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Monday, 22 September 2014 21:35

CAD the Easy Way

Getting started is often the hardest part of creating a design for a custom part. I often have customers come to me looking for a particular mechanical part that they just want tweaked a little bit. I often tell them that their best bet is to find a CAD file that's similar to what they need, and make the changes that they require. My two favorite resources for CAD files for mechanical parts are McMaster-Carr and SDP/SI. In this article, I will show you how to use these incredible free resources to jump start your project.

SDP/SI

SDI/SI is one of my favorite sources for parts for my robots. They sell a variety of mechanical drive components including bearings, gears, pulleys, and the like. Their online catalog also lets you download CAD files in a variety of formats for almost everything that they sell. From their home page, you can click the "BUY ONLINE" tab to get to their online store where the CAD drawings are located.

 

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Illustration : SDP/SI Website


For example, let's suppose we want to find the CAD drawing of a gear. Their online shop has an expandable list of items that they have for sale. First we can click on "Gears" to see the different types of gear.

 

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Illustration : Choosing a category from SDP/SI


Then under "Spur Gears", we can select "Metal".

 

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Illustration : Choosing a subcategory from SDP/SI


On the right hand pane, a list of all the metal spur gears will appear. We can click on the part number to show the details of that item.

 

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Illustration : Choosing a gear


The product details will appear in a new window. There's a link that says "AutoCAD Drawing", but this link didn't work for me. However, I was able to get the drawing via the "3D CAD Models" link.

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Illustration : SDP/SI product details page


SDP/SI wants you to register before they will let you download any CAD files. You can use your existing SDP/SI login or click the "Click here" link to create a new account. The new user registration page (not shown) is easy to fill out and doesn't require you to jump through any hoops like a confirmation e-mail before allowing you access to the CAD models.

 

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Illustration : Creating an SDP/SI account


After you register, clicking the "3D CAD Models" link will now show you a download page like the one shown below. Before you download, you need to set the file format in the drop down list, as well as any dynamic attributes for the part.

 

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Illustration : The SDP/SI download page


For most of my CAD work involving waterjet or laser cutting, a simple 2D DXF file is quite sufficient to model my final parts. This is one of the formats that SDP/SI can provide.

 

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Illustration : Getting an SDP/SI file in DXF format


This may help with rendering performance in your CAD tool. In this case, I want to get a model of the whole gear, so I enter 8 teeth for the "# of Teeth to Display on CAD Model".

 

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Illustration : SDP/SI dynamic attributes


After clicking the "Download 3D Model" button, the web page will indicate that the CAD model is being generated. When it is done, you will see a link that lets you download the CAD drawing. When you click the link, your web browser will begin downloading a ZIP archive file containing the CAD drawing.

 

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Illustration : Downloading an file from SDP/SI


Here's what the downloaded file looks like in QCad.

 

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Illustration : A downloaded file from SDP/SI


Note that this design isn't quite ready for waterjet cutting yet. If you wanted to waterjet cut this gear, you would have to delete the extra views, as well as any lines other than just the outline of the part.

McMaster-Carr

McMaster-Carr is legendary among makers. They carry nearly half a million products of every sort, including nuts and bolts, raw materials, hydraulic components, cleaning supplies, and tools, just to name a few things. If you haven't seen their website yet, take a look.

 

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Illustration : The McMaster-Carr home page


Their website does a good job helping you sort through the giant variety of stuff that they sell, but getting to a particular part might mean selecting 5 or 6 different parameters. For instance, for machine screws, you have to choose the material, head type, thread size, length, and so on. I'll spare you all of that and just choose a particular screw with McMaster-Carr part number 91241A083. To get to this part on the McMaster-Carr website, just enter the part number in the search box on the home page and click "Find".

 

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Illustration : Getting a part by part number


This will bring up the product detail page for the part, a type of socket head cap screw. You will notice that this page has a link on the left-hand side for a "Technical Drawing". (Note: this link will not be present if McMaster-Carr doesn't have a CAD drawing for the item).

 

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Illustration : The link for the CAD file


Clicking on the "Technical Drawing" link brings up a measured drawing in your browser. This is nice, but not quite a useful as a CAD file. You can click the "DOWNLOAD" link at the top of the page to select a CAD format file to download.

