Dimensional Accuracy  

Re: Dimensional Accuracy

Same applies for horizontal slicing. Ignoring any overlap settings for the extrusion, if you have a model which is 2mm in X direction for example and slicer does an extrusion width of 0.45mm you'll get 2/0.45 = 4.444 lines which has to be either rounded up or down and it will result in a model X dimension of either 1.8 (rounded down) or 2.25 (rounded up). Applying this to your model you have a space of (7.9-5.5)/2 = 1.2mm between exterior and hex nut wall. Slicing that at a default extrusion of 0.45mm would give you 0.45 * 3lines = 1.35mm. Therefore the hole would be approximately 0.15mm*2 = 0.3mm smaller.

That's incorrect. When moving in X and Y there is no limit on where the nozzle can go. The X-Y space is NOT divided up into "cells" defined by trace width. The slicer will, for example, take the desired outside boundary of an object, and move the center of the trace for printing that outer boundary to he desired location minus half the trace width. It uses the full available resolution of the printer to do that (in fact, the slicer doesn't even know the X, Y, Z resolution of the printer; it sends dimensions rounded to the nearest 0.001mm, and the printer itself has to round those numbers to the available resolution given by the stepper motors and the belts).

When you have an object small enough in X and Y that there is no "infill" and the part is printed entirely with Perimeters, even then the slicer tries to adjust and make the external dimensions correct by placing the outermost traces correctly and over-filling or under-filling the inner traces.

As I mentioned, I am not completely aware of the internal workings of a slicer software. However, I have done some designs which take into consideration things like extrusion width and layer heights and they usually print out more accurately than just rounded numbers. And, as far as I can tell, layer heights aren't adjusted to fit the model, but rather slice at whatever interval you set them to (again, I might be wrong or missing some settings about this).

RE: Dimensional Accuracy

@dale-d3

Hi Dale,

I am using Prusa Slicer and I cant find the console mode, is there another way to make this adjustment?

RE: Dimensional Accuracy

Hi Stephen, 

Extrusion width adjustment is an 'Advanced' option, change to 'Advanced Mode' under the 'Configuration > Mode' drop down menu in Prusa Slicer
and you will find it under the 'Print Settings > Advanced ' Menu

regards Joan

RE: Dimensional Accuracy

I am guessing you printed this object nut recess down?

If you did - elephant foot got you. Recesses will always have a little lip you may need to clean off.

Drawing the nut in with a screw works too...

RE: Dimensional Accuracy

And adding another note to the choir: what you are fighting is the basic extrusion width.  Variables are extrusion multiplier (the basic print 10mm of filament and move the motors that precise amount) and filament diameter (1.75 mm filament is a fantasy, all filament is different, and never exactly 1.75 - so you need to measure the filament and plug that average diameter into the slicer). 

Measure your filament in several places at several angles: average these and plug the result into slicer. Print a 40 mm cube in vase mode.  This will provide a wall of extrusion that should be 0.45 mm (if you use a 0.4 mm nozzle and default 0.15 mm quality profile);  measure precisely and if needed, then adjust the extrusion multiplier (0.45 / 0.47 = 0.957).

RE: Dimensional Accuracy

@joantabb

Hi Joan,

Thanks for your reply, I must apologise as my question was very poorly worded.

I am trying to understand how I can calibrate the belt on the x and y axis and I understood from the above posts that I could do this through the slicer console.

Based on you experience with pronterface is it possible to calibrate the the belts this way.

If you have a different solution I would be grateful for you experience.

Thank you in advance. 

RE: Dimensional Accuracy

Hi Stephen,

are you trying to adjust X & Y tension or X and Y travel

X and Y travel are relatively easy to check with Pronterface.

the rings on the target above become BOLD when pronterface is connected to the printer  these allow you to move the axis by fixed ammounts, measure from a fixed point on the printer to a fixed point on either X or Y axis (in direct line of movement for the axis), then move say 10mm or 100mm and re measure, the difference is the actual distance moved

I don't know of a way to adjust belt tension using pronterface

regards Joan

RE: Dimensional Accuracy

Hi Joan,

Thank you for your reply, I am trying to calibrate x and y travel so your response will assist me greatly.

Belt tension is not an issue for me and I have that covered.

