Helical cutterheads
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Surface quality compared to other cutterheads. November 18, 2002
Question
I have been searching for scientific articles about helical cutter heads to be sure about their advantages. Literature says that helical cutter heads are quieter, but there is almost nothing documented about surface quality in comparison to straight knife cutter heads. Does anyone know of reports of statistical data or practical observations that prove that helical cutterheads yield really better surfaces in planing operations?
Forum Responses
What type of machine are you intending on using it on? The amount of stock to be removed also plays a critical roll.
From contributor C:
I have sold the Newman Whitney head both in new and rebuilt machines ever since it came out (I'm not sure when, but sometime in the late sixties, I believe).
The Newman Whitney Quiet Cut head does not finish as well as a high speed steel head primarily because it is carbide. No carbide head will finish with the slick mirror-like finish that you get with high speed steel jointed knives.
The practical aspects are these...
If you are going to sell dimension to someone who is fussy, use high-speed steel knives. You will wear yourself out grinding and jointing, but your customer will hold the stock up to the light and smile.
A lot of wood goes into products that get very little sanding and these products will look much better if made with high speed steel knives. However, if your product is going into ordinary furniture, which is sanded with great care and attention, the carbide spiral head is the way to go. I do qualify that as there are a lot of spiral heads - some are good, some terrible. There are Newman Whitney Quiet Cut spiral heads making every kind of furniture you can imagine and with great success.
On the other hand, if you are selling dimension...
Any feedback on how helical insert heads work on tear-out prone woods?
From contributor C:
There is no such thing as no tear out. But I do believe the spiral is much better. You hear a lot about shear cutting. I prefer to describe it as screwing the wood off. Whereas with a straight knife, you are beating the wood 3600 times per minute. The big screw stays in contact with the wood constantly, so it is not hammering on it. Sounds flippant, but think about it.
From the original questioner:
Contributor C, do you think we could do without sanding by using helical cutter heads with very high rotation speeds and very low feeding rates, in order to reduce the width of knife marks?
About the cutting depth: I would work with depths inferior to 1 mm.
I have an import top and bottom planer which has not helical but a chevron pattern to the insert tooling. It always shows lines in the material the width of the inserts, I imagine from one ever so slightly high knife, but you can't feel it and the lines sand right out. It handles difficult and chippy materials way better than steel straight knives, which we ran prior to this machine in a single sided planer. We outsource planing for other companies, and they, along with us, face glue right off the machine. Extended run times between blade changes, improved chip removal, and faster feeds are also things that have benefited. The biggest benefit, though, is the noise reduction. You can be removing a 1/2" of material and stand next to the machine and carry on a conversation. Not scientific data, but real life observations.
From contributor C:
You will not get by without sanding on any high quality product using a helical carbide head. The Newman Whitney does not leave the scratch pattern others leave because of the knife location in the head.
Material is always removed in the rotation direction. This sometimes creates material blow out on the side the chips are removed. If blades are kept sharp, this can be greatly reduced. Check out AceCo. They have shear cut molder heads which can be ground on a profile grinder with a special attachment and run with HSS.
We have a couple of the shear heads at the school and have had excellent results in improved finish and feed rates with all of our tests.
Dave Rankin, forum technical advisor
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor A:
We have a 30" Buss 6 Knife head jointer/planer with high speed steel knives. The question of carbide always comes up, but we have not been able to convince ourselves that the noise reduction is worth a) cost and b) finish. Since we mill our lumber, one big issue is not catching metal in the lumber before processing. In regards to tear out, we mill mesquite, pecan and live oak. All of which have horrific potential problems for tearout. We have reduced this effect by utilizing what is typically only done with metal working. That is, grind a relief angle on the knives. We prefer a 33/38 degree profile, but have to settle for a 33/42 degree because of the sharpening jig used on the Buss.
Comment from contributor B:
I used a spiral (multi-tooth) head on the last bottom for a while. Everything was good in the finishing department until someone wanted a stain instead of our normal tung oil finish. No matter how much we sanded, those carbide teeth (rubs, I guess) stood out like a sore thumb. Just the way they cut the wood differently, I guess. Never would have known if it wasn't for that stain order.
