How to make 6 to 14 extension forearm mechanism ??

Hi!
I am making a cylindrical coordinate arm. I am using an rc servo and plastic turntable as a revolving base. I am using an acme/lead screw
and stepper motor for the lift mechanism. For the forearm I need a mechanism that extends from 6 to 14 inches. I thought that I could stack three 6-inch pieces of channel/framing stock such that they hang and slide on each other. One profile that came to mind was a T on top of a C whose opening is downwards, like: _ | || - -
Obviously the above drawing is not to scale in any way, but it shows that 3 pieces with that profile can hang one from the other, by having the T at the top of one piece inserted and slide on the downward C at the bottom of another piece.
Anybody knows of a channel/framing plastic or aluminum extrusion with a similar/equivalent profile??
Thanks in advance.
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Would a full extension drawer slide work?
- James B

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Hi!
I considered that option. Unfortunately, all the full or hyper or over extension drawer slides come in 10 inches or longer. I could get one and try to cut it down... One downside of single bottom drawer slides is that they have some lateral jiggle when used as a forearm.
For now, I am going to buy aluminum extrusion in hollow box and solid rectangular profiles, route them and glue them to make what I need...
Thanks for your suggestion and consideration!
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