Once I know the exact distance the x or y axis moves, per your reply how do I do the following per Dales post.

Print a cube of known dimensions.

In the 'console function' of your slicer, or Octoprint, execute an M503. This will retrieve your printer's settings. You're looking for Steps per unit: M92 X100.00 Y100.00 Z400.00 E140.00. Your numerical values will be different, of course.

Measure your calibration cube and execute the formula: Steps* dimension expected/dimension measured. For instance if your step value was 100 and the cube was 20mm and you measured 20.2mm, then you would calculate (20*100)/20.2. that gives you 99.01. If this was your X dimension, then you'd execute M92 X99.01, then do the same for the Y and Z axes.

After you've entered the new values, execute M500 to save them to your printer's firmware.

Can I make this change through Pronterface?

Regards Stephen

RE: Dimensional Accuracy

Shrinkage of material is also a factor to take into consideration.

I designed a case with pins of 3.2mm and holes of 3.2mm and it did not fit, and forcing the parts together just split the 3.2 mm holes which were more like 3.1mm.

Next version, the pins remained at 3.2mm and the holes were 3.3mm. It was still  tight, but the two halves went together nicely.

So whatever you design, you will probably end up doing the first assembly print twice.

It's just the nature of FDM printing.

RE: Dimensional Accuracy

Posted by: @stephen-h

Hi Joan,

Thank you for your reply, I am trying to calibrate x and y travel so your response will assist me greatly.

Belt tension is not an issue for me and I have that covered.

Once I know the exact distance the x or y axis moves, per your reply how do I do the following per Dales post.

Print a cube of known dimensions.

In the 'console function' of your slicer, or Octoprint, execute an M503. This will retrieve your printer's settings. You're looking for Steps per unit: M92 X100.00 Y100.00 Z400.00 E140.00. Your numerical values will be different, of course.

Measure your calibration cube and execute the formula: Steps* dimension expected/dimension measured. For instance if your step value was 100 and the cube was 20mm and you measured 20.2mm, then you would calculate (20*100)/20.2. that gives you 99.01. If this was your X dimension, then you'd execute M92 X99.01, then do the same for the Y and Z axes.

After you've entered the new values, execute M500 to save them to your printer's firmware.

Can I make this change through Pronterface?

Regards Stephen

 Hi Stephen, 

If you create a cube with 40mm sides. then slice and print it, the resultant cube should be in the region of 40mmx40mmx40mm
if it is wildly different there may be need to change the steps per milimeter for one of the axis...       

As mentioned by Chocki, contraction may be a problem...  but contraction should be addressed by revising the model to take account of the contraction, not modifying the steps per milimeter    

regards Joan

RE: Dimensional Accuracy

@joantabb

Thanks for your reply, I understand the issues around contraction and this is not the issue I have.

I have been printing for a number of years and still use the original Mk2, I have attached a image of my machines statistics.

Fortunately I have a job where I can print for work and my printer is constantly working, I have never bother upgrading as it does everything I need.

But at the moment I have a project which requires high accuracy, and while I have no problem making parts that fit together this new project needs another level.

I have all of the other parameters working well, I just need to squeeze the last bit out of my machine by calibrating the steps on the X and Y belt.

I am getting too old to spend much time on forums but I thought this might be the quickest way, I really need to know what software I should use to set the steps per millimetre.

I have Slicer, Cura and Pronterface, but I cant see how to do it with either of these, is there a better software.

Regards Stephen

RE: Dimensional Accuracy

To revive an old topic:

The OP got a model from thingiverse and found that the M3 nut he sourced wouldnt fit.

Not all fastener manufacturers adhere to strict ISO ANSI etc standards and the obvious answer is the creator used a nut that was not std or visa versa

The only way to check this is to open the original stl and dimension that hex, pretty sure that the print was accurate

I have a i3 MK3+ and have printed a series of cubes in PLA, 5mm, 10mm, 20mm the printer is pretty accurate in Z only 0.02mm variation, X, Y have more variation

due to the nature of FDM printing

I use my printer for practical manufacture of small parts that have to fit with other components if there is something critical I will do a series of test prints in whatever filament I'm using and either tweak the scale in the slicer or rework the CAD model to get what I need.