Designing for 3D Printing – Making useful things – Part 1

I’m starting a series of articles and accompanying videos on designing for 3D printing, using 123D Design as a starting point.  As I learn more about other software such as Solidworks, I’ll try to pass that info along.

Disclaimer:  I’m not an expert, I just figure things out and make notes here on my blog.  If those notes help you that’s great!  If I make mistakes or you know of shortcuts that I could benefit from, please leave me a comment!

This first article will discuss how to make a small simple part for a 3D printer project: A nut!  Yep, a simple nut, but this nut is for aluminum extrusion!

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A good 3D printer design emphasizes a solid frame as its foundation.  Some good inexpensive material for this is called Aluminum Extrusion.  A really good supplier for this material and many accessories is http://www.misumiusa.com. Another fine distributor is 80/20, Inc. http://www.8020.net

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As you can see in the above image there are slots on all four edges.  Special nuts are made to fit inside these slots.  But sometimes you need a few extra, or just want to do some quick and dirty prototyping.

In this article, I’m going to show you how to make a nut that will fit inside this profile.  Some extrusion profiles are small enough that you can just use a regular metric or SAE nut and slide it in and tighten it.  However, with the larger extrusions, the slot is too big and the nut won’t seat properly or you will have to use a really big bolt.  The nut we’re going to make is called a pre-assembly nut:

preassemnut

 

On Misumi’s website, they provide a great amount of details and dimensions to help us decide which part to pick.dimensions

It’s difficult to know which way is up with these things and our dimensions can get confusing.  The way the nut fits into the extrusion should help us:

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I’m going to call 6.3 the width, 15 the length, and 14 the height, because that is basically how it will load into 123D Design.

In the above image you can see the dimensions for our part.  I will note these here for reference later:

Width:  6.3 mm
Length: 15 mm
Height: 14 mm

You can use the product configuration tool to order parts and download 2D/3D cad drawings of certain parts.  However, for the nuts you can only download the 2D profiles.

Misumi Part Config Tool

nutconfig

Now that I’ve made my choices, I’m going to download the 2D cad file.  Here is the file that I downloaded if you want to follow along. Here is the part profile that I downloaded. It is for the HFS6 30×30 extrusion profile.

Inside the zip file are three .DXF files.  Each has a different profile design and I’m going to use the one that gives me enough room to insert a standard M4 nut into the back of the 3D printed part so that I can tighten the screw appropriately.  The three choices for this part are:

 

nutprofile1

 

nutprofile2

nutprofile3

I picked HNTT6 because of the wider bottom (which is pointing right).  This gives me room to create a nut capture hole for the M4 nut.

Opening the .DXF files in Inkscape allows me to edit them and remove all the stuff I do not need, so that I can save it as an SVG file.

Here is what it looks like after I cleaned it up:

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I’ve selected all the parts (Control-A Windows). Then we have to click on Path, Stroke to Path then Object, Combine so that when we load it into 123D design we do not get an error message stating it could not find any valid paths.

Save the file as an .SVG on your desktop.

Now we’re ready to import it into 123D design.  Open 123D Design, the click the 123D Menu drop down to open the menu, and select Import SVG, then As Solid.

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Here is what it looks like after the import:

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Looks great!  However, you need to inspect this closely.  The file I have imported seems to have two faces.  So when I click on the top of the solid body, and move it over, this is what I see:

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You can see there is an outer shell.  So I drag the solid to the left to reveal the entire shell, then I select all of it except the solid and hit delete.  This is easier done from the TOP view:

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Now we’re going to do some measuring.  We want to measure the length, width, and height, and we’ll need to put these somewhere so we can recall them.  I use Google Docs/Spreadsheets for this so I can do the math there as well.

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Use the measuring tool and measure from one edge to the other being careful to select just the edge and not the face.  Make sure you select furthest parallel edges to get the overall size.

As you can tell, it is wayyy too big.    So we need to scale it.  But as far as I know, 123D is not a “Parametric” design tool like Solid works.  So I haven’t really figured out the easiest way to re-size something to specific dimensions, so I’ll show you “my way”

I measured all the dimensions, and put them into Google Sheets.

I then added a formula column to show me the scale factor.  This is determined by dividing my desired dimension with the measured dimension:

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Now, I can go back to 123D Design and select my object, then select Scale, Non-Uniform, then enter the values above.  However, 123D Design only allows 3 digits to the right of the decimal, so we have to round to 3 decimals, so I added that to the sheet:

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Now we can scale it properly.  Sometimes it’s hard to know where the X, Y and Z are relating to our dimensions, so just change one and observe how it shrinks, then you’ll know.

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After we’ve scaled it, we can re-measure each dimension to see how close we got.

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My end results were 6.322, 15.008 and 14.00.  These are totally acceptable!

Now we need to make a hole for our screw and a nut socket.

You should use some inexpensive digital calipers to do your measuring.  Here I am measuring the diameter of the nut.

PLEASE NOTE:  I didn’t have any M4 Nuts!!!  Argh, so I had to use an SAE nut that was approximately the same size.  The dimensions below should work as well for M4.

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We’ll need a cylinder about 4.2 mm in diameter for our M4 screw, so we’ll enter 2.1mm for the radius.  Note, we’re making the hole for the screw, not the nut.  Drag the cylinder around until it “snaps” to the center, and enter your dimension of 2.1 for the radius and 20 for the height:

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Next we need to position to make the face of our cylinder and the face of our shape to be flush:

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Now at this point we could “cut” the cylinder from the shape leaving a hole, but let’s add our polygon first.  Use the Draw Polygon tool:

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We want to “snap” the polygon to the center of the cylinder:

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The diameter of an M4 nut is 9.45 mm, so we need to divide that by 2 and give it a little extra, so we’ll go with 4.75 which will come out to 9.5mm.  We need 6 sides for our polygon.

Now let’s extrude our polygon into the object and that will create a 6 sided hole:

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The nut is 3.2 mm thick so we’ll enter that as our depth:

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Now we can delete the sketch that was left behind:

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And lastly, we can cut the cylinder from our shape and we’re done!

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Now let’s print it, and see how it fits!

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Perfect!

In my next post, I’ll show you how to take an STL file, and convert it to a 123D Design object that you can edit!  Stay tuned!

 

 

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