Spiral vs helical vs straight knives

[blanning]

I'm getting ready to buy a jointer and a planer.  In the past I had straight knives and they were fine.  I later upgraded to helical and had some problems.  They left a good finish.  But when I tried to replace some inserts, I found that even with a torque wrench, I cracked a few inserts in half.  I also noticed that even though they said they were indexed, it was really easy to get them misaligned and leave an uneven surface in the board.  It always seemed like I trapped sawdust under the insert even though I made sure it was clean.  It's been a while so maybe these are solved problems now.

From what I understand, spiral heads have the inserts square with the table, while helical turns the inserts slightly for a shearing cut.  I'm not sure if that makes much of a difference.  Although the helical inserts seem like they're slightly rounded vs the spiral heads that are straight.  That makes me wonder if the sharp corners on the spiral heads ever dig in and cause grooves.

I guess I could always go with straight knives and upgrade with a byrd head later if there's a good reason to.

Any opinions on this?

[jteneyck]

I'm getting ready to buy a jointer and a planer.  In the past I had straight knives and they were fine.  I later upgraded to helical and had some problems.  They left a good finish.  But when I tried to replace some inserts, I found that even with a torque wrench, I cracked a few inserts in half.  I also noticed that even though they said they were indexed, it was really easy to get them misaligned and leave an uneven surface in the board.  It always seemed like I trapped sawdust under the insert even though I made sure it was clean.  It's been a while so maybe these are solved problems now.

From what I understand, spiral heads have the inserts square with the table, while helical turns the inserts slightly for a shearing cut.  I'm not sure if that makes much of a difference.  Although the helical inserts seem like they're slightly rounded vs the spiral heads that are straight.  That makes me wonder if the sharp corners on the spiral heads ever dig in and cause grooves.

I guess I could always go with straight knives and upgrade with a byrd head later if there's a good reason to.

Any opinions on this?

Another option with some brands is a Tersa head.  They are straight knives but super simple to change, like a couple of minutes, and self setting, so you can use a worn pair for roughing stock and switch to a new set for finish work.  

John

[fredhargis]

I've only used the Shelix inserts, but I know Papa Grizzly (when he used to be around) always insisted there was no difference in the cut made with skewed inserts versus the squared ones. He (of course) at the time sold the squared under his name.  But i've read others that have both types share that opinion.  I am curious about the cracked inserts. I've got the Byrd on both my jointer and planer and while I cracked one on the planer head when i installed it, I haven't cracked on since. Clraning the seats before installation and using the torque wrench (actually, for me it was a torque screw driver) has worked very well. I do know that since I bought my heads, Byrd has some re design because of the complaints of the lines left in some cases with the older units. The new design is supposed to eliminate that problem.

[blanning]

I've only used the Shelix inserts, but I know Papa Grizzly (when he used to be around) always insisted there was no difference in the cut made with skewed inserts versus the squared ones. He (of course) at the time sold the squared under his name.  But i've read others that have both types share that opinion.  I am curious about the cracked inserts. I've got the Byrd on both my jointer and planer and while I cracked one on the planer head when i installed it, I haven't cracked on since. Clraning the seats before installation and using the torque wrench (actually, for me it was a torque screw driver) has worked very well. I do know that since I bought my heads, Byrd has some re design because of the complaints of the lines left in some cases with the older units. The new design is supposed to eliminate that problem.

At the time, I decided that the cracked inserts must be because the torque wrench was out of spec, and I was actually overtightening them.  I stopped using the torque wrench and went by feel and got better results.  Part of me still had a hard time believing the torque wrench was that far out of spec though.

This was 15 years ago.  So maybe things have improved.

[kurt18947]

I have a Jointer-Planer with straight knives and with domestics have not had a problem with tear-out. The jointer beds are 12" and I skew boards when I can. I've never used a machine with a segmented head so can't compare them. I'm sure if I used figured wood my opinion would be different. I also don't find changing straight knives onerous which I know is not universal. I am not high volume so change knives maybe once per year.

[jteneyck]

I have a Jointer-Planer with straight knives and with domestics have not had a problem with tear-out. The jointer beds are 12" and I skew boards when I can. I've never used a machine with a segmented head so can't compare them. I'm sure if I used figured wood my opinion would be different. I also don't find changing straight knives onerous which I know is not universal. I am not high volume so change knives maybe once per year.

Same here.  Love the 14" width of my J/P.  I looked into putting a segmented head on it.  Just can't justify the $1200.  I have a drum sander so tearout isn't an issue.  

Having said that, if I were buying new, I'd get a machine with an insert head of some sort.  

John

[rwe2156]

If I were buying a machine today, no way I'd go with a straight blade planer. If I did, I'd also buy a drum sander.

I kinda doubt many people buying those machines are getting straight knives.

Helical head planers will save you a lot of headaches, and mostly the "heartbreak of tear out."

[blanning]

If I were buying a machine today, no way I'd go with a straight blade planer.  If I did, I'd also buy a drum sander.

I kinda doubt many people buying those machines are getting straight knives.

Helical head planers will save you a lot of headaches, and mostly the "heartbreak of tear out."

It sounds like you're saying if you have a helical head, you can skip the drum sander.  Is that right?

I was thinking to get a 20" planer with a helical head, and a 26" drum sander.  I've been going back and forth on the drum sander though.

[Brian in sunny FL]

It sounds like you're saying if you have a helical head, you can skip the drum sander.  Is that right?

I was thinking to get a 20" planer with a helical head, and a 26" drum sander.  I've been going back and forth on the drum sander though.

I think the drum sander comment was because before the indexable cutter heads the only way to avoid tearout was to use the drum sander and your final dimension machine

I had a Tersa, they tearout too.

As far as cracking inserts, the basic spec is 45 inch pounds so if that was misconstrued for ft pounds gonna have a problem.

[FrankAtl]

"It sounds like you're saying if you have a helical head, you can skip the drum sander.  Is that right?"

I couldn't. I use my drum sander for other things like hand sawn veneers, sanding segmented rings etc. I guess it depends on the type of work you do.