3D Printed Threads Modelled in Fusion 360

I recently posted an idea for a 3D printed depth setting jig for use on my Myford Big Bore lathe. A couple of readers had run the STL files and struggled with the fit of the mounting boss thread (M35 x 1.5) that mates with the thread on the end of the lathe spindle. This is a known problem with 3D printed threads where the accuracy of the 3D printer and the size of the thread being printed can interact and have an impact.

Fusion 360 does not have a tolerance tweak in the thread creation tool. This is not a problem in that you can use the Face Offset tool to adjust the thread geometry. This does not take long to do. The process also allows you to add fillets to the thread peaks so they are less aggressively ‘sharp’ and therefore more likely to survive longer.

Select the Inspect/Section Analysis to view the cross section of the thread to be adjusted. Choose any axis for this. Manipulate the view so you can see the cross section face and the around to the side of the 3D model. Do the tweaks shown below by selecting the appropriate faces of the thread and making an Offset Face adjustment and then adding a chamfer. The difference is very minor but it makes the thread less ‘sharp’ and aggressive to its mating half which is likely to be a metal component. If you are working with a modelled threaded hole rather than a rod then the changes are the same. The values shown are nominal and will change with the modelled thread size. If you overdue the offset the thread will become very sloppy.

The only tricky part is Manipulating the view in Fusion to allow the appropriate face selection otherwise the Offset command is straightforward.

To a degree some of this could be achieved in your 3D slicer but adjustments would become global rather than specific to just the thread geometry.

If you want a more detailed explanation then I suggest you watch Kevin’s post on Product Design Online.

I have modified the geometry of the Depth Setting boss threads to give more tolerance and reposted the STL to match on the link below.

If you have a Myford Small Bore lathe and would like to send me the bore size and end thread I can create a new version of the depth setter to match.

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The “Modern Clock” by Goodrich

I have been working on a John Wilding ‘Scroll Frame Skeleton Clock’ which has been somewhat entertaining. Getting the clock in beat has caused some frustration. The pendulum crutch is elbow hinged to allow the beat to be adjusted but the adjuster sits behind the pendulum rod. It is easy to tweak the hinge angle but the pendulum rod then masks access to the tightening screw. In the end I resorted to getting the beat somewhere near and then fine adjusting it using the levelling adjuster feet on the base. It now seems to be running nicely, the beat sounds strong and timekeeping is looking good so far. As shown below I’ve got the light sensor of the Microset Timer on it at the moment so we’ll see how well it performs long term.

To revert back to the post title, John Wilding’s book on this particular skeleton clock makes reference to two books as being worthy of any clockie bookshelf – Britten’s ‘Clock and Watchmaker’s Handbook’ and ‘The Modern Clock’ by Goodrich. The latter is a bit of misnomer in that it was published in 1905 but it is a very detailed book and worth a read.

Not having either of these books I did a search. The Britten book is available from Amazon. The Goodrich book is available as a free download from the Gutenberg library. The download is possible in various digital formats, one of which is EPUB3 which is Kindle friendly.

To load third party documents into your Kindle you have to email the document as an attachment to your personal Kindle upload email address. This address can be found in the Settings section of your Kindle. I use this quite regularly to store interesting documents such as technical PDFs. I now have quite a collection of personal and third party techie documents stored alongside John Le Carre, Gerald Seymour and others. You never know when you are going to be bored while sitting on a beach and in need of some technical stimulation.

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Streaming camera video from an Arduino Giga

A close friend has been trying to get a video feed from an Arduino so he can make astronomical observations from a gizmo he has made that will sit in the garden and observe the video in the house over USB.

We tried various methods including using the Processing app but did not have any success. The release of the Arduino Giga with Display Shield and onboard plug in camera (OV7675) has changed things. Using these integrated modules with the OpenMV application produces good quality video over the USB connection. An image of the Giga from the Arduino website is shown below.

There is a write up on using OpenMV on the Arduino forum. This is easy to follow and works very well. If I understand it correctly OpenMV loads specific firmware into the Giga rather than an Arduino based code uploaded in the normal way.

There are a few minor things to watch out for. The Giga seems to like a double reset to clear out any existing code before loading the OpenMV code. Likewise when reverting the Giga back for Arduino use you must also do a double reset.

As mentioned in the article you need to load the display.py demo example code but the demos are not available for selection until OpenMV detects the board in use. Once the boards is detected you will get details on the bottom status bar.

The other minor thing that is not immediately obvious …. if the video and the histograms are not present on the right hand side of the screen you need to drag them into view using the side arrow.

Here is a screen shot showing the code on the left hand side and the video feed and histograms on the right hand side,

The Arduino Giga is a very sophisticated module and the various example sketches that are available to run on it are impressive. It will certainly stretch my ‘cut and paste’ coding….

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