Off-Center Nozzle during calibration

[cyber.shifter]

Soooo... I've learned a lot reading through everyone's posts here, and have changed my calibration methods a good bit just from what I've learned. I now use feeler gauges instead of paper, and have gotten proficient at stepping through the process. However, I've noticed something odd today, and the other day when I did a print. It seems like my print head is somehow drifting off center. When I do a calibration and end in the center script the nozzle is not center. I was reading about Rollin's software calibration and someone said one thing about it maybe being a delta issue, but it didn't elaborate. Has anyone else seen this? If I Z down using the control panel of the machine it goes to center, but not when I run the calibration script. I haven't made any changes other than the ones mentioned in the manual (as I am fairly new to this and still lack experience to make expert changes) so I can't imagine why it would change on its own (as it was centered before). Any ideas?

[BenTheRighteous]

Are your cheapskates nice and tight to the towers?

[cyber.shifter]

Yeah, I checked them. They haven't ever gotten really lose, but I have had to tighten them up a couple time. It's harder to tell what's a good adjustment once the belts are on. Has anyone figured out some sort of way to measure belt tension on the tower belts? I was just thinking it would be nice to have a quantitative value for belt tension.

[IMBoring25]

Belt tension in applications where it's important but not important to use a tensioning idler is typically measured by applying a specified amount of force at a specified point in the belt and measuring the resulting deflection. I've not attempted to develop such data for the printers.

[cyber.shifter]

This even happens when I bring the extruder down using the actual machine controls. I checked my belt tensions and the Z was a bit lose for my tastes, but that still didn't fix the problem... I'm reallllly getting aggravated at this point. I've got an important print to do and it seems like everything that could go wrong, is. Ugh.

[cyber.shifter]

Yeah, I've done it in cars before, but I'm at a loss to apply that to this application. Maybe if I had a low-end torque wrench... I dunno.

[ZakRabbit]

As far as the belt tension, if it's that important, you could always use a fish scale.
things that come to my mind that might be having an affect:
make sure the set screws holding the toothed pulleys to the stepper motors are actually tight and on the flats: not on these, but I've tightened a set screw down before thinking it was on the flat only to find that somehow the flat had been on an angle. After a little bit of use, it "came loose" and would rock back and forth.
is it possible one cheapskate is actually too tight, causing drag and possible missed steps?
Is the bowden tube or the wires for the fan/hot end fouling on anything or is it simply tight?
Have you checked the "U" joints on the arms for binding? It doesn't take much to pull/push the effector out of alignment
That you can manually move it to center tells me the configuration is at least close, and that the problem is probably mechanical in nature.
Basically, look it over with a fine toothed comb.

[cyber.shifter]

The problem is that I don't have enough experience to know what the optimum's look like, which is why I was searching for a way to get quantitative data. I'm able to print objects, but their center is always off and I'm getting print artifacts. I'm guessing that since no one has figured out how to test belt tensions and cheapskate tightness, I'm going to have to tear the machine apart to check these things. By the way, the cheapskates suck. They are my least favorite part, mostly because their proper setup is the most touchy-feely, ambiguous, non-quantitative part ever. No one can ever seem to give me a straight answer about how to tell when the bearings are optimum. Ugh. Ok. /endrant. Sorry, just frustrated.

[cyber.shifter]

It's just funny, because I haven't seen any sort of problems in the past couple months, and now that I need it to work fine so I can get this print done, it's acting up. I can only laugh at Murphy at this point.

[cyber.shifter]

The manual recommended a dry lubricant for the "U" joints, is graphite suitable for this purpose? I was thinking of just proactively hitting each of them with a little puff of it.

[ZakRabbit]

Yeah, gotta love Murphy... Best way I've heard to check the cheapskates is to make sure that each wheel cannot slip against the rail yet nor is it tight enough to bind. That means, if you can hold a wheel still while moving the cheapskate up and down it's too loose. There's always the Trick Laser trick trucks with only three
wheels and one eccentric for adjustment.
As far as the "U" joints, I hate to say it, but it is best to take them apart and asses each joint individually. The best advice I can give here is to look at mhackney's build thread as he goes into detail with what can happen if they're not smooth acting yet without slop.

[geneb]

Yeah, this is so horribly vague.. https://www.youtube.com/watch?v=3nzUM2d05qQ

If you REALLY hate the Cheapskates, go grab the current manual (3rd. Ed.) - it shows how the new carriages are installed. If they really get your motor going, try contacting SeeMeCNC and see if they'll sell you a refit kit.

g.

[cyber.shifter]

Lol! Sorry, I was working on it at the time and was getting frustrated, can you tell? I had to step away for a bit from it. I understand how it should feel, and when I first assembled it, mine behaved exactly like they should. But all that changes once the belts are on. The only way to check it again would be to pull the belts off. Side note, I was thinking it would be better to set the tension from the get-go at the cheapskates, with the tension pulleys all the way down. What do you guys think of that?

[cyber.shifter]

So I checked my u-joints. The white plastic has some mold remnants around some of the inside edges of the holes. I noticed something else too, some of the pins for the u-joints had a noticeable amount of wiggle inside the holes in the delta arms. I trimmed off the mold remnants but I'm not sure what/if to do anything about the holes in the arms. If my nozzle is a bit to the left, should I be looking at the X-tower? It's centered in the Y direction.

[cyber.shifter]

I should also note that if I print something, it is also off-center. I guess that makes sense, but I figured that eliminated any possibility of calibration script code errors. I also just noticed that if I'm watching the 3D view of the print in Repetier-Host, where it says the printer is printing is actually quite a bit ahead of where the head actually is.

[BenTheRighteous]

To get rid of the slack introduced by the arm hole / u-joint pin fit, you can rubber band the delta arms together at both ends. That will probably require you to recalibrate your end stops and horizontal radius.

I'm not positive but I think RH shows you the progress of the commands sent to the printer, not where the printer actually is. There's a buffer so RH is probably showing you 5-10 commands ahead of where the print is.

When you make a print, do all the layers at least look aligned?

[cyber.shifter]

The prints actually aren't that bad. Here's a couple pictures.

Cubish object in print.

Finished

[BenTheRighteous]

Well that looks pretty damn good!

Are you totally, positively convinced that you've actually got a problem, and this isn't some trivial mistake like your script is actually sending your nozzle to 7,9,0 or something instead of 0,0,0?

It's hard for me to tell from your pictures but just by me trying to eyeball it, that looks pretty centered.

[cyber.shifter]

The center of the bed on the X-axis is centered between the two white boxes around the caution warnings, if that helps you see how much it is off. Also, the dimensions are off by a bit over half a mm over the whole 20mm of height. The reason it really is a problem right now is is because I'm trying to print a square object that will be at the print area edge. If it's not centered, part of the left side won't print. I didn't think about the script thing, but this is happening when I use the on-board functions of the machine to drop the Z-height for calibration. So maybe it could be something in the firmware?

[BenTheRighteous]

If I Z down using the control panel of the machine it goes to center, but not when I run the calibration script.

I didn't think about the script thing, but this is happening when I use the on-board functions of the machine to drop the Z-height for calibration.

So is it centered when you calibrate Z height from the LCD or isn't it?

[KAS]

What slicer are you using?

[cyber.shifter]

My apologies, I meant to say it happens both when I use the LCD controls and the software. I do not know why I wrote that the way I did. I am using Slic3r at the moment. Point of interest, another user is experiencing something similar to me in this thread:

http://forum.seemecnc.com/viewtopic.php?f=37&t=8784