Re-scaling the printer output from the source file

JoeMickley

For reasons unclear I am having a problem getting a finished part to come out to the same size as the source. The problem is showing up in the X axis only. The error is about 2.5%. Is there any way to have Repetier re-scale a single axis by a percentage?

Where is the resolution (steps per unit of distance in the part) being decided/stored? Yes, this is a hack. I have gone thru the printer H/W several times and am not finding anything that looks abnormal. I will freely admit that with a stepper drive and a cog belt this should NOT be possible, but it is happening, so I am forced to start looking at alternative solutions.

Repetier

Actually belt is on tension all the time and can expand over time a bit which can change x or y resolution. If x is alwazs 2.5% too wide reduce x axis steps by 2.5% and see if it fits. Or put a ruler at it for x=0 and move 200 to right. 2.5% is 5mm at that distance so if you are at 205 then it is really x resolution.

There is no compensation in server - only solution is to scale objects 97.5% in x and then slice instead, or as proposed fix printer resolution so printer moves again correctly.

JoeMickley

Can I do that scaling in Repetier ( X axis only) prior to slicing?

Repetier

Not in Repetier-Server but in Repetier-Host or in any Slicer, they all have a scale function for the original stl file.

JoeMickley

Will that work for 3DS files as well? I have a problem sourcing STL files and have moved to 3DS.

Where in Host do I find the scaling settings? I am using Cura slicer, can I find the scaling in that as well?

FYI, I opened a Gcode file to look at the locations it is feeding the printer. My test item is a 2 inch (50.8mm) disk so I can easily measure the finished item. Cura does not use arcs, so there are about a kazillion straight line segments to generate an arc. From watching the printer I can see that it is generating a layer spiraled from the inside out. I went down in the Gcode until I saw a Z increment, then looked at the locations for X and Y just before the Z jump. I found the min/max X and Y values, did the subtraction, and they are correct, so the Gcode is good.

I made up a step block with a 100mm offset. I intend to mount a small dial test indicator on the print head and check for axes accuracy. Thst should tell me if I am having mechanical positioning problems.

Repetier

I"ve never used 3ds files so can not say which slicer can read it.

> I found the min/max X and Y values, did the subtraction, and they are correct, so the Gcode is good.
Position is center of extrusion so you need to add 50% extrusion width on left and right so normally one extrusion with for outer perimeter for real width.

In cure it is the second icon on the left or mark object and press S for scale. By default is scales all axes the same so don"t forget to disable the uniform scaling checkbox.

JoeMickley

Found and used the scaling. Took me a bit to pick up on the padlock icon and unlock the axes so I could change just the one axis. (I sometimes do poorly with icons). Scaling was successful and produced an acceptable part. Thank you for your able assistance.
I am still left with the mystery of why this is happening. This may have been in the machine since the beginning. I don't often have a need to have the finished part be an exact size, so I may have never noticed it before. It is clearly only in one axis, but I am stymied as to the exact problem. My positioning measurements showed that the axis was accurate, and in fact the positioning was very slightly (average of 10 trials: 0.05mm) undersize. The parts, however, come out oversize. Further, the error is dependent on the part size in that axis. Friction in the mechanism should, (I think) produce undersize. More work needed. This just keeps getting stranger.
And so it goes ...

JoeMickley

Just a final FYI, import of 3ds works fine. Apparently, whatever warts my CAD system has in making an stl file does not carry over into making a 3ds file.
I am not positive of the following but it appears that Cura may be doing a 3ds to stl conversion prior to slicing. The log file is somewhat unclear to me, but it appears that a file named "composition0.stl" becomes the source for Cura to slice. I do not actually care as the end result (the gcode) is good but it solves my CAD export problem with stl.