Haimer Taster and vacuum table retrospective thoughts

Today while in the workshop running a CNC metalwork job and then following this with running a quick PCB artwork, the following came to mind.

These days since I bought the ITTP Hallmark probe I rarely use my Haimer Taster to do my referencing.  It still has its uses but less and less so.   A good example is when remounting the CNC vice on the tooling table. I use the Haimer to give me a running check on the vice jaw axis tracking.  Beyond that the ITTP in conjunction with PathPilot probing routines meet all my referencing needs to a level of accuracy that suits.

The other thing that stuck me is how automated my process for milling printed circuit board prototypes has become.   Fusion 360 Electrical module becomes more familiar to me with each passing project. It exports my PCB designs as Gerber files to import into FlatCAM.   After a few clicks in FlatCAM I have a GCode file for drilling and routing.   The PCB blank is gripped on my small vacuum table ready for milling and the ITTP probe references the spindle.   My recent use of kitchen anti-slip material as the sacrificial layer between PCB and vacuum table top surface has made the grip on the vacuum table so much easier to achieve.  The overall PCB process, whether single or double sided, has become quick, easy and repeatable.   Once the board is milled I can get a reasonable looking tinned finish using a hand soldering iron and copious amounts of flux.

Techniques almost subconsciously evolve and sometimes you need to step back and see how far you have come along the road.  The alternative view might be that this ‘lazy man’ has just become even more lazy.

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Dewpoint alarm monitor to help avoid rust issues in the workshop

A Dewpoint Monitor to protect the workshop

I have recently read a number of posts on workshop forums about rust degrading workshop assets.   When the temperature of the air reaches close to the dew point then the moisture in the air will condense on the cold surfaces in the workshop and moisture will inevitably lead to rust forming.

You can protect against this to some extent by ensuring that all exposed surfaces are coated with lubricant of some sort such as WD40 and only dry sources of heat are used in the workshop.   A better protection solution which was popularised by the clockmaker William Smith, is make a 50/50 mix of linseed oil and thinners and coat this on the objects needing protection.  This works well but does not last forever.

Looking around on the internet there are various Arduino projects to create a dewpoint monitor using the DTH11/DTH22 which are combined temperature and moisture probes.  Such devices, with a little bit of maths, can provide an alarm output if the dewpoint reaches close to the air temperature.   This could be used to turn on a heater and raise the air temperature and avoid moisture being deposited.  I opted to have the sensor remote via a cabled connection.

The dew point calculation I used is the Magnus-Tetens formula (Sonntag90).  This provides accurate results (with an uncertainty of 0.35°C) for temperatures ranging from -45°C to 60°C.

The dew point is calculated according to the following formula:

Ts = (bα(T,RH)) / (a – α(T,RH))

where:

Ts is the dew point;
T is the temperature;
RH is the relative humidity of the air;
a and b are coefficients.

The Sonntag90 constant values are : – –

a = 17.62 and b = 243.12°C;

and this is the final formula needed : –

α(T,RH) = ln(RH/100) + aT/(b+T).

I made a prototype using an Arduino Pro Mini as the controller and I used the above equation to calculate the dewpoint from the humidity and temperature readings input to the Arduino from the DTH22 sensor.   Once the dewpoint reaches within a defined limit of the temperature, a relay is closed to allow heaters to be turned on.   This trip point also causes the LCD display flash to warn that a trip point has been reached.

The working circuit was drawn in Fusion Electrical and a printed circuit board layout was created.   Fusion’s Electrical CAM output as Gerber and Epsilon files were converted in FlatCAM to CNC GCode.  The CNC files were than posted to my Tormach PCNC440 to mill the copper traces.

I designed the PCB using through hole components to make assembly easier for my more mature eyesight.

The trigger output from the PCB can feed any 5V coil relay that is rated with contacts capable of feeding the AC voltage and current needed for the heaters.  

Humidity Monitor and Heater Controller write up

UPDATE 18/12/2021

Due to demand I have ordered a small quantity of offshore manufactured PCBs for the Dewpoint Monitor.  If you are interested in one then send me an email as per address below.  First come first serve.

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    Vacuum table update for PCB milling

    I have mentioned in the past my home made vacuum plate for holding printed circuit board material flat while milling the copper trackwork.   As a technique this works really well and the results are very consistent using 5 and 10 thou miniature milling cutters from Think and Tinker.

