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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Experiences and understanding FlatCAM PCB milling program

FlatCAM Write Up – Experiences and Procedures

After a lot of editing I think the attached document will give an in depth understanding of how to use FlatCAM based on Version 8.5.   The document is based on our experiences and a steep learning curve.  We now have a repeatable process for milling PCBs from Gerber and Excellon files exported from a PCB design package.

The document may well have mistakes and we would appreciate feedback good or bad.

Latest version is now based on FlatCAM v8.991

FlatCAM v8.991 and milling pcbs 2021

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Supply, IC2 and USB connections over CAT5 connection

CAT5 Breakout Board

One of our group of ‘silver experimenters’ is building an Arduino based celestial camera tracker.   This will be deployed in the garden and he needed all control to be routed back inside the house.   The garden installation consists of a USB webcam mounted on a servo controlled platform all powered by 12V DC.

We pondered long on how we might remotely connect to the garden.  The crucial thought was that the Arduino servo board was a two wire interface using the I2C format data exchange.   Given that the USB needed four wires and the DC supply two wires we had a need for an eight core cable connection.  It seemed like a length of CAT5 cable would do the job and we could elegantly use standard CAT5 sockets.

The PCB was designed in Design Spark and milled on the Tormach PCNC440 using FlatCAM.

There is a problem with running USB over more than 5m but I did some tests at 10m and all seemed fine which should be adequate for the application.   

The breakout boards had a male and female USB connector fitted and the connections had to ‘cross over’ on one of the breakout boards to maintain continuity.   We also paired the Data + and Data – connections with the +5 and Ground twisted pairs in the CAT5 so the Data + and Data – were not twinned together.

Nothing technically magic but a simple solution to a project need.

CAT5 breakout board for USB, I2C and DC supply
CAT5 breakout boards for USB, I2C and DC supply

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