Palmgren 84929/Craftsman 6" jointer knive removal
 

I have a Palmgren 84261 jointer, same as Craftsman 6 1/8" benchtop
jointer,
its about 4 months old.

Am trying to remove the knives but cannot get the holding screws out
There are 4 holding screws per knife and they are listed as 1/4-20 X
5/8" pan head.
Think the size listing is incorrect as a 4mm hex driver fits them.

Anyway these things are torqued or frozen big time and will not loosen.
If I use much more force I'm either gonna strip the heads or break the
hex key.
I don't want to bang on them with a screwdriver type impact driver
because of the stress that will put on the cutterhead bearings.

Any ideas?

TIA

Joe