UM2 Accuracy

[mostlyatomicbob 34]

Good Afternoon fellow Ultimakers,

I have a question for the wise owls out there.

I have been printing some fairly close tolerance parts on my UM2 but I am finding that they are not printing to the correct sizes.

Now I expect some shrinkage from PLA but the dimensions are smaller than I would expect.

On my UM Original i can set the 'steps per mm' on the Ulticontroller but I have had a look on the UM2 and I cannot find the same!

Am I missing something?

I don't really want to have to start scaling my models to compensate this deviation.

Cheers

Bob

 

[illuminarti 18]

No, it's not available in the User Interface on the UM2, and since you can't include start gcode either with Ultigcode, there's no easy way to do it.

You could change your gcode type to Reprap/Marlin, which would allow you to include your own start gcode, and then add the relevant gcode commands in the start gcode (along with the necessary codes for homing, heating etc).

Alternatively, you can build your own version of Marlin, and change the steps setting in the configuration.h file.

All of that said, the steps-per-mm should be a fixed function of the components - pulley teeth pitch and diameter. So the default setting should be exactly correct, by definition.

How large are the errors that you are seeing?

 

[gr5 2,167]

If your print bed is at 75C, the bottom 5mm will be very distorted so keep that at 60C instead.

PLA is expected to shrink about .3% once it gets below the glass temp and it shouldn't shrink much before then. That is what typical injection mold people use as a rule of thumb I believe - .3%.

There are many other factors and they are different depending on PLA additives (coloring), temperature and printing speed.

So even though you don't want to scale your model, I think it's worse than that. For example vertical cylindrical holes shrink much more than say cubes. And the Z axis shrinks much less than X or Y axis. And lower levels (close to the hot bed and where fan wasn't on at full) tend to shrink differently also.

So you might need to add a taper at the bottom 5mm to compensate for something.

Most people who need very tight tolerances just print everything twice but as you learn how much things need adjusting for your given filament and print settings you get very good at predicting the model changes ahead of time.

 

[mostlyatomicbob 34]

Thanks fellas,

Mucking about with the g-code scare the willies out of me!

I guess I will have to start looking at scaling my models.

If PLA does shrink around 0.3% that would be more or less in line with the shrinkage I am getting.

Thanks for your help.

Bob

 

[gr5 2,167]

Mucking about with the g-code scare the willies out of me!

 

You mean the STL?

If you are designing stuff in CAD then all you have to do is measure the result after you print it and then adjust the high tolerance areas a little bigger as needed. If you are printing out someone else's "high tolerance" part then I don't know what you can do other than scale (the x,y only) in Cura.

 

[Daid 306]

Seriously, messing around with the steps per mm is wrong. We did careful calculations and measurements to ensure that the 80steps/mm is the correct value for the UM2.

 

[mostlyatomicbob 34]

GR5, a bit of both really, the file i was having troubles with is now all sorted thanks.

Daid, No worries, taking all things into account I am very happy to leave my UM2 alone, well apart from the feeding issues, but thats another matter (which I know will be sorted soon)