User:Jdittman8063/ENES-100/project 3

Continuation of project 2 on Combo Lock Pick.

Team Page: https://en.wikiversity.org/wiki/User:1sfoerster/enes100/fall2013/p3Combo

Week 1
I searched on thingiverse for a gear which could be printed on the maker bot. The goal of this gear would be to replace the second gear we have been using, to improve meshing with the primary gear from the motor. I located two designs that could potentially work with few modifications. The first gear has the correct tooth shape but has a larger number of teeth. The second has a skeltonized body which would take less material and time to print, but the wrong shape and number of teeth. Both gears have a center hole with a hex shaped section for a bolt to feed through. By inserting a nut into the hex-shaped area the gear will turn in time with the bolt and provide more positive contact when trying to turn the lock.

Here are the first and second gear designs I have considered.

The first gear design will be the focus of next week's work, as it requires only minor modification to work for our purposes. By scaling the entire gear to achieve the correct tooth size and spacing, the gears should be able to mesh correctly. At that point the code for the motor can be altered to correct for the ratio of step size to degree of turn on the motor. To determine the proper sizing of the printed gear, the number of teeth per mm must match that of the primary gear.

I already know the primary gear to have 32 teeth and a diameter of 41.75mm from previous measurements. This yields a circumference of 3.14*41.75=131.095mm and the number of mm per tooth is 131.095/32=4.0967. For the new 60 tooth gear to mesh properly it must have a circumference of 4.0967*60=245.8031mm and a diameter of 78.28mm.

Using makerware I can directly scale the size of the new gear to match the desired diameter. The next step is to verify all measurements before properly scaling and attempting to print a gear.

Week 2
This week I attempted a first printing with the Makerbot after properly scaling the above noted gear. The first couple of layers seemed to be printing correctly, but when it began to print the open sections of the gear it was discovered that the object contained inverted normals. These are areas where the object switched what were supposed to be each solid and hollow areas, resulting in solid disks being printed as opposed to the open circles. This was odd in that not all of the areas printed inverted, even though to me they all looked identical before printing. I stopped the printer after two layers with inverted normals, and proceeded to remove the slim gear section from its raft.

I then compared the printed gear to the project's primary gear to ensure that the fitment between them was correct. The two gears do mesh together correctly, showing that the above calculations for size of the gear were correct. The next step was to convert the gear file from .stl to .skb and use Google SketchUp to attempt to correct the issue with inverted normals. At the same time, other minor changes to the gear can be made, including a change to a completely flat bottom side to the gear. This will increase the ease of printing and decrease the likelihood that there will be any issues with supporting the main section of the gear while it is being printed.

Week 4
I continued to improve the google sketchup gear file by removing unnecessary lines and cleaning up the object. In the process I found a few more areas of the gear that had incomplete surfaces as well as surfaces within the gear. Removing the interior surfaces and smoothing out the exterior of the gear should eliminate issues that were evident when previewing the gear in makerware.

After cleaning up all surfaces of the gear I used the sketchup stl extension to export the file in stl format. After updating makerware on the school computer I previewed the object and looked at it layer by layer to reveal any remaining errors. While there are a few questionable areas within the preview, it does look as though the gear will be able to successfully print and should function as desired with minimal cleanup. The two main areas of concern are the odd base section which is evident in both the sketchup and stl files, and a small cross section near the top of the gear that appears in preview but not in either file up until that point. The file was then exported to an sd card to be printed on the makerbot at a later time.