In defense of straight blade thickness planers *LINK*

agree

Bill Tindall, E.Tn.

I have put thousands of bdft of lumber through our 18" Powermatic. It is a rare event that I generate unacceptable tear-out. If someone gave me a spiral head I would not bother to install it for it would provide no significant benefit (I have an on-board knife grinder). It may be that the variable speed infeed on my machine is important to tear-out mitigation. I usually finish plane at the slowest speed.

Re: agree

TMStock

For abrasives, insert tooling is useful. Ipe and anigre will kill the edges on a HSS blade in a single pass through the machine.

Sure

Dick Coers

If you going to run that kind of stock, no question. Personally I have no interest in exotics. Especially don't see any reason to run ipe through a thickness planer anyway.

Re: Sure

TMStock

We're still on our first set of inserts after 3 years... not bad for a $240 option on an 8" jointer. Steel was fine for plain figured, plain vanilla stuff, but one of our most popular woods is curly anigre...and the stuff eats CS and HSS for light snacks.

Re: agree

James Heaston

Bill T. I would have to assume that you put an 10 degree bevel on the front of your blades then install them. Then with the on board grinder you sharpen your blades so many times till the 10 degree is all but gone then remove the blades and grind a 10 degree bevel on the face again.

How far into the back of the blade do you grind the 10 degree angle?

have no idea what you are talking about

Bill Tindall, E.Tn.

All the grinding that has ever been done is done with the blades in place. No idea what you mean by ten degree bevel. The on-board grinder does two bevels, P and S.

Re: agree

Keith Newton

back of the blade do you grind the 10 degree angle?>

James, I've been grinding a FACE BEVEL of about 15º on my knives which are set at 25º in the head, to reduce the cutting angle down to 10º in both my jointer and planer. The face bevel only needs to be as wide as the thickness of the chip your taking. However it's a lot easier to just make it wider so you don't need to deal with it on every sharpening.

While this does eliminate most grain tearout, it does also increase the power requirement which might be a problem for most consumer sized equipment.

Tear-out mitigation

Bill Tindall, E.Tn.

If I follow this discussion accurately some are grinding the back of the knife and this reduces tear-out.?. I have an 18" Powermatic machine with variable feed speed which I always run on slow for finish planing and high for skip planing. I have never seen the back of a jointer or planer knife altered from flat in any shop I have been in. I have run tens of thousand bdft of N. American hardwood, typically FAS1F and Better grade, through this machine (almost no curly maple). We never had a complaint from a customer about what came out the other end. After skip planing I would adjust the direction of feed as needed. For the lumber we planed I never saw any need to do anything different. On rare occasions I did encounter an impossible to plane piece of lumber. Never understood what caused these boards to pick out as they did but the problem was too rare to consider doing anything about it.



The picture shows a figured walnut top I had no problem planing. Why I don't consider tear-out from thickness planing, or jointing , a significant problem while others do is a mystery to me. Is it the species, technique, experience, machine....? Fed slow enough I can joint anything no matter the grain direction.

Re: Tear-out mitigation

Keith Newton

Bill, The only information you have given is the length of the blade, which has nothing to do with this. Do you know what the cutting angle of your knives are? Maybe your cutter head already has a low angle, while mine are in a head for running softwood, which causes more tear-out on hardwoods, that happens to be what I use most.

This is not pure speculation on any of our part, just read the link that Dick Coers posted. That information by the Charles G.G. Schmidt & Company' has been out for many years, and used throughout the industry. I might note that what Dick posted is only part 5, so if you don't find what you hope to understand, there are about 170 pages to dig through.

Re: Tear-out mitigation

Bill Tindall, E.Tn.

I have provided that the machine is a Powermatic 18" planer "out of the box" with no modification. It is yellow but I have no reason to believe the cutter head is any different if it was green. I was not offered any cutter head angle option and certainly no "softwood/ hardwood" choice, nor have I ever encountered this choice as an option in the two light industrial machines I have bought- one Delta and one Powermatic (both had variable feed which is significant in tear-out performance). If Powermatic ever offered a cutter head angle option- and honestly I don't know what this term means- I would like to be made aware of this fact.

One difference could be significant. I rarely planed anything but FAS1F and Btr lumber grade. This grade has few knots and my customers never included material near a knot in their cabinetry. Hence, knot tear-out was never a factor in my planing, where it could be in others planing. And I planed zero foreign wood.

