Cutting a Bead on a Curved Backband Moulding

      Tips on fine-tuning an elliptical shaper jig so that it will profile a bead correctly on the inside edge of a curved piece. June 24, 2007

I've got this project that requires a laminated arch, curved casing, and a curved backband. The arch and casing are cake and I've already finished them. The pain is the backband. I wish I had the time to draw this moulding, but alas I don't.

2" wide. Typical 1/4 x 3/4 rabbet for the casing. The profile is a two sided 1/4" diameter bead. I'm running the edge on the shaper with a bearing. The top cut is on the W & H moulder.

I've got the shaper set up and working. The problem is the elliptical jig on the Hussey. It compensates for irregular patterns by a spring loaded bearing. Hence, the outside of the curve is deciding where the bead is cut on the inside of the curve. Typically on a casing, this is no big deal. Pushing a little paper makes this go away. In this case it has to perfectly match the bead coming off the shaper. Basically I need 2" templates that are consistent around this curve. I was thinking about sizing with a pin and a router bit. Please don't tell me how great a CNC would be in this situation.

Forum Responses
(Architectural Woodworking Forum)
From contributor T:
Are there no CNC'ers in your area that you can go to for a good clean template? Or
have them cut it for you. Just so you know, I have a CNC and made plenty of arched pieces, but have never run an arch on our W&H.

From contributor B:
I'm not really clear on your problem other than the bead isn't coming out correctly on the inside edge of the moulding. Here are a couple things we do, though, with this type of situation. First, you can apply your backband to a 3" to 4" wide bottom template/form. This will keep the spring-loaded pressure bearings further out from the fixed post side bearing and balance out the curved travel under the head somewhat.

Second, you can put a larger fixed bearing on the post side. This is not done in combination with solution #1. This might give you more pressure on the backband depending upon what the minimum distance between fixed and spring loaded points is on your fixture.

Also, you can try the knives at different locations on the cutter head... close to posts and far from posts. This might make a difference. Make sure you cut your rabbet after profiling so as to keep the bottom width of the backband at max thickness during the W/H process.

As a last alternative, you can see what it would cost for a shop like ours to get you out of the jam...

From the original questioner:
Contributor B, thanks for the suggestions. We're not really in a jam. I was called in to bail my good friend out of his jam. He's too busy on a jobsite and the boys in his shop don't have a clue. I inherited the jam. All of my templates had to be made off of that imperfect curve.

Before you got your CNC, how did you cut your templates for accuracy like the one I've got? The inside/outside situation rarely come up, except when fussing around with matching edge profiles, otherwise an inconsistent width, smooth pattern runs just fine.

I've got a couple of extra table bearings (like the Hussey ones). I plan on bolting one to a big router table, and size my patterns between the bearing and a 3/4" router bit. They will end up 1 3/4" in width.

I appreciate your advice. Next time I'll get my friend to outsource the templates to a CNC guy.

From contributor B:
Prior to the CNC, we cut templates just like everyone else… whatever would work best for the job. A lot of spinning routers on sticks, etc. A serpentine would have been bandsawn and sanded to the line, most likely. Not the best or easiest way!

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