Nozzle height changes upon direction change.

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Nozzle height changes upon direction change.

Post by bot » Wed Jan 21, 2015 7:40 pm

I've noticed that most "low" or "high" spots on the bed are actually produced when a tower (or a combination of towers) changes from moving down to moving up or vice versa.

Here is a a series of pictures that illustrates the results. Look at the brim, how on one part it's too squished into the bed, and how it's exactly related to the direction a tower is moving. Is this a belt tension thing? It's pretty consistent to each tower.

IMG_2139.JPG

IMG_2140.JPG

IMG_2141.JPG
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Re: Nozzle height changes upon direction change.

Post by Polygonhell » Wed Jan 21, 2015 8:17 pm

Then you have something "loose" or binding somewhere. It's what backlash looks like on a delta.
I would start by checking the UJoints on the effector all move freely.

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Re: Nozzle height changes upon direction change.

Post by bot » Wed Jan 21, 2015 9:59 pm

The u joints all move easily. They are the acetal variety. I also have tension on the arms. I'm starting to suspect my belt tension is too loose as I previously had thought it was too tight and loosened them all off. I wanted to get some more thoughts before I adjusted anything. I agree that there is "backlash" somewhere, but I'm not sure if it's in the u-joints.
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Re: Nozzle height changes upon direction change.

Post by Polygonhell » Wed Jan 21, 2015 10:06 pm

You can usually see backlash in the carriage motion, write some GCODE to just move the effector up and down, watch the carriage and belts, put you finger on the drive pulley and watch them again.

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Re: Nozzle height changes upon direction change.

Post by bot » Thu Jan 22, 2015 2:47 pm

Hmm. Thanks I'll try that. I'll do a full tune up check tonight.
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Re: Nozzle height changes upon direction change.

Post by Jimustanguitar » Thu Jan 22, 2015 3:23 pm

If you have the motors locked in position (just home the machine) you can wiggle things to see how/if they move. Try wiggling the hot-end, try moving each tower up and down, see if one of your arms moves more than the others, etc.

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Re: Nozzle height changes upon direction change.

Post by DavidF » Thu Jan 22, 2015 4:12 pm

Check the set screws on the steppers pulleys also.
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Re: Nozzle height changes upon direction change.

Post by RegB » Thu Jan 22, 2015 8:25 pm

Watch the belts through the slots in the columns, if you see any slapping they are slack.

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Re: Nozzle height changes upon direction change.

Post by bot » Thu Jan 22, 2015 10:09 pm

Well the hot end feels very very firm in place when the steppers are engaged. When I try to move the cheapskates up and down there is a TINY amount of movement, with the wheels turning a tiny tiny bit as a put a reasonable amount of pressure. Should the belts be tight enough that I can't move the carriage vertically at all?

Also, when I try and twist the cheapskate, the wheels are firmly in place, but the arms do deflect a little bit as if they are rotating a bit somehow...
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Re: Nozzle height changes upon direction change.

Post by Khalid Khattak » Thu Jan 22, 2015 10:26 pm

I had a similar issues. My top pulleys are overhung, i supported all the three top belt pulleys with bearing and the problem resolved.. Its a mechanical issue...

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Re: Nozzle height changes upon direction change.

Post by bot » Thu Jan 22, 2015 11:57 pm

What do you mean overhung? My top belt pulleys have always been a concern, re:level and tension. The belts also wear on the extrusion a bit but I can't seem to fix that.
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Re: Nozzle height changes upon direction change.

Post by DavidF » Fri Jan 23, 2015 12:19 am

bot wrote:What do you mean overhung? My top belt pulleys have always been a concern, re:level and tension. The belts also wear on the extrusion a bit but I can't seem to fix that.


Our friend does not have a true rostock, delta yes, but not a rostock.
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Re: Nozzle height changes upon direction change.

Post by bot » Fri Jan 23, 2015 12:34 am

Ahh hmm I see. I wonder what he meant, though. I might still be able to learn from his experience.

BTW, David, can you cast this in aluminum please and thanks: http://www.thingiverse.com/thing:330127

:)
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Re: Nozzle height changes upon direction change.

Post by DavidF » Fri Jan 23, 2015 12:40 am

If I can get a decent print of it I think it will cast ok. Loks like a bugger to print though..
Did you check those set screws on the pulleys?? could be rocking on the flat of the shaft. My timing belts almost "drum" when plucked, but i still get some movement...
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Re: Nozzle height changes upon direction change.

Post by bot » Fri Jan 23, 2015 12:42 am

I have not checked the screws from the motors. I will do that soon. I made sure they were very tight and applied loctite so I didn't really suspect them but I should check.
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Re: Nozzle height changes upon direction change.

Post by DavidF » Fri Jan 23, 2015 12:50 am

if you follow the print back to the tower (Z axis??) your problem will be there. kinda like following the yellow printed road LOL If you can feel a difference in that tower you know you got it!
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Re: Nozzle height changes upon direction change.

Post by Jimustanguitar » Fri Jan 23, 2015 8:03 am

DavidF wrote:if you follow the print back to the tower (Z axis??) your problem will be there. kinda like following the yellow printed road LOL If you can feel a difference in that tower you know you got it!


An excellent point. Often people ask how should this feel or how should that feel... Luckily we have 3 of just about everything, and if one of them is different than the other 2, you've found your culprit :)

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Re: Nozzle height changes upon direction change.

Post by bot » Fri Jan 23, 2015 5:37 pm

Yeah, this happens going in all directions... it's not specifically towards the Z tower. I'm accustomed to finely tuning machines, so each tower is very consistent... but they may all be consistently out of proper spec, which is what I'm trying to determine. I think I might print some belt tension adjusters...
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Re: Nozzle height changes upon direction change.

Post by bot » Sun Jan 25, 2015 2:31 am

So I checked my stepper pulleys. Rock solid. I removed my arms to adjust the cheapskates...

Hahahaha... oops. Again. It's always oops. They were rattling around they were so loose. (didn't seem so loose with the tension of all the arms on them).

I'm sure this will be it. I'm also tightening the belts a touch.

Thanks for the pointers... should have just checked myself. I was having too much fun printing (it was still doing pretty well).
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Re: Nozzle height changes upon direction change.

Post by Mac The Knife » Sun Jan 25, 2015 9:17 pm

bot wrote:Yeah, this happens going in all directions... it's not specifically towards the Z tower. I'm accustomed to finely tuning machines, so each tower is very consistent... but they may all be consistently out of proper spec, which is what I'm trying to determine. I think I might print some belt tension adjusters...


I've been contemplating a belt tension indicator, If for anything else, to have all three belts tensioned the same.
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