My point is that all the fuss over knife angles and spiral heads is likely irrelevant for the majority of people working hardwood lumber. Persons deciding options should not presume they need these features. The concept of working on the back of a knife was so foreign to me that I had no idea what the person that asked me about it was talking about. Yet he thought "everyone" did it. I have never heard of anyone doing it until the recent post.

I have seen tons of knives at Misenheimer. Never seen one with a bevel on the back of the knife.

A plane by any other name is still a plane.

Mark Hennebury

Lest we forget the lessons learned with the hand plane.

A low angle of attack in "good" grain cuts fine

A low angle in "bad" grain will tearout.

A high angle blade will be more of a scraping cut, more pushing than lifting, but will work acceptably in most situations.

A low angle with a chipbreaker cuts very cleanly and also prevents tearout in "bad" grain.

A thickness planer works in a similar fashion to a hand plane, with the main difference in being variable speed. So the feed speed affects the chip size which helps to prevent tearout. But the blade angle also helps, as does the chipbreaker, the lack of a chipbreaker will offer no protection against tearout.

Read below, the excerpt from Powermatics patent application of 1980

Cutterheads operating in the gap between in-feed and out-feed tables of planers, jointers and the like wood cutting apparatus are provided with a body of increased diameter and a gib having a chipbreaker pocket shape that will expose only a minimum projection of the knife before the chip must curl into the pocket thereby reducing the potential bite of a kick back such as might occur by a tipping of the wood workpiece or by a pull out of the wood grain during the feeding of the workpiece to the cutting knives. The knives of the cutterhead protrude only as much above the cutterhead body as is required not to interfere with the advance of the workpiece per revolution of each knife, the gib is positioned with its chipbreaker pocket down from the tip of the knife no further than is necessary for chip thickness, and the chipbreaker pocket has a radius just sufficient to accommodate the curled chip at the maximum depth of the cut. Since the cutterhead body is larger and the blade exposure is less, the gap between the tables of the planer or jointer and the cutterhead is reduced. In addition, since the exposure of the knives above the body of the cutterhead is reduced, a lesser fan effect is achieved to decrease noise levels when the planer or jointer is idling. The cutterheads and gibs of this invention thus reduces the possibility of kick back, reduce the severity of kick back should it occur, reduce the severity of injury should contact with the blades occur, reduce chipping out and grain pull out to improve the quality of cut on wood burl or other swirl grain type wood workpieces and produce a tight curl chip that is easily handled by dust collectors.

Re: Tear-out mitigation

Brian Holcombe

I have a Tersa head in my jointer planer, I like it because I can install fresh knives when the prior get dull in a few moments. It cuts cleaner than any spiral head I have dealt wth and the surface finish considerably nicer.

Here are a few pages from the next chapter 6 *LINK*

Keith Newton

Just to make sure you understand, since you said, "Never seen one with a bevel on the back of the knife." We're talking about Face Bevel, on the front of the blade as it hits the wood.

Think of it in terms of a saw blade. Rip blades have a lot of hook, or wider angle relative to the radius from the center to the front of the blade. If you cross cut with it, it will really splinter. Whereas a crosscut blade has a face only a few degrees from the radius, which makes more of a scraping cut and doesn't splinter as much.

I knew a man about 35 years ago that worked in a mill setting up and maintaining the equipment that told me, " sometimes I would turn the knives around backwards with the top bevel forward to prevent the tearout in some of the hard wild grain woods. "A blade with a 30º sharpness angle in a head with a 30º cutting angle turned backwards would have a 0º cutting angle, which would do the trick.

You ought to download that whole manual, it has lots of good research, like what feed-rate, or knife cuts per inch work best for each species relative to MC.

Inquiring minds want to know!


http://www.woodweb.com/knowledge_base/Knife_Grinding_and_Woodworking_Manual_6.html

Re: Tear-out mitigation

Mark Hennebury

Some planers have a knife with a built in chipbreaker, some use the gibb as a chibreaker, some didn't quite figure it out.

Tersa head are excellent and leave a beautiful finish and can be changed out in a few minutes.

Thickness planer chip breaker

Bill Tindall, E.Tn.

The chip breaker on my machine is connected to a handle in the front that enables it to be lifted. Under certain conditions boards "wedge" and feed is interrupted. Lifting the chip breaker reduces this friction and feeding may proceed. Over the nearly 30+ years that I have fed lumber through this machine I have had many occasions to lift the chip breaker. My conclusion is that what ever it does for tear-out is minimal. In fact I know of one shop that just set it high to improve feed.

