A flat panel door can be defined as a door in which the panel has no bevel or hip raise. It can still be considered a five piece door, as it consists of two stiles, two frames and a panel. The stiles are the vertical members of the frame, while the rails are the horizontal members.
The first step is to mill the wood for the stiles and rails of the doors. I am building three doors for some base cabinets. All three doors are the same size and the cabinets will be painted white. I am using poplar for the frame of the door and 1/4″ plywood for the flat panel. The stiles and rails are 2 1/2″ wide, 3/4″ thick and I cut them an inch or so longer than what I needed. While I was preparing the wood I also took the time to make some scrap pieces the same width and thickness to be used for test cuts. You can also see my set up block in the picture. You can also see my raised panel router bit set. For this project I will only be using the two bits on the left, the monster raised panel bit will stay in the box.
Mount the bit for cutting the profile on one edge of the stile and rails. I use my set up block to adjust the height of the router bit, although I still plan on making some test cuts in scrap wood. The profile in both the stiles and rails will be cut with the face side (the outside of the door) down.
A close up shot of my set up block. I keep this in a drawer right next to my raised panel router bit set.
The fence is then moved so that it is flush with the bearing of the bit.
After routing a profile in a scrap piece of wood, I use the rail section of my set up block to see if the two surfaces meet flush on the top surface. I got lucky this time and the fit was perfect 🙂
I then routed the profile on one edge of all the stiles and rails. Remember the cuts are made with the show side down. For this project it was not that important as the doors will be painted, but if you are not painting the doors you will want to take care to chose the best side of each stile and rail and then to route it with that side down.
I then took the stiles to the table saw and used a cross cut sled cut them to length. To calculate this length I measure the height of the door opening and added 1 /4″. My crosscut sled was not quite wide enough to enable me to use its stop block, so I used a fence clamp and a block of wood as a stop block.
The next step was to calculate the length of the rails. I wanted the door to overlap the door opening by 5/8″ all round. The depth of the groove in the stiles was 3/8″. The width of the stiles was 2 1/2″. So the length of the stiles needed to be:
(Door opening width) + (2 times 5/8″) – (2 times 2 1/2″) + (2 times 3/8″)
To many years in school dealing with the metric system means that I suck at working with fractional inches, so I always reach for my handy ProjectCalc Plus at times like these!
The router bit for routing the sticks in the rails is mounted in the router table and set to height using the set up block. Again the fence is positioned so that it is flush with the bearing.
Remeber those scrap pieces of wood. Route the profile in the end of one of them. When making this cut it is important the the rail be kept flat on the table face down and that it remain at 90 degrees to the fence. It is also important that the cut be backed up to prevent tear out as you are routing end grain. There are a number of commercial rail coping jigs that will allow you to achieve this easily. I don’t have one, although every time I build some doors I promise to buy myself one. So what I normally end up doing is to cut a piece of 3/4″ plywood or mdf, making sure that one corner is a perfect 90 degrees. Then I use that sacrificial piece of plywood to hold the rail square to the fence and to back up the cut.
Satisified that the set up of the router bit was correct, I made the coping cut in all of the rails. Remember to make this cut with the face side of the rail down!!
Calculating the size of the panel is pretty simple. Measure the frame opening, then add for the 3/8″ groove all round and then subtract to allow for expansion. With a solid wood panel you would want to subtract at least 1/8″ all round. With the more stable plywood panel that I’m using I subtracted 1/16″ all round. The groove is 1/4″ wide so the undersize 1/4″ plywood fits pretty loose in the groove. However with a couple of coats of paint it should fit just right.
Test fitting the panel.
I like to paint the panel before gluing the door together. That way if there is any expansion of the frame then there won’t be any unfinished part of the panel exposed. This is probably more important with solid wood panels, but it is a good habit to get into.
When gluing the door together the panel is not glued into the groove. Glue is only applied to the coping cuts on the rails. The glue should be done on a flat surface so that the door will be flat and it should be checked for square. I really find the square check for tape measures useful when checking for square.
In closing, and before you head out to the shop to start making a set of doors, I invite you to review a previous post on router feed direction and bit rotation.