Horsepower Issues with Helical Cutterheads

If you switch to spiral knives and you want to keep hogging out deep cuts, you may need to upgrade to a more powerful motor. July 8, 2014

Question (WOODWEB Member) :
I came back from IWF and ordered a Byrd Shelix cutter head for my Powermatic 100 12" planer. I've had this machine 20 plus years. After running for a week we are pleased with one exception. The machine has the factory spec. 3hp motor and it is bogging down with a 1/4" deep cut. The planer is rated for 1/4" max depth cut and we occasionally go that deep, not often but it is a nice feature when needed. We never had a problem with this with the old cutter head. Most any wood species at any width would cut at 1/4" deep.

With the Byrd head I could cut 8" wide African mahogany 1/4" deep but not poplar or oak. This surprised the tech at Byrd. He'd seen similar reduction in power capability with small table top planer but never on an industrial machine. His very logical explanation is that a three knife head has a time gap between each planer knife strike for the head to rebuild rpm speed. The Shelix head always has a knife in the wood so can slowly draw down the cutter head rpm speed. The solution is of course a larger motor which I can do but would rather avoid. I'll have to decide if it's worth it for the few times we would cut 1/4" deep. Has anyone else had a similar experience with a Byrd Shelix head?

Forum Responses
(Solid Wood Machining Forum)
From contributor M:
When your straight knife hits, it takes a full cut (100%) when a helix cutter hits, what is it 5%? Add up all of the length of your inserts for a full revolution, and compare it to the 36" total length of your straight knife head. Who knows, perhaps because of the cutter overlap, ti is requiring the motor to do more work. Perhaps, it just clears the chips less efficiently, or the side-of-the-cut-tearing-friction really adds up?

From Contributor M
Did you double check your reassembly, belt tension and bearing heat?

From Contributor O:
I do not have direct experience with this, but have heard second hand tales of it. I remember when the Whitney spiral knives/heads came and it was said you would need 25% more power. The ability for a three or four knife head to catch up between bites allows it to do more apparent work is the way it was always explained. What it comes down to is 3hp isn't much and a 1/4" deep cut is. Not what you wanted, but upping the motor to 5hp should be easy and not too expensive.

From contributor R:
When I added a cyclone to my dust collector I had to go to 20HP from 15HP. So I have a 15HP 3600 3ph motor sitting here to sell. It's seen one-two years of use. 15HP ought to do it! Of course it may bend a shaft or two as well!

From the original questioner:
I had just upgraded my old system from 5 hp to 7 1/2 hp a number of years ago when I found I suddenly needed to do a more significant upgrade to a new Oneida cyclone system. That six month old 7.5 hp 3-phase motor is still sitting on the shelf waiting to find a use. Plus I have the 5 hp single phase motor that I originally upgraded from on the shelf as well. Maybe I can put that on the planer.

From contributor F:
I do wonder though if you’re not playing with fire trying to take off 1/4" of hardwood per pass on that planer? That's an awful big bite for a medium duty planer! To be honest I'm surprised the planer can handle that much at all. My 20" with a 9 hp motor won't feed more than about 1/8" or so. I think I'd opt for a second pass vs removing that much material at one shot, but that's just my opinion.

From the original questioner:
The Powermatic 100 is an all cast iron heavy duty industrial machine. It is the little brother to the 18" and 24" industrial planers. The original operating instructions manual covers the 100, 160,180, 221 and 225 planers. That's why it's rated up to the 1/4" cut. The only thing it lacks is a segmented infeed roller that I would love to have on it. They also make a sharpening head unit but I've always thought that the mounts would be in the way.

From contributor F:
I have the sharpening unit on my SCM and can't say enough good things about it. I can give the knives a quick touch up in five minutes when needed. However, from what I've read from other users the Powermatic setup is not quite as easy to use, so you may have chosen the better solution.

From contributor W:
I am guessing it has to do with the gullet depth. Most top mounted straight cut insert heads have a max depth of cut of 3/16". A standard cutterhead has a knife projection of between 3/16 to 1/4", plus the depth to the radius or angle on top of the gib which allows for a greater depth of cut. Maybe two passes at 1/8".