We used to get some of our lumber skip planed. At a uniform thickness it piles in racks better. Lumber that came to us from huge industrial machines that were set up optimally was largely tear-out free even at feed rates that left a noticeably scalloped surface. One source produced severe tear-out that we had no trouble correcting on our machine in finish planing mode. So obviously the machine or its set up has some significant effect.

I do not question that diddling with the grind on a standard knife could be beneficial in some cases. However, I have not experienced in my shop or from my experience with others that it is necessary in most cases of hardwood lumber planing with light industrial machines from Delta or Powermatic.

Turning a planer into a power scraper seems like it is going to vastly increase the rate of dulling. I only suffer two annoyances with my planer- feed issues and having to sharpen. Without on-board sharpening, increasing the need to sharpen for me would be too steep a price to pay for the minor tear-out improvement I might experience.

That head would solve a significant problem

Bill Tindall, E.Tn.

Would it? I can go years without sharpening jointer knives when I am only edge jointing planed lumber. I start the fence at one extreme and move across the head in 2" increments as knives get dull.

Face jointing is like thickness planing. There is all sorts of junk invisible in the rough surface ready to nick knives. I have longed for the luxury of one jointer for face jointing and another exclusive for edge jointing, but it is not practical in my small shop.

Is knife changing quick enough that it would be practical to install "face jointing knives" at the start of a project and flatten one side of the project; then install "edge jointing knives" for the weeks to complete the project? Repeat every few months.

Fastest knife changes *LINK*

Mark Hennebury

These knives take a few minutes to change. and the are double edged, so you can use one edge for rough and the other for finishing.


short video

Re: Thickness planer chip breaker

Mark Hennebury

The chipbreaker or pressure bar, was not what i was referring to; sorry if i didn't explain.

The pressure bar / chipbreaker is important to hold the stock flat to the table on a thicknessplaner to help in preventing snipe and to prevent tearout, it is not close enough to the knife edge to prevent small tearout it is similar to the mouth opening in a handplane.

The chipbreaker that i was referring to is the gib itself that in some machines is close to the knife edge just as a handplane. Others like the fist picture are too far away and not shaped to put back pressure on the chip to be of any good.

Below is the powermatic cutterhead the gib/ chipbreaker is closer and shaped to provide resistance pressure to the rising chip to help prevent tearout, just like a closely set chipbreaker on a hand plane.

Sorry you don't see any benefit to my suggestion

Dick Coers

Gosh Bill, sorry you don't see any value to my option. The bevel I'm talking about is on the front of the blade, the back already has the sharpening bevel on it. I used that profile in my custom woodworking business for 8 years. It's not a power scraper, the geometry change is very subtle. I will attest to the fact it worked for me, and it put groceries on my table, running hours in a session. It now is making money for another studio woodworker. You can dismiss this if you like, but what I state are facts based on years of professional experience, these are not speculative opinions.

my machine configuration

Bill Tindall, E.Tn.

I have a pressure bar that eliminates snipe when adjusted properly. I also have what they call a chip breaker. And I have the knife configuration described in the patent.

Re: my machine configuration

Mark Hennebury

In your photo; the chipbreaker is the equivalent of the leading edge of the mouth opening in a hand plane. so it works to help prevent tearout and to keep the board flat to the table to prevent snipe. If it is precisely machined and properly set it will certainly work well; it is spring loaded and set slightly below the bottom dead center of the knives and will rise up as it rides over the stock that is entering the planer, so it has to have enough blade clearance to ride up over the stock without hitting the knives, so it alone wont stop tearout because unlike a handplane it cannot be set that close to the blades.

So the next part the affects surface is the hook or rake angle of the knives in your cutterblock, Planers can have knives set at different angles, and they can have different size cutterheads which also affect the finish. Similar to the bed angle of handplanes. Some people modify the knife angle by putting a back bevel, it need only be s very small bevel not much bigger than the thickness of a shaving. But it works like a steeper bed angle on a hand plane.

The feed speed makes a big difference as that affects the shaving thickness, and a slower feed makes a much thinner shaving with less tearout.

But the big difference as with handplanes, is the use of the chipbreaker on the knife. On thicknessplaners and jointers, this is the gib.

A properly designed gib will function just like a chipbreaker on a handplane. It will be close to the knife edge, and shaped to put backpressure on the chip to push it back to prevent splitting ahead of the knife edge exactly the same as a handplane.

Some cutterheads with disposable knives have a knife with an integral chipbreaker.

The problem with thicknessplaners is that you have variable feedspeeds which gives you variable shaving thicknesses, but you have no adjustment for the gibs, so they have to be set for the largest shaving.

So its all a bit of a compromise, That works well enough for people to buy them.

