Issue with Preform


#1

I’ve come up with a new issue with Preform. Unwanted solid between pieces.

In the STL file and in the Preform screen there is not solid between 6 small parts that are a group STL file. But, when printed there is a solid structure between the parts that can’t be easily removed. The parts within the group STL file are more than apple in distance between each other. I have many other such parts that are done the same way and don’t have this added structure.

This is not a support, those are all accounted for. It’s added evidently when the Preform file is sent to the printer as is shows nowhere else.

Anyone run into a problem like this?


#2

Are the parts really close together?


#3

Here’s a photo of the printed item. The two on in the front are very similar and spaced apart the same. The one on the right is the one with the issue, one on the left printed perfect. There were printed one right behind the other. Not the pile of scrap parts in the back as I print 360 at a time. These are for 3/64" stryene rod. I did a complete set of 7 different parts smaller for 1/32" rod.


#4

When loading the stl does the new PreForm want to do a repair? If so then did you try bringing in an obj of the model rather than stl.

Just wondering if it might be a model repair tweak that might be causing the troubles in some models.


#5

Yes, it does ask to repair when the STL file is opened. But, there is no connection between items on the build. I use this same file for 4 different scales of the elbow. None of the others have this issue. Also, I do 7 different fittings in this scale all with the parts close together and no issues.

I went in and spaced them further apart and ran the job again with the same results.

I’ll give the OBJ file a test. Also might test and see if not repairing has any effect.

Thanks for the input Ken.


#6

That looks exactly like a solidity corruption. That is, like it or not there are a couple of points in your otherwise perfectly solid model that are SO close together that when you scale them down, the two points get ‘averaged’ to the same location in space- resulting in line segments with zero length and two points in the same space.
I have seen lots of errors like this over the years due to simple scaling down or up in an app that has a spatial resolution set too low.
That is- if two points are only 0.0015 mm apart- and your modeling space has a detail level of 0.001- then scaling that file down by 10% will result in those two points being averaged to the same coordinate.
No modeling space can juggle potentially infinite decimal places in its cartesian space- so every point in space is averaged to a certain number of decimal places.

On import- chances are that Preform ‘sees’ one or both of these as a hole and the point gets connected to some other point on the far side of the model that has an unconnected point.

The problem is- Preform does not generally RENDER these kinds of bridges caused by unattached points.
they show up in the print… but not onscreen-

If this is the cause, then you might want to try decimating your model before scaling it. I don’t know what resolution limit Preform is set to- but given that the printer can only deal with 25 micron layers- its likely not juggling a lot of decimal places when it coverts the model to printer profiles.

if its happening on import into preform or you are doing the scaling in Preform, once it has made this change to the model, scaling that changed model back up will result in the flaw scaling up, too. You will need to trash all the models that are printing like this at any scale.


#7

When exporting an obj make sure you use all triangles. Quads may not parse well in Preform and N-sided will generate cross faces over openings.

I have better luck with obj into preform than I do with stl.


#8

Easy enough to rework the 3D CAD drawing in that scale. I’ll do that later today.

Thanks for the input.


#9

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