Not them all! Seen a few ;) and been inside more than I have used.
Well actually that looked rather good compared to slinky little linear rails. They say "solid bar" but it looks like a very thick wall tube. They must pump oil into the bearing. The rear slideway looks to be a box way or something else. There is no doubt a limit to how long they can produce a Z axis in this form. Shorter the better.
They seem to be using linear rails on the X axis.
The best linear rail machines I have seen still used an iron base, but it's still relying on all those little bolts. As machine tools can be very resonant beasts it can cause problems.
My homebrew hot wire foam cutter uses leaded bronze bushes (mounted in ali box sections cut from a builders level bought in a sale) sliding on plain ordinary unground stainless steel rods - I didn't want to use ms or cast iron for the rods in order to avoid any possible corrosion problems, although the frame is 18x18 mm MS box section. I did polish the rods a bit, by hand, but I don't know that it mattered.
Uses B+Q 6x1 mm threaded rods for leadscrews, and four small very cheap
200-step steppers directly connected to the screws. Uses the bearings in the motors for reference points, with just a loose hole in the box section for location at the other end, though I once planned to fit a sleeve. If there is any play, I can't see it.
~1310 mm long with two 240x120 mm X-Y areas, used for cutting wings from
1220 mm long foam blocks. As accurate as I could wish, repeatable to within a thou or better :). Runs on a BBC micro though, so it's a hassle to input wing sections.
The forces on a router will be quite a bit larger than on a hotwire cutter, but I'd guess that wouldn't cause any real problems. I'd use thicker rods - mine are only 8mm, for a small router I'd go to at least 16 mm and maybe more.
If you want real rigidity though, and you might, try 25/30 mm cast iron bar
- College Engineering sell it "proof machined", but it ain't cheap.
The used front suspension struts Tom mentioned also sound interesting. But bronze will do for bearings.
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