 

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Illustration : Download a CAD file from McMaster-Carr


In this case, I want a 2D DXF file, so I will select that and click the "SAVE" button. This starts the download process.

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Illustration : Choosing a file format on the McMaster-Carr website


Here is the drawing from McMaster-Carr as shown in QCad.

 

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Illustration : A file downloaded from McMaster-Carr


Again, files you get from other people will

Monday, 22 September 2014 21:08

SolidWorks

When using SolidWorks to design a part to be waterjet cut, you will need to create a drawing file from the part.
Let's take a look at a part designed in SolidWorks which we want to cut. The part is open in SolidWorks in the picture below.

 

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Illustration : A part in SolidWorks


To turn this into a drawing, choose File | Make Drawing from Part from the menu.

 

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Illustration : Creating a drawing


A dialog box will appear. Make sure you have un-checked the “Display sheet format” box, then click the OK button.

 

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Illustration : Removing the sheet format


The drawing sheet will appear. Drag the drawing view (1) onto the drawing (2). You will typicaly want the Top or Bottom view. You should then press the escape key or click the green checkmark to indicate that you are done adding drawing views.

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Illustration : Adding the part view (1) to the drawing (2)


You then need to make sure that the drawing scale is set correctly. Click on the drawing view within the drawing. Then choose the “Use custom scale” radio button and pick “1:1” scale from the drop down list on the panel.

 

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Illustration : Setting the part scale in the drawing


Finally, you should save the file in a format that's compatible with the waterjet cutting system. Most waterjet cutting systems accept the DXF file format. Choose File | Save As... from the menu. Pick DXF from the “Save as type” drop down list. Enter the file name and click the Save button.

 

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Illustration : Saving the drawing


At this point, you now have a file which can be used to turn your SolidWorks design into a real part.

Sunday, 21 September 2014 19:19

Exporting from 3D modeling tools

Waterjet quoting and final cutting is driven from 2D vector format files. However, many people use 3D modeling tools for their designs. Popular software packages in this category include Pro/Engineer, Sketchup, SolidWorks, Inventor, and Geomagic (Alibre). Generating an appropriate 2D file generally means going though an export process to get the correct projected version of the parts to be made.

The biggest stumbling block here is that many 3D design tools will add perspective information, such as hidden lines, to the final output. Lines in the drawing to indicate perspective simply confuse the waterjet software. Below is an example of this problem. The original design was exported as a 2D drawing from ViaCAD (though this problem is by no means unique to that package). When zoomed out, the part looks like a simple outline.

 

 

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Illustration : ViaCAD part export, zoomed out


However, when you zoom in on the upper right hand corner of the image, you can see that the software has drawn the front and back of the part in perspective, plus a middle line. The extra lines will simply confuse the waterjet software, as there is no real indication which line represents the outline to cut.

 

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Illustration : ViaCAD part export, zoomed in on the problem area

Using your favorite design software

Most graphic design and CAD software allows you to export your design into a DXF format compatible with most waterjet cutting services.
Note that DXF format is a vector file format, as opposed to a raster or pixel based file format. Vector formats allow precise creation of curves, lines and other shapes. Examples of vector based desgin software include Inkscape, Adobe Illustrator and Corel Draw.

Exporting from design software that supports vector drawing to DXF is typically a matter of choosing File | Export from the menu or File | Save As..., and then picking the DXF format.

 

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Illustration : Exporting in DXF format

If you don't yet have design software

If you are just getting started and don't yet have CAD or graphics design software, don't worry. There are many great software packages out there, all of which are free to use and are of professional quality.

1. Free vector based drawing software for Windows, Macintosh, and Linux:

Inkscape 

2. Free Computer Aided Design (CAD) software for Windows:

Solid Edge 2D

3. Open source Computer Aided Design (CAD) software for Windows, Linux, and Macintosh:

QCad or Librecad

4. Freec Computer Aided Design (CAD) software for Windows, Linux, and Macintosh:

DraftSight

5. The Big Blue Saw Designer, an online tool for Java-enabled web browsers.

 

 

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