an Allen wrench into them and turning. There's nothing for me to cut off, and drilling them out would probably destoy the female threads inside the block.
I've got to get them to turn, or I'll have to buy a whole new assembly :-(
Then it is just plain easy. Drill them out retap the threads and use a larger allen screw. If there is clearance use bolts. So much easier when they get seized.
>> These screws are countersunk into an aluminum block
Cylindrical screw heads? You can notch the heads for a quality flat-head screw driver. Force down on the screw driver while using a wrench to rotate it. You can notch the screw head with a drill. Again, pre-apply a lubricant for a few hours.
Another idea... what about torx drive? It’ll probably spin but it’s worth a shot. A torx drive is gonna be harder than the screw and that might be enough to grab within the allen hole.
Less painful to just shave first, then you don't have to worry about catching the knife. You can avoid having to snap them off if you cut all the way through on the first pass. But you're not going to find very many liberals who haven't already had this done.
A number of methods are used with success for removal on each of these methods...What works on the first one may not work on the 2nd or 3rd one...One thing I have done on numerous cases is to drill the head of the flathead screw using a drill the same diameter as the screw...Done right, this will pop the head of the screw off...If off center use a slightly larger drill to go back in the hole...The idea is to remove the head of the screw without damaging (too much) the chamferred surface that mates with the head of the screw...Drill only deep enough to pop this head off...
This will do 2 things...First one is that it will eliminate the pressure on the threads in the base...The second is that it will allow you to remove the piece bolted down...What will remain, depending on how thick the removed piece is, is the screw portion which will be extending out of the piece it is stuck in...This allows you to grab it with something to work it back and forth to get it out...
It the stud still will not move, the next option has almost always worked for me...
Set a quarter inch nut or five sixteenths over the exposed end of the protruding stud and have someone quickly put a weld tack inside the nut welding the nut to the stud...Wire welder with a quick burst so as not to get the stud to hot...
This give you a nut to put a wrench on to work the screw back and forth...
May sound like a lengthy process but it really isn't...Have had great success with this procedure with the 40 years of my experience as a Millwright...Just go slow and think about each maneuver as you move along...If this fails, all that's left is heli-coil time...And yes, there is nothing better or as good as Kroil (if the screws are vertical and hot horizontal...Good luck...
As has been suggested, an impact driver is a good option...Another suggested a chisel...I've used a center punch off center of the screw head pointed in the direction you want to go with good success...Just to get enough 'shock' to break it loose...