Attaching cross-cut sled runners

[George Hoppen]

I built a cross-cut sled more than a few years ago, with an adjustable mitre bar. It sits unused against the wall in my shop becuase I cannot get a runner on it without it binding or being wiggly, and I hate wiggly. I've tried an Incra runner and a Kreg runner. I also bought 2 pieces of 3/4" x 3/8" cold rolled steel, but they don't run smoothly without a little binding (in the long run, I'd rather have a softer runner material than my table saw top). I can get the Incra and Kreg runners adjusted and running smooth through the table slot with no trouble, until I attach them to the jig. Then it's either bind city or wiggle-rama. For safety, I really want to build a sled that uses both table slots, but haven't even attempted yet - if I can't get one runner to run smooth, how do I do that with 2 runners.

I have a Jet table saw. It's been a some time since I checked, but with a dial gauge I believe the slots are quite parallel to each other. But back to the initial problem!

How do I attach runners to the cross-cut sled successfully? Thanks in advance for your ideas, as I may not get back to the forum for a couple weeks.

[glenn bradley]

If the slots are parallel and of a consistent width throughout their length this should be a fairly trouble free task. The level of difficulty you are having makes me suspect the machining on the saw. I would be diligent and eliminate that before you start back down a road you don't want to follow.

The runners cannot be soft or their purpose is defeated. The feed path of a sled needs to be well aligned and well controlled. A tablesaw only cuts straight and 'deviations' from this path during a cut are what kickbacks are made of. Can you get a runner to slide smoothly along one of the miter slots? If so can you do this with the other runner in the other slot? Until you achieve this there is no need to move forward.

Once you have a runner to slot pairing that moves correctly you can address the issue of parallelism. I put double stick tape

4 trim tape.jpg

on the top of my pre-drilled runners,

3 tape on rail.jpg


place the runners in the slots on top of spacers that will hole them a bit above the table surface; pennies or thin strips ripped off solid stock work well for this.

5 rail lifts.jpg

I position the fence (assumed to be well aligned with the saw) at the position that I want the right hand edge of the sled. Press the sled edge against the fence while holding the sled off the table at a bit of an angle. Lower the sled onto the taped surface and press.

I use this method regardless of the runner material. Now carefully lift the sled, turn it over and drive in the screws that will hold the runners in place.

6 guide rails on.jpg

In this case I used straight grained white oak. These runners have been trouble free since 2007. The bottom of the sled is shellac'd and the runners are paste waxed. I have sleds with wood, metal and UHMW runners. The UHMW is best kept to smaller sleds as there can be some flex in it. An advantage of wood and UHMW stock for runners is that if things don't go just right, you can tune the fit with a card scraper.

I have also seen folks slide the sled back enough to put in a couple of screws for each runner from underneath and then slide the sled forward and do the same at the opposite end. Then take the sled off, turn it over and finish up.

[andy bessette]

Yup, oak for the runners. Screw one runner in place. Then nail the other one using brads; flip the sled over to screw it on.

[Tom Bender]

My sled is only on one side of the blade and it works great. Oak runner. Wiggly, yes a little but with just a little practice I always push the slop out the same way and it's real precise.

[George Hoppen]

Thanks all for the great tips and info!!!

[Steve Demuth]

I prefer UHMW polyethylene for runners. I attach them with countersunk #6 wood screws. If they are overly snug, they are easily trimmed while attached with a shoulder plane or card scraper. If they are slightly loose, tightening the screws will expand the plastic to firm up the fit. They are essentially pre- and permanently self lubricated. And they are very dimensionally stable, both with respect to humidity and temperature - something that matters in my non-climate controlled shop. If your miter slots are parallel (and all 4 sides of the two slots must be parallel), you can dial in a near perfect, stable fit. The only change I make on mine is to maybe back off the screw driven expansion of the guides in the heat of summer ever so slightly - warm steel and humidity can make for an ever-so-slight binding.

But, if your slots aren't really parallel, nothing will work, plastic or otherwise.

[Jeff Ramsey]

I also attach the runners while they're in the slots. I use my fence to align the sled top to the runners so it's parallel, making the sled fence perpendicular to the blade. I think the key is; attach the runners while in the slots.

[Mike Cutler]

I pretty much do mine the same way Glenn does.
The first runner I align on the bench. I have the sled marked where I want the runner to be, then move it to the bench and install it with a square. This way I know that my sled is very close to being square before I try to attach the second runner. The second runner, if I use one, is done on the saw.
You should be able to get the first runner installed with no issues. It references only to itself. If this is not working, something is happening in the process of installing it.

If each runner is capable of freely sliding in the miter slots on their own, then I would follow Glen's recommendations and find the source of the issue. Either the manner in which they are attached, or the miter slots are not distortion free and or parallel.

Don't lock yourself into insisting on two runners. One will do the trick unless the sled is overly large.

Good luck.