    When the artwork design needs holes drilling through the PCB material, care has to be taken not to drill through into the aluminium surface of the vacuum table.  To protect the carbide drills and the surface of the vacuum table I use a sheet of 3mm MDF underneath the PCB material to act as a sacrificial  board .  While the MDF is ‘transparent’ to the vacuum suction it does degrade the downward vacuum grip and this has always been a frustration.   If the board does not need through holes then the MDF is not required.

    My wife uses an anti-slip perforated rubber sheet on the kitchen sink draining surface.   This is very flexible and looks like a weird cobweb of holes.   It struck me that this could be used as a sacrificial sheet between the PCB material and the vacuum table surface.   The rubbery material is not perfectly flat but is very easily compressed to become consistently flat over a large area.

    I begged a sheet of the material from the kitchen ‘sub stores’ and mounted it on the vacuum table with the PCB on top.   I measured the overall depth of the PCB and the mat under vacuum compression to be circa 80 thou and I usually set the depth of cut for drilling to 68 thou.  This looked like it should leave a safety margin to avoid damage to the drilling tool and the vacuum table surface.

    Using anti slip rubber sheet as a sacrificial spacer
    The rubber mat in place on the vacuum table

    The idea worked a treat.   The PCB was very rigidly clamped  in place and no damage was done to the drill bits or the vacuum plate.  Here is an image of the first board being run using this backing material technique.

    Test PCB being milled using the rubber sacrificial mat
    Test PCB being milled using the rubber sacrificial mat instead of MDF

    This looks like a step forward in my PCB milling process and has the added advantage that the rubber sheet can be hand washed afterwards and re-used.

    Anyone needing some 3mm MDF ?

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    Update on CNC milling printed circuit boards on a homemade vacuum table

    Update to the use of FlatCAM to mill PCBs

    There are quite a few entries on my blog regarding using FlatCAM to convert PCB design software manufacturing files into CNC code.   I also have mentioned my small home made vacuum table and a floating foot compression device both for holding the PCB blank flat while the milling takes place.

    I have revised my original write up to focus on FlatCAM version 8.991 and also pulled together notes on these other techniques.   If you like it let me know.  If there are mistakes also let me know.

    FlatCAM and milling pcbs updated notes 2021

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    Floating pressure foot for the CNCEST3040T mini milling machine

    A new idea for keeping PCB material flat while milling artworks

    The vacuum plate mentioned elsewhere on my blog serves me well when milling printed circuit boards on the Tormach PCNC440.   It keeps the PCB material flat and makes the cut widths repeatable when using V cutters.

    The plate cannot be easily used on my CNCEST3040 due to the restricted Z height.   We have experimented with various techniques to keep the PCB material clamped flat on the smaller mill with varying degrees of success.

    Idle hands and brain during social distancing has produced a possible solution that might be of interest and stimulation to others.   It consists of a circular pressure ring that sits around the spindle chuck and tool.   There is a second ring that sits on the spindle body connected to the lower ring with rods which have coaxial springs pushing down on the lower ring.   The magic is to use mini ball transfer units on the lower ring to press down on the PCB and glide friction free around the PCB as the cutter does its stuff.  The assembly is held in place on the spindle with 3 gripping screws.   The downward pressure is adjusted by 3 screws that press against the spindle mounting frame.

    The ball transfer units come in all sizes and are very common in baggage handling systems at airports and in industrial conveyor systems.  The ones I used came from RS and have a 4.8mm ball and a M2 mounting shank

    The prototype was made using 3D printed rings.   There is an image below.  Apologies for the yellow PLA but finding any PLA at a decent price is very difficult in the present circumstances.

    Bottom view of pressure foot for CNCEST3040
    A view of the underside of the lower ring and the four ball transfer units. In the background is the upper ring that sits around the spindle with the pressure adjusting screws and the spindle gripping screws.
    Pressure foot for the CNCEST3040 in place on the spindle
    View of the pressure foot in place on the spindle showing the tension adjusting screws and spindle grip screws

    The idea seems to work and has produced some good consistent quality PCB prints.   It does have disadvantages in that you need to have a larger PCB blank to allow for the larger footprint of the pressure ring.   It is probably only of practical use for PCB milling but then the problem of flatness is less critical in drilling the board and routing the profile.

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