Here's the problem: When you install dentil molding, how do you get the corners to come out evenly? Below, Michael Dresdner and Rob Johnstone address the sometimes inexact science of evening-up dentil molding in their response to a question from a Woodworker's Journal eZine reader.
Q. I have seen a couple of methods of making dental molding including using a table saw or a router indexed to the previous cut. But how do I determine the size of the dentil molding so the proportions look correct and come out even on the ends?
A. Michael Dresdner: "Proportions will look good if you make the "teeth" square. The height is usually controlled by the size of the molding they will adorn, and that automatically gives you the width. Making that come out even on the ends is a bit tougher, since not all moldings will be the same length, or even a multiple of the same length. In cases where there is only one size, you can divide the width of tooth and space by the total length, adjusting the size of each tooth to make it come out right, with a full tooth (not a space) on each corner. Where that is not possible, do what you do with dovetails -- shift the molding so that there is half (or some percentage) of a tooth on each end. That will look better than having two spaces, or having a space on one end and a tooth on the other. In most cases, no one will be looking at the corners, and if they do, seeing something that looks uniform and intentional is just fine."
A. Rob Johnstone: "Any evenly spaced sequence will work out well for one application and not so well for another. The trick, in my opinion, is not so much getting the molding to 'come out even' at the ends (technically possible ... but probably only for those from obsession; you know, like scroll saw experts), but adjusting the miter or end cuts so that they are balanced. Proportion is a matter of taste within accepted norms. The advantage of making your own dentil molding is that you can please your own taste. For example, you might want a wide raised section and a narrow lower segment ... go ahead and knock yourself out."
From the Woodworker's Journal eZine 2004 archives
For your projects, if you do what most of us would do and buy pre-made dentil molding, there's still an easy way to make things work out perfectly - provided you're building the piece to which the dentils will eventually be attached and have the freedom to make minute changes in its dimensions: Buy the dentil molding first, find "perfectly even" segments of dentil molding that are close to the dimensions of the thing you want to make, and build accordingly.
On a couple of occasions I've had the honor of trimming a room or two with a crown molding that came with a separate pre-made dentil molding. From doing so I remember two things: getting pre-made dentil molding to "work out perfectly" in trim work is virtually impossible, and worrying about it too much is counter-productive.
Apart from the evening-out problem, dentil molding can be a pain to cut on a chop saw, owing to its small size, and for the pre-finished variety, its slipperiness. If you're planning use a miter saw to cut any amount of pre-finished dentil molding - or any trim at all, for that matter - I sincerely recommend using a blade with a negative hook angle, anti-vibration reeds, and an appropriately high number of teeth, like this one from Freud.