Z-axis problems. Bent lead screws & Belt slips off pulley.

[darus67]

I have my H1.1 assembly mostly complete. I have motors mounted and it is moving under its own power.
I'm seeing 2 problems, which may or may not be related.

First, the 2 pieces of threaded rod for the Z-axis lead screws were not perfectly straight. There's just enough
bend to cause visible wobble of the pulleys as the screws turn. I bought a new length of threaded rod from
the hardware store and will be replacing them soon.

The bigger problem I'm running into is that the Z-axis drive belt slips off of the leadscrew pulley when I drive the
Z-axis up. Going down it stays on just fine. This makes me think my Z-axis isn't square. I think the pulley wobble might
make the problem worse, but because it depends on the direction of motion, I don't think its the root cause.

Does anyone have any good tips on squaring the Z-axis?

[tom10122]

My threaded rods got bent too, I went out to home depot and got some 1/4 inch threaded rods

[Titeo]

I have this problem before and fix it by putting the nut with the silicone or rubber on it. The nut that's hard to screw onthe screw rod. Dont really know how to say it in word so i gonna take a pic tonight after work for u.

[stienman]

The diagonal bars in the front and back of the machine keep the z axis square, or not as the case may be. The two left side bars hold the left side square, and the two right side bars hold the right side square.

Once I got the machine mostly assembled, I first squared the y axis to the frame since all your squaring after that will be from the bed. This is done by affixing all the pieces loosely, then tightening the one back corner bracket close to the motor, since that one has so little room next to the motor. Then I squared that right y axis rod to the bottom frame parts (which I squared during assembly by measuring the distance from corner to corner), and affixed the right front bracket. I then affixed the left side brackets according to the bearing distance so the y axis moved smoothly and wasn't skewed on the right rod I had so carefully aligned.

Now it's time to square both the x and z axis. Unfortunately there's no separate adjustment for x and z, they are both secured by the top brackets to the bent front and rear rods.

Loosen the nuts on the top brackets, and loosen the rod holders for the x axis so the rods can move as you adjust the x axis distance. Make sure the bottom of the machine is square to itself, and the bent rods are secured in their bottom brackets.

On the left side of the machine you need to move the vertical rod and lead screw so they are perfectly vertical relative to the print bed. This requires squaring it in two directions - move it from side to side, move it from front to back. I used a thick piece of card stock I knew was square and eyeballed it. Put the card stock on the bed vertically, move a few feet from the machine, close one eye, and see if the rods on the left side are as vertical as the card stock edge. Then turn the card stock ninety degrees so you can check how vertical the rods are from side to side. Once you've got the rod and lead screw perfectly vertical, tighten the nuts on that side. Be careful to tighten the nuts so the rods stay in place, if the nuts move the top bracket you'll lose the squaring you just performed.

Now turn your attention to the right side. You need to make sure that the distance between the two vertical rods is the same at the top as it is on the bottom. As long as you squared the left side correctly, you can now loosen the nuts on the top right bracket. Measure the distance from the right vertical rod to the left at the bottom of the machine. Now, at the top of the machine, push them together or pull them apart so they are the same distance they were at the bottom. This will take care of squaring the left to right movement of the vertical rods, but you'll need to use a square or card stock as I used to make the right side vertical from front to back. Follow the same process for the front to back movement, just make sure that the right to left movement is resolved by measuring the top and bottom distance of theoretical rods, otherwise the z axis won't go up and down smoothly.

Once you've squared the right side and secured it, you can turn the rods until the two z axis brackets are at the same height, then secure the horizontal rods between those brackets that controls the x axis. Move the z axis up and down to verify that it doesn't bind by hand(slow and tedious, but it will verify that the distance you measured is good, and ensure the machine can move quickly without losing steps later).

It could be that there's an easier way, I'd didn't follow the manual for my build, and I can't say my machine is fully calibrated yet, so it may not be perfect, but it doesn't bind and everything I've printed so far has come out satisfactorily. I'll probably be doing further tweaking as I improve the printing quality.

[BrainSlugs83]

I went through a lot of trouble replacing all kinds of things, trying to figure out why the Z-axis rods had wobble in them (to be clear, one did have wobble, the other did not, it was clearly visible, and when the belt was properly tensioned you could clear a clicking noise at regular intervals as the belt moved). This is my topic: Replacing the Z-Axis rods?

It seems the biggest issue is just the bottom of the lock nut being flat and flush (and not at any slight angle) -- if you can't get that (I couldn't) -- put them on the other way, and don't tighten it down against your z-axis base all the way -- just make it a little bit loose (only loose to the point where you can control the wobble, and the nut no longer dictates the wobble).

I haven't got my unit completely finished yet, but I've got the X-axis caddy on, the rods do not wobble or move, spinning one axis moves the other, I can hand turn the Z-axis rods and move the X-axis caddy up and down and there does not appear to be any residual issues. (I plan keep the other post updated if I find out otherwise.)

[darus67]

I solved my Z-axis problems.
First I replaced the bent leadscrew with a fresh piece from the hardware store.

As I was re-assembling after that, I realized that my Z-axis guide rods were about 1/4" closer together at the top than they were at the bottom. I believe the belt tension on the x-axis carriage was enough to pull the whole machine together at the top when I raise the carriage up. I wasn't confident that I could tighten the crossbar blocks that hold the x-carriage rods enough to keep the x carriage from contracting, so I installed a crossmember connecting the top ends of the z-axis guide rods. There happened to be 2 extra crossbar blocks in my kit. (Spares? They worked perfectly for attaching a length of threaded rod between the top ends of the Z rods.

[Fiero2M6]

I've been thinking about adding a top brace. How much does the brace limit your z-axis travel?

[stienman]

Nice fix. Now that I've retention end the x axis, I might have to check my z axis at the top as well.

[darus67]

I've been thinking about adding a top brace. How much does the brace limit your z-axis travel?

I'm not sure, exactly, but not a lot. I'll measure it and let you know.

It does make it impossible to replace the extruder and hot end with a Dremel tool, however.

[Fiero2M6]

I think the reduced height would be worth it. I've also seen people add an lateral bar that's offset from the center line.

[darus67]

I finally measured my machine. I loose about 5/8 of an inch of Z-axis travel due to the horizontal bar I installed across the top. If I ever decide it matters, there are alternative ways to mount the bar that would not decrease my Z at all.

[PartDaddy]

The top brace does help. I omitted it in the final design to allow higher Z travel.

It also helps to support the Z linear shafts against the table.