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  #1  
Old Thu 09 July 2009, 13:51
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
Main Beam - Structural Channel vs Ship Channel

My local supplier has both structural channel (with tapered flanges) and "ship" channel (with squared flanges and no taper). The ship channel is heavier than structural but has wider flanges. For example, the structural channel closest to the specs in the plans is 7" x 2.3" @14.75lbs/ft. The comparable ship channel is 7" x 3" @17.6lbs/ft. It costs 1.5 times as much as the structural channel. Alternatively, they have ship channel of 6" x 3" @15.1lbs/ft which might be closer in price to the structural version.

Is there a reason to use structural vs. ship channel (other than price) and, if I do use the ship channel, will the 6" x 3" material suffice?

Thanks
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  #2  
Old Thu 09 July 2009, 20:27
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Taper vs parallel is a small issue when you are bolting and the bolt heads (or nuts) must carry on the taper, but there are tapered washers to compensate for that. 7" x 2.3" @14.75lbs/ft will work 100%.

If the channel gets too low, it reduces the clearance height under the gantry for thick work-pieces. If it goes too high then the z-axis must reach low down and there is a risk of excessive flex. Too wide, the router/dust foot may hit it. Too light, it can flex. Too heavy, its expensive. But there is a lot of leeway - maybe I should give a range of weights ons the drawing . . . . .
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  #3  
Old Thu 09 July 2009, 20:40
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
Thanks. I will just go with the Structural.

Joe
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