# Poly on MDF for table saw sled?



## WoodNube (Jan 17, 2019)

I am almost finished making a table saw sled, just a basic cross cut sled. Parts are all cut, runners attached, used the router to round over the fences. I need to sand, then start screwing the fences on and it will be ready to use.

It's made out of MDF, reclaimed form someones bulk trash pile. It's not going to be pretty, and that's fine.

They had painted one side of the MDF, sort of a brown color to try and make it look more like real wood, I suspect, so part of my sled is painted, part isn't. I don't plan to change that.

Should I put a few of coats of poly on it? Or linseed oil? Or should I just leave it alone? It feels like poly would help protect it, and I would expect MDF to soak up the first coat pretty heavy, so several will be needed.

If I'm going to put any kind of finish on it, I suspect I should do that before I screw the fences on.

Any advice would be welcome. I'm a newbie, I need all the help I can get.


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## bondogaposis (Dec 18, 2011)

Poly will work fine, like you said, it will drink it up like a sponge. I like to dilute poly 50:50 with mineral spirits for the first coat. It will disappear, but helps with subsequent coats. It does help to toughen up the surface a bit.


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## WoodNube (Jan 17, 2019)

Thanks. I've done my sanding, and done for the night, but I'll start on poly-coats tomorrow.


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## OSU55 (Dec 14, 2012)

Poly thinned 1:1 or shellac


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## RichT (Oct 14, 2016)

I leave my MDF fixtures, like table saw sleds, plain. I like the friction to keep the workpiece in place.


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## Redoak49 (Dec 15, 2012)

I use shellac.


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## therealSteveN (Oct 29, 2016)

Poly, and use on table surfaces can be problematic, unless you actually do wait until the manufacturers suggested "cure time" has passed. The poly can get gummy on your top, and clean up isn't so easy. If that happens and dries unevenly it can be a real mess. Cure times will vary by product, but they are all a lot longer than dry to the touch, most are closer to 30 days.

Wax on the other hand can make for a slicker moving top with either sleds, or just the wood we use. If it get's out of sorts, it's easily cleaned off with Mineral Spirits. *Apply it directly to the saws top*, and then you can do as Rich suggested and keep the sled, fixture, or jig naked. It will still go zip…..

Waxing both the top, and the sled can create a gummy sludge, almost but not quite as bad as Poly. Both can bring slick easy sliding to a direct halt.


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## Lazyman (Aug 8, 2014)

Poly is fairly slippery and will make the bottom slide a little better. One reason to put some sort of finish on MDF is that bare MDF will absorb any moisture that comes in contact with it. One drip of sweat or if you spill a few drops of your beer on the MDF could cause it to swell in that spot and affect the accuracy of your sled. I would also add some paste wax after the poly is cured. I probably would not put anything but wax on the slides. I've never experienced the problem that Steve mentions with wax on both table top and sled but I use as little wax as possible and just reapply more often.


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