Ways to Machine Radiused Casings

Woodworkers discuss various methods of making curved mouldings, including CNC and moulder techniques as well as ways to join segments. December 2, 2006

We are getting a CNC this summer. I'm looking for info on running radius casings on it. We currently make forms and glue and strip our casing. On stain grade, we keep the strips in order to keep the grain pattern. I thought we could cut the forms on CNC, and then glue and run on our arch shaper. Seems like we should be able to run it all on the CNC. Can you get a head for CNC to run corrugated steel? We have over 900 different profiles that we run on our Weinig moulder and use those knives for radius casing.

Forum Responses
(Architectural Woodworking Forum)
From contributor T:
It sounds like you should consider a machine with C axis capability and then look into a moulder head to cut the casings direct on the machine.

From contributor G:
We (Courmatt) market an aggregate head that accepts a moulder head. Needed info would include type of machine and toolholder type.

From contributor C:
I also considered running a moulder head on our CNC to make radiused mouldings. I decided not to pursue this option for the following reasons:

1. One of the biggest challenges with narrow parts is holding them down on a CNC. We have a machine with pods, so in addition to making a form to bend the laminations, we would need to make a dedicated spoilboard to hold the blank on the pods. Running one or a hundred, there is no economy of scale to offset the cost of fastening the blank to the spoilboard with screws and removing them for each run.

2. The CNC only knows coordinates. It cannot compensate for springback or any deviation in the blank's radius.

3. I couldn't find a moulding aggregate that would accommodate a knife longer than 100 mm (~4").

4. All of the heads and aggregates I saw were small in diameter and thus could only take corrugated knives cut for shapers, and thus couldn't use the knives cut for the moulder. If we were running MDF mouldings with profiles shorter than 4" wide, I'd give the CNC option more serious thought. For now, we cut the bending forms on the CNC, and send the (curved) blanks through the Mikron.

From contributor A:
900 profiles. I didn't know that many existed.

From the original questioner:
Thanks. You have some good points that I didn't think about (springback). And yes, we have 900 profiles and are still going. We grind our own knives and we match moldings on historic houses or whatever our customer comes up with. If the home is considered historic, the contractor has to match the existing trim in the house. Try and find that trim at Lowe's! We just made 20 knives for a historic home last month. We have a lot of knives that we probably will only use on one job.

From contributor L:
We run a lot of radial parts with profiles, including casings. Our system works well for us: you need a router with C-axis, a horizontal spindle aggregate (ours has an outboard bearing, and I think the maximum width of head is 140mm), and *make sure the router has enough Z axis stroke* to accommodate the aggregate with tooling, plus pods, plus the part thickness, plus flyover clearance. Many routers do not have enough Z stroke to accomplish what you want to do.

We use pods, rout the radial parts, profile, then using a sawing aggregate, we make the end cuts as well, the parts go to the bench and are assembled. Parametric radial programming saves us a ton of time.

From contributor B:
Well, I've said it before and I'll say it again: a CNC router will do almost anything well, but it is not always the best machine for every job! What with programming, cutterhead setup, hold down issues, etc., it hardly makes sense (to me, at least).

Once we cut our blanks out on the CNC (11'6" max chord length in one blank), we run them through the Timesaver to clean the backs. Then they're off to the moulder for a few passes through and they are done. No programming (we create the cutting files for true radius blanks right at the CNC) needed and very fast.

You have an arch moulder already, so you aren't talking about a one time solution to a problem here. I can't imagine the CNC being able to profile more efficiently than your moulder.

From the original questioner:
I am looking into the option of butt jointing my paint grade radius, but have not found the glue I am looking for. I want a strong glue that dries fast. I talked to someone and this is how he said he did it, but I can't find his phone number and I don't know what kind of glue he is using.

From contributor B:
If you are talking about a straight butt joint with no joint work, then the only glues that I know of that will work at all are epoxy and PUR adhesives. As you probably know, there is no strength in a butt joint with traditional adhesives, as they are sucked into the end grain. Epoxy will work if you pre-sand the butt ends, but is costly and time consuming. PUR adhesives will work, but leave a rubberized raised seam at the butt joints after profiling. The knives seem to compress the dried glue, which then springs back up.

