Deformed circle issue

Hi everyone,

I have this issue during circle's printing. (See attachment)

Circle is deformed in a un-axial directions, when x axis change direction.

I am using a 0.9 nema 17 with 1/16 DRV8825 stepper and 20t pulley, with a result of 160 steps per unit.

Using (for X and Y) 160 and 160 spu, a small cube (20x20) result very precise in Y (20,00mm) but X goes wrong (19,6mm)..
So I thinked that my circle problem was the X axis loose gear on the pulley or in the belt (GT2).

I have added a new value in firmware (Marlin), I changed the steps per unit of X from 160 to 162 (for a "Hysteresis" solution)
So in a new small 20x20 cube the result was optimal...X and Y was 20,00/20,02..but not for the circle..
Now my error is from 30,1 to 30,6 mm (0,7mm of error).

If i look from top layer, the circle appears ovalized, in correspondence of the X change directrion point, there's two small teeth..at 45° between X and Y..

I have attached an image for understand the problem.



I don't know where is the problem, if is mechanical, or the problem is in a bad firmware configuration...

Anyone can help me?

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"Never send a human to do a machine's job"

Take a look at the examples I attended to this post:

[forums.reprap.org]

Some times the scale factors in the slicers aren't correct and you need to adjust them manually. I don't know if that is your problem, but you can try that first and if it doesn't help then we can try something else.

You've already stated what I think it is. The belt or pulley.
If you are using printed pulley. Get rid of it and buy a uniform metal pulley.
Make sure your set screws are tight. Make sure your pulley is the right size for the motor's shaft. If the pulley is sitting off center, just like a printed pulley, you'll never get an accurate print.
Your belts need to be tight but not so tight to bend any support structures.
Also check your bearings. Any side to side wobble (cheap/old skateboard bearings) you won't be able to get tight belts.

Something else since you are using drv8825, did you adjusted micro stepping in the firmware?

Are the axes orthogonal? If not you'll never print a round circle or a square square.

Print a rectangular solid and measure the diagonals in each plane. If the axes of that plane are orthogonal the diagonals will have the same length. If they aren't, you need to tweak the position of the end of one or the other axis.

You can download a spreadsheet here: [mark.rehorst.com]

It will tell you the error based on the diagonal measure and tell you what needs to be adjusted and by how much. The title says "X and Y" but it is applicable to any two axes.

Quote
the_digital_dentist
Are the axes orthogonal? If not you'll never print a round circle or a square square...

Thank you. I keep forgetting to tell people that. That's a major thing to overlook. I keep thinking about the more common minor things.

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the_digital_dentist
Are the axes orthogonal? If not you'll never print a round circle or a square square.

My cube are not orthogonal ><

Probably the problem is a mechanical failure of the X axis..it require too much force and is a little hard in movements.

I have enhanced the error by removing one of the four bearings on the X guideline.

I had a similar problem with holes. My cubes turned out correct but holes were oblong. I played with e-steps and that screwed up my cubes so that wasn't it. Turned out my Y axis belt was a little loose. Tightened it up and my holes were round again.

Quote
SpeedyDad1
I had a similar problem with holes. My cubes turned out correct but holes were oblong. I played with e-steps and that screwed up my cubes so that wasn't it. Turned out my Y axis belt was a little loose. Tightened it up and my holes were round again.

I'm a little dazed. I've understand that the problem is mechanical.. but this problem hasn't occurred once.

I have a 300x300 printer and a few month ago I was working with the coreXY (HBOT) system..the circle problem appears immediately.

So I have decided to translate the Hbot in a ordinary X Y cartesian system... but the issue carry on.

Is possible Y axis isn't straight respect the guideline?

Quote
Faiotech

Quote
SpeedyDad1
I had a similar problem with holes. My cubes turned out correct but holes were oblong. I played with e-steps and that screwed up my cubes so that wasn't it. Turned out my Y axis belt was a little loose. Tightened it up and my holes were round again.

I'm a little dazed. I've understand that the problem is mechanical.. but this problem hasn't occurred once.

I have a 300x300 printer and a few month ago I was working with the coreXY (HBOT) system..the circle problem appears immediately.

So I have decided to translate the Hbot in a ordinary X Y cartesian system... but the issue carry on.

Is possible Y axis isn't straight respect the guideline?

Just a small remark, CoreXY is NOT Hbot. So, which one do you have? If it's Hbot, it could be your axis binding, since the technique is prone to doing that.

However, if it's after going to cartesian.. Well, then there might be the case of your frame not being square or indeed a problem in your software. Can a faulty stepper motor cause these problems maybe?

Edited 1 time(s). Last edit at 03/21/2015 10:19AM by Ohmarinus.

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