Consult the Build Tab. Today I added files for Version 2 (5/12). Files listed below pictures

Version 2 has beefed up mounts for the Z screws, a streamlined extruder, the control box with control board on the bottom with box top being easily removed for maintenance.

 

Print the glide body (with cavity) and the bushing inserts on the same print, with the width of the cavity and width of the insert being both set by the Y axis travel. That way, regardless of how close your printer is calibrated, the cavity and insert get the same variation. Guaranteed, if you print the cavity width set by Y travel and insert width by X travel, you will get a mis-match.

Have you had a chance to mount the aluminum sandwich build plate? Is the aluminum film strong enough to take the pressure when setting the eccentric spacers and how well do the holes it hold up to usage. Also, what saw blade did you use for trimming the size to get a clean edge? I'm truly amazed that no one offers a 216x216 blank build plate and am always on the lookout for a plate where I'm not paying double for some idiotic 20 holes punched in it. The only thing I can find are 2mm thick which are to thin for the eccentric

 

I use 1/8 microstepping on Z & E0 which produces smooth enough movement but with more power than 1/16. So I pondered this first layer landing too. But, then I realized I was overthinking the situation.

The reason for one motor is because a motor will frequently land on a full step instead of a microstep. My gearing produces 0.005 per step, yours 0.02. 1/6th or even 1/8th of 0.20 is insignificant, unless you are using two motors. With two motors that difference on one motor but not the other would put them out of sync - and on the Z axis screw that is cumulative. So back to the problem at hand. I use Marlin soft-landing when homing (down, then up 5mm, then slow decent) so I get two opportunities for landing on a step instead of a microstep. Then I use .4 first layer height, 1/8th of 0.02 is infinitesimally small. And it really doesn't matter if it takes 5 layers or so to land on a full step, the difference is going to be infinitesimally small, the amount of squish against the bed on your first layer is going to vary way more than that. But once it does land on a full step, it will continue to do so.

In other words, this problem exists only in an algorithm, but in practice (Using only one motor) it's undetectable. Quit worrying about it.

 

Annoy away, that's what this forum is all about!

Like you, I too studied ways to combat level creep, thinking of building my own concept. But I realized everything out there treats the result of level creep but no one treated the cause. I had my old 2 Z motor BldrBot. I unplugged one motor, drilled out the brackets at the top to fit bearings in the holes and around the 6mm Z screws, drilled out 2 5mm ID pulleys to 6mm and mounted those on my 6mm Z screws under the bearings to hold these bearings in the bracket holes. I did not have a close looped belt the right size, but I had 50 lbs fishing line. I wrapped the line around each pulley, tied a knot and added an idler to tighten it. After adjusting the two screws to the same height, I had the prototype of a trueup. That setup, with unplugged motor and fishline, has been printing over 10,000 hours (3 yrs) with never a leveling issue. It's actually my most trusted printer, a Click-Print-And-Walk-Away.

BTW there is a poor-man's-solution to doing this, w/no belt, w/two Z axis motors. Before I settled on cobbling up the single motor/ belt idea, I read tech on microstepping and realized it's impossible to sync two motors running any microstepping. so I just changed both Z axis motors to full steps. Once leveled the X axis stayed level over 200 hours and dozens of prints. But MAN oh MAN, that full stepping is noisy and instantaneous, producing quite a jerk. But if that's not annoying, it causes no harm, and is a poor-man's-solution. The main reason I changed to the belt was for marketing - 1) there was a visible something different to point to 2) if you just tell customers "oh we fixed that leveling problem down at the theory level" and then give them a jerky, noisy machine, they'll think you're nuts.

Before getting too far into it, take a look at the Assembly Manual for more detail on what an upgrade would need.
http://dev.3dwrx.com/TrueUp/Kit-Manual2/index.html

 

I think I've found what I want to change to for the build plate - 12"x12"x 1/4" (.250") ABS PLASTIC SHEET. It cuts easily on a table saw to 214mm square and drilled holes are clean. 1/4" is rigid enough so camming the eccentrics creates no bend on the plate (1/8" allowed a slight bend) and camming the eccentrics had no effect on the eccentric holes. heat bed is at least 1'4" above it so that's not a problem. And turning the textured side up is a great finish. Plus, I've just put 3mm threaded holes in the corners, so I do spring adjustment from the top with no need for a nut on the bottom. So far it works great. $12 by the each and $8.50 in 8/pk.

 

By each
Amazon.com: 12"x12"x 1/4" (.250") ABS PLASTIC SHEET TEXTURED FRONT SMOOTH BACK VACUUM FORMING THERMOFORMING BLACK: Office Products
By 8 pk
ABS BLACK Plastic Sheet 12" X 12" X .250 (1/4") (Qty:8) | eBay

I am converting my 6 workshop printers over to 214mmx314mm beds so I can get 8+ hour print jobs and a 12"x24" can be cut for those. Another thing I really liked was how the table saw handled the cuts - now chaff - it all went into the bag below the blade (used 84 tooth aluminum blade) That means I can bring that table saw inside for the winter instead of out in my unheated shop!!

 

Whoa. Kydex 100 0.125" is better price (5.30 ea), more rigid than ABS, and works. When wheels are adjusted tight it has less than .5mm bow in the center - which actually "pre-loads tension" on the wheels against the rail slots.
Pk of 4 Amazon.com: Kydex 100 Plastic Sheet 1/8" x 12" x 12" - Calcutta Black (4 Pack): Industrial & Scientific

 

I think I rounded off price/shipping.

One thing about using Kydex is to use 100 grade, not X or Y grade. It's stiffest.

 

It's fixed now. It was 2,000kb short??
http://3dwrx.com/TrueUp/kit2-assembled.zip

 

Jack, take your nylon nuts down to the hardware store and try them on various M8 bolts from the bolt bins. If they fit them snugly, your Z screws are defective. If they are loose, the nuts are defective. The reason the design uses nylon nuts is that nylon nuts are purposefully manufactured to be tight since they will deform to fit. Usually I have to run a M8 tap through mine to loosen them up a bit. I got the idea from OpenBuilds' backlash-free nut block for acme lead screws. Nut Block for 8mm Metric Acme Lead Screw

Another thing to consider is the dimensional quality of your Z screws. Use ONLY stainless steel threaded rod. Zinc coated threaded rods use a different die with a minutely smaller diameter that theoretically gets filled in with zinc galvanization.

 

That all depends on how you plan to "nut" that screw. Look back over this discussion earlier, this subject has been covered with numerous perspectives and examples.