This is called snipe. On most machines the cutter head is above the wood
and supporting the end that is out away from the machine and even lifting up
slightly on it will help. What you are seeing is for the first 3-4 inches
the board is only being held down to the planer's surface by the roller in
front of the cutter head. Until the board travels through the machine far
enough to contact the back roller the board can tilt or lift up into the
cutter head causing more wood to be removed from the leading edge. The same
thing can happen at the trailing edge if the board is not supported when it
comes out of the machine.

Eric

"zz" wrote in message
news:42f4a532.31505923@news-server...
hi
when putting a piece of 6x2 hrough a planing machine [thicknesser they
call it] i notice that at the start of the board after it pulled
through that there is a depression at the front of the board like the
knves really dug in for the first couple of inches then the rest is
pretty flat all the way along. They guy who was showing me how to use
it said thats normal [community access wood workshop].

is it normal??
or is it a badly set up or low quality machine??

I have some very high quality mahogany i want to machine and dont
really want to waste that leading edge if i can help it

also is it beter to do the edges with a jointing machine or a bench
router and fence??

as you can see i know very little so thanks for answering my very
basic question
zz