I tried to run some s4s with a Lobo 6 head moulder with jointer style infeed. The s4s came out fine on the sides, but flatness really sucked. The material came out as if I'd used a regular single sided planer. All it did was mimic the already wavy bottom. I thought the jointed infeed was to flatten material before entering the moulder. What am I doing wrong?
(Solid Wood Machining Forum)
From contributor M:
The first thing that comes to mind would be to check the air pressure on the infeed rolls. If you have it set too high, you'll flatten the board before it gets to the first bottom head, just like a planer does. I don't know how Lobo does it, but on mine I have a separate air regulator for the first roller and have it set with no more the 1 lb. of air pressure so it mimics the amount of downward force you would have hand jointing. (The air cylinder does have a spring in it, so there is more than 1lb. of downward pressure). On the second roller, I have more pressure, but I still don't overdo it. Somewhere around 5-10 lbs. After that is when the air pressure gets dialed up to hold the board down. Start with that.
This may seem obvious, but don't let the knives get too dull on your bottom head. I find that I have to change those more frequently than I do on my other heads.