Relief Cuts for the Back of Mouldings

Advice on dimensions and moulder setup for making relief cuts on the backs of mouldings. April 21, 2011

Question
On mouldings with a profile, base, cases, etc, what is the best way for the back side relief profile? Many half moon cuts, one big relief cut, two, or many small slots?

Forum Responses
(Solid Wood Machining Forum)
From contributor D:
The main reason for relieved backs on such moldings is to ensure that the visible edges of the moldings stay tight against the surface they're nailed to, even if the molding cups outward a bit. Any method that leaves parts of the molding towards the middle untouched (i.e. slots, half moon cuts, etc.) won't achieve this. You're looking for a wide, shallow recess.

---

From contributor J:
I have never used more than one relief on the back of a moulding. I usually go about 1/16" to 3/32" deep +/- for personal/customer preference, and about 2/3 the width of the moulding. It is usually centered unless the customer has specific nailing preferences. 45 degree angles on both sides of the cut to prevent tearing of the wood fiber. Many small cuts help to take up some of the swelling in wide pieces of flooring, but most mouldings don't experience this issue, they are simply not wide enough. Bottom line is to find a technique that works for you and keeps the customer happy.

---

From contributor J:
The most efficient way to make a relief head is to use a six inch head, four knife, most profiles are not over six inches. If it is, use the same technique below, but with a bigger head. Use the first two pockets for straight knives, leave them there all the time, just touch them up now and again.

The second two pockets use to change out three sets of relief cutters. I say three sets because I have always used three sets, different widths, this technique works for just about everything. The straight knives produce the finish on the bottom face, the relief cutters should be set 1/16" to 3/32" higher than the straight knives to leave the proper relief. It would be nice to make individual sets for different profiles with just two knives, but no one I know does it, too costly.