How do you accomodate for small openings?

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(Mike Miller) #1

How do you accomodate for small openings? I’m designing a cam for a Halloween prop (That being one of the main reasons for building the printer), and want to use 1/4" square rod as the shaft…only by the time the printer’s done printing, it’s nowhere near that size. Likewise, I’ve attempted to print pieces that would have a captured nut, only to have the opening swell shut due to overextrusion.

Is this a PLA thing, or a calibration thing? Or do I just design with the expectation I’m going to have to drill holes to clean it up?

(Carlton Dodd) #2

Personally, I’ve chased that ultimate setting where inside and outside dimensions are perfect many times. I end up settling for really good outside tolerance, and slightly small inside tolerance. I design for it, or just drill out holes.
That said, if you’re over-extruding, make sure you’ve calibrated your extruder steps/mm and measured your filament diameter. Between the two, I found I was over-extruding by 12% when I started!

(Andreas Thorn) #3

I’m with @Carlton_Dodd . Calibrate as much as my patience allows, with outside dimensions as priority. Then modify the design to make the holes come out right. Ah the beauty of a parametric design in OpenSCAD.

(William Frick) #4

Depending on the overall part I sometimes scale it a few percent until Goldilocks appears !

(Mike Miller) #5

It other words: It’s an inexact science. :slight_smile: The Extruder seems well calibrated, if the base layers are any indication (lines touch, upper surfaces are smooth, 10mm = 10mm, etc.)

I’m wondering if the features I’m designing are too small. If you’ve got a screw hole, and the inside diameter and outside diameters are too close together, does the slicer account for that, or does it try to shove two layers around the outside, and two layers around the inside, making for a nasty mess?

(William Frick) #6

Depending on the material you also ‘heat sink’ the nuts in using a soldering iron to press them into place.

(William Frick) #7

The extruder gear I printed for you was so close that if you were not perfectly aligned it would not accept the m3 nut and likely a press fit on the shaft.

(Wylie Hilliard) #8

The bead of filament tends to pull toward the inside of curves, depending on the radius of the curve. Maybe someday slicers will take this into account but for now you just need to increase the diameter of the holes in your model

(Andreas Thorn) #9

@Mike_Miller , also see https://plus.google.com/115941911408278491291/posts/hoWePopuA4b

(William Frick) #10

I knew @nop_head had blogged about but no time to find it. His ‘Story so far’ blog collection is a good read for those wishing to understand these finer details of how and why we got to where we are with DIY 3D printing.

(Brandon Satterfield) #11

Mike I had brought this up as well recently. No solid and conclusive answer seemed to work with my slic3r setup. I design with it in mind now. Only the insides are a concern, outside dimensions are on, and I can get very close to accurate running a single parameter, small nozzle, and uncheck “detect thin walls.”

(Mike Miller) #12

@William_Frick I don’t think I’m using a nut…just the friction fit! :slight_smile:

(Nathaniel Stenzel) #13

@Mike_Miller Perfectly calibrated extruder? I guess that means you can print the 2 piece puzzle and have the pieces fit together? That currently eludes me. That is a calibration design on Thingiverse and perhaps other places, btw.

(Mike Miller) #14

@NathanielStenzel Which one are you talking about? This one? http://www.thingiverse.com/thing:316810

(Nathaniel Stenzel) #15

@Mike_Miller http://www.thingiverse.com/thing:181115