Penpal
Grand Master
I am referring to all the woods, you have uniform dark lines on the light woods and light lines on the dark woods.
This is indicative of sanding material filling the grain.
It's a fundamental mistake many of us make in our early days but if not pointed out we can carry on not knowing what or why it is happening.
When you finish your cuts, before sanding seal the wood with some ca or sanding sealer, that will clog the pores of the grain with clear sealer and stop the dust entering.
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Show us an example of yours Brian it always helps mate. I remember so many of Woodies contributions and explanations they have helped me. Thanks

Peter.