# Planer Sled Construction



## rbterhune (Jul 31, 2009)

I will soon have a need to face joint 8"-10" wide boards 3'-4' lin length. I am new to woodworking so my tools for this task are limited to a table saw and a benchtop planer.

I have completed much research on planer sleds for face jointing. Everyone references the FWW sled but that looks like overkill. I subscribe to the KISS method. The simpler, the better, as long as it works.

Other options I've seen reference are plywood, MDF, and melamine sleds with simple shims. My biggest concern with these are flexing under the feed rollers…especially the mdf and melamine.

I have purchased a piece of 21/32 mdf that I will cut in half and double up the thickness for the sled. (I chose mdf over the stiffer plywood because I trust that it is flat and it is smoother overall) Even with this double mdf layer (now over 1 1/4") I have a little concern for flexing.

What do you think? I know many of you have used this simple version of a planer sled. Any issues with your 3/4" versions flexing?

Lastly, to assist/eliminate the flex should make my infeed/outfeed tables flat rather than tuned properly to 1/8" higher on the outboard sides?


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## Julian (Sep 30, 2008)

Do you have a 6" jointer? You can plane boards up to 10" wide on it by just planing one side, then run the board through the thickness planer with a 1/4: piece of plywood under the side that has been planed down.


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## rbterhune (Jul 31, 2009)

No, unfortunately I do not have a jointer. I've spent way too much on other equipment to justify that right now…both to myself and my wife!


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## PurpLev (May 30, 2008)

curious - if you are concerned about MDF flexing because of compression from the rollers - then even if you double it up- it will still compress just as much as the forces applied on the same material are still coming perpendicular to it's face.

I think you should be good with one layer of MDF and shims. remember - you are trying to work against twists/cups in the board, not against small hollows. if the MDF is compressed by the rollers- it'll compress throughout it's length the same amount, so the cutters would still cut the lumber just the same.


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## rbterhune (Jul 31, 2009)

PurpLev…I wouldn't have much concern for flexing but the outside edges of the infeed/outfeed tables should be a little high to avoid snipe…that creates a space under the sled/cutter head, right? As the sled first enters, the leading edge will be on the middle table but as the leading edge exits and climbs on the outfeed a space is created until the trailing edge comes down the infeed…as I envision it. With this scenario a board with a concave/convex shape along its length would come out the same way. It seems I've always been told a cupped, twisted, or bowed board going into a planer will come out a smooth cupped, twisted, or bowed board. Maybe I'm missing something.


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## treeman (Dec 15, 2008)

A single layer of MDF should be more than sufficient IF your board is properly shimmed WHILE the MDF sled is on a perfectly flat surface. I think a planer bed should be perfectly flat, or at least mine is. I have used an MDF sled numerous times with good results when I take the time to shim properly. I generally place shims every 4 to 6 inches on both sides of the board until I get it completely stable on the sled. I make sure nothing can move or shift when it passes through the planer. I take light passes and pretty soon I have jointed a board wider than my jointer.


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## PurpLev (May 30, 2008)

infeed/outfeed should be parallel and flat with the planer main table.

you are correct in your understanding that if you put a twisted board through a planer on it's own, it'll come out smooth but just as twisted. BUT - this is where the sled comes to play. the sled simulates a "flat/jointed" bottom of your board. the shims hold your twisted board in place, so what happens in practice is that the planer is surfacing the top of your twisted board to be parallel to the SLED which is flat (hopefully…lol). regardless of the boards' underside. so in effect your board is not really being milled paralel to itself (which is twisted) but to another flat surface - which makes the top of the twisted board FLAT. then you flip it around, and thickness it as normal, and then it'll surface the 2nd face parallel to the first one that you had already flattened using the sled. and you get a flat and parallel board.


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## AaronK (Nov 30, 2008)

i agree with the comments posted above.

another option is to fabricate what is essentially a super long planer bed, made from mdf. in addition to a sled which travels through the planer, the long bed (ie, some feet in length) might help. never done it myself, but have read about it. can anyone with experience chime in?


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## sbryan55 (Dec 8, 2007)

Here is another version of a planer sled posted by GaryK. Essentially Gary's method involves milling two grooves in the board and then putting runners in the board to keep it parallel to the planer knives while on the planer sled.


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## rbterhune (Jul 31, 2009)

Sounds like I'll be able to use the single layer for sure…but I'll have to lower the outside edges of the infeed/outfeed to be completely flat with the planer bed.

Scott…not sure I could trust the two sticks thing of Gary's. I'm pretty new to this woodworking stuff.


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## AaronK (Nov 30, 2008)

is that right? (re: lowering the in/out feed tables to the bed height). maybe i have been doing it wrong then…


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## rbterhune (Jul 31, 2009)

AaronK…As I mentioned in another post, I'm new to woodworking but from just about everything I've read, the outboard sides of the infeed/outfeed should be adjusted to create a 1/8" gap between a straight edge and the main planer bed…to reduce snipe. That's why I was wondering about the flex in mdf when I create the sled.


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## AaronK (Nov 30, 2008)

right - sloping the feed tables is what I've been doign to reduce snipe.

i'm just wondering about doing that while using the sled. i might be getting confused with the comments in this thread, but it seems that you had concluded that they should *not* be sloped - ie, should be made level with the bed - while using a planing sled. i think when you say the "flex in the mdf", that's what you mean. it looks like Purplev said something about that - and that's what i question.

it seems that as long as you have shimmed your board to the mdf sled *while the sled is on a flat surface* any deflection caused by the sloped feed tables would be irrelevant - the part that matters is the scant 1/4" under the cutter head. so: am i completely off?


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## MarkM (Sep 9, 2007)

I think that Aaron has it correct with respect to the planer tables. The "slope" in them is to reduce snipe and that is still necessary when using a sled. Snipe occurs because the workpiece (with or without a sled) moves when under the compressive force of just one of the feed rollers and the cutter head.

As already stated, the biggest issue with using a sled like this is the shimming process. You need your workpiece stable when it is being cut by the planer cutter heads. if it can move or deflect, that with be translated directly into the cut that is being made.


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## rbterhune (Jul 31, 2009)

AaronK & Mark Mazzon…when you guys put it in those terms I see that you are correct. I DO need to maintain the 'sloping' feed tables. I just need to shim the workpiece while the sled is lying on my tablesaw or benchtop to ensure its stability.

Thanks to everyone that has replied so far.


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## AaronK (Nov 30, 2008)

heh, ok. the laws of physics do apply! whew!


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