The thing to remember is not all manufactures actually understand chipbreakers and employ that knowledge in their design.

About 30 years ago i saw Japanese thicknessplaners with adjustable gibs so that you could adjust the setback of the gib from the knife edge, just like a chipbreaker on a hand plane.

Having said all of that, you have a great planer, that has a well designed head and gibs.

Of the catagory- Information You Can't Use

Bill Tindall, E.Tn.

First there is a credibility issue with this information. Nothing said about on-board grinding is accurate, at least by my experience with my machine. I did not want to spend the money for on-board grinder. The tech person at Powermatic implored me to spend the money for it. It delivered all the benefits he claimed and I have been thankful I followed his advice. In addition to the obvious benefit that knives will always be perfectly aligned there are other benefits. With on-board grinding I sharpen when knives first show dulling. As a result knife wear is something like 10 times less. One set of knives will last a lifetime. There is no loss of knife strength from the hollow. This same bogus claim is made for hand tool hollow grinding. You can't loose temper in M2 or M42 steel grinding it, who would ever grind into the cutter head, etc.

When a writer exaggerates disadvantages to this degree they usually have an agenda to promote some other option. One could be suspicious that this writer works for a company that sells a variable angle cutter head or knife grinder.

It leaves me wonder what else about the information is inaccurate. There are a lot of claims made. What data was collected that led to these claims? It would take a staggering amount of experimentation to arrive at valid conclusions about all the variables.

That said, if it is valid that this wood requires this angle and that wood that angle how can I use the information? I am more willing to believe Powermatic designed the machine for the average shop running the average mix of lumber which fits my case. I simply can not adjust my machine for moisture content and species given the range of these variables I encounter.

Granted, if someone else's shop is planing mostly wood that benefits from some set-up other than "average" these guidelines will be beneficial for trying something different. Again, I rarely have occasion to plane curly maple. I have planed tightly curled ash and done well. And I have had the occasional ash board that picked out no matter the feed direction.

Why not set up for worst case? Because as planing moves toward scraping there is more demand for power from the motor (which will limit depth/width of cut) and a big price to pay with knife wear. Guess where this extra work goes- into heat at the knife tip, and more wear. My advice remains- don't mess with the knife grind that comes with the new blade unless your experience with your machine and lumber shows that something different is needed.

Re: Tear-out mitigation

Brian Holcombe

I really enjoy using the Tersa head, it's nice to be able to change knives in a brief moment. After reading many a lament about how long it takes to turn the knives on a spiral head I decided against it. The surface finishes have been really wonderful.

I think the trouble with spiral heads, in use in most shops, is the reluctancy to replace the tooling. It's great when it's sharp, but a dull set of cutters is going to cost $600-$800 to replace, by comparison I would need to wear out 24 sets of knives (two sided, so 48 complete changes) before the costs become equal. One set of knives on one face have so far lasted me 4 months and were only in need of changing because I missed a broken off stable in a piece of stock. The results were still livable so the knives are good for roughing work on nasty material.

Re: Tear-out mitigation

Derek Cohen (in Perth, Australia)

I think the trouble with spiral heads, in use in most shops, is the reluctancy to replace the tooling. It's great when it's sharp, but a dull set of cutters is going to cost $600-$800 to replace, by comparison I would need to wear out 24 sets of knives (two sided, so 48 complete changes) before the costs become equal. One set of knives on one face have so far lasted me 4 months and were only in need of changing because I missed a broken off stable in a piece of stock. The results were still livable so the knives are good for roughing work on nasty material.

Interesting Brian.

My Hammer A3-31 (12" wide) combination jointer-planer(thicknesser), with a spiral "silent" head, uses about 40 inserts. These are carbide and cost $3 each. That is $120 to replace. Now each insert has 4 faces, so effectively each set costs $60, if they were using only 2 sides, as with your knives.

I have had the A3-31 for 5 years now, and only recently turned one side of the inserts. Keep in mind that the wood I work is especially abrasive. My machine is used most weekends. Still, if used 10 days in the week, the face would have lasted 1 year. That is 3x the duration of yours.

I would argue that my cutters are way ahead of your cutters, both in longevity and cost!

The other advantages of the spiral inserts is (1) they are MUCH lower in noise levels. Indeed, I can hold a conversation while standing next to the machine. (2) If a face chips, all I need do is turn that face. With knives one must either regrind or move the knife to another position.

How long did it take me to change (turn) a full set of inserts? About 20 minutes - I was working carefully as it was the first time. 20 minutes per 5 years is not much time spent.

Regards from Perth

Derek