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Dimension errors Ender-3 Pro

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David Tocher01/02/2021 14:04:52
36 forum posts
1 photos

I recently bought a Endr-3 Pro. I use the Cura slicer supplied with the printer. I make a panel to take standard electronic components but found the printed size wasn't quite right and it needed fettling.

As a test for dimensional accuracy I printed a 20mm cube with a 10mm cubic hole in the centre of the top face and a pillar 10x10y20z using PLA and the standard settings.

Using vernier calipers to measure the printed parts;

20mm cube 20.2x19.36y19.68z

10mm hole 9.82x9.2y10.1z

pillar 10.1x9.7y19.76z

Am I expecting too much from a cheap printer?

Is it usual to have to scale each axis separately?

Andrew Johnston01/02/2021 14:21:10
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6602 forum posts
701 photos

Print size is affected by a number of factors such as how the width of the nozzle divides into the X/Y dimensions. If it's not an integer then there may be errors. The smaller the dimension the more important this becomes. Also the plastic shrinks slightly after printing. If needed I scale around 0.5%, my parts are usually slightly smaller than as designed. It is normal for Z to scale differently to X/Y although unless you're chasing the last thou or so a blanket scale factor will work fine.

Andrew

David Tocher01/02/2021 18:07:13
36 forum posts
1 photos

My observed error on the y axis is about 2%, z axis about 1% but the x axis is OK. I would have expected the x and y to have similar errors. Because the filament is laid in the xy plane the z axis could behave differently as you suggested.

Journeyman01/02/2021 18:39:01
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1159 forum posts
235 photos

Don't have direct knowledge of the Ender Pro 3 but most 3D printers have fine tuning to get measurements correct. This All3D Article on calibration may help. It is also likely that there are firmware tweaks that will alter the distances travelled in X and Y these may be well buried in the on-board system and essentially tune the stepper motors. Setting the Z axis can be difficult as the layer height is pretty well fixed so everything is a multiple of this and of course the 1st layer will be slightly under height to get good bed adhesion. Z is perhaps best dealt with in the slicer (Cura) where a suitable multiplier can be applied to end up with the correct height.

3D printers are far from being plug and play and it can take quite a bit of experimentation to get things right. Of course every time you try a new filament things will change again. Just keep going it gets easier. A bit of time spent on calibration will be well worth the effort.

John

P.S. The Ender firmware is Marlin and there is definitely a multiplier function that sets the distance travelled in X and X. This can either be altered in firmware if you are into programming via Arduino or similar. Can also be added as startup g-codes to each print. Bit vague (sorry) someone who knows more will be along soon. I can remember doing this for my 1st printer (Factory3D).

Edited By Journeyman on 01/02/2021 18:54:29

Henry Brown01/02/2021 20:53:24
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552 forum posts
117 photos

Nothing scientific here but have you tried the same test with the standard Prusa slicer? I've been printing a couple of end plugs to go into the end of some 40 x 25 ali box, the Cura sliced end plug came out slightly larger and needed a little more general fettling where as the Prusa supports were a devil to get off but the dimensions were pretty much bang on using the ali as a gauge. All done at standard settings with the same filament in a warm living room.

Jeff Dayman01/02/2021 21:51:13
2225 forum posts
47 photos

One thing I found on my Ender 3 was that the Y axis belt must be very tight , and the table to crossrail bushings adjusted for zero play, or my Y dimension tolerances were off on the finished parts.

A good nozzle is also important, they do not last forever.

By far the biggest variable though is filament quality. PLA even from same maker varies a lot roll to roll and some colours print BADLY where other colours print fine. The ProPLA rather than generic PLA seems better. Not sure why, whether it is made with better resin or less fillers or ?.

I usually design part to part fits with some extra clearance so there is minimal filing and sanding. For under $300 CDN the Ender 3 has done an fantastic job for me, with minimal tweaks. However, it is not a $150,000 commercial FDM machine or a $500,000 SLA machine, and I don't expect tolerances as found in those machines from my $300 one.

Steve F01/02/2021 22:19:15
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93 forum posts
25 photos

Hello

Getting the extrusion correct can have a large effect on X Y size Dont be tempted to fiddle with X Ysteps /mm as they are fixed by the mechanics

On the Ender 3 the extrusion E step value is more than likley wrong. In Configuration/Advanced settings/Steps mm.The value for E/steps mm that relates to the extruder. It meters the filament input. I think the default value is 93. So this gives 93 steps to move 1mm of input filament. I think the value should be 99. Its easy enough to do.

Measure and mark the filament 120mm from the extruder. Heat up the hotend and tell it to extrude 100mm. Obviously there should be 20mm left. If not you need to adjust the 95 value to correct the error. You only do this once.

Next you need to calibrate the extrusion multiplier. Draw up a cube 20mm square. Tell it to print 0% infill and select say 0.8mm wall thickness. Stop the print part way through and measure the wall. It should be 0.8mm. If not you need to adjust the feed rate to get this .The default is 100% so if the wall was 0.9 you are over extruding and the value should be 0.8/0.9 X 100 = 88%. You need to do this every time you swap filament rolls to get a value for the new roll. You will end up with a value to match each roll because different filament melts and squirts differently.

I put these values in startup G code and comment out the unused values.

;M221 S100

;M221 S136 Fibrology petg

M221 S95 Colorfabb XT

Happy to talk more via PM if needed

regards

Steve

David Tocher02/02/2021 14:05:24
36 forum posts
1 photos

I looked at the belts - y axis tight as suggested but the x axis was on the loose side. I checked the extrusion setting; measured the actual extrusion at 93 steps/mm and changed it to 96.87 steps/mm.

Before going further I printed my test cubes and measured them. The x and y are now spot-on but the z is slightly low. I measured the depth of the blind hole which is again spot-on. There's a slight elephant's foot at the base of the print which is about 1.5mm high. The pillar doesn't fit the hole because the hole is 0.2mm undersize. The finish of the print is certainly better.

Thanks for all the useful suggestions.

Jeff Dayman02/02/2021 14:57:30
2225 forum posts
47 photos

Hi David, I forgot to pass along some suggestions made to me about Ender 3 Z axis, that have worked well - make sure the screw to motor shaft coupling is tightened securely, it can loosen over time, and put a drop (a drop, not a lot) of light oil on the leadscrew periodically.

Nozzle being in good shape has a big effect on Z dimension being controlled. Also can affect "elephant foot" condition.

BTW I run a glass bed (big improvement over stock bed mat) at 66 deg C bed temp, and 210-212 deg C nozzle temp seems to be best for the various PLA I run.

Edited By Jeff Dayman on 02/02/2021 14:58:08

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