[Curt Harms]

I prefer UHMW polyethylene for runners. I attach them with countersunk #6 wood screws. If they are overly snug, they are easily trimmed while attached with a shoulder plane or card scraper. If they are slightly loose, tightening the screws will expand the plastic to firm up the fit. They are essentially pre- and permanently self lubricated. And they are very dimensionally stable, both with respect to humidity and temperature - something that matters in my non-climate controlled shop. If your miter slots are parallel (and all 4 sides of the two slots must be parallel), you can dial in a near perfect, stable fit. The only change I make on mine is to maybe back off the screw driven expansion of the guides in the heat of summer ever so slightly - warm steel and humidity can make for an ever-so-slight binding.

But, if your slots aren't really parallel, nothing will work, plastic or otherwise.

True about the 'plastic' runners - UHMW, polyethylene whatever. I have a one sided 'Norm style panel cutter'. The runner is 3/8 X 3/4 steel. I didn't think about the runner being harder than the table top, I was still new at this stuff. The runner was a little oversized but a few minutes with a file fixed that. I wax the runner whenever I'm in the 'wax the tops' mode. If I were doing it again, I'd likely go with plastic or possibly aluminum from an online metal supplier.

[Robert Engel]

1. Attach the runners while they are in the slot. Use glue.

2. Place the screws no more than 6" apart. (Be aware if the hole size isn't big enough the runner will bulge at every screw.)

3. If adjustment is needed I use a spare plane iron. Register the side of the iron against the bottom of the sled and scrape the black areas of the runner (this is where its binding).

4. Quarter sawn wood is best for runners.

5. Try using Azek for runner material.

[Johnny Barr]

I use Incra's miter sliders. I make sure each one is a perfect fit then I place them at exactly the start of the slots (with washers/dimes in the slots first) and then use double sided tape and with the body of the sled against the fence I lower it onto the bars and screw them in. Works every time.

[Nick Decker]

Agreed on the Incra miter bars. Also, you can leave openings from above to readjust the fit if necessary, or if you move the sled to a different saw.

[Ross Manning]

Resurrecting this discussion as I've been thinking about building a sled recently. I don't understand why all the sled design & build information I've seen shows constructing the sled base from a single sheet. The process makes it way more difficult that it should be. This is the way that they all seem to do it - it goes something like this:

1. Cut a sheet of material for the base
2. Attach a front bridge to keep sled together, with the center higher than maximum height of saw blade
3. Attach a rear fence with screws to allow later adjustment (fence in center higher than maximum cut)
4. Make runners for miter slots
5. Spend a lot of time fiddling trying to attach runners to the base while keeping both runners parallel & sliding well (double sided take, glue, adjustable screw slots yada yada yada)
6. Raise saw blade & cut the zero clearance slot
7. Final adjustment of fence to give a true 90 degree cut.

Is there any reason that the following would not work? It seems WAY simpler to get things lined up:

1. Cut two sheets for the base, an inch or two wider than needed
2. Cut the sheet in half
3. Make runners for miter slots
4. Attach left runner to one of the sheets, so that the excess width lies in the path of the saw blade
5. Run the base through the saw. You now have a left side base with zero clearance.
6. Repeat step 4. & 5. for the right side miter slot & right side base sheet. You now have 2 base pieces each with zero clearance & each running perfectly on their own runner.
7. Align the two base pieces on the saw table & attach a front bridge to both base pieces to keep sled together, with the center higher than maximum height of saw blade
8. Attach a temporary bridge to rear of the base pieces (but in front of fence position), using double sided tape or similar temporary attachment, to keep zero clearance slot alignment. Then invert sled & attach rear fence with screws to allow later adjustment (fence in center higher than maximum cut)
9. Raise saw blade & cut the zero clearance slot through front bridge & rear fence
10. Final adjustment of fence to give a true 90 degree cut.

This will completely eliminate all the fiddling with miter slot runners.

Have I fundamentally missed something, or do you guys think this approach would work OK? Attaching the bridge & fence to free running base pieces seems so much easier than trying to get precision alignment of runners on a single base sheet.

[Simon MacGowen]

I use Incra's miter sliders. I make sure each one is a perfect fit then I place them at exactly the start of the slots (with washers/dimes in the slots first) and then use double sided tape and with the body of the sled against the fence I lower it onto the bars and screw them in. Works every time.

This is the instructions that come with the Incra's mitre gauge bar, and I wonder if the OP has had a chance to go through it. I have installed sleds (3 of them) using Incra's adjustable bars and no failures on all those occasions.

If your shop is subject to big humidity swings, hardwood runners unless they are truly quartersawn won't work. They will bind or become loose one way or the other. The Incra's can be adjusted if needed, but since they are steel, movements are rare. So far, in 7 years of those sleds in use, no adjustments have been made despite a humidity change of as much as 30% and more.

Simon

[Prashun Patel]

I believe fine woodworking suggested the same as you are thinking, Ross.