Yesterday, I was planing a load of cherry. During the process, I got a call from a customer who wanted to pick up some cherry boards planed to 3/4". No problem.
For skip planing, everything went fine but when I went to plane down to 3/4", I got really bad tearout on one end of the board . First I thought it was just the grain on the board. Then the same thing happened on a second board. Turned the boards around and got tearout on the other end. No matter which way I turned the board, I would get tearout on one end. I checked the MC and it was at 5.5%.
I've narrowed it down to fluky boards (from the same log) or maybe the boards were too dry. So that is my question. If you get below 6% MC, does the wood become brittle to the extent that tearout can be more common?
I try to begin sterilization when the MC is around 7.5%. During sterilization, it does seem to drop another 1-2%. This is probably due to some air leakage where some moisture gets out.
I did put a brand new set of blades on the planer 2 weeks ago. I planed QS white oak with no difficulty so I doubt it's the blades
I don't know doodley squat about machining wood but I believe that over drying makes wood more brittle. How did you get 5.5%? That is too low for a meter and you would have to do some careful baking to get 5.5%.
Depends a lot on the tree. If there was a curve or flair, the grain will dramatically run out at the end of the boards. Look at the grain direction and you should see two opposite directions. No correct way to run those. I've actually had a chunk fracture off the end if the grain starts to go more vertical. Especially as the wood gets under 1/2". Moisture has nothing to do with boards like that. Hard maple can do the same thing, both woods can be brittle.
Quote from: Den Socling on September 25, 2016, 09:52:38 PM
I don't know doodley squat about machining wood but I believe that over drying makes wood more brittle. How did you get 5.5%? That is too low for a meter and you would have to do some careful baking to get 5.5%.
In this particular case, I used my Lignomat with the E12 depth electrodes. I agree that the meter itself is not that accurate at low MC but the E12 seems to give me a better reading. I don't know why it seems to help.
(https://forestryforum.com/gallery/albums/userpics/37307/moisture_meter_DXC_gym_floor.jpg?easyrotate_cache=1474889447)
The spiral head with the carbide inserts has completely eliminated tear-out for me.
If the the lumber is truly 5.5% then I would certainly say that the tear out is because it is over dried. Here is a quote directly out of Mr Wengert,s, Mr Denig's and Mr Simpson's Drying Hardwood Lumber
"As the wood becomes drier, its strength increases. The strong
fibers do not cut easily, but rather tear out in large chunks. If
cutting causes the grain of the surface to dive into the piece,
the tear-out follows the grain, creating a depression in the
surface. Small knife angles (very slender knives) contribute
to this failure, but the major cause is low (<6%) MC."
It could be caused by a couple of things, the moisture or lack of you guys have already brought to the table. Figured wood also was mentioned and can be the culprit. The depth of your cut has not been discussed and it could be to deep causing stress and tear out (if it as at the end of the board not the beginning). If the tear out occurs at the end of the board try running butt to butt another board right behind it through the planer and see if that helps the situation. (by running the boards against each other the second one provides support the the first board's end.)
I've got a 25 inch woodmaster straight knife plainer and a spiral cutterhead is my next purchase they have almost no tearout regardless of grain direction and they are much quieter.
Quote from: Farmerjw on September 26, 2016, 12:21:44 PM
It could be caused by a couple of things, the moisture or lack of you guys have already brought to the table. Figured wood also was mentioned and can be the culprit. The depth of your cut has not been discussed and it could be to deep causing stress and tear out (if it as at the end of the board not the beginning). If the tear out occurs at the end of the board try running butt to butt another board right behind it through the planer and see if that helps the situation. (by running the boards against each other the second one provides support the the first board's end.)
I was only taking 1/32" to 1/16" at a time so I don't think that is the issue. The tearing was not on the ends of the boards but within the boards. I think that I encountered a combination of some difficult grain and boards that are a little dry. Most of the boards planed out fine but there were a few spots that caught my attention.
The article from Dr. Wengert seems to be quite accurate. MIsawyer, I appreciate you posting it.
A pin meter cannot read under 6.5% MC accurately and 5.5% could be 3.5%. So, over drying seems #1, probably accompanied by grain angles.
Any grain angle greater than 20 degrees all but guarantees tear out. Taking a real heavy cut can help mitigate the issue.
Glenn
Quote from: GeneWengert-WoodDoc on September 26, 2016, 11:47:42 PM
A pin meter cannot read under 6.5% MC accurately and 5.5% could be 3.5%. So, over drying seems #1, probably accompanied by grain angles.
I was waiting to hear from you Doc. Unfortunately, I think that you are right. What is strange is that I air dried to boards using oscillating fans going on and off periodically(more off than on) and always having them off from 8pm to 7am. I took your course in Hickory so I learned about the moist evening air. Humidity was always over 40% as I have a controller that turns off the fans if the humidity drops below 40%. The pin meter said that the wood was at 8%-10% MC. I thought that the lowest I could go was 14% in my region.
