Making MDF crosscut sled - t-tracks?

[Matt P]

If I use 1/2" mdf for the base of the sled, will that be thick enough to use T-tracks for hold-downs? Do I really need hold-downs? I'm a little confused!

p.s. Can I also use mdf for the fences (1" or so thick)?? Or should I use two glued up pieces of 3/4" oak?

Thanks in advance,
Matt

[Dewey Torres]

Question 1) No it won't be enough for t-tracks with 1/2 mdf

Question 2) No you don't NEED hold-downs but depending on what you use your sled for they may be very useful. I might try it without them as a sled is super useful even if bare bones. Sleds wear out and sooner or later and if you are like most you will build another someday and then you will better know what options you like / don't like / need.

Question 3) Do not use MDF for the fence unless you are using them as replaceable inserts like the one shown in the link below. MDF is good and flat but not strong and you need strength for the fences if you want it to last as you will be cutting though them.

"The Ultimate Shop-Built Crosscut Sled," AW #75, October 1999, page 38 (for reprints, aweditor@readersdigest.com).


And the related thread:
http://www.sawmillcreek.org/showthre...=crosscut+sled

[Peter Quinn]

I'll second everything Dewey said, and add I don't think 3/4" material will be much good for using t tracks and hold downs either. It winds up warping the material a bit by transferring the clamping force to the base material. A warped sled base is of little use. I like t tracks for stops but haven't found them useful for hold downs that take any real pressure except in very thick or stout material, or on 3/4" bases that are secured to other iron tops.

I don't find hold downs to be necessary with a sled anyway, the most I have done is clamp a piece to the actual fence which I always make from hardwood or a plywood lamination with a hardwood face plate, never MDF.

I have made very simple small sleds, like miter sleds, using 1/2" mdf base and an MDF fence, but these each ride in only one miter slot, the fence does not span the blade and connect two sides.

[Greg Hines, MD]

If I use 1/2" mdf for the base of the sled, will that be thick enough to use T-tracks for hold-downs? Do I really need hold-downs? I'm a little confused!

p.s. Can I also use mdf for the fences (1" or so thick)?? Or should I use two glued up pieces of 3/4" oak?

Thanks in advance,
Matt

1/2" MDF is too thin for most T-tracks. But then again, so is 3/4" essentially. After you have routed the 1/2" depth of most T-tracks, you only have 1/4" remaining. That makes it rather weak, particularly if your dados run from one side to the other. If, on the other hand, you plow a groove that does not run all the way from one side to the other, it would help to have some full thickness stock to keep the rest of it structurally sound.

I have a fence made of MDF and it has held up well.

Regardless, the main thing to bewar of is water. If your MDF gets wet, you are done for.

Doc

[Larry Edgerton]

I would not put holddowns in a sled but I disagree with those that do not like MDF. It has its uses. I make signs out of it that have been in Northern Michigan weather for twenty years and still look just fine. For jigs, and I do like mdf for jigs, I use West system epoxy to hard surface the mdf. Surfaces that a router bit will run on for instance need to be hardened.

Get you sled/jig done perfectly the way you want it and then paint with West System, especially in the areas that receive wear. Heat the epoxy up to say 120 degrees and it will soak in farther.

MDF is very stable, so that the jig you make today will work the same after hanging in the rafters for many years.

Before I had a sliding carriage saw I used sleds and I had holddowns that fit into holes in the overtall fence. The fence was about 5"tall, and there were holes every inch in a staggered vertical line. I made a handle with a hook that fit through the holes and one side held the material to the sled and then to a handle. This way it fit any size wood, and held the material down and pushed forward at the same time. I do not have one any more or I would post a picture. Sorry.....