TS sled 1 vs 2 runners

[Jay Knobbe]

Good Morning,
Building my first TS sled for my Dewalt 7491. Being a contractor saw the t-slots probably aren't as accurate as one with a cast iron table.
I see some folks use 2 runners, others only 1. I suspect in a perfect world if both TS slots were parallel I would use 2 but what are the chances of that on my 7491.
Looking for some advice from those that have gone down this path.
TIA

[Charlie Jones]

I used two on my last sled. My Dubby uses one and it is perfectly accurate. I don’t think it matters.

[Dan Cameron]

Jay, there is a thread earlier in this forum "Crosscut sled, my version". Read
it and then buy or build a single adjustable miter bar for your sled.

[Bruce Wrenn]

Dubby uses one, and my NYW style panel cutter also uses one. Tapering jig also uses one. Don't really see the need for second runner.

[al ladd]

As Jay suggests, poor quality slots, as will be the case with any job site saw, amplify the argument for using one runner only, as misalignment between the slots will make good results from two runners hit or miss--or impossible.

Runners for sleds should be pretty easy. The sled stiffens the runner, so you can use plastic or plywood, easily precision fit to your saw groove with a thickness planer, and fairly easily with a table saw. Then, with bar in place in its slot, double stick tape to your sled and screw in place.

The boutique market for expensive runners for sleds seems silly to me. All the adjustable ones are a compromise over one that simply fits well. I suppose a slot with lots of internal variation makes a case for a runner with spring compensation, but the metal is so soft on job site saws it can be corrected to tolerable with a file and a little patience.

I've been thinking about miter bar design obsessively for a few months. The challenge is a lot greater for a miter gauge than for a sled.

[Dave Zellers]

First, I agree that 1 runner, if it's tight is fine but I prefer 2 runners.

Second, I would do a test on your saw and find out if your slots are parallel. Maybe they are. I have built a couple large sleds, the largest is 50" between the front and back fences so I can cut plywood square. Not a full sheet but easily a 4'x4'. For that I want 2 runners.

To simplify, I believe 2 runners are better but not necessary for smaller sleds. It did take over a year of tweaking the runners on the big sled while they adjusted to my environment to get them to perform perfectly. Since then, it's been maybe 8 years without any adjustments needed at all.

Be very patient when you are adjusting the fence. Learn the 5 cut method. Don't stop adjusting until you get consistent results every time. There are just too many variables with wood.

An accurate sled that can cut say 24" perfectly square is such a dream.

[Dave Zellers]

The boutique market for expensive runners for sleds seems silly to me.

Totally agree. I use ash and look for as close as I can get to vertical grain. Often when working on a project I'll come across a piece that looks perfect for a runner (or something else) and if I can, I'll set it aside even though I'm not looking for that at that time. Then when I do need it, there it is!

[Cameron Wood]

Totally agree. I use ash and look for as close as I can get to vertical grain. Often when working on a project I'll come across a piece that looks perfect for a runner (or something else) and if I can, I'll set it aside even though I'm not looking for that at that time. Then when I do need it, I can't find it!

FIFY extra characters...

[Dave Zellers]

Yes... sometimes true, sometimes true.

My new thing is when I buy a replacement part for something and won't need it for a while, I don't care how obvious it seems at the time what it is for, it gets labeled exactly what it is for.

[roger wiegand]

My big wooden sled uses two wooden runners and seems to work very well. I also have a smaller one that uses a single machined metal runner, it also works well. Intuitively it seems like two runners would average out slight imprecisions in the runners or slots.

[Dan Cameron]

My big wooden sled uses two wooden runners and seems to work very well. I also have a smaller one that uses a single machined metal runner, it also works well. Intuitively it seems like two runners would average out slight imprecisions in the runners or slots.

Not so, Roger
If the center to center distance of the two runners is greater than the center to center distance of the miter slots, even by a tiny amount, the outside edges of the runners do the guiding and the inside edges don't even touch the slots. Else if the center to center distance of the two runners is less than the center to center distance of the miter slots, even by a tiny amount, the inside edges of the runners do the guiding and the outside edges don't even touch the slots. Just two edges do the guiding like a single runner configuration.

[roger wiegand]

Not so, Roger
If the center to center distance of the two runners is greater than the center to center distance of the miter slots, even by a tiny amount, the outside edges of the runners do the guiding and the inside edges don't even touch the slots. Else if the center to center distance of the two runners is less than the center to center distance of the miter slots, even by a tiny amount, the inside edges of the runners do the guiding and the outside edges don't even touch the slots. Just two edges do the guiding like a single runner configuration.

That assumes the runners and slots are parallel to each other, and that the runners are of uniform width, no? I'm not sure I'd trust that either of those conditions are true, even if they once were, for my wooden runner homemade sled that's been banged around for two decades now. I'm quite surprised it still make cuts that are square to my ability to measure them.

[glenn bradley]

I'm in the two-runner camp since I cross cut some heavier material. I use two runners on my smaller sleds as well but that is just because I am used to making them that way. I have wood, aluminum and UHMW runners on various sleds. All work fine. Straight grained oak, ash, or pecan runners have been in use for years in my shop.

[Dan Cameron]

I'm in the two-runner camp since I cross cut some heavier material. I use two runners on my smaller sleds as well but that is just because I am used to making them that way. I have wood, aluminum and UHMW runners on various sleds. All work fine. Straight grained oak, ash, or pecan runners have been in use for years in my shop.

Glenn, the two runner approach does not help with heavy lumber. When one runner is under load, the other is unloaded, not sharing the load. Also, it is not possible to make a two runner sled with as little slop as with a single runner. The distance between the runners comes into play, and this is subject to variation with humidity This variation may be small but it is not zero.

[Bill Howatt]

Years ago at work, I had to have made a piece with a runner, similar to the TS sled idea, and the aircraft industry experienced machinist told me that having 2 runners when one will suffice is a bad idea. I think his concern was binding.