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Fusion360 stl file problem

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Hi,

 

I started by using Sketchup but quickly learned that it is not ideal for 3d prints.

I have now spent some time learning the basics of Fusion360.

It is very impressive, but I now ran into an unexpected problem.

My idea was to print a gauge block that would allow me to check the precision of holes printed in various objects.

I drew a block with one row of holes starting from 2.8 mm to 3.5 mm and one row going from 4.8 to 5.5 mm

I attached a copy of the stl file.

Nominal 3 & 5 mm holes are in the framed section.

When printing this the quality deteriorates badly towards one end of the print.

The end where the numbers 3 and 5 are printed comes out reasonably fine, but at the other end it becomes more of a topographical map of the rocky mountains.

Very rough and the printing nozzle snags on the hilltops during travel.

I have tried to adjust the resolution of the export from Fusion 360 and tried binary and ASCII file formats but no difference.

I also tried to reorient the printout to see if there was a mechanical problem with the printer in that area, but the problem occurs at the same location of the print every time. 

I use Cura 3.2.1 to slice and a CR10 printer.

Any ideas why this goes wrong.

I am not worried about this particular item, but understanding what the cause is might help in more serious applications 

I have printed several other objects drawn with F360 with great success, and by the way, the holes printed with very good accuracy.

 

Gauge.stl

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I think you would best post a couple of photos of the print, both a general overview, and close-ups. Anyway, expect the holes to become smaller than designed, due to the elasticity of the molten material when the nozzle draws the outline of the holes: it is pulled inwards. Just like a rubber band would be pulled inwards, if you try to lay it down in a circle and apply a bit of force to it. The smaller the hole, the worse this effect is. So, a 3mm hole is likely to end up as a 2 to 2.5mm hole.

 

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This seems to be a bit like when you have a problem with your car and bring it to a garage.

Once the mechanic is there the car works perfectly fine.

I had made 6-7 attempts to print this with disastrous result.

They were all binned, so to get a sample to take some photos from I tried printing again, and it came out fine!

The only change I had made between the files was that I had added a 2 mm fillet to the top edge around the block.

Hard to see how that could make any difference.

Holes did come out better than expected.

A 3 mm precision steel shaft has a press fit in the 3 mm hole and a float fit in the 3.1 mm hole.

 

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I've checked the file in Cura, and looked at the mesh in Fusion 360, and there doesn't seem to be anything wrong with either that would explain why you would get a problem at one end.  The mesh is very consistent across the whole of the top surface, adding the fillets would have introduced more polygons but I wouldn't expect that to have made the improvement that you saw.

If you got that level of accuracy on your final print then you have a very good machine, usually to get a press fit you need to add a compensation of around 0.2mm to the true size, and a float fit usually needs around a 0.3mm - 0.4mm compensation.

If you experience the problem again be sure to re-post so we can see why this is happening.   

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