Machining crown moulding
One of the biggest problems I have is teaching operators how to set crown mouldings. The method I use is profile from the top head. Adjustable angle cutters from the side heads. To do this, you must have two right heads and parallel the second right head fence. The first right head is used to dress the edge of the board for control. The bottom head is a straight knife. I have never seen a crown that had two points parallel enough to run from the bottom head. I suppose you could make them this way to accommodate this. Running the profile from the bottom will flatten any points that are supposed to stay clean and sharp. Also, if you run the underside to include the angle cuts, that can include a large swing that may not fit or cause problems, forcing you to open all bed plates and chip breaker assemblies to the point of losing control of material.
As far as holding the profile down from the top head, we use a simple custom-made pressure plate to be able to make contact with the two most outside high points of the profile. If you only have a single right head, you must make a knife that is capable of the angle cut along with the straight to be able to dress the entire side. This custom-made pressure plate has been a real asset. We use it for everything. It's very simple and safe. We do not run axial constant, all you need is the ability to measure your tools axial. We use sample pieces to set with. It normally takes 15 minutes per profile. We try to run our crowns back to back. We tried at one time to run profile from bottom and run the straight with angles in the top head. What we got was a large inventory of various bottom knives and templates.
The best way for most companies to run crown is to let the side heads only to cut a single angle. This allows the side knives to be used for many different crowns. Be sure to make your total angle 92 degrees, not 90. Carpenters can not build a square wall and this allows for that.
With the side cutting the single angle, the top head can be positioned to cut the rest. When I set a crown, I lower both sides' cutters down a little. This will produce a small flat on both sides. This allows me to make sure that the top profile is exactly where I want it. I then raise the side heads just until they blend. This way the moulding is held secure against the fence of the moulder. Otherwise, the wood can move under the top head.
This was an article in a back issue of "The Profiler", the Grinderman's Association newsletter.
Dave Rankin, forum technical advisor
Comment from contributor A:
For any normal crown (or bed mould or inside corner) up to about 5" or so wide and 1 1/4" finish thickness I run good face down and profile with the last top and bottom heads.
Here is the thinking: Good face down = better yield with scant material. The exposed profile always cleans up when cutting with the bottom head, just like t & g.
Profile with top and bottom heads = 2 head changeover, much easier and quicker than a 3 or 4 head change when profiling with the sides. Plus I typically have more horsepower per profile length on the last top and bottom compared to the sides.
I lift up the feed roller after the last bottom head so as not to impart shine on the finished (down) profile surface, and run an OSHA-approved chaser stick to clean out the last good piece of crown.
Leave straight knives on the side heads, just change the top and bottom, rock and roll.
Some like to make the bevels on the top and bottom knives blend a little away from the right hand fence. Whatever works. I don't use the movable left hand fence after the last bottom head at all when running crown.
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