Need help with making a bracket for BBQ

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I am making a BBQ for myself and I need some help/suggestions on how to make a bracket for holding the adjustable grills.Here is a drawing of what the BBQ will look like when it is finished.The rails that the grill will be raised and lowered on are 2" C channel.  I am sort of stuck on how to design them.  Last time I made one of these I used unistrut that was about 4" long and rode in the channel.  This time I am wanting to make something out of steel that will be a little more rigid.  I was thinking about maybe adding bearings that would contact the C channel but am not sure if this would be too complicated.Here is a pic of the last one I made:One thing I learned on the last one is that I need to allow for some additional clearance for when the steel supporting the grate expands due to the heat of the fire.Is there any literature anywhere that will tell me what linear expansion I can expect when steel is heated from room temp up to 300-500 degrees?  I am guessing if i leave around 1/8" on both side this should be enough to prevent it from binding up.  One grill will be 3' long and the other will be 2' long. Made out of 3/16" 1.25" angle iron.ThanksGarrett
Reply:That's a Santa Maria style grill.
Reply:How about make the uprights out of unistrut with a smaller box tube that slides up and down inside the unistrut? You could make the uprights bolt on so they could be removed for maintenance or repair. Sometimes we get so anxious to weld that we forget about sectionalizing our projects. http://hyperphysics.phy-astr.gsu.edu.../thexp.html#c3http://hyperphysics.phy-astr.gsu.edu.../thexp.html#c1"The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:Machinery's Handbook has a table showing linear expansion valuesfor steel and other materials.Mine is at work.Anyone out there have one handy?Miller a/c-d/c Thunderbolt XLMillermatic 180 Purox O/ASmith Littletorch O/AHobart Champion Elite
Reply:Pookie:  Yes it is   I just figured most people on here would not be familiar with that term.Sandy:  Thats a good idea, but I wanted something a little more rigid that I think the unistrut would have been.  Also I dont know how comfortable I would be with having an open fire lapping up on that Zn or galvanized strut since if it vaporizes the Zn then that would be a bad thing for the food. Thanks for the links I will see if I can figure out what the expansion should come out to.Jpump5: I will look online and see if is can find that.
Reply:Coefficient of thermal expansion for steel is 0.00000645 in/in deg F.So if your grate is 4 ft long then....4' = 48"difference between cooking temp (400 deg f or whatever) and room temp (assume 70 deg F) = 400 - 70 = 330 deg FSo, .00000645 x 48 x 330 = .102168",,,call it 1/10" of an inch.That's probably more than you'd actually get cuz I'm guessing that the ends of the grate may be cooler than the middle or if there's a breeze then.....OK, I'll stop now.  Just leave an 1/8" gap and call it good.Miller 211 w/ spool gunMiller Dynasty 200DXLongevity 60i IGBT plasmaO/A w/ crappy chinese torch/gaugesSouth Bend 10K latheGrizzly 4029 10x54 millGrizzly 7x12 hor bandsawangle grnders, bench grnder, bench belt sndr7.5 hp 80gal cmprsor