This might help,
http://www.instructables.com/id/Chea...-Office-Chair/
Probably a lot more to it than just welding it together. Car seats are heavy, probably need to center it, and then how about when you sit on it, where is most of the weight going to be and what not. Get the widest base of rolling wheels imo. Also, wouldn't it suck to sit in a car seat all day? My arse falls asleep on road trips...
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