Can't get round circle's

[hvam&t 0]

Hi all,

For a school project we had to assemble a Ultimaker. But now that the printer is assembled we can't get him to print round circle's. We are trying to fix it for quite some time now and tried multiple solutions.

-Belt tention

-Different settings in Cura

-Axis alignment

and i think we tried some more things but i can't even remember.

We are testing the UM with this file: http://www.thingiverse.com/thing:170922/ and use the 10mm version.

As you can see in the pictures the squares are good, but the circles arent round enough.

We hope you guys can help us!

Dear Regards

 

[IRobertI 521]

it seems you forgot to include images of the problem.

But, in general, roundness of circles is almost always a case of getting the short belts to the correct tension.

 

[gr5 2,295]

Without a picture it is hard to help you.

Did you watch this video as belt tensions (especially short belts) are the most common problem with oval shapes but I'd love to see the first layer - take a picture of the bottom - I want to see if your infill is making a particular pattern where every other line touches:

 

Also be aware that for several reasons, vertical holes through a part will be smaller than desired. One reason is shrinking while cooling. One reason is that when you create a cylinder with cad it instead creates a polygon with for example maybe 10 sides. These 10 sides cut through the circle making the circle smaller. Using 50 sides will increase the inner diameter slightly. A third reason has to do with the material properties of liquid PLA: it acts a little bit like a rubber band before it is a solid so you are pulling on this string that you are laying down and it tries to pull inwards towards the center of the circle. These 3 affects vary depending on temperature, and additives to the PLA such as dyes. The best solution to this effect (not the ellipse effect) is to print a few layers, abort the print, measure your result, then adjust your CAD model.

 

[hvam&t 0]

Thanks for the reply's. We now added the belt tensioners but it doesn't seem to matter much. As you guys can see in the picture the round shape still isn't perfectly round.

I also uploaded a picture of our slider blocks, since we made a adjustment there by adding some spacers for the axes. otherwise they were to loose, could that be the problem?

 

[Daid 306]

Did you tension the short belts? That's way more important then the long belts.

 

[gr5 2,295]

You're picture is not so clear. It's very small even when I click on "large". Iphone's usually take excelent close up shots - maybe you need to get closer - make sure the circle is focused before taking the picture.

However from what I see the cricle is not an ellipse but is a strange polygon shape. I checked the cad file for the 10mm hole and it has hundreds of line segements in the circle which is good. I don't understand why the larger one (20mm) only has about 25 line segments. I would have done it the other way around (large circle with 100, smaller circle with 25).

So I think the cad file is fine. I think the most likely problems at this point are bed height and speed. Probably just bed height. Whatever speed you were printing at, try running 50% for the first few layers to see if that makes any difference.

MUCH more likely I think you have a levelling issue. Levelling is amazingly important. Your bottom layer appears to be too high off the print bed. If it's too high you don't get good adhesion and the filament moves across the tape like a rubber band and doesn't get laid down in a circle.

So re-level (because the bed moves from day to day) and then if you are still getting this issue, loosen the 4 screws by a 1/4 turn and try again until the filament is being *pushed* into the blue tape better.

Here are my instructions on levelling (other people's instructions vary):

How to level:

leveling here is defined as setting the Z height and also leveling. It's one procedure that does both at once.

Optionally heat up the nozzle to 180C because a cold nozzle shrinks and you will be setting the bed to the wrong height. Make sure tip of nozzle doesn't have any plastic on it or you may level to the wrong height. I usually prefer to level with a cold nozzle but if you want extra accuracy then use hot nozzle. If you have a heated bed that should also be warm for the same reason.

Home the z axis only. If you must home all 3 then you need to disable the steppers once it's done so you can move the print head by hand. Move the head as close as possible to each of the 4 screws in turn. Once at a screw tighten the screw and then slip a piece of paper between the nozzle and the print bed. Make sure the paper slides very freeley. Then loosen the screw until the paper gets slightly stuck. You want the paper to easily be able to slide in and out under the nozzle with one hand pushing the paper. If the paper gets stuck it's probably too tight under there. While levelling try rocking the bed across both opposite diagonals to see if one of the screws isn't touching the bed and to see if the bed is "hung up" or stuck on the threads of a screw instead of on the screw head.

Repeat this procedure for the other 3 screws. Then go back to the first screw and repeat on all 4 screws again. Then repeat on all 4 screws again. Then again. It may take you 20 minutes to do this the first time but the second time you do this it should take much less time because you are both better at it, faster at it, and because there isn't much to adjust the second time.

Note that the act of putting the screwdriver in the head can apply weight to the bed and change the height. You have to be careful to put as little weight as possible when testing with the paper.

If you leveled with a cold nozzle you are done. If you leveled with a hot nozzle you should then loosen the 4 screws 1/8 of a turn to compensate for the thickness of the paper.

Once done leveling rotate the z screw by hand to keep the nozzle off your bed. This makes it less likely to damage your bed surface and gives the nozzle room to leak.

On a new ultimaker repeat this procedure before every print (at least every hour) because the print bed can move/droop like a new guitar string. After many months the droop slows down.

 

 

[kukucov 0]

Similar problem here.

 

Tried tensioning the belts, no dice. everything else prints good. No drift on high objects. Thoughts?

edit by gr5: fixed link

 

[illuminarti 18]

This is almost certainly a backlash issue - the head simply isn't making small movements on one of the axes - looks like Y, if I'm reading the orientation of your photos correctly.

As others have noted, this is almost certainly due to issues of short-belt tension. You may need to file the motor mounting slots slightly longer in order to be able to push the motors down far enough to get good tension.

Also, power the machine off, and try moving the head around by hand, by pushing with fingertip pressure on both sliding blocks for each axis in turn. It should move fairly easily, and uniformly - all the way across each axis, and when comparing axes.

If either axis seems difficult to move, try lubricating the rods with a few drops of light machine oil (such as sewing machine oil) - also check the end caps over the axis rods aren't too tight, and restricting rotation.

 

[gr5 2,295]

Something is very wrong.

You appear to have play caused by something too loose or too tight. The problem seems worse in Y axis as Illuminarti says.

Too loose:

Hold the Y motor from moving with thumb of left hand and push the head and see if it moves a little. Does it move as much as the error in your circles? Maybe the nozzle is loose? Maybe the bearings in the head are loose?

Too much friction:

Push the head in X and Y with power off. Does friction feel the same? Check endcaps. Check belt tension too tight? Needs oil? You should be able to push the head around without the UM sliding around on the table (just barely though). You should be able to push the head with your smallest finger (but not easily).