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

FWW's Planer Sled Notes

Awhile ago, I built the planer sled shown in this video on Fine Woodworking's online site: Keith Rust's Planer Sled.  I don't have access to the article so some of the observations below may have appeared in the article.

Voilà, my sled:

The first difference you'll notice is that I didn't use bungee cords to hold the levelers in place (my term for them).  Rather, they are in a box.  You'll see why later.

The base is a torsion box that I took care to make flat.  Turns out there is a slight variance over the whole length, but not too bad.

My levelers actually look a lot like Keith's including the bungee slot I decided against.  In my case, I put a fence near the back for the victim board to register against and prevent movement.  It is only 5/16" taller than the levelers.

The tape on the top of the levelers and the bottom of the wedges is 3M's safety tape.  Very sticky and very consistent grit; available at a borg near you.  Cheaper stuff at Harbor Freight was very inconsistent, which concerned me.

I drew a red mark on one side of the levelers.  Note the direction of the wedges.  When placing a board on the sled, I want all the red lines facing away from the back fence.  In this way, if the board moves a very little backwards during the planing operation (or after shuttling it back and forth for repeated passes), the planer will be pushing the leveler into the wedge tightening it rather than loosening it.  I didn't think of this ahead of time.  On my first trial board, it became an issue and thus the red pen pulled out.

The first board I had to run through had an evil twist/cup combination.  Normally you'd run a board through cup-down, but with the twist, I had places where I needed support for cup-up meaning support on the outside edges, but since it dipped down in the middle, there was no room for the full length of a leveler.  Follow that?!  So, I made a batch of "half-levelers" that I can put on any spot.  The portion that faces down (leftmost tape in this picture) is gently planed so as the far side is raised with the wedge, there is always flat contact somewhere along the tape.  The portion that faces up (rightmost tape in picture) is gently rounded so it, too, always has contact depending on the wedge angle.  This proved to be very useful for this odd board and likely will be useful in the future for a bloodwood board with serious attitude on my rack.

Here is a piece of sapele with a bit of twist.  The only wedge used is the one in the foreground.  Notice again how the wedge is on the fence-side of the leveler so the action of the cutters pushing the board towards the fence will only tighten the wedge, not loosen it.

Another important point has to do with the type of planer you have.  I have a floor-standing (floor-crushing?!) Powermatic 20"planer.  Unlike my Ridgid lunchbox planer, it has power rollers, not pressure feeders (after this post, I'll post about those differences).  "Power" in this case really means it, unlike "power" meaning anything in "power chord" of 80's metal.  Note the following picture:

this is the correct way to place the leveler... there MUST be a leveler at the board extremes.  If you do the following:

the power rollers will press down so hard on the first unsupported inch of the board that the other end will pop up in the air.  Likely your leveler settings will be in disarray or, worse, everything might go amuck while being fed into the planer.  While I'm sure you can see how this would happen on this tiny sapele board, the board from which it came from was 7' long, 11" wide 4/4 sapele.  I had about an inch before the first leveler like in this picture.  The back of the board popped up 3-4 inches as the roller pressed down then when the roller was over the leveler, it slammed it down.  I nearly had very embarrassing laundry.

Monday, October 19, 2009

Help when Eye-Balling Router Bit Height

I don't have any photos to include here as my router table is currently dismantled awaiting a weekend to install it in the right extension wing of my new SawStop.

Many times you know the bit height needed by relative measuring.  That is, you have placed a scrap piece into the project and marked it directly off the project.  This is always more effective than trying to measure "a heavy 1/4 inch" and marking it.  Normally, you sight down the edge of the table to see where the bit will cut in relation to the score line you made on the scrap.

What I do instead that helps greatly is to put a penlight flashlight on the table casting the bit's shadow onto the scrap.  It is very clear, even in daylight, where the top of the bit is located.  If the penlight is small and the bit height quite high, you can get an error due to the predominant incidence angle of light, however the error will be in cutting shy not too heavy.  Generally my 1" diameter penlight gets me dead on first try with the scrap with no squinting.

Domino Butt-Joint to a line

This is a post I made on The Woodwhisperer Community forum about how to butt-joint a member into the middle of another with a Domino joiner.  Normally you use registration surfaces to create Domino'd joints, but here you have a line.  Voilà the post:

When you have the Domino standing up on a board, the tenon's centerline will be 10mm up from the bottom edge of the Domino. Note that this is to the centerline so it does not matter which size Domino tenon you are using (4, 5, 6, 8, or 10).

Here's a walk-through:

Voilà, two boards to butt joint:

The line on the wide board represents where the reference edge on the narrow board will line up.

Next, set the Domino on that line and line up the mark on the bottom of the unit to the tenon's position.
Notice how the centerline of the tenon is 10mm up from the reference line. This is constant since there is no adjustment for it.

Now, you'll need the mortise centered 10mm down from the reference surface of the second board to join. Since this other board uses the 90-degree fence, set it to center the mortise 10mm down from the fence; since the gauge on the side centers the mortise on a thickness, you set the gauge at 20mm to put the mortise 10mm down from the fence.

Mortise the end of the narrow board using the 90-degree fence like you are used to.


One other important point: when you adjust the height of the 90-degree fence, adjust it with the fence in the upright position. If it is tilted down 90-degrees when you set it, I've noticed that the fence may lock tilted. With the fence up during the adjustment, I can't get it to lock tilted when trying.