From the original questioner:
How do you glue yours together? I am currently strip gluing mine, and this is okay, just time consuming ripping all the strips. That is what I thought about butt jointing, but I talked to a guy when I went to a class in South Carolina, and he uses a glue that dries in 30 seconds, and you have to use quite a bit of force to break the joint. That's what got me interested. I have a 3m hot glue here I am going to try. It supposedly can be used for almost anything. We used it for attaching wood to Corian. Thanks for helping. I may just have to stick to my old ways.

From contributor Y:
We also have hundreds of knives for our Weinig. We strip form. After glueup on the adjustable form, we flush and thickness through the widebelt and then put them through the Stegherr arch shaper (one pass). It tracks the shape pretty well. If I were to buy another arch shaper, it would be the US Concepts machine.

From contributor B:
The 3M hot melt is the PUR adhesive I referred to as leaving a raised bead at the joints. As to a straight butt joint, I'd be skeptical of anything other than the PUR or epoxy. Even with those, I'm not comfortable. I expect our mouldings to still be intact for generations down the road. Butt joint glue ups aren't exactly a "best practices" operation. We usually do segmented construction. Typically, that means either finger joints, our own CNC rear mount recessed wafers system, or a double layer moulding with staggered straight butt joints.

From contributor O:
I've been thinking a CNC router could save us tons of time on radius casing as well. Right now, we're cutting out blanks on a band saw, sanding them on an edge sander, then sending them through our Mikron. We make our own knives as well for our moulders, so I like the Mikron for its capability to use regular moulder knives. I just need a faster way to get it there. Any recommendations for an entry level CNC router that can handle this? I have other uses in mind, but this is the main application right now. Most of our radius moulding is 3/4" to 1-1/2" thick and hardly ever wider than 3-1/2" A local company is pushing a CAM-Wood "smart 35", but I'm quite new to the CNC stuff, so any advice would be appreciated.

From contributor P:
I have a cabinet and millwork shop. We do primarily residential homes in the upper price range for our area. I have a CNC router with drill heads. I also have a Wenig moulder with a grinder and the whole bit. I also have a Mikron 645 for my arched, oval and elliptical casings. (This moulder takes the Wenig knives.)

I use the CNC to do countertops, cabinet sides, I cut my templates for my knives for the moulder, and I run my blanks for the Mikron. I also have a Williams and Hussey for the tight radius casings. There are some casings that the Mikron just can not cut.
I get my arch drawings for the windows and doors directly from the manufacturer by E-mail if I can, run a sample on the CNC and if it is okay, I run my casing. If it is a paint grade, I will cut the casing from MDF, very inexpensive. If the customer wants wood, and if the profile will allow it, I will make a drawing, put toggles on the back and cut it from one board with the CNC, putting the toggle cut outs in with the CNC. Or I will rip wood strips and glue up a blank oversized and cut it to size on the CNC. The hardest part about this is holding the piece down on the table. We glue it and sometimes we have to run some screws into is as well.

The CNC is like magic, but you have to have the work for it. My machine cost me $80,000 and you really need to have work for it. I do a lot of different things to keep it going.

I also do curved balcony railings with this machine. But there is a real learning curve. I have a shop with about 8 to 10 people, and I run the shop, but I do all of the drawings. When I got the machine, I hired someone with experience to run it, which turned out to be a mistake. He didn't know enough about what we do to make a real contribution. We never got any significant work out of that machine until I learned how to run it.

There is a real learning curve, and you will make many mistakes and, depending how your shop is run, you will get an earful, especially from some of your more talented people. (They could do it faster, etc.) But once you begin to master it, you will do work you never could have, to much tighter tolerances, and it will be like magic. Ours is not a large shop - we do about a million, maybe a little more, a year in sales. Our CNC is used primarily on cabinets.