Problem printing circles

OBELIKS · 19 Jul 2018, 10:36

I hope this is true.
I really need to reduce weight of the bed assembly. I ordered PCB bed without ALU and thinner glass. That should save me around 500g, and if this goes well I will replace the bed frame for ALU also, at the moment I have inox. That would mean at least 200g.

sigxcpu · 19 Jul 2018, 11:24

Unless you have very shitty belts that strech like crazy, there is no reason for the weight of the moving things to generate backlash. I have it too in Y on my CoreXY, but I am sure it is not the axis weight which is pretty thin.
If you suspect the weight is an issue then you can play with motors currents and/or acceleration and see if there are any changes.

timcurtis67 · 19 Jul 2018, 11:43

@sigxcpu said in Problem printing circles:

Unless you have very shitty belts that strech like crazy, there is no reason for the weight of the moving things to generate backlash. I have it too in Y on my CoreXY, but I am sure it is not the axis weight which is pretty thin.
If you suspect the weight is an issue then you can play with motors currents and/or acceleration and see if there are any changes.

I agree with this. @deckingman probably has the heaviest print head axis combo of everyone on this forum and he doesn't complain about backlash.

Ian, do you want to comment about this?

OBELIKS · 19 Jul 2018, 11:57

My bed assembly is in the region of 1,5kg

deckingman · 19 Jul 2018, 11:58

@timcurtis67 said in Problem printing circles:

Ian, do you want to comment about this?

Not really ............................

But since you asked...... I have 4kg split between two gantries so roughly 2 kg per XY mechanism. "No name" 6mm GT2 belts. Max X axis speed 50,000, max Y axis speed 35,000, accel 1,000 for both, jerk 600 for both. I have experimented with high print speeds up to 300mm/sec and my default non-print move speed is 350mm/sec. No sign of backlash but everything is pretty rigid. It'll print OK at higher accelerations but with the mass being over a metre above the floor, the printer tends to start to rock about a bit at high speeds.

As an aside, I don't get ringing either - one advantage of high mass

OBELIKS · 19 Jul 2018, 12:06

Hah, I have a i3 style printer. So it is moving a lot.
I will investigate the whole mechanics of X and Y, something is wrong there, that I am certain.

Aaaand, he deleted the post

deckingman · 19 Jul 2018, 12:08

@obeliks said in Problem printing circles:

Hah, I have a i3 style printer. So it is moving a lot.
I will investigate the whole mechanics of X and Y, something is wrong there, that I am certain.

Aaaand, he deleted the post

Yes, I realised my mistake - hence I deleted the post. For some reason I thought yours was a CoreXY the same as mine.

Edit. So in which case, you could well have backlash or movement issues in Y

Phaedrux · 19 Jul 2018, 19:48

You could try reducing the accel and jerk for your Y axis. I think in your config you have X and Y the same. It's not uncommon to use different values for i3 style printers because of the bed weight.

OBELIKS · 20 Jul 2018, 07:22

I was thinking, and in the end it is probably a problem with the sintered bushes that I use instead of bearings.
Image by Toolson

I made a stupid decision and lubricated them, and they still move, but the moves are "sticky". I will try to clean them, and maybe switch back to linear bearings. I just need to find good ones.

Is this still the right category for this thread?

OBELIKS · 22 Jul 2018, 07:46

I took X and Y axes apart, cleaned all the components, so now it is gliding as good as it can. Positive is that printer got quieter, negative is that the circles are still flat on top and bottom.
I am slowly running out of ideas.
The only part that I still need to investigate is the print head. But it is rigid as it ever was.

deckingman · 22 Jul 2018, 09:42

@obeliks Did you ever try lower acceleration for your Y axis as someone suggested? I note that the motor currents are set to 800mA so presumably the motors are rated at 1Amp? If your bed weight 1.5kg, the Y motor might be struggling so either try lower acceleration, increase the current if you can, or a bigger motor.

OBELIKS · 22 Jul 2018, 09:48

I actually just ordered Wantai 42BYGHM810
It was on my to do list, so...
Then I just need 24V power supply and Anet A8 will be no more.

My motors are rated 1680mA, not sure if that is correct. And I had them running, at 1400mA and the circles were not great. But they heated up over 80°C So I stopped that.

And at the moment I am printing a puzzle box for a gift, it has mostly straight lines, so the circles are not a problem.

OBELIKS · 13 Aug 2018, 08:16

So, with Wantai motors the circles are circles. So either the stepper for X or Y was bad or the 0,9° vs 1,8° makes the difference. Or it was something else that I did not see and was fixed on reassembly. But I did that before the stepper change and there was no difference.
Motors are also quieter and cooler (both around 5 down).

The only thing left is to figure out what to do with the old electronics and steppers. I might need another printer.

Q: What AWG wires do I need for the steppers? I will need to clean the wiring now.

wilriker · 13 Aug 2018, 12:49

@obeliks said in Problem printing circles:

Q: What AWG wires do I need for the steppers? I will need to clean the wiring now.

I started rewiring now and will use 0.5mm² or 20 AWG for the wiring of my steppers. But you have to get wires with rather thin insulation to still fit into the Molex KK crimps. I use LiYY 4x0.5mm² cable for this.

dc42 · 13 Aug 2018, 13:26

20awg is rather thick. I suggest 22 awg, or 24awg for lower current motors.

OBELIKS · 13 Aug 2018, 13:50

I have 2.4A motors, so 22AWG?

dc42 · 13 Aug 2018, 14:22

Yes, 22awg is suitable.

wilriker · 13 Aug 2018, 14:23

@dc42 Is there any reason not to use 20AWG except for the stiffness of the cable if it needs to move?

OBELIKS · 13 Aug 2018, 14:24

@dc42 thank you

dc42 · 13 Aug 2018, 14:40

20awg should be OK, the crimp pins we supply are intended for 20 to 24awg.