Optimizing Cut Quality on a Door-Making Shaper

With a specialized machine designed for profiling door parts, it can be tricky to adjust RPMs and feed rates for a good, clean cut. July 11, 2007

We've recently purchased a door making machine similar to the Unique 250. It makes all parts of a raised panel door. Is there a particular cutter design that works well when shaping the arched (cathedral) header of a raised panel door? What we are using now tends to give a less-than-perfect cut with frequent tear out and a bit of roughness as the cutter is heading out of the arch. I know the ideal solution is counter rotating cutters and coming in from each end, but this is not an option right now. What about hook and shear angle or number of wings? We currently have a 4" Royce, 3 wing, one piece insert cutter for making this cut and the Royce people tell me I am dulling the tool after 2 or 3 cuts because we are feeding too slow. The machine turns at 9000 rpm (a little fast) and we can only feed at 6 - 10 fpm because we need to follow a template. They tell me I need to feed at 60 fpm. Anyone using a Unique 250 or a Panel Crafter type setup knows this is impossible. Any advice as to a cutter design to give the cleanest, smoothest cut possible?

Forum Responses
(Cabinetmaking Forum)
From contributor L:
Try to figure out your rotational speed and feed speeds so you get about 30 to no more than 60 knife marks/inch. 8'/m*12=96*45=4320/3wings=1400rpm. It seems like even 3,000 rpm would be a great improvement. So 9,000 rpm looks like it is making way too small of a chip to carry away the heat and the tool is doing more rubbing than cutting! Heat dulls tools! Before a cutting tool actually starts to cut, it compresses the wood fibers some. The compressed wood fibers later absorb moisture from the air and they cause the surface to feel crummy (technical term!). The fiber raise can occur after finishing so the sanding often doesn't take it all out. You will get less of this affect by increasing the chip thickness.

If the motor on your machine is inverter rated, that may be an easy but not cheap fix. That way you could easily change the speed for the process. Variable speed pulley? Multi step pulley?

From contributor J:
Just confirming what contributor L stated. Finding a way to slow down the speed to match your cutter and feed rate will solve many of your problems. Like he said, the cutter is doing more rubbing than cutting. I would also imagine you need to push the stock a bit harder than you would like... which, in the long run, is not good either.

From the original questioner:
Thanks for your responses. That is exactly what the cutter people are telling me. The thing that still puzzles me is why people like Unique make a machine designed specifically for this purpose but it runs at 8000 rpm with a 3 wing cutter supplied by them? It is impossible to feed that machine at the required feed rate following a template. Is it possible that after all the years of making this machine, they've been doing it wrong? The machine I am using has a 10hp motor and it can be outfitted with an inverter. So, you're telling me that if I was to slow the rpm's down to 2-3000, I would get a better quality cut with less tearout and fuzzing?

From contributor R:
Just a few things to add to the other post, which I think are very helpful. Fuzzing sounds to me like a moisture issue. Please check the moisture content with a meter. I would imagine 6-8 % would be the range you're looking for.

Also check the tool to see if it has side clearance built in the tool itself. This will help the knife disperse the wood chip through that avenue and will keep the heat from building up. Typical 5 degree side clearance would be normal. It makes a world of difference. Anything from 60-90 degrees incline in the tool should have some side clearance.

From contributor T:
There are a couple of changes that could be made to the cutters for your application. You could try one or all of these changes to improve your situation.

1. Reduce the number of wings to two. This will create larger chips at the same speeds.

2. Have your cutters made with alloy tips. Alloy materials start out sharper than any carbides. They are a high temperature cutting material that can handle heat far better than carbides.

Changing the hook angles and shear angles will probably not help very much. I do have to agree with the previous postings, though - you need to slow the RPMs a bit.

From contributor B:
Have you looked at grain orientation in relation to your tear out? Are you using solid stock? If so, you may be coming back across the grain, causing tearout. Just something to think about.

From contributor L:
I'd like to hear Unique's reply.

From contributor R:
I have a different setup but same problems. I ordered new inserts for the Byrd heads, and even though I didn't believe the old one had dulled, I put the new knives in and slowed shaper down to 8K RPM, and no burn in soft maple, micro tear out leaving the arch. The dull set of knives worked fine on straight stick cuts - so good I would not have thought that new ones would have made such a difference. I wonder just how many arches they will cut before dulling. Anyone know of a tool company that builds diamond tips for insert cutters?

From the original questioner:
I am using solid hard maple and yes, I am cutting across the grain when the head is coming out of the arch. That is part of my problem. I'm just wondering if there is a way to minimize it.

Contributor R, they tell me that 8000 rpm is still much too fast for a slow feed rate. They say it will quickly dull your cutters. I'd be curious to see how you make out.

Like contributor T, another person tells me that cutter design is likely not the solution. They say the proper rpm's for 8 fpm would be 1500. I can't grasp that one. Have any of you cut anything on a shaper at 1500 rpm? I plan on getting an inverter installed and playing around with the rpm's to see what happens. While we are on the subject, I discovered something else. When I make a straight stick cut on this machine at 8 fpm and 7000 rpm's, I tend to get knife marks (scalloping) along the length of the cut. Would dull cutters cause this?

From contributor G:
Pretty much everyone who has contributed was positive. Hook and shear angles are very important in a cutter design. Your inserts should not be dulling after a few doors. Reduce your rpm's to 3600; reducing further may reduce your horsepower somewhat. Also, there are 3 types of inserts. One is a standard least expensive. This will do an okay job, but not the best choice. There is an insert that is made for solid wood, which you should be using. It is designed to provide a superior edge finish and longer lasting tool life.

From contributor R:
With the new knives, feeding by hand, I can feed fast enough to stall 3HP shaper, and fast enough to increase the tear out, so I don't believe in my case faster is going to be better.

I do know a local door shop that builds 500-750 doors a week and he told me he switched to diamond cutters and was not sure how long they were going to last. When he told me that he had been running them for over 2 years, he said they where cutting just like the day he put them on. He told me cost was 1K plus per cutter. I would think that someone would custom build diamond inserts for insert heads at a fraction of that cost.