When I design a part that is 130 mm long I want it to print 130 mm long. I have found that applying the 0.5% to the steps/mm gives me exactly the designed size. I print with ABS 95% of the time, and temperatures are consistently set to 235C and 105C.

Sure I could use Cura and scale the print every time I slice a part, but why would I do that every time I slice, and why would want to restrict myself to using only Cura? Steps/mm is the right place to make the correction because I only have to do it once.]]>

Quote

**Mikk36**

That's a bit stupid way of solving it, if you have known constants of the parts.

You might get even false results from that with bad measurements.

That's a bit stupid way of solving it, if you have known constants of the parts.

You might get even false results from that with bad measurements.

Actually, using the math gets you close, but if you're concerned about accurate printing, the final calibration has to be done using measurements of prints. I have found -0.5% error (when printing ABS- shrinkage?), so my steps/mm values correct for that (yes, I'm

Quote

**the_digital_dentist**

The OP asked what is the gear ratio of a 32 tooth pulley driving a 20 tooth pulley. The word "ratio" tells you what to do: 32/20 is the ratio, by definition.

Well, yeah, guess I was also overthinking it.The OP asked what is the gear ratio of a 32 tooth pulley driving a 20 tooth pulley. The word "ratio" tells you what to do: 32/20 is the ratio, by definition.

That's a bit stupid way of solving it, if you have known constants of the parts.Quotecozmicray

How about

with known Steps / mm set in firmware

Command Z axis movement A

Measure the Z Axis distance moved B

A little calculation

Reset steps/mm

until

commanded distance = distance moved

Record result --- so you can put it back when the EEPROM loses it.

:S

You might get even false results from that with bad measurements.]]>

Command Z axis movement A

Measure the Z Axis distance moved B

A little calculation

Reset steps/mm

until

commanded distance = distance moved

Record result --- so you can put it back when the EEPROM loses it.

:S]]>

So 200 steps = 1 revolution (360degress / 1.8 degrees per step). So with 1:1 gearing 200 steps = thread pitch (in this case 8mm). So 1mm is 200/8 = 25 steps. But your gearing is 32:20 so the steps per mm are 25 *20 / 32 = 15.625. If you multiply that by 16 you'll get the 250 micro steps that DD came up with.

Personally I don't like to rely on micro stepping for positional accuracy (just something I read somewhere). But if you simply switch the pulleys round you get 25*32/20 = 40 steps per mm which I think is a much nicer number than 15.625. You'll also increase the torque but lose a bit of speed but that maybe is better for the Z axis.

Juts my twopence worth]]>

The OP asked what is the gear ratio of a 32 tooth pulley driving a 20 tooth pulley. The word "ratio" tells you what to do: 32/20 is the ratio, by definition.]]>

Since you're saying that you're running 32 teeth on the stepper and 20 on the screw, you're running 1.6 : 1 gear ratio, anything else doesn't matter about the belt system.

Since that calculator doesn't do floats in the inputs for the ratio, it's easiest to put in 16:10 ratio unless you want to find out the lowest integer ratio equal to yours (though it isn't that hard, it's 8:5).]]>

The screw has a 20 tooth pulley. When the motor turns one rev, the screw turn 32 tooth/rev / 20 tooth/rev = 1.6 revs.

The screw lead is 8 mm/rev. When the motor turns one rev, the screw turns 1.6 revs so the Z axis moves 1.6 rev x 8 mm/rev= 12.8 mm

It took 3200 usteps (1 motor rev) to move the Z axis 12.8 mm, so 3200 usteps/rev / 12.8 mm/rev = 250 usteps / mm]]>

A bit of of info on my set up -

1.8 deg nema 17 (59Ncm I think, so should be beefy enough)

16x microstepping

1140 tooth closed loop gt2 belt

2x tr8x8 lead screw, 4 start. 8mm travel per revolution.

32 tooth pulley on the nema 17

20 tooth pulley on the leadscrew

The pulleys are what I had lying around, although I'm not sure what an effective ratio would be here? Any suggestions on this would be great as well]]>