straight blades vs. spirals - goal is accuracy

[Will Blick]

As in most ww tasks, different goals produce varying "right tool for the job" . Planers are used for a lots of different reasons.... some just need to hack some thickness down, some are shooting for an ultra smooth surface, some need low noise due to close neighbors, etc. So different planers fit different niches.

What I am interested in .... if the goal is near perfect parallelism on the planed surface with the jointed surface, which blade type is best? Asssuming all else equal of course...i.e. not comparing lunch box planer with top of the line floor model. This assumes a perfectly flat jointed surface as a starting point.

Planed surface preferably smooth as well - but this is secondary consideration, as this can be accomplished by sanding.

To this end, I would think straight blades would have an advantage.... I would think trying to hold tolerances on so many blades / holders is much harder than aligninging 4 blades which are "straight" to beging with.... leaving only your ability to align them equally? Lets assume excellent aligngment via the glass / magnet system or something similar.

Agree? Disagree?

Anyone ever test the board thinckness on both sides of a board, spiral vs. straight? are the differences a few thous, or a few hundreds?

TYIA

[Eiji Fuller]

I would say the spiral heads are going to be alot easier to set since you dont have to set any blades. Just adjust the outfeed table once and your are never going to need to adjust blades again.

As far as surface smoothness goes you arent going to see a whole lot of difference unless your straight knives are just sharpened or brandnew disposables. The straight knives start out sharper but dull quickly to leave a surface about what your are going to see with the carbide spirals. The carbide spirals only have nearly 0 tearout. While as the straight knives go you can have tearout using the sharpest knife in the world and it only gets worse as they dull.

If you need a perfect surface for glue ups just one pass with your jointer plane will remove the milling marks. On other surface prep you will need to sand or scrape milling marks regardless of which knives you are using.

[pat warner]

Caveat. Not a problem chasing finish quality and precIsion, 2 things I do everyday. Notwithstanding, blade wear is such (especially with HSS), that it is eminent and quick; I'm talking <a few hundred feet. If you indicated (measured with straight edges & dial indicators) a jointed 5-8" wide stick you'd probably see + or - .001-.005" in flatness (across the width) depending on blade wear. And note:
If you joint edges <2" widths for an hour and joint faces 4-7" wide in the next, you'll see the wear of the first 2" of the blade expressed on your stock. Difficult to overcome this, unless you edge joint on the full width of the blade and few do.
Now then, if you put that in the planer, given a well tuned machined with spiral, skewed or straight blades, the parallelism will be no better than that which came off the jointer. Efficiency, blade life, production speeds, finish etc. are all related to the design and sharpness of the blades but not necessarily parallelism. Moreover, whence these blades start going so will your parallelism.
Bottomline: One usually sands the mill marks off project stock no matter what feed, blade speed, or (blade) design created it. So isn't the chase-time for the perfect blade, better spent on stuff you can do something about?

[Rich Neighbarger]

Spiral blades are carbide and can be rotated when you see a difference.

[Jeff Duncan]

OK I'll disagree. Straight blades do not necessarily stay straight. In fact the longer they are the more chance for them to bow as you tighten them in the cutterhead. I have to be very careful on my 16" jointer to keep the blades straight as well as set correctly.
Now how accurate a machine is I believe is far more related to the quality of said machine and accuracy of set up than which knives are installed. And I don't believe an insert head will be any less accurate than a straight knife head. Inserts need to be set correctly, that is true. But no more so than straight knives. And if 1 or 2 inserts were out it wouldn't effect parallelism of the cutterhead. More likely just affect the quality of the surface.
Of course you could always buy 2 identical planers and change one of the heads to test your theory
good luck,
JeffD

[Van Huskey]

I disagree. The carbide inserts index and wear VERY slowly so it reduces both errors. In reality the small differences in well set up heads of either ilk will be lost in the remainder of the finishing process, sand for instance will almost certainly add more "error" to the parallel issue than either set of cutters properly aligned.

Though not the focus of you question my strongest argument for carbide insert spiral heads revolve around setup time and accuracy and long term cost savings versus the actual finish and or thou level accuracy.

[Will Blick]

good responses... thanks guys...

Yes, I realize, other than initial cost, insert type heads seem to have nearly every advantage... easy change-out, easy alignment, no tear-out, long life, quiet, etc.


Pat, your point is valid, it is something I have thought about, but have not seen expressed in the absolutes values you mention...but then again, I do change out jointer blades more often then most...no high volume here... I consider 5 thou of blade wear signficant... it all adds up.


