Bottom sled stabilization. using constant force spring and rolling trolley?

http://www.unistrut.us/index.php?WP=cat_detail&S=S05&P=P2750
Would there be any benefit to using a spring to hold down the bottom of the sled versus just making the sled heavier? I think using the above trolley with a strip of unistrut channel and a constant load spring like these
https://us.misumi-ec.com/vona2/detail/110302307050/

would allow one to have the benefits of more chain tension without the drawbacks of the increased friction.

My main concern would be saw dust getting into the unistrut channel and then causing the trolley to not move smoothly thus resulting in the sled being pulled at an angle instead of straight down.

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we have discussed this many times, the bottom trolly has several problem, the
trolly will always lag behind the position of the bit, it will also gather a lot
of sawdust.

But, we could be wrong, it would be good to get someone to try this so that we
could point at the result rather than just discussing it.

thanks, I thought it was discussed previously but could not find the topic.