Issue with Forstner Bit

[Dmod]

My experience with the Forstner bit is that it tends to rip out a small circular section from the back of the MDF I'm drilling.  I drilled my holes top down using a power hand drill and it's the weight of the drill pushing through the last layers of MDF that cause it to break off some of the MDF at the exit.

I usually end up with a clean hole on the front side, but not so much on the back.

Is this a common problem, or is there an error in my technique?

[MustardTent]

I think it is a common problem for people new to woodworking, like I was when I built mine.  I know there are people here better at woodworking than I, but I would suggest one of two things:

1)  Drill from the front of the piece to the back so anything like this is hidden, or
2)  Place a piece of scrap wood under your piece to prevent this kind of thing from happening.

[fatfingers]

2)  Place a piece of scrap wood under your piece to prevent this kind of thing from happening.

This is definitely the way to go with almost any drilling, in my experience.

[ScottS]

As others have suggested, placing a piece of scrap underneath the hole will tend to prevent "blow out" on the back side of the piece.

You might also think about improving your technique, however. One thing I'd suggest is that putting a lot of pressure on the drill causes the wood to break when it gets thin. You might have better results if you ease up on the drill as it's about to emerge from the back of the piece. In addition, sharper bits tend to work better. MDF, in particular, is very hard on tools. If your forstner bit is dull, it will tend to rip, crush, and break wood fibers rather than cutting through them cleanly.

BTW, sometimes you simple can't get a scrap block in place as a backer. For instance, you might need to drill holes for new controls in an existing panel. An alternative to the backer block, which isn't quite as good, is to cover the back of the wood with duct tape. The idea here is that it'll hold the wood in place until the drill bit has a chance to cut through it cleanly. Again, you'll need to ease up on the pressure as the bit is about to exit the piece.

[needlesmcgirk]

I think this problem might also be directly related to the quality of the power drill.

[Kaytrim]

Rip out on the back side is caused by one or both of the following reasons.  Too much pressure on the drill or a dull bit.  It sounds like your bit is dulling which is normal with MDF.  When I am drilling a hole in a piece of MDF I drill a small pilot hole 1/16" or 1/8" at the center point of the hole.  Then I drill through partway on one side and finish it off from the other.  If the bit is dull or I am pushing to hard I never get a rip out when I finish the hole.  I also use a hole saw or spade bit when I cut the button holes or joystick holes.

l8r g8r

[NiteWalker]

Scrap block underneath FTW.