Installing plenum board

[Ken M]

Just started building a 48 x 96 PRS. Installed the deck and was going to put on the plenum and noticed that the decking is 48 x 96 and the MDF is 49 x 97. Should the MDF be cut down to 48 x 96 or does this really matter? Not sure if this is critical. Thanks

[bleeth]

You need to be very sure of where your x and y zero lines are. Then have the plenum overhang them a bit (1/4-1/2 inch) and then trim them to zero with a heavy bit (3/8-1/2). This gives you registration for the future. It also allows you to check very well for square. On first go round you may want to temporarily set it with a few screws, check for square, readjust if necessary after squaring the gantry, and then put it down permanently. A little hanging over the high sides of x and y is fine, but I like to trim the plenum to an even 48 x 96 and will have the spoilboard hanging over a little. Don't forget to seal the edges when you seal the top and plenum channels. I also like to trim the deck at the zero lines.

Welcome aboard!

[curtiss]

On the near side open end, You might want the bit to overhang/ reach about 1 inch past the end of the bed.

That way you can engrave into the edge/ end grain of a small item if you want.

[Ken M]

Does the plenum board need sealed with polyurethane? I see several mentions of it in the forum but it does not mention this in the shopbot supplied directions. Is this step optional? If needed suggestions on type? Thanks

[curtiss]

The plenum board should be sealed with several coats of poly after you cut the zones as desired.

Not sure what you are using above that, but that layer would not be sealed except for around the edge, as you want air to pass through the upper surface.