fence material (jig)

[drumpriest]

I am building a new cross cut sled, and my last one had a fence made from 2 pieces of 3/4" baltic birch laminated together. I live in the northeast us and the humidity changes here quite a lot over a year's span, and the fence did not stay perfectly straight. I was thinking of using 3/4" mdf laminated together for the one, anyone think this is a bad idea? Any bad experiences using MDF for fence material??

thanks,

[Larryl]

MDF for fence

I have usually made my fences from ply but I would think the MDF with several coats of poly would be as stable as anything else made of wood. Having said that my sacrificial fence is made of two 3/4" MDF pieces glued together and it seems to be very stable. HTH.

[LarryG]

The only problems I've had with MDF for such applications are (1) the hassles associated with using mechanical fasteners (do-able, just fussy, requiring special care or techniques); and (2) the material's softness makes it susceptible to dings. If the edge gets whacked in the wrong place it will compress and raise up, possibly compromising the jig's accuracy.

All that said, I've used MDF for all manner of jigs and fixtures with generally good results. My router table fence is faced with MDF and has been in service for five years (although it's currently in cold storage). And I usually don't even apply a finish, although I agree with Larryl that doing so would be a good idea.

[cabinetman]

Surprising to hear that BB (3/4" twice) didn't stay straight, especially when fixed to a length like the edge of a sled. I like BB and have used it for fences. I've also used MDF. Here in South Florida we have extreme humidity and temp swings, which plywood seems to have a better survival rate. Other than MDF being more fragile than plywood, IMO, it doesn't hold screws as well as plywood.

I've made replaceable fences, which is easier than making new sleds.
.

[cgallery]

I live in the northeast us and the humidity changes here quite a lot over a year's span, and the fence did not stay perfectly straight.

Wasn't it glued/screwed to the sled?

[poolhound]

Keith,

Although we dont have hardly any humidity here except in the monsoon period of the summer and even then its only in the 50% range The fence on my sled was made from a 6/4 piece of SYP (or similar). It had a few coats of poly and is solid as a rock.

I also use MDF for lots of jigs but would also wonder how its ability to hold fastners may affect it for the fence of a sled.

I just made up a simple horizontal miter sled last weekend for mitering the corner joints of boxes and used some old 2x4 as the fence. As the fence is only 2' wide and held with screws every 3" or so I dont see much chance it will warp on me.

[bmyers]

MDF is ok for jigs if you use glue instead of screws. You can also wrap edges with hardwood to protect them from accidental bumps. Seal with clear poly.

I built a sled from an old desk. It is 1" thick particle board with mica-type covering, like a kitchen counter top but covered on both sides. Check out used office furniture places or your favorite dumpster and get a cheap metal desk with a laminate "wood" top. Remove all the metal, cut to size and seal the edges. Great stuff.


Bill

[JR]

I'd be afraid that MDF would fail to stand up to the rigors of a cross-cut sled. A sled is moved and removed, with the tendency to grab the fence to lug it around.

Having said that, my fences are two 3/4" pieces of hardwood laminated together. I use a nut and bolt arrangement, threaded through oversized holes. The holes run from top to bottom of the fence and through a matching hole in the base. Using this kind of setup could mitigate the problem with fasteners in MDF, as mentioned above.

JR