But more importantly, I think your post has made a stronger case for insert type blades in a jointer vs. a planer. It's easy (and good practice) to plane boards on the entire blade length (no fence to adhere to)...but due to using the fence on the jointer for the edge jointing, it will surely wear the blades more towards the fence. Although my original question was comparing the two different Planer blades for parallelism, I think you exposed a weak link in the chain ... i.e. straight jointer blades seems to be the "wear link" for consistent parallelism. (and also "weak link")

hmmmm...this being the case, I almost think spiral jointer blades are more important (for parallelism) vs. planer blades. Would you agree with this? Of course now after your post, I think spiral in both would be ideal...

Jeff, fully agreed on the "quality of the machine" as well as set-up, hence why I mentioned, "all else being equal"...trying to narrow the discussion to the blades...

Moving on.... I have a 12" jointer Grizz Extreme, (currently with straight blades) So what justification can I have to buy a 20" jointer vs. the more common 15" ? Any significant advantages? Since I can't go any wider than 12" on the jointer, I can't think of any valid reason to buy a 20" ?


Not to start any wars...but from reading previous threads, it seems Byrd sprials are slightly preferable over Grizz... ?

Who makes a planer with Byrd heads, just Powermatic?

[Neal Clayton]

i thought we arrived at the conclusion once that byrd makes the heads for grizzly too?

either way, the primary difference in planer vs jointer spiral heads is the diameter on the planer heads are typically larger, and thus the cut quality better. the smaller diameter on jointer heads will leave a bit more scalloping.

why not just get the spiral head for your existing jointer from grizzly? unless you just really wanna get a bigger jointer .

[Will Blick]

> why not just get the spiral head for your existing jointer from grizzly? unless you just really wanna get a bigger jointer


It's the planar I am considering upgrading..... hence the question...

but thanks for this contribution, as I must have missed this point in previous threads ...... i.e. about wider diameter planar heads vs. jointer heads... (making the spirals ultra desirable in the planer)

In which case, I may keep the straight blades in the jointer and pay closer attention to wear patterns that Pat mentioned above.

[Neal Clayton]

ahh, i gotcha.

yea, in that case, the planer i think is the better machine to have them on, if you have to choose.

[Thomas S Stockton]

I don't think it would matter at all. What is most important is machine set up, are the blades parallel to the table in the first place. Yes since spiral cutters are indexed they are more likely to be in the correct place when changed, but it really isn't hard to install a straight knife correctly, and on either set up if the cutterhead isn't parallel to the table you will have problems.
Tom

[Will Blick]

Tom, I agree.... I take my time setting up... I am meticulous...yes, sometimes it takes longer than expected and is a PITA...but its a hobby, I am not running a production shop.... If I was, I would only use spiral to eliminate all the guess work and downtime... But I have no problems setting straight knives ...welll...straight..... oh yeah, and also co planar with the outfeed table. Since I only run a few hundred board feet per month, I have never noticed any issues...

But what Pat mentioned was a valid point regarding uneven wear on a jointer vs. a planer....as we all over use the portion of the blade near the fence.

However, I was not aware the straight blades would wear to those amounts he suggested, ... my solution there is to check this more often, and change blades when, (if) and when it becomes a problem... thanks again for the heads-up on this Pat...

I never realized that the planar heads have larger diameters than equal length jointer heads. Makes perfect sense that larger diameter heads will produce superior results vs. smaller diameter heads...

Now 15" or 20" ? I only see Byrd heads on Powermatic planers?

[Neal Clayton]

i woudln't be surprised to find that byrd makes most of the heads out there for the manufacturers that offer the spiral head as an option, regardless of whether the manufacturer advertises that or not. pretty sure there was a thread about that awhile back. maybe pm shiraz from grizzly and ask him? he's a member here. http://www.sawmillcreek.org/member.php?u=5851

[Curt Harms]

is that Byrd head inserts are mounted at an angle to the cutterhead where Grizzly inserts are square. So the Byrd inserts meet the stock with sort of a slicing cut, the Grizzly individual inserts meet the stock straight on though the insets themselves are on in a spiral pattern. In use is there much difference? I dunno.

[Mike Cruz]

Actually, I would argue that the most important machine (if only one is being upgraded) would be the planer. Why? Because while you use the jointer to flatten one side of a board, you then take it to the planer. When you plane, you want to remove equal amounts from both sides. So, even after you get your board parallel, it most likely won't be the finished thickness, and therefore, you'll be flipping your board over. So much for that non tearout cut that you got with the spiral head on the jointer...

So, that said, I would say if you were to do only one, I would do the planer.

THAT said, I just bought a Byrd head for my 8" jointer, and have straight blades on my 20" planer... Unfortunately, the 20" Byrd is cost prohibitive right now. Soooooome day, I might get it... But I could spare the $300 for the 8" jointer.