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I want to use a plough plane (stanley #45) to cut dadoes (cross grain). The spurs/knickers are useful in preventing tearout and defining a clean knife wall, but they score past the bottom of the dado, like in the following image (dado profile outlined in red).

This is obviously due to the knickers cutting ahead of the iron, but if push the iron further out to a depth equal (or close to) the spurs, the operation of the blade is much less smoother -- broken shavings, and at the far edge, it results in breakout.

outline of dado right-hand-side spur

So, is there a way to produce perfectly rectangular dado profiles with this tool? Would one re-adjust the depth of the blade relative to the spur, or are spur marks to be expected regardless?

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    Surely you just rotate the spur when you're close to final depth? Re. breakout at the edge, the bottom of the groove should be defined with at least a gauge mark, which should prevent or minimise this. – Graphus Apr 23 '18 at 12:40
  • Thanks! As a new user of this, I'm perhaps overly questioning the design. It makes sense to readjust spurs during a cut, but depending on set depth, the depth stop's foot is in the way of the spur's locking screw -- so re-setting the spur to non-cutting position needs a depth stop reset (depending on angle). Yes, no gauge marks here, I was doing sample runs. I should do a proper test. I have very limited experience, but I wish I could reverse the direction of the fence already, it's tough to make the bottom level. – ww_init_js Apr 23 '18 at 23:42
  • Re. the gauge mark, this would be on the edge of the board, showing the final depth of the groove. – Graphus Apr 24 '18 at 15:15
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Once you get close to your final dept, remove the spurs and you can score the corners with a matte knife (like the spur) but stop short of the ends.

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    or go to finished depth with a router plane. – aaron Apr 23 '18 at 11:48
  • In my dream, "7-planes-in-one" was all that was needed. I'll be less reliant on the spurs. – ww_init_js Apr 23 '18 at 23:52

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