Every table saw sold for practically ever has had a miter gauge with a metal bar, so using metal will not be a problem, I think many use plastic or wood because it is easier for the average DIY'er to work with. Any material with a good fit in the slot will work, personal preference in many cases.

 

Uhmw will have less friction, metal is more durable. Decide which is worth more to you

 

Friction, how much?

Friction between similar materials will be different than between the same material .... all other things being equal. See this chart:
http://engineershandbook.com/Tables/frictioncoefficients.htm

Most table saws have a cast iron top and many router tables do also. The jigs may slide directly on the table surface or they may have a bar to keep a constant dimension from the cutter. There are no cast iron miter bars I am aware of. So, now we have steel against cast iron, plastic Teflon, or UMW against cast iron, wood against cast iron, aluminum against cast iron or wood against cast iron. Now, change the cast iron top to anodized aluminum and you have a whole 'nother set of varibales. Does it really matter? :surprise2: Not in my experience, not enough to get all worked up about anyway.

There is one more variable which is the "tightness" of the fit of the bar in the slot. This can change everything :|

Then, there is the expansion of the supporting substrate holding the bars which can vary. It would be impossible to account for each distinct condition in my opinion and I have not spent a whole lot of energy worrying about it.

Finally, there are jigs that slide in the slots and jigs that ride along the fence each having a different friction component. Then, absolutely the last component will be whether the surfaces are coated with a non-stick lubricant and this may be the most elementary and easiest to fix in a "sticky" situation... :smile3:

 

So I'm going to try aluminum tracks and use steel flat bar as the feet for the jig. Something I failed to take into account was how I would lock it down to hold the jig in place. Unfortunately, the aluminum isn't a t slotted piece so I can't use a nut or washer to hold it. Any suggestions?

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I know people who use Uhmw for combat robotics. It's pretty good stuff and as far as that goes holds up dang nicely! I wouldn't hesitate to use it for sled "runners" and such.

 

IMHO if you use steel runners in aluminum tracks there is chance that the runners will prematurely wear the tracks.