Running Radius Moulding: Shaper Technique

Tips for a newbie on making curved mouldings for an arched door jamb casing. January 26, 2008

I'm having trouble creating a curved molding for a door jam of poplar. I set up a cradle and placed the wheels of the feeder on the molding to hold it down and feed it at a continuous slow rate. I've used stacks of finger boards to hold it against the fence, but I still get a lot of tearout on these poplar boards. Also, the knives make a popping sound as the material passes. Is this a knife problem, a setup issue, or am I off base on everything? I'm using a shaper from 1930 with a head with 4 knives.

Forum Responses
(Architectural Woodworking Forum)
From contributor A:
Stop experimenting immediately until you get some good advice from the Forum. The older the shaper and the more knives, the more fingers you will lose.

From contributor J:
Source it out. Unless you are set up to make radius or elliptical trim work, there is no money in it. There is a guy that I think has an ad on here... [contributor B]. He seems to be the most experienced in this stuff. I would get him to price it for me. I am saying this from experience. I farted around with this stuff for a year until I realized I am better off outsourcing to someone who knows what they are doing and has the proper setup to do it and spending my time doing what I was set up for.

From contributor B:
There are a few key issues here, not the least of which is safety. First, in my experience, a popping noise coming from a shaper cutterhead is often caused by too slow an RPM for the head. We occasionally run a 4" diameter 2-knife cutterhead on the shaper for curved work and try to strike a balance between RPM and a relatively safe feeling when doing the operation. I say "relatively" because I never feel completely safe when running profiling cuttheads on the shaper... just too much exposure. I had a knife break a number of years ago and it was one scary event!

As to the proper RPM, I try to tune it in to the minimum required to get a clean sounding hum, with no popping noises, when running the moulding.

As to the feeder, we do most of our work on the shaper with a 3-wheel feed that is tilted so only one wheel is touching the moulding. We almost always do this with a bearing or rub collar on the shaper spindle above and/or below the cutterhead. The feeder wheel is angled at about 45 degrees to the feed direction of the moulding to both push the wood and drive it up against the bearing.

If you would like, I'd be happy to quote the moulding for you.

From contributor P:
I've run this setup many times. Every time I find a different problem and another solution. In your setup, the rollers are doing all the work. They feed the stock and keep the pressure against the fence. They react all cutting forces too. Since the rollers are spring loaded, the cutter can try to push it away. The rollers and cutters fight each other and this movement can cause popping sounds and tear out. This is due to the bouncing of the stock. Your fence needs to be very stiff too. Old shaper or new, does not matter, it's your setup. Hopefully it is a 1.0 or 1.25 spindle.

I usually make a lower (outer) cradle and an inner cradle so your stock runs in a track. I allow just the minimum space for the knives to protrude. Wax this track nice and smooth. Wheel position is critical, and it seems each time I do it, I find a different way. Your grain direction can come into play too. Your choices are laminate, brick lay glue up or just a regular glue up. Laminate is probably the best, but is time consuming and the glue line can nick the knives.

Everyone says to outsource. I say learn it if you are comfortable with a shaper. There is a lot of money in curved work once you got it down. Plus, it's fun.

From the original questioner:
Thank you for all of your responses! I'm using corrugated heads and 1 1_4 spindles with new knives on these jambs. The trick was to remove only small amounts at each pass. They came out beautifully!