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Hey guys, I could not find much information on this in the forum so I thought I would ask. I have ALWAYS had issues with my hole sizes being two small. My linear dimensions are spot on, but my hole diameters are ways off.
I came across this interesting write up
http://hydraraptor.blogspot.com/2011/02/polyholes.html

My question is do most folks here suffer the same fate? Are there solutions out there besides enlarging the holes prior to printing?

Yep, I cop it all the time.

If I have holes that need tight tolerance to fit other things, I usually leave the CAD dimension the same but run 'em with 4 perimeter layers to get the edging nice and thick, then go through the hole with a ream or even a drill bit after the print to get them right.

If I can't do that (because of the length or positioning of the hole) I do a test object prior to the main print containing holes of each size in the model, measure the actual cooled/printed hole diameter, correct in the main model, rinse and repeat until I get what I need.

It's a bit of a pain.

Yeah, I pretty much do the same thing. But it is getting old. There should be a way to get true hole sizes.

aerouta wrote:Yeah, I pretty much do the same thing. But it is getting old. There should be a way to get true hole sizes.

Have you tried a different slicer?

It's not a function of the slicer, it's a side-effect of the FDM printing process. Hydraraptor's write up covers it pretty well.

g.

aerouta wrote:I have ALWAYS had issues with my hole sizes being two small. My linear dimensions are spot on, but my hole diameters are ways off.

Other than the write-up you quoted explaining things very well, I have to note though that the symptoms you describe are also symptoms of over-extruding if I'm not mistaken.

And on the anecdotal side of things, I recently printed this:
http://forum.seemecnc.com/viewtopic.php?f=41&t=4196

And the bits slight right in and are held in place nicely (tight fit). So I think you *can* get your printer dialed in to a point where at least the larger holes are near perfect.

Something something about Eaglezsoar's "holier" than thou attitude to slicers?

I thought it was punny.

On a more serious note, from what I've seen it's pretty consistent so printing a drill bit template and checking with verniers, calculating and tabulating the correction factors at different sizes might not be a bad idea. From then on, have one layer in your model with the "real" numbers and then offset the bore faces by the correction factor immediately prior to print on a "corrected" copy layer.

Captain Starfish wrote:Something something about Eaglezsoar's "holier" than thou attitude to slicers?

I thought it was punny.

On a more serious note, from what I've seen it's pretty consistent so printing a drill bit template and checking with verniers, calculating and tabulating the correction factors at different sizes might not be a bad idea. From then on, have one layer in your model with the "real" numbers and then offset the bore faces by the correction factor immediately prior to print on a "corrected" copy layer.

Eaglezsoar's "holier" than thou attitude to slicers?

holes

holier.

punny.

Captain Starfish wrote:holes

holier.

punny.

You are the only one finding humor in it. I will assume you meant it as a joke and we'll leave it at that.

Oh absolutely as a joke, no offence or confusion intended mate.

If undersized holes are a known issue with some standard corrections available why are some corrections not incorporated into slicers?

Captain Starfish wrote:Oh absolutely as a joke, no offence or confusion intended mate.

Okay Mate, friends forever. I would hate to drive that far anyway......

aerouta wrote:If undersized holes are a known issue with some standard corrections available why are some corrections not incorporated into slicers?

because different extrusion rates, materials, and tempatures have a large effect on the size.... experience beats the computer on this one...

True, but resizing all your models to get the correct hole size is kind of a pain and a configuration managament nightmare. Ideally you would like the change made only to the gcode rather than the actual model.

I just print with enough shells to be able to drill or ream to the proper size....

True, that is always an option assuming printing with several shells/parameters doesn't create additional problems.

If you want perfect, as-drawn holes, then go plunk down $50k+ for an SLS or STL printer. It'll never happen with the current state of the art FDM printers. It's just the nature of the beast.

g.

Figured as much: just one of the limitations.

I use the drill/ream when I can (hence 4 layer perimeters and generally a fudge factor into anything smaller than 5mm dia) and only resort to the print test / adjust to suit / print real thing sequence when I can't get a drill or ream at the hole due to the part geometry.

Sitting in the shed, boring out the "pilot holes" in the print, a thought occurs to me. Despite these manual steps required, the overall print job still takes orders of magnitude less of my time than it used to take to do the same thing using manual mill, drill, lathe and other such gear and I'm producing parts that I NEVER would have been able to achieve the old fashioned way.

Even though I can't always enjoy the convenience of pulling a finished part off the bed at the end of the print job, I'm still light years ahead of where I was a couple of months ago when I bought the Max!

Isn't it wonderful? I keep wondering where we will be five years from now as the technology progresses.
If nothing else it is a fascinating hobby.