Wednesday, October 28, 2009

Floor-standing Planers vs Lunchbox Planers

No, no, no, a lunchbox planer does not flatten your lunchbox or your big heaping pastrami sandwich.  It's a cute term of endearment for a benchtop planer.

They are very different beasts and it is well worth knowing the differences.  Here are my observations after going from a Ridgid lunchbox to a Powermatic 20" floor-standing planer:

Lunchbox planers have pressure rollers.  Basically picture a long roller pressed down with a spring.  Floor-standing models have power rollers.  These press down with much more force.

Let's break down this observation to see what it means:

Since the pressure rollers are just rollers, it will press down until it hits the tallest thingumajig you are running through it.  If a board has a rough surface, the roller will follow the highest point.  This isn't a big problem.  The problem comes when you start a narrow board through and decide to push a second board through beside it.  If those boards aren't exactly the same thickness, the roller will press on the thickest one and leave the other one free to kickback (fly backwards) due to the cutter's direction of cut.  This means you can't run two boards through simultaneously without risk.  If you insist on doing so, you could put one on each extreme side of the planer's width and likely get away with it since the springs on each side of the pressure roller would get some contact; side-by-side, however, is bad news.

On a floor-standing planer, the power rollers look like helical cutters with a long spiraling tooth. It is also set with springs, but decidedly stronger ones.  Further, there are anti-kickback fingers hanging down in front of the roller.  Each finger operates independently to prevent a board from kicking back.  If you run two boards of significantly different thicknesses through simultaneously, the anti-kickback fingers will stop the thinner one from kicking back, though it won't make any progress through the planer unless you push it.  I say 'significantly different sizes' because I've found that some difference is easily tolerated by the stronger power rollers.  I still keep them to the outside edges, though, and resist the temptation to put a third board between them.

Another difference these rollers make is in the woodworker's saying "never run a cupped board through a planer as it flattens it, thins it, and it comes back out cupped".  The saying is true, if you are using a planer with strong rollers and you are trying to take a lot off at once.

Assume a board is going through cup-down in a lunchbox planer set to take 3/32" off.  The roller will press down relatively lightly and do nothing to deflect the cup before taking off 3/32" off the top.  In a floor-standing planer, the rollers are set to press hard right up to the level of the cutters.  On this planer, it will press hard through the 3/32" difference between the rollers and cutters and may be able to flatten the cup with the stronger springs.  In this case, the board is flattened, some removed, then it springs back with a curved surface.  Hardly useful.  For floor-standing models, flatten the top of the cup by taking very light passes so the rollers can't deflect the board