Machining S-Curved Crown Moulding
Woodworkers weigh in on a complex machining challenge: crown moulding with both an inside and an outside curve. September 5, 2006
Question
I need some advice on a setup for running some curved crown. Regular cove and bead about 3.5 inch. Tricky part for us is that the crown is an S-shape as opposed to just a convex or concave shape. We have a good shaper, but I am unsure of what sort of head/knife setup we should use. Shaper is also tilting spindle, if that helps. Any ideas?
Forum Responses
(Architectural Woodworking Forum)
From contributor P:
For an S-curve, the tilt will not do you much good. The problem is the rub collar is on the spindle and does not ride well against the template. It is also hard to keep the spindle axis in the correct orientation to the template.
You did not say if it was paint grade or stained. Your method of glue-up must be considered. You have to anticipate what it will look like once you hog it out.
A bent laminate is hard to control under a feeder due to its narrow width. I usually start with a large glue-up or stock that is thick enough to begin with. This has extra meat on it to hold on to.
I create a template to ride against the rub collar and calculate to offsets. I would take several passes using smaller rub collars in increments or reposition the template relative to the piece being shaped after each cut. You can use a standard corrugated knife head. Be aware of knife projection from the head. I have run some enormous heads with scary knife projections in the past. Not fun. Be careful, use your feeder, and enclose the cutter area with a plywood box that has adequate dust collection.
From the original questioner:
Thanks. I have access to a lock edge head with an attached rub collar. I guess I could just make successive passes with knife adjustments instead of bearing adjustments. Little bit weary of the power feeder sending something in a direction I don't want. Does it work well?
It is paint grade.
From contributor P:
I'd be weary of adjusting out the knives every time. By the time your profile is cut to depth, you will not have much knife buried in the head.
I'd go with the incremental adjustment of the template. If you use screws to attach the template to the work, be extremely careful of their placement. I can tell you firsthand of what that is like.
Make sure the template projects past the end of the stock you're cutting. You want the template to contact the rub collar before the knife makes contact. Make the template out of 1/2 inch MDF and large enough to hang onto. This will help you steer it under the feeder. Wax your table and don't put too much roller pressure on the work. This is not a real efficient method, but for only a few pieces, it works slick once you get the hang of it.
Pay attention to your glue-up so you have a minimal amount of "against the grain" cutting. Do a dry run with the feeder without shaper running to see how it all behaves.
From contributor D
Paint grade? Don't even make it yourself. Check Ooutwater - they've got all kinds of flexible mouldings.
From contributor B:
There are machines designed to do serpentine crown and a tilting arbor shaper does not fall well into that type of category. As mentioned, the geometry of having to keep the moulding dead-on lined up with the front center of the cutter is a nightmare.
A standard shaper is too dangerous, in my opinion... from experience! We have made modifications of our moulder to make these. If you want to email me specs I'll give you a price.
From contributor A:
I agree with everything contributor P has said. If you can't change the rub collar, then make three or four templates. Slowly sneak up on that final pass. That insert tooling is a scary setup with the knife sticking out of the head like that. Check E-bay. There are the big crown moulding cutters on sale there cheap. I bet I have bought 10 of them. Usually less than 100 bucks. Really important to have that template longer that you need it. You can also install a pin in your table. This will give you something to bear against when you start. Sometimes this helps and sometimes it doesn't.
From the original questioner:
How about a custom 3 wing cutter? I've been told this will solve the knife protrusion issue.
From contributor A:
These are the best for running the crown that you are talking about. Just remember to run them at low rpm's. The Williams and Hussey knife is the exact copy for the straight runs.
Cherry crown:
From the original questioner:
Thanks for the input. We've made curved crown before. However, the S-shape seems to throw in a whole new set of issues. I'm talking with the guys at Schmidt today to see what they can do for me. Also having Ballew Saw & Tool price out a 3-wing cutter. Thinking of sending contributor B our glue-up and moving on to more productive things. But hey, us woodworkers can't say no to a complicated task like this.
From contributor J:
While good woodworkers can't say no to a complicated task like this, a smart businessman can. I'm confident in my ability as a craftsman to build just about anything. Often I'll think a complicated task through to the end, listing procedures in order, doodling jigs and fixtures, thinking of safety concerns and calculating material and labor costs. All the time knowing that the most important tool is the telephone. And the most valuable knowledge is not knowing how to build it, but why not to. I'm in business to make money, not molding.
From contributor A:
This is some that I made last night after the guys left. 4 pieces, 4 hours with only one slight mishap. The wooden blank needed to be 4 and 7/16" tall, so I ran the first piece at 2 and 1/8" tall. I then glued on a 2 and 5/16" top and staggered the joints. Ran the piece again on the same pattern without ever taking anything off of the pattern. Seems simple enough, but I will concede probably the most dangerous thing since I dated my old girlfriend's little sister.
After the second pass:
We trimmed the ends and placed the 4 pieces today.
This was the last piece that I did last night and was looking in the garbage can for drops. That is why this last piece hangs over with no support. It was that or go out to the trailer in the dark for another board. This was the piece with the mishap, but all's well that ends well.
From contributor A:
To the original questioner: What did you end up doing with your crown moulding?
From the original questioner:
Very nice job. The job that I was working on stopped due to a lack of paying on the owner's part. Now over a month later, we've just re-started the job. I just ordered a custom made three wing cutter for the curved crown. We're excited to produce the S-curve.
From contributor P:
If this is something you continue to do, you may want to look at a Mikron or USconcepts machine. Both have the capability to make "eyebrows," or convoluted arches. I know USconcepts also made a flexible feedwork for shapers for a while, but they can be a little scary - I launched a 7' piece of maple bar rail across the shop with one!
