How Much Wood to Take Off Per Planer Pass
Question (WOODWEB Member) :
This means that each piece will have to go through the planer six times to achieve 38mm. Most of the boards are about 8" to 10" wide. I'm of the opinion that 1/8" passes are fine. I've also been told that taking many light passes is actually harder on the blades than just using the machine to its capacity (it's making more cuts). The machine is a new 20" Scm 'nova' with HSS tersa knives. I'm not sure how big the head is.
I wouldn't make a big deal about it, except for the fact that the difference between four passes through the machine and six could equal days of monotonous drudgery. What are your thoughts? Do you have rules of thumb for the cut you take regarding species and board width?
From contributor G:
I take as deep a cut as possible with my planer but it is mechanically limited to 1/8". Time is much more expensive than having the knives sharpened. Tell your boss that there is such a thing as 7/4. With the amounts you are using it wouldn't be a problem with the mill doing a special order at that thickness. It'll save time and material costs. Or, have the mill send you skip planed lumber. It's usually 10 cents a BF more but you don't have to deal with all the chips and it already comes in flat and somewhat true.
On this volume I would order it pre-sized. You never make money doing this as a one-off in a shop. We stopped dimensioning lumber years ago!
From Contributor O:
You need to use your phone to call a local shop with a molder to process the stuff in one pass for pennies per l/f. If I couldn't take 1/4" off a 4" piece of maple with my 18" Powermatic "old Iron" - and do it all day long - you would have to tie me up and anesthetize me.
From contributor A:
The variables are width of cut, depth of cut, surface finish, and chip removal (the one people most often forget about). The planer is somewhat limited by the geometry of the cutterhead. However that is not the limiting factor. The load on the motor increases as the width of cut is increased. The 20" should be able to run two boards side by side at the same time, taking a reasonable cut. Surface finish is related to taking too much of a cut or too little, however the first and second pass get cleaned up by the third and fourth pass. Chip removal can be a limiting factor if the dust extraction system or the ducting at the source cannot get enough material away from the cutterhead. I would expect a 20" planer to cut 1/8" across the entire head.
From contributor H:
My old Powermatic would take 1/4" no problem, my new General 24" is lucky to take 2mm. Not because of horse power (it has 15) or dust extraction, but rather because of the way it is built. The chip breakers and pressure shoe just don't have the travel that the Powermatic did. A newer design I guess is not as good in my opinion. It would be nice if your planer had an Amp gauge, in that way you would know how hard you were working the motor on the hogging passes. My guess is the iron will take it.
First of all, you are correct in that many light passes will dull the knives faster than fewer heavy passes. It's the leading edge of the knife that dulls, and once it's in the wood it doesn't care how much it's taking. The other thing that struck me was that you are using HHS in hard maple. Hard maple is brutal on knives and your boss needs to bite the bullet and go with carbide. You'll get at least 10-15 times more material through before the knives dull.
From Contributor O:
While you are standing at the planer, endlessly feeding in boards, do the math on a pad with calculator and pencil. Or do it during a break/lunch. Once the job is done, add up your man/hours and compare that to how long it might take to have a molder run it, or to take off more for less passes. Do so accurately and professionally, so your information is clear and accurate, with no bias. You will learn more and perhaps your employer will see that you more just a feeder. Compare your real man/hours to estimated hours for more passes and for a molder in one pass, with handling and shipping added in also. I have tracked production information for many years, and can tell you two things: Exactly how much something will take to produce, and that it isn't always as simple as your opinion may tell you.
From the original questioner:
I've settled on taking one pass off of each face, then straight-lining and ripping oversized, then back to the planer. After reading the above posts, and a little experimentation, I've found that the sweet spot is 10/100" passes, with blades that are working sharp. This gets me to the thickness I need in five passes, and the planer isn't breaking a sweat. Everyone in the shop is okay with this. I've found out that this is an unusual job for this company to do in-house, and that they usually outsource this type of work, so I won't be throwing my shoes into the machine just yet!
From Gene Wengert, forum technical advisor:
A bit more technical info: The larger the cut (that is, the deeper the cut and the more wood taken off with each blade), the higher the risk, especially with maple, that you will get some chipped grain. Chipped grain is a defect that goes into the surface and so requires sanding, several very light cuts (maybe 15 to 18 marks per inch) but not too light, or putty to get it smooth. If with a deeper cut, you slow the feed down, then you will get more rubbing and heating of the knives and they will wear faster. It is from this perspective that you co-worker told you not to take a deeper cut. A deeper cut with the same feed speed is a good idea (exempt for chipped grain). The drier the MC and the more swirly and sloped grain, the more chip out. Also, with hard maple, you might want to consider a smaller rake angle for the knives - the slender knife is ok for softer woods. As you also seem to appreciate, very shallow cuts with low feed rates will have more rubbing (and fine planer dust) which means quick dulling.
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