Henry, when I hit the pause button on woodworking20 years ago the only heavy metal I sold was my jointer. I am going to use the small sled to flatten one side of a board. I would be interested in seeing your thread.I guess there are at least two versions of planer sleds.
1. What I see in above responses is likely what Keye (OP) is asking about, given his mention of plywood.
2. There are also planer sleds that are used when one does not have a jointer and needs to establish that first flat or straight face or edge on a rough piece; a planer will establish a parallel face and a consistent thickness, but does not create an initial flat or straight face/edge without a sled. I have made and successfully used one of this type of planer sleds to take the twist out of a piece of timber - and if interested I can dig up the NCWW thread where I show that. Note that this is NOT my design or idea, I believe I saw the idea in FWW mag (online).
Do you need a special blade to cut melamine? I seem to remember you can ruin a blade by cuting MDFI use a melamine covered piece of shelving from the big box store. Without looking it is about 12 inches by 36 or 48 inches. I also put wax on it every now and then.