Planer Sled 101 Failure

OK, so I decided to build a planer sled. Just a simple one mind you, it just ain't working!!!

So, I took a melamine shelf and glued-and-screwed to it a 3/4" piece of MDF. It was resting on a flat surface, and I weighted it down with bricks to dry. Took the bricks off, looked great, set it in the shop for a few days, and BINGO!! The whole thing bowed in the middle. AAARGH!!

Back to square one. I know there are numerous threads on here with many options, but I need something that has really been tried and tested. So, as I need to build another one, any suggestions from real world experiences, and not was just in some article.

Oh, I will build it a little over 6' long, so weight is an issue. The one I built was the max weight I want.

Thanks!!

I have no experience with a sled, but I think I would be looking at some sort of torsion box design using 1/2" ply to keep the weight down

You don't need a planer sled to be particularly strong or heavy. All you need is for it to be flat when you place your stock/shims on it, and for it to not allow any of your shims to slide around.

Here is my technique:

http://www.jpthien.com/ps.htm

Just a note that you HAVE to use a flat surface during setup. My bench top is a solid core door and is very flat (to within about .007" over the length of the thing). Any deviation in the surface of the benchtop will transfer to the lumber you're trying to flatten.

I realize you said "not from some article", but I built a very simple torsion box jointer sled according to the design of Kieth Rust (FWW #175, Feb 2005 page # 59+). His was 4' long by about 12" wide, but I extended the length to 8'. There are just two outside long divider strips, plus a center one, and the flatness and stiffness when everything is glued together is excellent. I used this as a jointer sled with a cheap Ryobi planer when I did not have a jointer. I glued and screwed the divider strips to the bottom "skin", and then glued and screwed the top "skin" to the divider strips.

I used it for 5 years without issue, and then gave it and the Ryobi to Habitat. I imagine that it is still in use.

Mine is a 3/4" piece of MDF, with 3 MDF "runners" underneath. As Phil says, the set up area has to be flat, or, you need to shim the sled to get it flat before shimming and hot gluing the piece to it.

OK, so after all the frenzy. let me ask a question.

First off, I have an old "Buffalo" 15" planer. As I was actually looking at it, I thought about using the bowed sled. The bottom table is about 40" long with out feed rollers. There are two top feed rollers the are about 7" apart, which are forward and aft of the cutters. So, as I was looking at the planer, it appeared to me that it didn't matter if the sled was bowed. The position of the feed rollers, combined with the long bottom table, the portion through the plane should always be parallel to the cutters and the planer bottom table.

So, all I need to do is secure the object board so it will not be compressed going through the planer. It looks like the planer itself will compress the bow and the board should go through parallel. What am I missing here?

The only thing missing is to give it a try.

Quote:

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Originally Posted by Mark W Pugh

So, all I need to do is secure the object board so it will not be compressed going through the planer. It looks like the planer itself will compress the bow and the board should go through parallel. What am I missing here?

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It will compress the bow as it goes through the planer, the bow returns when it exits the planer. So your workpiece is bowed.

If planers could make flat boards out of bowed boards, we wouldn't need jointers. Or planer sleds.