Axial Constant Positioning of Back Bevels for Crown Moulding

by Russ Rego

This article will provide a thorough understanding on how to obtain axial positioning for generic back bevel knives while milling the back side of crown and cove mouldings during production.

When we talk about generic moulding knives, we refer to knives made for multiple axial positions while milling a wide range of profiles. Some good examples of generic knives are radius cutters, back bevel cutters and rabbeting knives. In this article, we will be referring to only generic back bevels for milling crown or cove moulding. In theory, the mathematical equations we provide will work on all the generic knives listed, providing the moulder is axially calibrated.

Manufacturing crown moulding can be very intimidating for many machine operators, this article will help you make crown set up techniques as quick and easy as possible, using all digital and mechanical counters installed on your machinery.

Years ago, before mechanical or digital counters were installed on moulder machinery, machine operators generally used a wooden sample for setup of what they wanted to mill on the moulder. Well in short, that sample shrunk or cupped over time, which made the task of duplicating a moulding difficult to say the least. Operators also wasted a lot of time and lumber trying to dial in a crown/cove without using any sort of measuring system. I remember what the walls around the moulder looked like with all those sample pieces we used for setup. Fortunately, today’s modern moulding machinery make it easier than ever to manufacture beautiful mouldings, with measuring systems in place on every spindle, on both radial and axial movements, they are only accurate if they are properly calibrated, and, if the moulding operator fully understands how the measuring system functions.

Look at the crown moulding design below, notice that it has a back bevel cut of thirty-eight degrees positioned on right vertical spindle, and a back bevel cut of fifty-two degrees on the left vertical spindle. Every crown moulding knife we design has back-bevel cutters of forty-five degree and lower milled on the right vertical spindle, and, all back-bevel cutters of forty-five degree and higher milled on the left vertical spindle. This specialized design feature will save thousands of dollars in knife steel cost over time.

Crown Moulding Design Layout

Below is a simple mathematical equation on how to obtain axial positioning for all back-bevel cutters while milling crown/cove moulding on an industrial moulder.

What I Have – Minus What I Need = Axial Moulding Knife Position

We have provided a height in inches of the bevels on the back side of every crown moulding we design, in this case.594” on the right vertical cutters, and .513” on the left vertical knives. Note; every crown/cove moulding will have different dimensions to work with, in every example, both the right and left numbers will represent “What I Need” in the equation listed above.

Look at the right vertical cutter, thirty-eight and one-half degree back bevel cutter below, the blue shaded area is the actual moulding knife itself. The brown number 2.312” represents the length of the moulding knife in the cutter head. The brown number 0.912” represents the distance from the edge of the cutter head, to the intersect point of the 38.5-degree bevel, this represents “What I Have“ in the equation listed above. The brown number 0.787 represents the total height this bevel-moulding knife can cut. Please refer to our article on Aligning Moulding Knives in the cutter head for easy reference, this article will help you understand the concept we are explaining.

Crown Bevel 38.5 Degree Layout

We provide the back-bevel height dimensions on each crown/cove design, in this case the number .594” on the crown moulding above, must be smaller than the numbers in height (in this case .787”) on the back bevel cutter, for this knife to be able to work.

Now, let's look at the left moulder spindle, fifty-two and one-half degree back bevel moulding cutter below. Again, the blue shaded area is the actual moulding knife, the brown number 2.312” represents the length of the moulding knife. The brown number 0.778” represents the distance from the edge of the cutter head, to the intersect point on 52.5-degree bevel, or, “What I Have” in the illustrated equation listed below. The brown number 0.591” represents the total height this particular moulding knife is able to cut.

We've designed both these bevels with a one-half degree back cut per side, this back cut assures we will touch both the ceiling and the wall when installed, provided the walls are square. This extra one half degree back cut helps balance cupping of the crown moulding after the milling process; too much back cut will change the overall desired height and projection of the installed crown moulding. Please refer to our article on Backout/Relief cuts for a better understanding on how to help alleviate these potential cupping issues.

Crown Bevel 52.5 Degree Layout

In summary, the mathematical equation, “What I Have”, is a constant built into the template and moulding knife design. “What I Need” changes with every different crown moulding design, these are listed on the backside of every crown moulding, the “Approximate Axial Number”, is the dimension on how far you must lower the moulding knife bevel below the bedplate. We color code all the dimensions for you, this will build confidence in your ability to find the proper axial settings quickly.

Let's say you have lost all your paper work for your crown/cove, and bevel designs, but you have a sample piece of wood. Here is another simple way to do the same mathematical equation we discussed earlier, with a straight edge and your digital calipers. From the reference side of your cutter head (this is also the .000” point on your moulder machine). Place the straight edge against this “0” point, then measure with the digital calipers from “0” point to where the bevel and straight (flat part of the knife) meet. The number on your calipers now represents “What You Have”. Next, take your sample piece of wood and lay it flat on a table, measure from the table to the intersect point of the crown, (where the top knives intersect with the side knives), that number on your calipers represents “What You Need”. Now subtract “What You Need” from “What you Have” it will provide you with an approximate axial number.

Simple math if you think about it, this basic system will save you time and money if you not able to afford an expensive Optic control-measuring stand, which is capable of measuring both the axial and radial dimensions on any moulding knife.

If you have any further questions on axial measurements contact us. for assistance, we would be glad to help you succeed.