MDF or Medium Density Fiberboard (not to be confused with OSB or Particleboard) is essentially a composite wood which is created by taking the remnants (wood fibers) from cutting traditional wood stock down and combining it - usually - with a wax/resin binder to create hard and durable sheet panels (usually 4x8). MDF is very dense and heavy, but since it's essentially made with 'sawdust and glue' it's usually far more prone to tear-out than plywood, softwoods, or hardwoods... hence Michael's question.
Great question! Hopefully I'm able to help out a little bit. First off, no, there are no problems with using Kreg Pocket-Holes in MDF... but there are a few a few things to watch out for and be careful of:
1) Plunge your drill bit at full speed. When drilling the Pocket-Hole itself, be sure and use a sharp Kreg drill bit and bring your drill up to full-speed before plunging down the drill guide. This will create a cleaner Pocket-Hole and reduce the chance of tear-out.
2) Use coarse-thread screws only. Using coarse-thread screws will improve your hold in the material and reduce the chance of strip-out of the screw.
3) Use SML screws only. Not SPS. Using the larger head of the SML screws will reduce your chances of the head being pulled directly through the material when tightened down. For more information on choosing the right screw, look here.
4) Use your drill's clutch settings. Because of MDF's density consistency and pre-disposition to strip-out, setting your drill's clutch setting appropriately should dramatically reduce the likelihood of over-driving the screw.
5) Use more Pocket-Holes. Since each individual Pocket-Hole created in MDF won't have as much holding pressure as it would in other materials, why not add a few more!?!
In addition, I would also tell you Michael to make sure that if you're using MDF to build a bed for children to make sure you overbuild everything to make up for any limitations the MDF may have and to also be sure that there's no moisture in the area. MDF can be incredibly strong in the right conditions, but becomes incredibly weak when exposed to moisture.
Good luck and good woodworking!
One thing to be careful about is that MDF describes a type of panel or board, but not a specific item. Just like particle board (and plywood), there are grades of MDF. Your home center may not have "regular" grade, which is 48 lbs. per cubic foot, and the cotrrect grade for furniture. You should always ask if the panels are not stamped or marked in any way. "Light" grade (and there is also "ultralight" and "superlight", which are used for mouldings and paneling respectively) - 38 lbs. per c.f. - is cheaper, but better suited to use as a surface covering than for furniture.
If you are using the right grade, you should have little problem if you follow Kreg's recommendations. Just stay away from moist or damp areas. MDF will swell.
You may think I am nuts (and my wife will agree) but I have noticed a definite difference in the MDF from the east coast and what we have out here in the west. I have jigs and a router table that has eastern MDF and it is as hard as cement, shapes nicely, cuts smooth, and drills without chipping, but the MDF out here falls apart when the humidity climbs over 50% (that's an exaggeration), but rumor has it that the 2nd little pig was using this for his house of wood. I have taken in samples of the eastern MDF to my different wood suppliers and they just shrug their shoulders -- no can do!
I am wondering if that is an issue with some of the replies here? If someone can shed some light on this it would be nice.
I use MDF quite a bit and I have not had any problems using pocket holes. The only issue I have had is just the finished look since your only option is to paint it.