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?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Site Timeline is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.