Tower out of square

[knohbody]

Hello everyone,
Some background:
I got a Rostock Max V2 a couple of weeks ago, got it together thanks to the Gene's build guide and the search feature of this site. I was able to print out a few small objects, including some calibration pyramids that came out pretty well, but I started getting the dreaded ABS curl when I started going to larger objects. I rechecked my and adjusted my calibration, ended up getting a PEI plate and adhering it to the glass bed. Even with the PEI, there are portions of the build plate that the ABS just doesnt' like sticking to. (I'm using the matte side up, and cleaning with 99% isopropyl before a print).

I remembered that I had a hard time getting the towers square to the bed, so went to check that again, and sure enough, the Z tower is off. The problem is, I can't adjust it. I loosen the tower bolts, pull it into place with a square across the bed and touching the tower, get it straight and hold it there while I tighten the top and bottom screws, then when I check it afterwards, its still off, and seems like it hasn't moved. I'd like to get this straightened out. Anyone have any suggestions?

I've also temporarily removed the PEI sheet from my glass, however, now I have that 3M 468MP all over the glass, and it's proving difficult to remove, as its solvent and heat resistant. Is there an easy way to get the tape off?

I've searched the forums, but maybe I've missed something. If anyone can shed some light or point me where to look, it'd be much appreciated.

[knohbody]

So, after scouring the web, I found the answer to the second issue, which is, as most things in life, use some Wd40 and a razor, then acetone to clean up the rest. I still have a bit more to clean, but I've gotten most of it off.

The first issue I'll have to look at some more. I've seen some posts regarding a digital angle finder that seem somewhat promising.

[Tincho85]

What temperature did you use for the bed when using the PEI sheet?
I've read that it needs 100ºc to perform well.

[knohbody]

I think I tried a range of temps, as I've found people saying 80c-95c. Not sure I made it quite up to 100c. I'll definitely try it out once I get these towers straight.

[ZakRabbit]

Read the PEI thread by mchacker, (I'd recommend the "long" thread, but the "short" version is good too) there are excellent and direct recommendations for bed and extruder temps for different materials.

[knohbody]

So I was able to get my towers pretty straight in relation to the bed, recalibrated, printed, and was still having issues. I found I wasn't compensating for the feeler gauge I was using while setting the z-height. (For other newbies, I used a 0.1mm feeler gauge to set the z-height, basically how gene's assembly manual says to do with the paper. Once I had everything the same height at all the towers and my horizontal radius set correctly, I lowered the z-height by 0.1mm and re-set the z-height.)
ZakRabbit, thanks for your input, I have been reading through the PEI threads in preparation for reinstalling. Currently I'm printing on the borosilicate with acceptable results.

[ZakRabbit]

Glad you got it working! My tape has arrived, waiting on the PEI itself...

[geneb]

You actually don't want Z zero to be in contact with the glass. Having it a bit above the glass will help ensure you're going to get a good first layer. You run the risk of a badly "over-squished" first layer otherwise.

g.

[U.S. Water Rockets]

You actually don't want Z zero to be in contact with the glass. Having it a bit above the glass will help ensure you're going to get a good first layer. You run the risk of a badly "over-squished" first layer otherwise.

g.

I have found that if I can get the first layer as oversquished as possible without jamming the extruder or stripping the filament then I get much better prints in several areas:

1) Smooth bottom with no lines/ridges.
2) Eliminates curling/peeling up of the part.
3) Less layer separation.

I think that the oversquished layer at the bottom benefits from displacing the air, creating a vacuum that holds the part to the plate, and also creating more surface area to grip the build plate. Having a first later that is squished out at the perimeters is not a concern for me, as I can sand this off in a few seconds. Having a glass smooth bottom surface with no lines is much preferred.

[ZakRabbit]

You actually don't want Z zero to be in contact with the glass. Having it a bit above the glass will help ensure you're going to get a good first layer. You run the risk of a badly "over-squished" first layer otherwise.

g.

Don't we want that for accuracy? Does the first layer print at Z0 or at Z0.2 (assuming we asked for a Z0.2 first layer thickness)?

[geneb]

Mic a bit of 20lb bond paper. That would be your "error".

The first layer is NOT gripping the glass via vacuum, but excellent WAG.

Consider that there's tens of thousands of 3D printers out there, all with the zero point calibrated in a similar manner. It's done to keep a good layer formation as well as to prevent over-pressure in the hot end from preventing extrusion. Take a peek at the photo in the manual that shows what a good first layer extrusion looks like. You're after something that if cut in half would have a racetrack shape to it.

You will NEVER print a first layer with no lines. It's physically impossible to do with a filament printer. You'll need either SLA or SLS to do that. You may mash the lanes down to where you can't hook them with a fingernail, but they'll always be there visually.

Another down side of having Z zero at the glass is the scratches the nozzle can engrave into the glass.

At the end of the day, you can configure it however you like. As long as you get the results you want, nobody here will care how you get there.

If however, you have first layer adhesion problems, don't yell if we point and giggle a lot.

g.

[Polygonhell]

You actually don't want Z zero to be in contact with the glass. Having it a bit above the glass will help ensure you're going to get a good first layer. You run the risk of a badly "over-squished" first layer otherwise.

g.

Don't we want that for accuracy? Does the first layer print at Z0 or at Z0.2 (assuming we asked for a Z0.2 first layer thickness)?

The first layer of every CURRENT slicer I'm a aware of is at the specified first layer height.

It used to be the case that Skeinforge (and I assume as a result very early versions of CURA) would print the first layer at Z = 0 which was incredibly annoying.
I usually use a 0.1mm feeler gauge, set Z = 0 and then add 0.1mm to the set Z.

Having said that doing the drag test with a piece of paper it's usually the case that the head is actually below the Z = thickness of paper which is what's providing the friction. So it makes sense not to ass on the thickness of the paper.

And having said all of that I still watch the first layer go down and if it doesn't look good I'll manually tweak the Z Height.