Tolerance Issues

[TheOneLasagna 0]

Hi, 

I'm quite new to 3d printing, and am having issues with gap tolerance on my new Ender 3. I doubt it is the printer, as I have it calibrated down to a 0.02 mm inaccuracy on 20mm test cubes on the x and y axes. Despite this, I can only get the .5 mm gap to work on various tolerance tests with the help of a screw driver. I have also had issues like holes being too small, and certain parts not fitting together well. I am using Hatchbox PLA filament at 205 degrees on the nozzle and 60 degrees on the bed. I am using the recommended settings on cura except with zhop and combing on all.

[Smithy 1,144]

Hi

 

here are some advises which helps a lot to get a better dimensional accuracy and tolerances:

 

Print slow
The slower the printing, the more positive the effect on dimensional accuracy. Ideally, you should print between 25-45mm/sec.

 

Print cool
The best results are obtained by printing as cold as possible. One way to find the right printing temperature would be to reduce the temperature until you see under extrusion and then raise it 5-10° again.

 

Unify speeds
One of the most important rules is to set all speeds in Cura to the same value. Cura usually calculates the print speeds according to a specific formula. Infill, for example, prints much faster than an outer wall. Due to the permanent acceleration and deceleration, a certain under or over extrusion always occurs, which in turn negatively influences our dimensional accuracy. 

 

Acceleration & jerk control
Acceleration and Jerk Control decelerate the print head before and accelerate it after a change of direction so that less vibration occurs when printing e.g. a 90° corner. However, as with the different speeds, over- or under-extrusion can also occur. This can be seen very clearly at a 90° corner, which is then slightly bulged outwards. For dimensionally accurate prints, the two options should, therefore, be switched off.

But there is also a disadvantage because if the print head then goes around the corner unbraked, vibrations arise which then show up through so-called ringing on the surface. But this ringing is only optically visible and not really measurable. So for technical parts, where the surface is not important, but the dimensional accuracy, Acceleration and Jerk Control should still be switched off.

You have to find a balance between ringing and dimensional accuracy. If the surface quality is important, the values for Acceleration & Jerk Control can be adjusted to obtain a good balance.

 

Elephant foot
The so-called elephant foot is created on the first layer, where the material is pressed into the print-bed to achieve optimum adhesion. This also displaces the material and creates a lateral bulge. The object is then slightly thicker on the underside than in other places.

The "Initial Layer Horizontal Expansion" option can be used to adjust this behavior. Common values would be -0.2 or -0-3 mm depending on nozzle diameter.

[TheOneLasagna 0]

Thanks for the advice. I’ll update you when I’ve tried that.

Edit: One question, should ALL of the speeds match? There seem to be a lot of values(travel speed, initial layer speed, top/bottom speed, etc.).

Edited February 4, 2019 by TheOneLasagna

[TheOneLasagna 0]

16 hours ago, Smithy said:

Hi

 

here are some advises which helps a lot to get a better dimensional accuracy and tolerances:

 

Print slow
The slower the printing, the more positive the effect on dimensional accuracy. Ideally, you should print between 25-45mm/sec.

 

Print cool
The best results are obtained by printing as cold as possible. One way to find the right printing temperature would be to reduce the temperature until you see under extrusion and then raise it 5-10° again.

 

Unify speeds
One of the most important rules is to set all speeds in Cura to the same value. Cura usually calculates the print speeds according to a specific formula. Infill, for example, prints much faster than an outer wall. Due to the permanent acceleration and deceleration, a certain under or over extrusion always occurs, which in turn negatively influences our dimensional accuracy. 

 

Acceleration & jerk control
Acceleration and Jerk Control decelerate the print head before and accelerate it after a change of direction so that less vibration occurs when printing e.g. a 90° corner. However, as with the different speeds, over- or under-extrusion can also occur. This can be seen very clearly at a 90° corner, which is then slightly bulged outwards. For dimensionally accurate prints, the two options should, therefore, be switched off.

But there is also a disadvantage because if the print head then goes around the corner unbraked, vibrations arise which then show up through so-called ringing on the surface. But this ringing is only optically visible and not really measurable. So for technical parts, where the surface is not important, but the dimensional accuracy, Acceleration and Jerk Control should still be switched off.

You have to find a balance between ringing and dimensional accuracy. If the surface quality is important, the values for Acceleration & Jerk Control can be adjusted to obtain a good balance.

 

Elephant foot
The so-called elephant foot is created on the first layer, where the material is pressed into the print-bed to achieve optimum adhesion. This also displaces the material and creates a lateral bulge. The object is then slightly thicker on the underside than in other places.

The "Initial Layer Horizontal Expansion" option can be used to adjust this behavior. Common values would be -0.2 or -0-3 mm depending on nozzle diameter.

Ok, I've tried all of the recommended methods but I still can't even get a 0.3mm gap on a tolerance test. Do I need to further calibrate until it's perfect? Could there be something wrong with my printer?

[Smithy 1,144]

7 hours ago, TheOneLasagna said:

Ok, I've tried all of the recommended methods but I still can't even get a 0.3mm gap on a tolerance test. Do I need to further calibrate until it's perfect? Could there be something wrong with my printer?

I don't know the Ender 3 in detail, but I have heard it has serious extrusion problems, so the extrusion is not very consistent. This can cause the problem. To get a good dimensions accuracy and good tolerances your extruder must be very good calibrated. 

 

There are some modifications for the extruder (something to modify the tension of the extruder spring) so maybe give it a try and search the internet for such modifications. 

 

I am sure, that if have tried my advice and it is still not working, then you have to check your printer hardware or calibrate your e steps.

[ftoons 5]

Try these settings:

 

 

[garybenade 0]

You can try setting a negative horizontal expansion when you slice, try -0.2 and then -0.5 if that doesn't work

You can also play with nozzle line width, sitting it 0.1mm higher than your nozzle size