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I'm slowly gathering accessories for my table saw. Most of the sled plans I've seen have wooden rails to slide in the table grooves. But I've also seen some metal rails and I wonder if they wouldn't be more precise. They aren't cheap so I wouldn't get a bunch, just a pair to move from jig to jig.

Given the different materials what would make me choose one over the other? What would I need to consider when choosing my rail material for my sled(s)?

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    I would not want to move the guide rails from sled to sled. A large part of building a jig is making sure it is square to the blade. The rails are what do this; if you're taking them off and putting them back on, you're probably going to get small amounts of play every time that compromise the squareness of your cuts. – Charlie Kilian Dec 30 '16 at 15:15
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In my opinion, the biggest advantage of cutting your own guides is that you fine-tune them to your table saw's miter tracks. The miter tracks have manufacturing tolerances, and are probably not exactly 3/4 inches. Worse, each miter track is probably a little different in width.

When cutting your own guides you can sneak up on the width for each track to have zero play while moving smoothly in the track. This should give you a guide rail that is the perfect width throughout its length, providing full support to avoid side-to-side movement for the entire cut.

The main disadvantage of wood that it will change dimensions with changes in humidity. Choosing a type of wood that has minimal variation with humidity changes (such as cherry) as well as aligning the growth rings to run perpendicular to the face of the table should minimize the problem. Plywood would be more stable, and some people use various plastics (HDPE springs to mind). I have had great luck with Baltic birch plywood for my guides.

Metal guides are much harder to fine tune, both if they are too narrow and when they are too wide. In addition, you are combining manufacturing tolerances on both the miter tracks as well as the metal guides. To counter that, most commercial guides have little plastic cams or small screws that you can rotate until the fit is perfect. But this only gives you so many contact points, and I would be concerned about their long term durability (since there is a small contact area rubbing against the miter slots).

Finally, the plan to move the rails from jig to jig will probably not work in the long run. Using small wood screws to hold the jig to the rail won't hold to many assembly-disassembly cycles. Using machine screws with nuts would probably be better in that regard, but I would still be concerned with re-alignment issues after reassembly.

  • Good points. It may also be a matter of how much work you want to do in fine-tuning the guides; saying that one can get a better fit one way or the other isn't quite the same as saying one will, or that the difference will matter. And an absolutely perfect fit with hardwood might not be perfect when humidity changes... So the ideal compromise might actually be UHMW plastic, which also has the advantage of being mostly self-lubricating. – keshlam Dec 30 '16 at 4:38
  • I made a really simple crosscut sled out of plywood with SPF rails. They catch a lot so I could easily slip using it. As long as they are smaller and the expansion allows it to not outgrow the slot you can also favor left or right with the sled as well for consistency. Again, for a simple sled – Matt Dec 30 '16 at 6:03

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