I have been tuning up my "new to me" Powermatic 15" planer. Having an unacceptable amount of blowout on reversing grain in both Birch and Aspen. Tried faster 20FPS and slower 16fps feed speeds tried two sets of knives (One set new from the factory with a micro bevel, and one set razor sharp of the water stones) Both have blowout. Also tried reducing the depth of cut to next to nothing.
Any tricks for planing reversing grain woods ??? I am thinking of trying putting on a very steep micro bevel on one set of knives.
I will not even tell you what happened to test piece of birdseye maple >:(
Max
Just to make sure I understand micro bevel correctly...it is a bevel on the reverse side of the knife which in effect reduces the cutting angle of the knife. Yeap, that is the best thing you can do to reduce blow out. Another trick is feed the stock at an angle or wiping the stock with a wet towel right before putting it through. Almost forgot...is your chipbreaker adjusted properly?
I ended up spending the cash to get a Byrd Shelix head. It tamed the wild grain (very expensive) woods and I think has probably paid for itself in less than a year.
The use of the term "blowout" to describe machining defect is a new one to me. Is it tear-out where the fibers are ripped up? i.e. not cut off.
Can't figure out what would 'blow' and fit that description when planing. (but I can still learn new things :) ).
A good (old but still good) book on machining is
Machining and Related Characteristics (http://www.fpl.fs.fed.us/documnts/usda/tb1267.pdf#search='Machining%20and%20related%20characteristics%20of%20United%20States%20hardwoods')
Yeah, I think it's tear out. ;) And this tipped and reversing grain is 'figured wood'. If I had much figured wood to plane, I would have an abrasive planer and wouldn't risk tear out. That tear out will bring tears to your eyes. :D
Yes I mean tear out ::) When you come in covered in wood chips frustrated you get your terms confused :-\
It is tear out in figured wood.
Den, yes an abrasive planer would do the trick but hand planes can be tuned to deal with difficult wood so I figure I should be able to improve on the factory cut of my surface planer.
Beenthere, thanks for correcting me as usual and thanks for the link I will check it out.
Larry, I meant a secondary bevel that actually increases the cutting angle. I get what you are saying use what I call a back bevel and reduce the cutting angle ;) Sounds sensible I will try it along with your other suggestions. Hopefully I do not need to get a shelix head, but it is good to know it is a option that would work.
Thanks
Max
Max Sawdust,
The secondary bevel lessens the cutting angle, envision polishing / rubbing the wood off instead of cutting it off. That is a bit of a severe analogy but it will help you understand the concept. I had an old two knife square head planer and that was the only way to get it to perform. The other suggestions are right on the money. Sometimes the wood just won't cooperate.
Abrasive planers are great but have huge HP/ space demands and are $$$$. If your wood is excessively wide (like some of mine) they would be the ticket.
The 12- 12 1/2" modern bench top (Dewalt comes to mind) units are super high speed (knife revolutions) compared to some of the stationary units and may be of some assistance for the occasional super wild grain, you just hate to spend the money on duplicate equip. The portables are good for light removal but not roughing or volume use as the motors are fairly "light".
Reid
Y'all oughta try some Spanish Cedar. That stuff tears out just looking at it. ::) ::)
Started installing a Shelix Head yesterday, but, got sick, again, and had to quit. Got some furniture to build, sooo, gotta get it installed.
If ANYTHING can plane Spanish Cedar, this MIGHT be it. Updates as soon as I get it running.
Reid,
When you say secondary bevel do you mean putting a small bevel on the back or flat side of the knife as Larry suggested? (As shown in red on this image)
(https://forestryforum.com/gallery/albums/userpics/12877/bevel.bmp)
Abrasive planers would be nice, but not in my business plan/wallet at this time. I could see if I was buying high dollar logs, but I am not.
Very interesting in-site on the portable planers. I just sold my portable 12" Delta :o It was old and I do not think the knife speed was that high.
FLA.
Hope you feel better, keep us posted on how the new cutter head works!
Max
Max
Reid is hitting on the likely solution to better results with the secondary bevel I think. In the Davis machining pub referenced, there are good drawings showing these angles and tables for angles to use for various hardwoods, as well as many other variables. Seems there is lots to know about machining wood.
Hope it works out for you to find the solution.
I'm going to second the dampening of the surface. bath_smiley Usually, I wait for the last pass to do this using an old Windex bottle. A nice mist comes out and doesn't flood the surface. If you wait 10 or 20 seconds a little deaper cut can be made. smiley_fused_bomb
Hello:
Aspen is one of my main woods that I finish along with a fair amount of white birch. I am curious what your moisture content is when you plane. Aspen has to be very dry if you want to get a "glass" finish on it. I dry to 6%-7% and then plane. Some folks say I over-dry but it works for me. I believe that 6,000-7,000 rpm machines also do a better job compared to the slower planers. And of course, sharp, sharp knives. Feed speed is critical too. And sometimes aspen just kicks you in the pants and keeps going. Interesting wood.
Mur,
As far as over drying, it depends on your use and your location. If you were in Az. then of course that MC makes sense as it would if you are doing glue ups. Remember it will reabsorb quickly if given a chance.
These are from Fine Woodworking Mag.
(https://forestryforum.com/gallery/albums/userpics/11262/Obackbevel1.jpg)
(https://forestryforum.com/gallery/albums/userpics/11262/Obackbevel2.jpg)
(https://forestryforum.com/gallery/albums/userpics/11262/Obackbevel2a.jpg)
Reid
Hello Reid:
Interesting reading. Going to talk to the fellow that does my knives and get him to try what you are saying on a few sets. Makes sense and I like your source for information.
Reid's example is the best explanation I have seen. Lot of compromise's go on in the design of a planer. Reduce the cutting angle to control chip out in figured woods and horsepower requirements go up quite fast while feed rates go down...the guy running straight grain RO or pine not gonna like that one bit.
Reid and mur also made a point about the bench top planers with the high speed universal motors. They do almost as well as the Byrd Shelix head on figured woods. A lot of the wood workers I sell hardwood to are running the Dewalts...I skip plane there wood and they finish plane it.
Another source of great info is the Charles Schmidt Co.
http://www.cggschmidt.com/
They wrote a book..."Knife Grinding and Woodworking Manual"...not for sure if it is still in print. They expounded a lot on the info in beentheres link so the average guy can understand...got a question give em a call. Might be nice if ya buy something to. ;D
I sure love this DanG forum 8)
This is real good info to work off ;D
Mur, I do not think I am at 6% more like 10% I know "green" Aspen will tear out like crazy ::)
Reid,
I am surprised at the amount of back bevel Fine woodworking is saying :o I think I will work up from a minor back bevel ;D
Max