Leveling/squaring axis questions...

For jigs to square the axies correctly, I plasmacut out some sheet metal strips the correct length, and have been using those to square the axies. I was just attempting to level the 4 threaded rod sections that join the area under the frog together (they join the z-axis mounts and tensioner/motor) and I noticed that these sections are not the same height. The middle two rods are higher than the outer two, and ...


Actually, I just answered my own question. Guess they were bending slightly because I over tightened the threaded rods. They're much closer to being even now, although still slightly off.

I guess I'll turn this question into something else now. How important/accurate does the spacing have to be for everything? how much room for error is there?

I'm about to try to get the Z clamp spacing correct by hanging a string with a weight like in the wiki, it'd be nice to know. I'm sure the closer it is, the more accurate the machine will be. Any information would be helpful on squaring/making everything level.

Cain Wrote:
-------------------------------------------------------
>I'm sure the closer it is, the more accurate the machine will
> be. Any information would be helpful on
> squaring/making everything level.


That is pretty much the deciding factor. How much more accurate do you want to go and how much time are you willing to spend getting it there? As far as having a bare-minimum working printer, you only need to get things close enough that the axes don't bind up. The Mendel was designed in a way that compensates for quite a bit of misalignment.

Pay extra attention to leveling the build plate and making sure that the X and Y axes are parallel to it though. This will be critical when it comes to getting parts to stick well over the entire range of build space. I haven't determined the actual tolerance range, but as a bare minimum, I would say that you should aim for less than your layer thickness in variation between the build plate and extruder tip. I'm using 0.28mm layers, so this means a variance of up to +/-0.14mm for me. Check this distance at the four corners and at the middle. By checking the corners, you will know that the build plate and x and y axes are parallel. The middle dimension should indicate if the rods are bent or the build plate is warped. It will be difficult to measure a dimension this small, so you might want to use a piece of paper or something as a feeler gauge instead.

That makes me feel much better about this, tonight I've been going nuts over trying to assemble the Z axis...

I can't figure out what I did wrong, if anything. From what it seems, the washers I got in the hardware kit are slightly too big for some areas. And using the standard instructions for the Z leadscrews won't work, the Z leadscrew mount is too deep to add the pulleys for the belt, I had to add 5 or 6 washers as spacers for it.

And now I just realized that, somewhere along the lines, I screwed up with squaring the axies. The base wobbles on a flat surface, one leg is slightly higher than the others....this is extremely annoying.

I'm sure it'll all be worth it though. Whoever designed the Mendel version is a genius, quite an amazing job with how everything fits together.

Cain Wrote:
-------------------------------------------------------
> That makes me feel much better about this, tonight
> I can't figure out what I did wrong, if anything.
> From what it seems, the washers I got in the
> hardware kit are slightly too big for some areas.
> And using the standard instructions for the Z
> leadscrews won't work, the Z leadscrew mount is
> too deep to add the pulleys for the belt, I had to
> add 5 or 6 washers as spacers for it.
Currently, I use two independent stepper motors for the Z axis. I did use the standard parts for a short time though. I used a pair of nuts on top of the bearing to hold the rod at a certain height, then I just trapped the pulley between two more nuts at the end of the rod. There was an air gap, but I didn't meed more spacers this way and I could lift one end high enough to slide the belt under it. This made it a little easier to install the belt and re-adjust the alignment between the bed and X axis. However, the belt would fall of if I accidentally raised one end while working on the extruder or lowered the z axis too far because my endstop wasn't adjusted right. They sent two great big metal and wood washers, which I assume were supposed to be used here, but I didn't use them because there wasn't enough room between the mendel and whatever table it sat on.

> And now I just realized that, somewhere along the
> lines, I screwed up with squaring the axies. The
> base wobbles on a flat surface, one leg is
> slightly higher than the others....this is
> extremely annoying.
Unless the rods are bent, I'm guessing that this might be caused by one of two things:
The vertex frames do not match - one is smaller or not forming an equilateral triangle maybe?
The z-axis lead screw bases are not aligned and it is causing the whole frame to twist.

You might want to double check that it is actually the base that is not level. It could be rocking on the y-axis motor and bearing mounts. Eventually I added rubber feet to mine, but before I did that it would rock on the washers at those y-axis pieces.