Creating Customised Threads in Fusion 360

As ever this started off with a need and from the need came some learning.  In my experience such needs are always welcome for the resulting learning benefit but inevitably lead to a few hours of frustration.

We have a small Jacuzzi spa at our home in France.   It has two cartridge filters that are screw mounted into the sump of the spa.   The threads on the cartridges are plastic and are loosely defined as 2” SAE spec. (I think SAE is a fine pitch thread (?) and as the filter threads are around 5mm thread to thread pitch, they don’t seem to me to be fine pitch).

When filling the spa from empty, Jacuzzi recommended that the filters are removed and the filler hosepipe nozzle is wedged into the outer vacated of the two filter holes. The nozzle has to be jammed in place by packing a cloth or sponge around it.   Filling via the filter mounting ensures the spa fills from the bottom up with minimal potential for an airlock in the pipework.

The problem with this is that the filler hose tends to have a mind of its own and when your back is turned it will liberate itself from the filter hole and whiplash round like a demented cobra and give you an unexpected bath.

After one such soaking I resolved to stop this happening.   What was needed was an adapter plug to fit into the “2” SAE” socket that would accept a standard hose push fit connector.  This would hopefully keep the rampant serpent retained during the filling process.

I opted to use a standard commercial male hose connector for the interface to the filler hosepipe. These have a DIN Pipe thread specification (G26.441 x 1.814 mm).   This left me with the need to model the 2” SAE from scratch which on inspection appeared to take the form of a pseudo Acme profile but with an asymmetric thread to valley ratio.

Having failed to find anything helpful on the Internet I set about creating a custom thread in Fusion 360. New experience ….

Here is the resulting adapter. 

The attached ZIP file below has the full write up, the STL file and the source Fusion file.

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TA12 USAF WW2 transmitter and 1938 Truphonic MA5T receiver

Like all engineers and particularly radio engineers I have a squirrel mentality heavily influenced by emotional attachment. I tend to keep stuff. This is part ‘might be useful one day’, a symptom of my ‘make do and mend’ upbringing and part not being able to bear parting with things.

This weekend is the Newbury Amateur Radio Club annual meet and sale. Together with two likeminded techies we have booked a couple of tables to offload some of our accumulated junk.

I have decided to take two items that meet the emotional attachment category. They both have a story attached that relate to how my interest in radio evolved.

The first is my maternal grandparents Truphonic MA5T domestic radio. As a family we regularly visited them at their ‘2 up – 2 down’ terraced house in York. The radio sat on their sideboard in the kitchen and it totally absorbed me as I would tune up and down the bands and fiddle with the preset station levers. Truphonic were a London based manufacturer and the MA5T was an upright version of the MA5, both of which dated around 1938. The valve line up was TH4B\TDD4\VP43\PENA4\1W3. When I wasn’t playing with their radio I was taking their torches to pieces and making circuits with light bulbs. The technical seed was sown.

The second piece for disposal is a TA12 USAF airborne transmitter as used in WW2 on board B17s etc. It runs a pair of 807s. The story around this is similar.

My radio interest had blossomed and through a contact of my father I had acquired a WW2 R1155A receiver from a radio amateur in York. I became an avid shortwave listener. Wire antennas festooned the back garden and I spent hours with headphones clamped to my head searching for signals from round the globe.

Those familiar with the R1155A will know that its short wave coverage begins at around 3MHz and completely misses the 1.8MHz to 2MHz amateur band known as Top Band. If you were lucky enough to own a R1155N this band was covered but the N model was much less common being used mainly for marine comms rather than bomber command.

However as a family we had a Pilot Blue Peter domestic radio which covered LW/MW and SW frequencies. Unusually it had continuous coverage across these bands. This meant it covered Top Band. This was somewhat unusual for a domestic radio. Occasionally I would switch it on and tune around and one night happened upon a very strong amateur signal on Top Band. Given that the Pilot had little or no antenna connected the transmission had to be local. This was my first contact with Alf Whitelock whose callsign was G3BNM. He was indeed local and lived in Alne which was around 9 miles away.

This was the start of a long and close relationship with Alf. He took me under his wing and taught me so much about radio both operating and building. He was regularly on Top Band with his nephew John G3WQM and Ted G3TNM. Alf ran a pseudo crossband duplex transmission retransmitting the incoming audio from John (4m) and Ted (2m) and so all three of them and anyone listening to Alf could hear everyone talking.

Alf helped me improve my R1155 with external pre-amps and converters so I had full coverage of all the amateur short wave bands. I would regularly bike to and from Alne and would always struggle on the return journey with so many donated radio parts strapped to my bike.

Alf was not young and inevitably he died when I was in my late teens. I was devastated. I felt like I had lost a very special adopted grandfather. He left me his HF station. It was a 6 foot high rack with huge power supplies, modulators and antenna tuner. The heart of the station was the TA12 airborne transmitter. While all the other components have long since gone, I could not bear to part with the TA12 and it has remained with me now for over 50 years. He voice came to me via this radio and it has a very emotional connection.

So what to do ? Two items of huge sentimental value that is personal only to me. My kids don’t care for granddad’s weird hobbies and my accumulated ‘junk’. On my passing both these radios will go to landfill or similar. Taking them to the Newbury event might stir some interest with a historic preservation body. I can then rest knowing that these two radios have moved on and will have an extended life.

But maybe I’m just hoping that nobody shows any interest and I can bring them back home and put them back in the attic for a few more years …..

UPDATE : Both the TA12 and the MA5T sold. Both went to heritage radio collectors. The buyer of the MA5T said he had never seen this particular model and thought it very rare. He was looking forward to restoring it. Result.

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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 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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