I put the boards into the Nyle kiln on Sunday at 120/75. Within 3 days, it said that I was down to 7%MC. I went to sterilization for 18 hours and turned the system off.
How could they have dried so quickly? There was no cupping and no casehardening because I did the test cutting fingers as suggested. They were perfectly straight.
Correct... the open air drying can get to about 12-14%. You careful use of fans could end up a bit lower, especially this year when we have abnormally low humidity in our area. I suspect the meter readings also could have some uncertainty. And that is why you seem to have fast drying...but 7% loss is three days is not too unreasonable. Your results are in the ball park.
I am in Albuquerque now for the balloon fiesta and is it dry here...20% RH right now at 4:30pm.
One thing I've noticed is I can't remember any time my moulder has caused tear-out. I run at least a couple of thousand feet a week. Its a constant problem with my Newman planer. I've often wondered if the angle cut on the knives is different. The planer knife angle seems to be greater.
Quote from: Cazzhrdwd on September 28, 2016, 08:09:50 PM
One thing I've noticed is I can't remember any time my moulder has caused tear-out. I run at least a couple of thousand feet a week. Its a constant problem with my Newman planer. I've often wondered if the angle cut on the knives is different. The planer knife angle seems to be greater.
Interesting difference between the moulder and the planer. This all started when I ordered and installed a new set of blades. I plan on contacting the manufacturer to see if the new blades could be causing the problem. I'm wondering if you have plans to measure the difference in the angles between the two machines. I'm guessing that a less severe angle would making the cutting go smoother. On my hand chisels, the angle was 25% for delicate work and 35% of mortise work.
Yes, my planer knives are due for a sharpening. My tech is supposed to check the angle. I think the moulder knives are at 12°.
If the problem started when you put in new blades, did you also reset the pressure bar and the chip breaker? With new knives that protrude from the head a different distance, these two items must be reset. Likewise, after a couple of sharpenings, they should be reset.
Quote from: GeneWengert-WoodDoc on October 01, 2016, 12:57:23 PM
If the problem started when you put in new blades, did you also reset the pressure bar and the chip breaker? With new knives that protrude from the head a different distance, these two items must be reset. Likewise, after a couple of sharpenings, they should be reset.
I am embarrassed to admit it, but it never crossed my mind. Thanks for the reminder. I'll get out the manual and learn how to do it.
Glenn...You mentioned that the tearout is happening near the end of the board, regardless of grain orientation. If your pressure bar/roller on the in feed is not over-tensioned, the board may be slightly lifting into the cutters. If the boards are only marginally supported on the out feed and allowed to sag even a little, it may be enough to lift the other end into the cutters. I used to occasionally have that problem, until I changed my set up to fully support the out feed in the same plane as the planer bed.
I reread what Glen posted, I don't think pressure bars or chipbreaker would do it. Seems to me those would only create severe planer marks on the board. Glenn said he narrowed it down to boards he thinks came from the same log. Could the log have sat around a bit causing the lumber to be a different moisture content on the ends? Or maybe a bit harder than the middle of the boards causing an abrupt change in the planing?
The greater the distance between the CB and the knife, the deeper and longer the chipped grain will be. The defect will be worse on the front or leading end of the lumber until the PB begins to hold the lumber tightly. A poorly set CN will affect about half the pieces...those where the grain is div9ng into the lumber.
I went ahead and re-set the blades, chip breaker, infeed, pressure rollers, and outfeed rollers. I was using a product called Planer Pal and I thought the blades were set accurately. I purchased a Rotocator which measures in thousandths of an inch. This made a big difference.
The planer is again putting out beautiful boards. Thanks for everyone's help.
I also have the rotocator.
Quote from: WDH on October 05, 2016, 08:20:53 PM
I also have the rotocator.
Me too, but mine's a homely homemade rig, with a block of wood and a dial indicator. No doubt, when setting a planer, thousandths matter
I changed to a spiral cutterhead on my 20" planer, its like day and night, the only downside is the price, but after that you wont regret.
Quote from: YellowHammer on October 07, 2016, 10:46:44 PM
Quote from: WDH on October 05, 2016, 08:20:53 PM
I also have the rotocator.
Me too, but mine's a homely homemade rig, with a block of wood and a dial indicator. No doubt, when setting a planer, thousandths matter
It's also useful when setting the clearances very precisely. Infeed roller, outfeed roller, in and out feed bed position and parrelelism, cutterhead depth, side to side height, chip breaker side to side and chip breaker depth, etc. It's a good idea to set go over everything, and reset to factory. For example, the chip breaker on my planer needed readjustment as the paint wore off, it's only a few thousandths, but it's the difference between purty good and flat as a mirror.
I am a "flat as a mirror" guy.