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My Planer Sled Technique
Copyright (c) 2012, all rights reserved.

I needed to condense my shop somewhat, and that meant my Inca 410 jointer/planer and Ryobi 16/32 drum sander would have to go away.

To ease the pain somewhat, I planned on a lunchbox planer that could go on a wheeled stand which could be tucked away when not in use.  After much deliberation, I went with the Dewalt DW734.

I've never used a lunchbox planer.  Back in high school we had some giant industrial planer.  And my Inca had a planer "head," which converted the jointer into a planer.  It worked GREAT, but lacked a motorized feed; you had to push the material through the planer.  It required quite a bit of force, too.

I've never really been without access to a jointer.  The Inca was one of my earlier acquisitions when I started getting more serious about woodworking.  And a jointer is really critical if you plan on working with any rough stock.  Planers are not jointers.  Planers will make a board thinner, but they won't remove bow or twist.  To remove bow/twist, you need a jointer, or a commitment to hand tools.

I've read about using "planer sleds" in order to "joint" the face of lumber, but I had never actually done this.  With my new Dewalt planer in place, it was finally time to give it a shot.

 
Where to start
Reading up on the various planer sleds, you come up with three major camps:  (1) The "Rust" sled, designed by Mr. Keith Rust and featured in Fine Woodworking Magazine.  (2) Sleds that are basically a piece of some kind of sheet good with a stop on the front.  These sleds use shop scraps as shims, sometimes held by friction, sometimes by hot-melt glue.  (3) Everything else, with my favorite being a sled that was at least four pieces of 3/4" particle board laminated to one another.  My back hurt just looking at it.

Many people are happy with their Rust sled.  I didn't want to spend the time to make one.  I know, I know, not that much to it.  Still.  And it looked heavy.  I was hoping for something on the lighter side.

I decided to try #2, and used a 12" wide by 60" long piece of BB plywood.  I attached a 1/2" high by 1" wide piece of scrap to the front to act as a stop.

 
My first attempt
Now that I had my sled, I grabbed a piece of soft maple and used some scraps and tapered wedges as shims.  I used hot-melt glue to hold some of the shims, and tape to hold others.

The results were just okay.  On at least one trip through the planer, or when I was moving it about, the workpiece shifted on top of the shims.  Also, as the board got progressively thinner, I got some waves in the final surface because I didn't have enough shims to support the thinner workpiece, and the rollers of the planer were able to compress it on the way through the planer.

 
Back to the drawing board...
I've been told by more than one experienced sled user that sleds need to be STIFF.  I couldn't understand why that would be required. As long as the relationship between the bottom of the workpiece and the bottom of the sled stayed a constant, then stiffness wasn't that critical, as far as I was concerned.

Much more important, I felt, was preventing the workpiece from moving in relation to the shims.  Any movement of the workpiece, or the shims, would result in a lack of support which would result in a high spot in the workpiece.

 
Eureka!
Seeing as I was already using glue and tape, I had a sort of eureka moment.  My first thought was, why not just use the glue as the shim.  The hot-melt glue doesn't easily compress.  You can flex a stick of the glue, but trying to squeeze it out of round is much tougher.

When the job was done, though, removing the old glue from the sled would be a pain.  A blob here or there, no problem.  I didn't want to have to spend minutes removing lots of glue blobs.

Here is my solution:  I place two strips of tape on the bottom of the workpiece, and two corresponding strips of tape on the top of the sled.  The strips of tape line-up with each other when the workpiece is placed on the sled, and the glue stays on the tape.

Next, I squeeze blobs of holt-melt glue onto the bottom of the workpiece (on the tape), flip the workpiece onto the sled (keep the tape aligned), and allow the hot-melt glue to drip down and form a shim.  Think of the glue blob as a stalactite that drips to the sled and creates a corresponding stalagmite.  The tite and mite stay joined in the middle to form the shim.  Gravity creates a hot melt glue shim of the ideal thickness.

Once the glue cools, I can run the sled (with the workpiece) through the planer and get a perfectly flat surface every time, no surprises.  I don't have to worry about the workpiece shifting in relation to the shims when I move the assembly from the bench to the planer, it is all locked together.  I can turn the entire assembly end for end without worry that I'll change the shim positioning.

And when I'm done, I just pry (with my fingers) the workpiece off the sled.  The tape typically breaks its bond from the workpiece and stays on the sled.  When I peel the bottom layer of tape from the sled, I get both layers of tape, with the glue trapped between.

 
The steps, a pictorial of sorts

(1) Just getting ready, I'm warming-up the glue gun and determining where on the sled I will need to apply the tape.

Note:  When using a thin (1/2") sled like this, it MUST be on a flat surface during the initial setup.  I use my bench, it is very flat.

 

(2) I've flipped my workpiece over and applied tape to the bottom, and I've applied tape to the top of the sled, as well.

 

(3) Here is a pic of the front of the sled, so you can see how the tape on the bottom of the workpiece should be aligned with the tape on the sled.  The entire purpose of the tape is to speed clean-up of the glue when I'm done, so the pieces of tape on the workpiece and the sled have to line-up.

 

(4) Now I've applied by glue blobs.  They are spaced opposite each other, about every six to eight inches along the length.  Most of them are a single trigger pull of my glue gun.  Where I have larger gaps, I will apply a couple of trigger pulls.

 

(5) Here is a larger gap at the front of the board.  The first 2-3 blobs on this side were double trigger pulls, so there would be more glue to fill-in the gap.

 

(6) Here is a different board I was working on, I got a pretty good side-shot so you can see the glue blob in there acting as a shim.  This is a single trigger pull for a gap of around 3/16".  It is all the glue that was required to prevent the planer's rollers from pushing down on the workpiece in that spot.

 

(7) I'm done with the planer and checking the board (still attached to the sled) using a "reference" board I had run through my jointer (while I still had it).  No gaps, perfectly flat.

 

(8) I've used my fingers to pry the workpiece off the sled.  You can see the two layers of tape with the hot melt glue trapped between.  All I have to do is peel the tape off the sled, the glue comes with it.

 

--Phil
phil@cgallery.com

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