Precision Adjustable Z Endstop Holder and Constraint

by raldrich, published

Precision Adjustable Z Endstop Holder and Constraint by raldrich Feb 17, 2012
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A precision adjustable optical endstop holder for Prusa printers, with an integrated Z screw constraint bearing.

I got frustrated with trying to adjust my Z axis endstop by sliding the clamp up and down the smooth rail, and found that the available designs for adjustable clamps wouldn't work for me, for one reason or another.


1) Print.

2) Trim off the support inside the bottom nut trap.

3) Ream out the inside of the Endstop Mount/Glide's M8 hole, so that it runs smoothly up and down your Z axis smooth rod.
    Note: I've found that the knurled end of a narrow X-Acto knife handle (with the blade removed) is the perfect size for reaming out M8 holes.

4) Install a 608 bearing into the bearing cup.

5) Attach an optical endstop to the glide, using 2 M3 X 25mm socket cap bolts and nylock nuts.

6) Optionally, run an M8 or 5/16 nut partway up your Z axis screw. This nut will be used to secure the top of the constraint bearing.

7) Assemble parts onto the smooth rod as follows (top to bottom):
    a) Glide/Endstop mount.
    b) 3/8" I.D. x 51/64" spring.
    c) Clamp/Bearing mount.

    Note: you'll have to loosen your smooth rod, and slide it up out of its lower clamp, then re-affix it once the parts are in place.

8) Attach the Clamp/Bearing mount loosely to the smooth rod using 2 M3 X 20mm socket cap bolts and nylock nuts.

9) Assemble the adjustment bolt onto the assembly as follows (top to bottom):
    a) M4 x 40mm socket cap bolt.
    b) M4 washer
    c) Glide/Endstop mount.
    d) 11/64" I.D. x 5/8" spring.
    e) Clamp/Bearing mount.
    f) M4 nylock nut.

10) Move the clamp into its final position, and tighten the clamp bolts.

11) Optionally, secure the constraint bearing to the Z axis screw using 2 M8 or 5/16 nuts.


2x - M3 x 25mm socket cap bolt.
2x - M3 x 20mm socket cap bolt.
4x - M3 nylock nut.
4x - M3 washer.
1x - M4 x 40mm socket cap bolt.
1x - M4 nylock nut.
1x - M4 washer.
1x - 3/8" I.D. x 51/64" spring.
1x - 11/64" I.D. x 5/8" spring.
1x - Optical endstop. I used a MakerBot endstop, but any optical endstop with 19mm mounting hole spacing should work.

Note: If you look carefully at the photo, you'll see that I didn't use #6/32 bolts and nylock nuts on mine, instead of M3, simply because that's what I had on hand. The .stl provided is sized for M3 bolts.

Note: The springs I used came from a spring assortment kit sold by Home Depot - Everbilt #471864.

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