Interior holes in printed parts too small

[BrutalEngineer]

I have spent hours upon hours fine tuning my V1 printer. I have finally achieved good prints with ABS, but I have a problem. I am printing a 1 inch thin square with a .25 inch hole in the center in order to calibrate the scale of my prints. The outside comes out perfect. 1.000 in. The hole is 0.196 in. I am printing this in the very center of the bed. I have custom carriages, so my thinking is that the carriage offset or delta radius is off. However, everything else seems fine. Straight lines are straight, layers are consistent, etc. I don't have much time for troubleshooting with the holidays coming up, but I do have many things I need to print. Does anyone have any ideas? Any tests to figure out the issue? I am thinking I should print a 2 inch square with a 1 inch hole and see what happens. I am assuming it will be greater than 2" on the outside and the hole will be spot on. But what would that mean for my settings? Thanks!

[Jimustanguitar]

This has come up a few times before. To save you the read, all CAD programs turn circles into polygons. Your "round" hole is actually an octogon, or has 12 sides, or 24 - whatever your setting or the program's default told it to be. Take that polygon, and turn it into a triangle mesh (stl file) and you've compounded the problem.

I haven't tried anything special to fix the problem other than just making the holes in my designs bigger. Perhaps others will chime in with their experience too.

[BONE]

This has come up a few times before. To save you the read, all CAD programs turn circles into polygons. Your "round" hole is actually an octogon, or has 12 sides, or 24 - whatever your setting or the program's default told it to be. Take that polygon, and turn it into a triangle mesh (stl file) and you've compounded the problem.

I haven't tried anything special to fix the problem other than just making the holes in my designs bigger. Perhaps others will chime in with their experience too.

Yep, that's what happens. This is just one of the things you need to figure out when designing for 3D printing. Kinda similar to designing for sink rates in plastic injection parts.

[BrutalEngineer]

I am using millions of polygons for the .25 hole. I use a stratasys fortus 400 everyday at work and don't have the same issue.

[BONE]

How much more are your holes coming out undersized? Have you tried using the same file on both machines and see what the difference is?

[geneb]

Enlightenment lurks within: http://hydraraptor.blogspot.com/2011/02/polyholes.html

g.

[BrutalEngineer]

How much more are your holes coming out undersized? Have you tried using the same file on both machines and see what the difference is?

Currently my .25 hole comes out as 0.196, which is way off for having millions of polygons defining the circumference. The stratsys always prints perfect holes aside from the seam. I never adjust them in Solidworks, they just come out nominal. I also printed a 2 inch square with a 1 inch hole on the Max. Again the square was spot on, but the hole was 0.967. There went my trigonometric scaling theory.

Enlightenment lurks within: http://hydraraptor.blogspot.com/2011/02/polyholes.html

Interesting. I am going to try printing a square hole rather than a circle and see what that does. Maybe I'll flip-flop the shape entirely. Circular exterior and square interior hole. My end goal is to find/make a software fix to automatically adjust interior holes to be correct. I want this to be, you know, like a printer. Just print what is on my screen with decent dimensional accuracy!

[redoverred]

How much more are your holes coming out undersized? Have you tried using the same file on both machines and see what the difference is?

Currently my .25 hole comes out as 0.196, which is way off for having millions of polygons defining the circumference. The stratsys always prints perfect holes aside from the seam. I never adjust them in Solidworks, they just come out nominal. I also printed a 2 inch square with a 1 inch hole on the Max. Again the square was spot on, but the hole was 0.967. There went my trigonometric scaling theory.

Enlightenment lurks within: http://hydraraptor.blogspot.com/2011/02/polyholes.html :D

Interesting. I am going to try printing a square hole rather than a circle and see what that does. Maybe I'll flip-flop the shape entirely. Circular exterior and square interior hole. My end goal is to find/make a software fix to automatically adjust interior holes to be correct. I want this to be, you know, like a printer. Just print what is on my screen with decent dimensional accuracy!

Depending on your settings for the printer, your slicer could also be making the hole too small or you could be extruding more plastic causing it to become smaller. Does the rest of your print seem like you might be over-extruding? If so, then fix that right away and if not then try oversizing the holes just a tiny bit or simply drill them through after.