Hole size issues
Hi - I am using Solid Edge to produce some simple parts for 3D printing. One part has a few 5.2mm diameter holes as clearance for M5 fasteners. I save to 3MF and then print on my Elegoo 2S machine. The physical dimensions of the holes are 4.8mm diameter, not 5.2mm. Not sure if this is a Solid Edge or a Prusa issue. I can deliberately make the holes larger on the SE model so they print to size, but a permanent solution would be good.
I hope someone can help.
Cheers - Simon
RE: Hole size issues
So you are using non-Prusa printer to print parts designed on non-Prusa software. Why that would be Prusa issue?
RE: Hole size issues
It's likely material shrinkage. It shrinks as it cools. This is completely normal and will vary based on the material being printed.
RE: Hole size issues
It's likely material shrinkage.
Shrinkage would make the hole bigger not smaller.
RE: Hole size issues
It's likely material shrinkage.
Shrinkage would make the hole bigger not smaller.
I don't think that's correct - shrinkage makes everything smaller, including holes.
Part of the problem may be to do with how the hole is represented in the exported file. It's probably a series of points around the circumference that are joined by straight chords. A higher resolution output may improve this, but most likely it's just something you have to take into account in the model. Print a small sample piece with holes of different sizes and then go with the one that results in the printed size you need.
RE: Hole size issues
Shrinkage always moves away from the outside towards the inside. A hole is outside of the object
RE: Hole size issues
It's likely material shrinkage.
Shrinkage would make the hole bigger not smaller.
That's not been my experience. I understand your thought process here, but I believe what happens is that the entire part shrinks including all the geometry around the home, which causes the home to shrink as well.
RE: Hole size issues
A thought experiment for you.
Imagine a block with a hole in the middle, now cut the block in half through the hole. Now shrink the block. Which way does the wall of the hole go?
It does though matter how much the shrinkage is, as if the shrinkage is very large the hole will reduce.
But in my experience printed objects only shrink a small amount and as the OP has a change of 9.2% I think shrinking is an unlikely cause, more likely it is an over extrusion or squish.
RE: Hole size issues
A thought experiment for you.
Imagine a block with a hole in the middle, now cut the block in half through the hole. Now shrink the block. Which way does the wall of the hole go?
In this thought experiment, what happens to the diameter along which you made the cut?
RE: Hole size issues
Assuming you are talking about a curved cut through the hole...
On one side the diameter increases (convex side) and the over it decreases (concave side). Shrinkage is always in the direction from air side of the cut towards the plastic side
RE: Hole size issues
No, I meant that if you make a straight cut across a diameter of the hole, what happens to the distance between the points where the cut intersects the circle. In my version of the thought experiment, since the whole shape shrinks, that distance will decrease, even though the centre of the circle has moved towards the plastic side of the cut.
RE: Hole size issues
Ok, you have two straight walls on either side of the semi-hole and a large mass behind the hole. Those walls and mass account for the majority of the object and therefore the majority of the shrinkage will be there pulling the plastic away from the semi-hole.
But as I said it depends how much shrinkage you are talking about, as if you have (say) 50% shrinkage the hole would get smaller but printed objects only shrink a small amount so the internal forces will be the dominant effect. However the 9% error the OP is getting is way too much to be accounted for by shrinkage whomever is correct.
RE: Hole size issues
I think we'll have to agree to disagree. I don't think it depends how much shrinkage there is - any shrinkage will shrink the entire geometry.
RE: Hole size issues
Oversizing the designed holes probably is the best permanent solution. Mechanical designs almost always add tolerances to allow for variations in production.
Shrinkage is a different subject altogether.
MK4S/MMU3
RE: Hole size issues
I agree with @largriff. .2mm clearance for a screw is smaller than the "tight" iso standard for shcs. Standard clearance is .8mm and if you wanted to go a little smaller .6 works well too. These standards are based on the iso standard for the permitted runout in the manufacture of the screws.
Whatever your view on shrinkage, the holes always come out smaller than they are modeled, and the more the particular plastic shrinks, the worse it is. Aka ASA holes end up smaller than in the same part printed in PLA.
That's my 2¢
RE: Hole size issues
Thanks for everyone's input here - much appreciated. For simplicity, I think I will model the hole larger in SE and assume that all holes regardless of diameter will need x% added on in the CAD model to achieve the desired finished size.
RE:
Do the (geometric) math. The design program you are using (probably) does not accept a specification for the nozzle diameter you are using, therefore the nozzle PATH will be the exact diameter of the hole you specify, in your case, 5.2mm. If you are using a 0.4mm nozzle, then it is laying down 0.2mm of plastic on both sides of this specified circle, resulting in a hole that is 0.4mm SMALLER than ideal or in your case [checks calculator] 4.8mm. This is 3D Printing/Additive Manufacturing 101, i.e., outside dimensions are larger than specified, holes/voids are smaller. Print a (specified) 5.2mm post with the same settings; it will likely measure 5.6mm.
Subtractive manufacturing (e.g., milling) is the opposite and possibly easier to visualize: Outer dimensions are SMALLER and holes/voids are LARGER than ideal/specified due to the kerf of the tool/bit.
3D printing nozzles can be considered to produce positive kerf.
This is a bigger problem with smaller holes. Do as someone else said and print a test card with many specified sizes and use the one the prints that closest to your specification.
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RE: Hole size issues
I was under the impression that the slicer takes the line width into account, such that the extruded plastic should stay within the model boundary, i.e. the nozzle path is slightly inside the boundary.
RE: Hole size issues
Not my experience, but someone smarter than me will let us know.
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RE: Hole size issues
I was under the impression that the slicer takes the line width into account, such that the extruded plastic should stay within the model boundary, i.e. the nozzle path is slightly inside the boundary.
It does.