# Hi, I'm new to the group.

Hi, I’m new to the group. I’ve built a Ingentis/Eustathios/rigidbot variant (i’ll post pictures later) and I have a question about calculating steps for a belt driven z-axis bed… how did you guys do it ? I have a 1.8 degrees nema17 motor with a 36 tooth gear connected on a 90 tooth pulley that drives a 8mm shaft that have the belts on the end (they’re each on a 36 tooth/8mm bore). i’m look for the formula that can give me the number I can put in the marlin firmware for the steps.

Any pointers are appreciated. Thanks !

Request 10mm travel, measure actual travel, change Z-steps, repeat

Distance between teeth = 2mm

We need what micro steps you are using to finish the calculations.

@Mike_Miller Yes, I did that at first but i feel that using a ruler is not precise enough… maybe its me ? hehe

@Eclsnowman Well, if you mean the motor rotations then its a 1.8 deg motor so 200 steps per rotations… but, now that I think of it, you must mean on the step driver… its set to 1/16th… should I use a 1/32th to have finer travels ?

@Jean-Francois_Coutur You may want to invest in a pair of digital calipers, they’ve gotten cheap enough. http://www.harborfreight.com/6-inch-digital-caliper-47257.html (understanding harbor freight might not ship to your part of the world, alternatives should be available)

Your gearing is 2.5:1 Your 36T pulley turns 2.5 times for every turn of your 90T pulley.

The circumference of your M8 rod is ~ 25.132741323 mm.

Therefore, for 1 revolution of the M8 rod your stepper must make 2.5 revolutions.

So your ratio is 10.05309649mm/rev, which now needs to be divided up into microsteps.

1x microstepping with a 200 step motor yields 0.05026548245mm/step, or 19.8943678894 steps/mm. Simply multiply this number by your microstepping rate.

At 16x that’s 318.3098862304 steps/mm

And +1 for digital calipers. They are not optional in this process.

And based in significant figures (and pi being a bitch) 318.31 should get you really close.

@Mike_Miller Yeah, sorry, I said ruler but ment caliper( I have 3 of them) The problem is, I’m unable to get that golden number (10mm, like you said, I actually tried that exact number) and I tought that by going with the formula, I could get closer to the right movement

@Matt_Miller @Mike_Miller : That is great… see, for now, I have “110” set in Marlin… something tells me that i’m WAY off or, i’m on the wrong micro step on the driver (the rumba board is king of weird to setup on the driver site of things).

Thanks alot, i’ll try my best to the final steps and send photos of the printer your way

Cheers !

Making a thin walled 20mm cube with low infill will give you something to work with…keep in mind that over extrusion can skew measurements some.

Yes, I use the 20mm_cube.stl file (fount on thingeverse) to compare results.

…and a detailed description of the process can be found here:

http://reprap.org/wiki/Triffid_Hunter’s_Calibration_Guide

@SirGeekALot Hi, Thanks. I know about the calculator (I’ve done printers with lead screws (turns per mm), no problem), what i did not know is how to do it with belts.

get as close to 10mm as you can, then switch to 100mm, that will give you more room to see the differences.

hey, that’s a great idea… thanks, will do

Just for clarification is this the setup:

Nema17 w/ 36 tooth -> shaft w/ 90 tooth input and 36 tooth output?

@Eclsnowman Yes, that is right… both belts are on a 36T/8mm(the shaft) pulleys. For now, looks like I have it dialed it at 112.1 in the Z-Steps in marlin.