Spiral Insert Cutter Finish Quality

Spiral insert cutter heads may leave faint lines on planed wood. October 2, 2005

This is on a 4 head Northtech moulder where the finish from the bottom head (spiral) is important. I'm not sure what brand of head it is, but there are almost 60 of the 14x14x2 carbide insert square blades. When they first get dull, I spun them a turn and everything was great. This time I spun them (you can do this four times), and I get these grooves from every tooth like someone dragged a scratch awl down the board several times. Twice I took every stupid insert off, cleaned everything really good… same thing. Now I have to sand my s/4/s stock to get rid of that. Is it possible that the inserts wear enough that when you rotate them, they don't seat into their position properly?

Forum Responses
(Solid Wood Machining Forum)
From contributor R:
Look at the edges of your knives real close. The are two types that I know of. Some are square, but the ones that I had the best success with have an ever so slight radius edge on them. This helps in the transition from one blade to another. Keep in mind that spirals aren't the best solution for a non-sanding application. You might try a straight knife, insert or corrugated.

From contributor J:
I don't think you really have a problem. If you are using square inserts, you will get the lines you speak of. I use the slightly radius type on my btm finish head and although this will not eliminate the need for sanding, the difference is dramatic. Terminus is great for straight knife finish. Check with Gladu for Spiromax insert heads. Radius inserts save me a lot in the long haul.

From contributor C:
The above posts bring up great points. The inserts you have in your head were never meant to provide a finish cut. To reiterate what was stated, even the radius inserts will leave a faint line. It does seem a number of tooling suppliers give the impression that these type heads will leave a line-free finish: in theory, possibly, in reality, no. Keeping the seats clean is very important to get the best possible knife life and surface finish. If you need a sand free finish coming out, you need a straight knife head. Terminus and Tersa are two common straight knife insert heads.

Your Northtech is a 4 headed machine. We supply a number of spiral insert heads for 1st bottom on moulders with 5 or more spindles, or for rough planing applications. In these situations, the end finish is not critical to the user. The radius inserts are available in a 14 x14 x2,0mm size. They are also more than the standard 14mm square inserts.

From contributor D:
I agree, for the most part, with the above responses. I have worked with a couple of cutter head manufacturers that can produce a line-free finish. This is with a new head before minor damage occurs to the head body. Many of the spiral heads are aluminum. Over time, you will slightly change the seats that reference the inserts. Even with proper cleaning, you will normally see small lines on heads that have some age on them.

It should be noted that very few manufacturers can produce a line-free finish even on a new tool.
If you must have a line-free finish, the use of a single insert is the best option. I use the Terminus heads and have had excellent results for many years.

As a side note, many manufacturers of S4S sand the faces.

From contributor U:
I have a Northtech 24" planer with the spiral head that came with square knives. After several thousand bf of lumber, I changed them to a set with the radius on it and the results were bad. The radius knives had a small amount of play in them and left terrible lines, so I switched back to the square knives with good results. Are certain heads made for square knives and some for the radius knives?

From contributor J:
That is a good question. I've thought about putting radius type inserts in my top cutter which now runs square type, but have not had the chance to do it. Mostly, I don't think the cost will justify the results. We sand both sides of our mouldings on a wide belt, anyway. Anybody know if a cutter with straight inserts will accept radius inserts?

From contributor D:
I bought Grizzly's 5 HP G5850Z 20" professional model planer with a spiral cutter a year ago and love it. We have had no finish problems at all. In fact, the only problem we have ever had was changing the blades the first time. The driver bits that Grizzly supplies were not up to the job. In fact, most of the other ones that we bought were not, either. The screws were bedded so tight (probably in the shipping cosmoline) that I had to buy special hardened driver bits. Even then, we had to give each screw a hard tap to loosen them off first.

But as far as the finish goes, we think it's as perfect as a planer can get. We have put over 5 miles of cedar and Douglas fir lumber through our machine and have rotated the knives only twice (we are on the third edge). An added bonus is that the planer noise is so quiet that if the dust collector was a bit further from the machine, we would not even need hearing protection.

We do use a belt sander to finish some of our boards, but certainly not because we get lines. I can't say enough about this machine or the other Grizzly equipment we own (8" HD jointer, 12" cabinet saw and 18" belt sander).

From the original questioner:
Yeah, our Northtec was the same way. I wondered why they included 30 of the Torx bits for changing the inserts. Those screws were so tight, snapped every one of them. They don't have to be that tight, do they?

From contributor D:
No, I don't think they need to be. We only had problems removing them the first time. I finally bought some case hardened Torx driver bits (Vermont American) to remove them. I even snapped a few of those. We then did a good job of cleaning up the screws and cutter seats and that seemed to fix the problem. Torque settings are provided in Grizzly's manual, but we only tighten them with a Torx screwdriver by hand (albeit with a good solid grip). That hasn't given us any trouble, either coming loose or in changing them again.