From the original questioner:
Yes, that was my first thought too. However the fact that I can cut 1/4" deep on the 8" wide African mahogany board seems to rule that out as the cause.

From contributor S:
I have a 15" Byrd head on a Delta DC380, and you definitely do not want to take a full depth cut, anywhere near the maximum width. I generally keep the gearbox set to the slower feed rate. Listen to the sound of the planer. If the motor sounds like it is struggling take lighter passes! Be mindful of this or you can burn out your motor. I would advise loosening the drive belts a little bit if practical to give a margin for error in the event you stall the motor. A local tech school had this happen to their planer when a student stalled the motor. I will bet the drive belt was probably too tight, and the motor was not shut off quick enough.

I have Byrd heads in two machines, and I am very pleased with them. They are a great investment, and after thousands of board feet I haven't even found the need to rotate any of my inserts yet. I also run knots, dried glue, end grain and all sorts of junk through them. I took the hood of my planer to inspect the inserts a little while ago, and I was surprised that none were chipped. Ninety of the time I do not need to worry about tear out. Birds eye maple can still be problematic and contrary to what some might say, you might see a little bit of tear out here and there with the tricky grain in any wood. With that being said I have heard third party marketing claims that require less force for feeding, etc. I disagree with these claims. I know for one on my jointer, I feed at a slower rate, and the resistance is slightly higher. I take lighter passes with my planer. I think that this is related to the continuous cutting action. There is no chance for the motor to rebound from AC cycles that fall in-between the cuts of a conventional head. I might be wrong about this, but I am not an engineer.

From Contributor A:
Basically to add what’s already been said, more knifes need more ponies. Even though a sheer cut takes less hp, adding more rows radially ends up taking more power. The small gullet that most insert heads have are not well suited for hogging applications. I was running inserts on the first and fourth head on a six head moulder and while they’re nice and quiet, I canned them. Also with moulders, I am sure to be true with planers as well, adding more knifes makes smaller chips and takes more dust collection. That PM series planer are great machines. Besides hogging cuts do you like the Byrd? I have a SAC jointer that I have been kicking around the idea of putting one on.

From the original questioner:
I have mixed feelings on the new head. I had two friends who had installed them and they were leaning on me to do the upgrade. That along with the quietness factor and one more plan for the head won me over. The other plan was thinking that we could run our 5/32" jamb strips through the planer once on each side to bring them down to 1/8". This would have saved a lot of time as we currently run them three or four times through the wide belt sander with 60 grit. I figured that with the elimination of significant tear out and blow up of thin material the planer would become a faster alternative.

That didn't work out. While the Byrd head did eliminate the blow out issues it still takes three or four passes. This is because the re-saw just isn't accurate enough to allow a uniform 1/64" stock removal per side. We still have to carefully watch each face and skim it slightly to get rid of the saw marks as we bring the thickness to the final 1/8". Since we can put three or four strips through at a time on the wide belt and only one at a time on the planer the wide belt still proves to be the faster method. Also, the surface of the boards after planing isn't quite as perfect as I had expected. No better really than the original 3-knife cutter head. So it seems to me the real advantage for us will be the quietness factor (which is outstanding) and having carbide tooling instead of HSS.

From contributor HD:

I have the same planer and took the 3hp off years ago and put on a 5hp, big difference. I have an 8" spiral head in a jointer with 2hp, and it’s nowhere near enough power. My spiral head 24" planer with 15hp won't take more than an 1/8". I was told that these heads require more power than a conventional knife head. It seems like that might be the case.

From contributor G:
I have an old Rockwell 13" that I installed a Shelix head on and it totally killed my HP. I changed the 5HP motor to a 7HP and it still has no power. I purchased an SCMI 20" with Tersa head and it does 99% of all my work. Knife change in ten minutes flat and switching to carbide knives for teak work and back again is a breeze. I keep the Shelix around for the birdseye maple stuff and 1/8" door skins that may want to tear. Shelix are very quiet though.