Making Crown Moulding on the Shaper

Tips on using a shaper to make crown moulding. August 26, 2008

I recently purchased a 4" corrugated shaper head to make custom moldings. I was wondering how most make crown molding with a shaper. I did a small run of 100'.

My procedure was as follows: Rip strips 1/2" wider than the knife stock. Then surface back side to 3/4". (I needed to finish at 11/16). Then run through the shaper centered on cutter. This left a 1/4" ear on both sides. This means the shaper fence was set with no offset. I then cut the back angles on the tablesaw.

This proccess worked really well, however it does seem wasteful. If I run a 3 1/4" crown profile that is ground on a 4" knife, I would start with 4 1/2" wide blanks. This seems like too much waste. Any information as to how others are doing it would be greatly appreciated.

Forum Responses
(Solid Wood Machining Forum)
From contributor U:
Most of the time 1/4" over the size of the finish moulding will do the trick. Your moulding is 3 1/4", the blank would be 3 1/2", giving you a 1/8" to take off on each side. There are no set rules on this and I am sure others will have much to add.

The knife was made at 4", most likely to incorporate what we call axial constant (constant reference point). This constant reference point helps reduce setup time and enables you to reproduce the exact moulding over and over with no differences. This axial constant is most likely 10mm or .394". If you set the base of your spindle this distance below the surface of the bed of shaper it would most likely set itself you to the size of your print or sample. Most manufactures of fine tooling will have some sort of constant built into their tooling.

From contributor J:
Contributor R is correct. A 3 1/2" blank is all you would need. Your blank can be smaller than your knife length. You won't get those "ears" as you describe so your shaper fence will need to be off set. Maybe even have a wood spacer tacked on to it. This should give you much better yield.

From contributor R:
There is no need to rip wide when running on a shaper, rip it net. Planing 1/32 to 1/16 heavy and offsetting the in-feed fence to match is good practice to insure no flat is left on the curved section. The out-feed fence should be aligned with the minimum radius so as not to snipe. If your fence is not independently adjustable a piece of plastic laminate glued to the out-feed side will work nicely. Sawing the angled relief works fine for the back side.

From contributor U:
Just a thought to add to Contributor R's post. If you make a shaper knife to run on the back side of your crown it may not be the most versatile way to do this. Maybe making a shaper knife for each side of the bevels would give you more adjustability for different crowns with the same bevels. Locking in cutters to that one size can cost you a lot more money if you do a bunch of different styles of crowns. Most common bevels are 45* 52* 38*. You could design the top cutters to always work together with the side cutters.
Just a thought before you spend too much of your hard earned money. You save labor because you still have to rip or shape both sides the other way.

From the original questioner:
Thanks for the responses. I'll try starting with a blank 1/4" over net next time. I agree that it makes more sense to have separate 38 deg and 52 deg knives. The last molding was a 2 1/2" with a 45 deg back bevel - kind of an odd duck. Guess that's why I had to make it. It'll probably be a long time before I make another 2 1/2" crown.

From contributor J:
I think Contributor R had a good point. If you are doing enough of one size, buy the back bevel knives - one pass. I really can’t see with crown moulding why you would want to buy shaper cutters for different back cut angles. The back-cut angles are not seen.

Why buy a cutter and make a pass through the shaper when you can tilt your table saw blade to any angle and make a pass through that? Just trying to think of the least expensive way out for you.

From contributor O:
I agree, buy two sets of knives, one for the top and one for the bottom. Run the bottom cut first, flip the piece over, and run through the machine again for the top cut. The reason you run bottom first is so that when you flip it over you do not damage the face of the crown.