12/22/2023
Planer primer.
My answer to a planer ? Re. snipe.
Hey David try this if it’s possible. Think about the pressure bar as a part of the planing system, that I have found often hides its involvement in the slowed or labored forward motion of your material which seems to increase with time, mostly between changing out knives.
The way planers work is that the wood is let’s say 1” coming in so the feed roller has to be set low enough to push it but not too low or you couldn’t get under it, then under the chip breaker that has to be higher enough to let boards that might be a little thicker go under it but still break the chips because some chip breakers are solid whilesome are weighted and the feed rollers are spring loaded.
Then the knives which are set let’s say at 15/16” so the board passed under the knives and is now 15/16” then it goes under the pressure bar that is supposed to be a few thousandths higher than 15/16” in order to allow the wood to pass under it but not be allowed to be lifted by the upward motion of the knives which is what causes chatter and snipe as it is planed and as the last end leaves out from under the first feed roller, under the knives under the pressure bar and now just held down to the outfeed table by the outfeed roller.l
Think about three point geometry and how the last of the three points of contact work together to not stifle forward motion but still prevent lift into the knives which is what causes chatter and snipe.
Everybody knows that if something happens to one or both of the feed rollers to lower their pressure and or surface friction you experience feed issues.
It is common knowledge also that loose stretched or worn belts effect the feed as well as it transfers the motor’s motion to move the material overcoming the friction of the bed and fighting against the push back delivered by the knives which are trying to kick the board right back out the front like a projectile.
There’s a lot going on in a little ole planer and if it’s not all set up right it can sometimes be tricky to read the problem/symptoms and attribute them to just the one puzzle piece rather than maybe a concert of minor individual changes that might happen over time.
The keyword is “might”. Because machines are engineered and manufactured to maintain their settings, change is not to be expected and when it does occur it is more often pilot error like under torqued rather than slipped adjustments.
Now for the unavoidable “fact”rather than “possibility” that I have discovered that has definitely affected the feed in my 18” wedge bed Rockwell planer over the last 24 years I’ve owned it. I do have to point out that this is not going to be nearly as much of an issue in our more modern segmented helical head planes with carbide incerts, but is a definite occurrence in straight knives.
The relationship of the distance from the knife at its lowest dead center point to the out-feed table and the distance from the bottom of the pressure bar to the table is crucial in determining how the material feeds because if they are the same there will be a small amount of friction. If the pressure bar is higher we risk snipe n chatter, but too low and your wood will actually have to be squeezed/forced under it.
Here’s the rub, no pun intended.
This is the given, no ifs or maybes.
When you use your planer the blades get dull and this happens as a result of three physical occurrences.
1. Abrasion from friction against the wood fibers and harder contamination like dust, dirt, or paint, and even minerals in some tropical species, removes material fairly evenly from the very edge of the knife which although only minutely, does change the dimension of the blade and thus that measurement from it to the table and the finished thickness of the wood.
2. “I believe”, and this is just my own hypothesis, that the pressure delivered to the metal at the very edge of the blade at every revolution actually moves molecules away from the very edge and back into the blade also minutely but still changing the dimension of the blade and further changing the vital distance from the bottom of the blade’s arch, to the table which you remember is the determining factor of the thickness of the finished wood that has to pass under the pressure bar.
3. When the blade randomly strikes metal, sand, and yes even some hard knots in wood like hemlock, aged reclaimed pine, and other very dry dense species, chips are knocked out of the knife edge which cause it to leave ridges in the surface of the finished board that encroaches into that vital clearance between it and the bottom of that unmovable element, the oft forgotten but important P.B..
Remember the song about the little ole ants and the rubber tree plant? “Whoops there goes another rubber tree plant”? Well when you change your blades dimensions by abrasion and material movement, and its edge profile/shape, by chipping, this will change the dimension of the exiting wood that actually will touch, then rub, then squeeze against the bottom edge of pressure bar and the exiting wood, even before many of us think we absolutely have to sharpen the knives, change them, or tweak the pressure bar settings.
So what I mean to give you is an option to try when you begin to experience feed issues. Check to make sure the changes in your knife edge dimensions aren’t limiting your depth of cut to the point that the wood is now dragging against the bottom of the P.B. I’m pretty sure that if you raise the P.B. A couple thousandths, oh and wax the table to decrease friction there, you will give the belt and feed rollers less work to do and at the same time help them last longer.
I found that I had to raise that pesky pressure bar at least once and often twice, and even three times if I would hone a micro bevel with a diamond stone to extend the life of my knives before I had to change’em out.
When the issue you experience is snipe the culprit is gonna be the difference in the thickness of the board your pushing through your planer and the board after the knives/cutters remove some of it and the distance you give it to creep out from under the pressure bar. Bottom line is too much gap the board’ll slap up n down n snipe, like too much is maybe.004”instead of .002” gap for my wedge bed. If your pressure bar is, .002” less than prescribed you’ll experience hard feeding even slowing and stopping and burning those pesky stripes across the nice finished face of your board that somebody’s have to sand or plane out as a of lack of proper set up.
Proper set up is your friend and understanding what your machine is needing from you will help you maintain the relationships of all the settings to each other n get nice results from your machine.
Sometimes you can overcome what is not right by how you hold your mouth, stand, n when and where you pull up, push down or pull on the material as well as having things ready to feed so the boards chase each other through by feeding them in touching end to end. And as some folks mentioned pitting out riggers on the boards. I always hate the job of spending an hr setting up a cantankerous machine but all th dancing, and adding outriggers, n snarling most often Robb’s of more efficiency and shop time than just understanding and keeping up with those relationships.
I hope this helps somebody. Let me know if it works for you.
A.T.
