This write up is a bit off piste to my usual engineering activities. With present social distancing in place because of CoronaVirus and the resulting shortages of some fresh vegetable foods in the shops, it has never been a better time to grow your own.
Spring time view of the vegetable plot
For a number of years I have cultivated a veg plot and it is now quite mature. Along the way it has become formalised and as a result it rolls along from year to year without really needing much thinking about. The only problem in recent years is we are quite often in France when produce reaches peak availability. Our house sitters therefore reap most of the benefit.
I had been using Hall Effect devices to modify my William Smith Gearless Gravity Arm clock and had been surprised by their ease of use and repeatable trip points. (More about this to follow in a separate post).
I had also been frustrated with my inability to set tool heights reliably in PathPilot despite using various methods all of which didn’t want to agree with each other.
This resulted in the construction of a Hall Effect based Tool Height Setter that appears to solve the problem. The write up is lengthy so I have committed it to PDF for download but here are a couple of images to give you an idea of the result.
A simple cross section sketch of the tool height setter concept using a Hall Effect sensor
Finished tool height sensor mounted on the PCNC440 milling table
Lots of activity to be documented and posted but let’s start off with a short note. Not earth shattering but might help someone somewhere.
I had the bright idea of using Micro USBs as a connecting medium on a couple of projects. This was driven by the need for a 5 wire connection. The design was finished and I dug out the Micro USB to Micro USB cable that had been bought in for the project and connected things together. All the LEDs went out on my project circuit board. Gloom.
After buzzing the cable through I found that on a standard Micro USB cable the Sense pin is linked to the Ground pin. There are not 5 independent and isolated cores as you would expect. Just four. What to do ?
By chance I had some Micro USB connector ends with solder tabs but no shells. I did not have any flexible small diameter cable with 5 cores. After some discussions with my other half she offered to plait 5 independent cables together for me as a cable form. These were soldered to the Micro USB ends. Two small end caps were quickly designed in Fusion 360 and took 10 minutes to print on the 3D printer. Job complete and project back up and running.
Custom Micro USB 5 core cable components showing solder terminal end connectors, 3D printed shell and plaited 5 core cable courtesy of my wife.
While I have been quiet for the last month or so there has been some intensive work by Dave and myself on FlatCAM. We are in the throes of doing a formal document to help others get to grips with the process and techniques for milling circuit boards.
I need to also put my hand up and admit going over to yet another dark side by experimenting with Arduino technology. This came about as a follow on to the work on silencing my Bill Smith Gravity Arm Gearless Clock. With the help of another colleague we have replaced the discrete timer logic board with an Arduino. I have learned quite a bit in the process and more details will follow.
Finally like many others round the world, myself and my wife are socially distancing ourselves at the moment but every cloud has a silver lining and this does mean I am spending even more time in the workshop doing ‘stuff’. It has also been a good time to look at the workshop and make plans to tidy, organise and structure things better. Some of the accumulated odds and ends are getting sifted and sorted and binned as appropriate.
Previously on Woody’s Workshop … I had spent time trying to get a consistently level PCB blank clamped to the tooling table ready to mill the traces using CNC. The results were not too bad but being anally fussy it left a bit to be desired, particularly if the board had a large area which magnified the variations.
Any variation of the level of the PCB top surface will produce variable width cuts when using a V shaped cutter. I had machined a clamping plate which was a simple open frame with a clamping step equal to the PCB thickness (1.6mm) and a sheet of MDF or hardboard as a sacrificial backing board.
Despite having more clamping screw holes than a magazine burst from an AK47 I still ended with the corners of the PCB being a few thou lower. Results were shall we say ‘variable’. I had reason to run a new prototype board this week and once again hit the same frustration. In the end it was a sit and look at it and have a think session.
The resulting revelation was maybe the sharp edges on the step are applying too much pressure ? What if I were to be more gentle with the clamping ?
I cut some strips of thin foam rubber and put this into the step such as to push down on the PCB. As a quick test I only fastened the frame down using the four corner holes.
Sketches showing the two methods of clamping the printed circuit board ready for CNC milling
Absolute magic. The PCB surface hardly moved the Hamer needle at any point on the surface. Milling result was an artwork to be proud of.
Issues – the current step on the clamping frame is meant to clamp to a hard stop based on the sum of the PCB thickness and the sacrificial material thickness. Adding the foam meant I had to do away with the sacrificial board. The frame step therefore needs to be deeper. The sacrificial material is essential to allow drilling to take place without breaking the drill as it runs into and potentially damages the tooling table. (For the board in question I drilled to only 1mm and then over drilled by hand off line to the mill).
So a worthwhile bit of experimenting and hopefully a better result going forward
