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Goal: To learn how to create a screw driver with interchangeable bits at TechShop.


I am creating this instructable project as I go. 

At TechShop, we could use all levels of AutoDesk Product Suite.  I will be using AutoDesk Inventor Professional 2013.   I would print my prototype using Maker Bot Replicator 2 - 3D Prototype Printer. I would scale and rescale this prototype till I get the a  working prototype with optimum dimensions.

I still don't know all that I need to get this project get done.  But I have no fear to venture to the unknown areas outside my current expertise.  TechShop staff and other members are always willing to help me out when I get stuck.

Join me in my journey and let's have some fun.



Step 1: Prepare the Screw Driver Body and Hex Socket

I searched Google for "Screw Driver stl".  A lot of  related CADs were found.  But I did not find exactly what I wanted.
I signed up for a free account at GrabCAD and downloaded a part that I need to get me started.

I figured that it is best that I start with this screw bit model because it already has a Philip tip. And the hex shape already included. 

I was not concerned about the final dimension since I knowing that I could rescale my parameterized my CAD easily to optimize my design my final stage of development.  AutoDesk Constraint function also would synchronize to make a fully scalable designed part.   I hope to learn a lot of CAD work through making a usable part.

In AutoDesk Inventor, I clicked file open and selected the file type to import.  GrabCAD used .SLDPRT and .STEP.  Either format could be imported to AutoDesk Inventor.  Thank you to GrabCAD and contributor AHTAHAC for the original CAD. (see picture).

Next step is to save this original CAD as my 1st piece. 

To make my screw driver body, I created a cylinder for the screw driver body.  I created a 2nd sketch and picture the same surface to create the head extrusion to the the screw driver bit.  

To make the screw driver handle, I created another 2D sketch, select the reference plane.(perpendicular to the end surfaces.
Create the cross section shown in next picture.  Revolve this section around the center axis.  

To the experts, one could see a problem with this approach. With your indulgence, let me continue on this path for now.  I have my doubt but I choose to find out what will happen.   The resulting CAD is shown in next picture.

I saved my CAD model first.  Then I exported using CAD Drawing and selected .STL file format.  I put the .STL file to a thumb drive and brought it over to the Maker Bot Replicator 2 - 3D Prototype Printer.   I opened the Maker Bot application and drag and drop the .STL file.   I use the longest axis and scale the part on Maker Bot.  I then rotated so that handle is resting on the platform.  Then, I select Make It!    I add support option since the part is so tall and could become unstable during printing.
 

Step 2: Prepare to Print, Result and Next Step.

Printing on Maker Bot & Results:
      The head and main body fused during the build.  The shaft is too short.  The Hex hole is too small.
The Hex is clearly defined.

Next Step
      * To avoid fusion of the head to the body during printing.  We need to print the head and stem separately.  The head need to be split into two halves.   I will add 2 shaft holes perpendicular to the long axis to strengthen the glued joint.
      * We need to enlarge the Hex till the metal screw bit fit.  We also need to enlarge outside diameter of the stem proportionately. to give it similar wall thickness and strength.
      * Increase the length of the stem by an additional inch.  The depth of the Hex also increased by 1 inch.
      * The head diameter could be increased for ergonomic reason.

Stay tune for the next revision and more photos 

Thanks for viewing my instructable.

Step 3: Revision & Lessons Learned

Lessons Learned:

    * In 3D Printing, holes made are always be tiny bit smaller. Conversely, male part are always a bit bigger
    * In laser cutting, both holes and male part is smaller than actual dimension intended

    * For mating hole and stud, adjustment need to be made on either part or both. Extrusion 3D Printers are just like this

    * The Maker Bot is great for testing concept but part finished are rough compared with commercial 3D prijnter costing 10x to 100x over.

    * I also learned that it may not advisable to make too many multiple parts.  The plastics temperature could cool down just by moving through the empty spaces.  If one of the part failed and got knocked off, Maker Bot won't know and keep ejecting plastic materials and the mess random fibers keep adding up and you could get no good part at all.

     * For this screw driver split head knob, I tried to make the mirror image so I could printer 2 parts at the same time.  Later, I found it is not needed since Maker Bot could quicky duplicate part and reposition each copy on the platform.  

    * Also, don't worry about part orientation, Maker Bot can reorient them as needed. But it is still best to use the global reference frame and not slant the part at some angle

     * Remember to record all your results  The original design dimension and CAD for 3D prototype builds could vary based on the material, 3D printer and other parameters.  

    * The bit socket turn out very nice. 

     * I might have overcorrected, on the head knob so I still have a few iteration to make.  Here's the current photos

      * I am very happy with the speed of my learning.  Amicable instructors, staffs and fellow members at TechShop make my learning more fun.

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