HI , Need help calibration of my Reprap Prusa i3 DIY 3d Printer kit, 1.75mm model 802m , good kit, The problems i have is using cal tests 10mm cube ok but larger tests eg. test 140mm sq and 90mm circle.
Am i doing this right, to set cal in mm for x - 140mm reqd/ 139.5mm actual = 1.0035842 x 140 = new value is 140.50179
my setting in firmwere is currently 100.0000 for x do i add or subtract this new value 0.50179 /
y - 140mm reqd/ 139.6mm actual = 1.0028653 x 140 = new value is 140.40115
z - 30mm reqd/ 29.8mm actual = 1.0067114 x 30 = new value is 30.201342
firmwere setting 400.0000
plus my circles are out x=69.4 and y=69.6 how do i keep them uniform, values ok if rest firmwere is x and y set at 100.0000.
any ideas are welcome. best regards Chris
5 Likes
Hi, Reprapper here: You’re calibrating steps/mm, right? If so, don’t use the archaic method of printing a piece, measuring the dimensions, and calculating the difference. Instead (for the XYZ axes specifically, not for E) do some math and calculate the exact number for steps/mm, then calibrate your E so that with the new steps/mm for XYZ the parts come out with the proper dimensions. If you don’t want to do math you can use the Prusa Calculator here: RepRap Calculator - Original Prusa 3D Printers The most common Prusa i3 setup I see is 20t GT2 belts for the X and Y axes, M5 threaded rods for the Z axis, and 1.8 degree steppers and 1/16 microstepping for all axes. If that’s what you have, I can go ahead and tell you your steps/mm for {x, y, z} should be {80, 80, 4000}. Hope this helped, -Karl
1 Like
The steps per mm equation is (what we asked for / what we got) * current steps per mm
To get “rounder circles” go ahead and tighten your belts
Sorry, but I’m going to have to disagree here. That equation is rather archaic, and the inherent problem with it is that it attempts to compensate for the extruder steps/mm by calibrating the motion, which isn’t ideal. It also works for only the size that you initially calibrated it at, and as your parts get larger or smaller than that size the error will start to grow.
What someone should instead be doing is calibrating the motion first, then calibrating steps/mm for the extruder to give proper parts with the finished motion calibration. I already detailed this in my earlier comment.
kockan
5
Hi,
Calibration is easy no the i3,you need to change your steps per mm. To get the needed steps per mm you have to measure how big the diffrence is beatwean the required and the measured. If you have a lcd go in to the menu and click on prepare.Use a marker to mark your start point. Go to the “move axis” menu and move the x axis 100mm. Mark the end point. Measure the distance that the extruder has traveled.
If it did not travel 100mm divide the 100mm with the measured distance. 100/(measured distance in mm)=x. Multiply x with the steps per mm in the fw. x*(steps per mm). Change the steps per mm until you measure 100mm, do this for all three axis. You should do this for the e axis too but I dont know if you have a bowden setup or a direct drive. If you have the direct drive you will have to take apart your extruder
extruder i direct drive. with pic to help thnk yo all
Hi Karl , thank you, tried 80 setup but whole print can out 2 3rds size and shifted whole print to left edge of y axis. so keeping it around 100 for now as base figure.
Remember, I said 80 only works if you have that specific setup. Since your value of 100 works, I’m guessing you have 16t pulleys instead. In that case, don’t just use 100 as your base value: set it as 100 and leave it alone, then calibrate the extruder to get the proper dimensions.
kockan
9
Have you tried calibrating the steps as I have instructed you?
Not all repraps have the same configuration.
Here a copy of mine
#define DEFAULT_AXIS_STEPS_PER_UNIT {67.38,41.13,3998,328.57} // default steps per unit for Ultimaker
bilsch
10
Chris,
you should have no changes made to the x/y/z steps per millimeter values - those are/should be constant. If you are using GT2 belts for x/y and 16-tooth with 1/16 microstepping your steps/mm are 100 ( read up RepRap Calculator - Original Prusa 3D Printers ). If you are printing a circle pattern and not getting consistent dimensions ( even if you over/under-shoot ) you have a few other things going on - most likely not a level bed or too much variance in your filament.
Go read through http://reprap.org/wiki/Triffid\_Hunter’s\_Calibration\_Guide and follow the guide. Once you finish it once, do it again 
hope that helps.
1 Like
if you want 140 [mm] square and print 139.5 [mm] square, while the reprap settings are 100 [steps/mm] your new setting should be 100.36 [steps/mm], resulting in 50 more steps and the extra 0.5mm.
Similar for both y and z axis.
Thanks to you all, am trying all mehods that you have advised, will let you know how i get on . Thanks again Chris
bilsch
13
Tim,
nope thats just wrong.
The belts and leadscrew accuracy should be close enough ( unless you have really crappy hardware ) to be within tolerances. The real issues as others have mentioned in the thread:
1) steps per mm for each axis based on hardware. Use the prusa calculator thats why he provides it!
2) tightness of the belts ( and anything else - there should be little to no play/wiggle ) and leadscrew / nut
3) esteps
I switched my X/Z chassis on my printer recently. The accuracy is just as tight was with the previous setup. All I had to change in the firmware/config was to account for tooth count of the new x config. The only pain point I had was getting the z min endstop positioned properly with the new setup - I kinda hate mechanical endstops for fine adjustment but the end result is worth it 
Other factors which can contribute to this are many. I have found the most common one with something like this - bearings and linear rail are not in parity. EG the diameter of the linear rods is crap or you have crap bearings. Look for score marks on the linear rails - if you see them you have a problem! ( Other problems: stepper current, over-heating of the driver and/or stepper, crap steppers - I’m sure there are others )
I knew the moment i hit enter, i just couldn’t find the delete entry. The calculator worked for me flawlessly.
It might be a combination between extruder-calibration (more or less plastic extruded) and stiffness/tightness of the belt.
I like to thank you all for your support, printer working great now nice models. a credit to 3d hubs, best regards Chris
