If you have followed Obsessed Woodworking over the last 18 months, you’ve read a number of articles on pocket hole joinery. We like pocket hole joints and use them often in our woodworking projects, and know a little bit about them.
You will find some of our past articles on pocket holes here:
- Picture frame joinery, including pocket holes
- Attaching table legs to a table apron using pocket hole joinery
- Screw sizes for pocket holes
- Pocket hole joinery strength for shelving
- Pocket hole joinery and plywood
We have a collection of pocket hole jigs, singles, doubles, and such. We know the story about Craig Sommerfeld and his wife’s request to hide the screw holes in the new cabinets he was building for their kitchen. We know his invention – the pocket hole jig – and the history of Kreg.
The Kreg jig is the standard by which all pocket hole jigs are measured. Whether single hole or even triple hole, the Kreg jig, in all of its configurations, clamping, and kits, is a worthy addition to your woodworking shop tool inventory. If you build picture frames, cabinets, or tables with aprons, or any number of other projects, it’s like you have a pocket hole jig or two.
For as little as $15, you can have a single hole jig and drill bit, and prices can be as much as $140 for a three hole jig kit. Still, it’s a bargain at any price for what you will be able to do with it in your joinery.
Certainly, pocket hole joints are effective with solid wood. This is a given. As for plywood, this is also a given. If you noticed, we have already discussed pocket hole joints and plywood, and it’s the last on the list of past articles above.
But what about particle board, specifically medium density fiberboard (MDF?
What Is Medium Density Fiberboard?
MDF, as it is called shorthand, is an engineered wood made by breaking down both hardwood and softwood residual pieces into fine particles that are then fused together with wax and a resin binder and formed into sheets under high pressure and heat. It is generally denser than plywood and stronger than particleboard.
MDF’s surface is very smooth and free from knots and mars, making it a good choice for a painted finish. It is also cheaper than plywood.
However, MDF is very absorbent and has a tendency to soak up water and swell. It must be sealed well on all sides and edges to prevent this from happening. In addition, since it is made from wood fibers and fine particles, it does not take well to nails and screws.
However, that does not rule it out as a suitable material for pocket hole joinery.
Pocket Hole Joints and MDF
Pocket jig kits come with a drill bit that is specially designed for pocket hole screws and joinery. It is stepped in shape and size and is tipped with a narrow width pilot hole drill, as well as a flat-bottomed counterbore shaft for the head of the screw.
The jig is set to about a 15-degree angle, and the drill stop collar is set for the width of the second piece to be joined so that the screw will reach the midpoint in that width. This will ensure a solid joint with good strength.
The screws that Kreg provides for use in pocket hole joinery are hardened and self-tapping and have a wide washer head that stops firmly at the counterbore shaft of the drill bit. The screw threads are long and deep and will grip the second piece strongly to the first piece and secure a solid joint.
Kreg pocket hole screws come in two styles, the use of which will be determined by the material being joined:
- Coarse-thread screws should be used with softwood pieces – the threads are deep and aggressive in their grip; and,
- Fine-thread screws should be used with hardwood pieces, as these will not tear the fibers and lead to splits in wood ends.
Most woodworkers will choose the coarse-head screws for joints involving MDF. Kreg itself recommends their use with soft woods, particleboard, MDF, and plywood.
Kreg screws for pocket hole joinery differ from regular wood screws. The underside of regular wood screws ends to be conical rather than flat like Kreg screws. That flat shape tends to send the drilling force to the screw tip, and with the pilot hole tip of the drill bit having prepared that path for the screw, it is unlikely to rip the MDF.
When asked directly about using pocket hole joinery for MDF joints, Kreg itself suggests that it is definitely a good choice but with one caveat.
Kreg Customer Service has stated:
“However, you will want to be very careful when driving your screws. If the clutch is set too high, your screw will continue to drive and will come out the other side. I have found it best to have your clutch setting low and work your way up until it seats the screw correctly and engages the clutch.”
Kreg’s pocket hole screws have a square drive that provides high torque while the screw is being turned. The washer top of the screw stops it well when it has reached the flat counterbore created by the drill bit.
All Kreg jigs come with a chart identifying the right size screw based upon the dimensions of the pieces being joined. This makes it very simple to choose the right size for your project, so simply follow the chart.
How To Drill the Pockets
Setting up the jig is easy. You’ll want the pocket hole to stop just short of the edge of the first piece and to exit the first piece at about the center of the second piece. As mentioned earlier, you will want the screw to reach about the midpoint of the second piece’s width.
The jig takes care of aligning the pocket hole properly for a strong joint. When the jig is attached to the workpiece, the angle is automatically set up properly for you.
Pocket holes should be at least one-half inch from the edge of the first piece being joined. This will keep the piece from splitting when the screw is tightened.
The set of instructions and charts that comes with a Kreg jig kit are clear and easy to follow, and all of the thinking has already been done for you.
If you’d like to see all of this in action, we found a very helpful video that shows an easy way to pocket hole MDF.
We put a lot of faith and stock into what Kreg says about its jigs, drill bits, and screws. If Kreg Customer Service says you can pocket hole MDF, we believe it.
Using the right screws, and showing care in the drilling of the pocket hole, are the keys to creating a strong joint that won’t tear the MDF.
The second video we watched in preparing for this article is a bit long at 14 minutes, but it’s a cool project – a home desk made entirely from MDF using pocket hole joinery.
If you’re looking for a new project and you have a need for a desk, this is a good project to consider.
We like pocket holes and pocket hole joinery at Obsessed Woodworking and have learned how to use it with a variety of materials, all with great success. Don’t hesitate to use it with MDF.