I think this was mentioned, but it is worth thinking about , is the plate
thin enough that the taepred part of the screw is binding in the hole?
Used to make 100 degree sheet metal screws for that. They might make
undercut screws If the threads are rolled, it usually takes up the
countersink at the top of the hole. MAybe try a big ass c sink[in the
tapped part] to see if it solves it

Nada. Doesn't make contact with the threads like that. Once the heads are
drilled off to remove really stuck ones, we remove the screw thread part by
hand.
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Regards,
Joe Agro, Jr.
http://www.autodrill.com
http://www.multi-spindle-heads.com

V8013

My eBay: http://tinyurl.com/4hpnc