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40 grit sanding before face or edge gluing stock12/29/14
I would have lots of face and edge gluing to do. I wanted prep the stock flat faster and I thought a 40 grit face/edge sanding of stock on a drum sander would make the stock flat and receive glue better.
Would this method work well?
It should work fine. I would sand a few test pieces to make sure the deep scratches don't result in a thicker glue line showing up in finishing. 60 grit works well but I haven't done 40 for a glue up.
Someone also told me 80 grit works fine too.. It would be more economical if 80 grit is the way to do it, because 80 is cheaper than 60 grit.
PVA likes smooth surfaces like freshly jointed maple.
Epoxy likes 60-80 grit abraded surfaces no matter if they are wood, fiberglass or metal.
40 grit paper is like gravel glued to cardstock. Not your best choice.
We edge sand many of our joints with 80 grit on the edge sander. Does an excellent job. I can't readily see where 40 grit would have a significant speed advantage over the 80 grit.
I would be concerned about trying this on a drum sander though. It would be too easy to get uneven pressure and cause a wavy edge. A fence would help a lot but still may not make for a perfect edge.
We've used 60 grit on a wide belt to face prep for gluing. Make your parts and extra 3/8" wide to allow for the inevitable edge dubbing and miss-alignment. Drum sanders don't do as well but might work. Leading and trailing edges will be dubbed so allow for a lot of trim.
The spread rate will change between 40 and 80...the rougher surface means more nooks and crannies so more glue is needed. Also, with 40 you will get more loose fibers so overall the joint will not be as strong.
A flat surface, within 3/1000", is required, so a drum sander may not do so well.