I was checking constant force springs on mcmaster -- maybe a prob for overseas shipping -- but a pair at 25 bucks each or so they seemed like a good options. I imagine if the spring tension was less than the gantry weight - you'd still get the same benefit of nearly no backlash and a lower cost spring. Good info at mcmaster even if you don't go that route.
Good project - looking forward to the build and pics - in my to do list too.
cheers - jim
ps a great way to get my parking space back in the garage.
Experience is the BEST Teacher. Is that why it usually arrives in a shower of sparks, flash of light, loud bang, a cloud of smoke, AND -- a BILL to pay? You usually get it -- just after you need it.