i finally got my head around the vacuum hold down/bleeder board concept and how it works. it amazes me that the mdf or trupan is porous enough to allow the suction of the vacuum to hold parts in place while cutting. i will have to see it to believe it. i will be purchasing the prs 96-48-6 soon and was wondering how long does the bleeder board typically last since it is also the sacrifical board that the cutting material lays on top of. i understand that this all depends on how much cutting you do but if i am cutting several shapes from a single 4x8 sheet of plywood how often will i need to change out the bleeder board? after two sheets? after three sheets?