Experiences CNC machining Aluminium Composite Material (ACM)

I had a recent request to machine some panels in 3mm thick ACM.   This has a polyethylene core sandwiched and bonded between two thin sheets of aluminium.   The sizes of the various panels requested could not be easily accommodated on my Tormach PCNC440 CNC mill so I had to dust off my CNCEST 3040T baby router.   Five out of the six panels would fit inside the 3040 working footprint but the sixth required me to revert to a two setup movement of the workpiece in the Y axis.  My write up of this stepping process for oversize objects can be read here.

The CNCEST 3040 has a maximum spindle speed of 10k RPM and is controlled using Mach3 with all the frustrations that brings to the party plus manual tool changes etc etc.

I received DXF drawings of the panels and these were imported into Fusion where they were simply extruded to 3mm before processing in Fusion Manufacturing.  Each CAM operation was exported as a separate function into Mach3 regardless of tool changes.  This gave me step by step control.

I used a 12mm thick MDF sacrificial (spoil) backing board to mount the panels.  As all the panels were of the same general dimensions this made mounting the panels a repeatable process using a fixed matrix of woodscrews into the MDF.  The 12mm depth of the mounting board made the tooling pin reference holes for the Y move much more rigidly fixed and as a result more repeatable to use.

The main problem encountered was that the ACM does not readily adapt to machining with conventional end mill cutters.   I tried using my stock 2 flute parts and these would skim on the top aluminium surface while the plastic underneath deformed to the Z axis increasing pressure.   Once sufficient pressure was exerted the tool would finally bite into the aluminium and punch through into the plastic with a noticeable ‘clunk’.  This played all sorts of havoc with the Z axis height referencing and also lead at one stage to the Z axis stepper coupling working lose.

The solution was to go to a single flute spiral cutter style. These were purchased from APT Tools (UK supplier).  Hot knife through butter comes to mind with the result of this change.

Single flute spiral end mill from APT Tooling UK
The single flute spiral end mill from APT Tooling UK

For straightforward hole cutting I used standard PCB carbide drill bits from Drill Services (UK supplier).  These are nice to use as all have a standard 1/8″ shank which makes tool changing a little bit easier.

Once all these frustrations were overcome the process became much more repeatable albeit with one or two curved balls due to Mach3 lock ups.  Have you ever enjoyed trying to manually re-reference a half finished job ? …..

The finished largest panel that required a two step movement in Y axis
The finished largest panel that required a two step movement in Y axis

More accumulated knowledge gained and lots of black plastic swarf (chips) to clean up before it could migrate everywhere into the house.

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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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How to square up a scrap piece of stock ready for machining

Can’t Remember How to Square Up Material Stock ready for CNC ?

I sometimes have to dig deep in the odds and ends heap of rough bits of materials to use on a project.  This results in having to square up the find so it can be easily programmed into Fusion CAM.   I always have to scratch my head on the process which is well documented by Tom Lipton and This Old Tony among others.  What I needed was something to pin on the wall to remind me. 

The result of this frustration is a write up and a graphic which you may find useful.  Here is a screenshot and the link below it provides both this document and the write up in a ZIP file.

Squaring Stock 

Hope that helps and if it isn’t well explained let me know and if it was useful also let me know.

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Adapter plate for a Tormach microARC to mount a Xin Dian centralising vice

I’ve made mention in another post of the arrival of the Tormach microARC to use on my Tormach PCNC440 CNC milling machine.   The microARC provides a 4th axis facility.

To date I have used this with the supplied chuck but there have been a couple of instances where a vice style stock mounting would have been useful.  I am indebted to David Loomes for bringing the Xin Dian centralising vice to my attention. 

Xin Dian centralising machine vice
The Xin Dian centralising machine vice

This is available from various sources on the Internet and at a delivered price of less than GBP100.   It is a lovely little vice.   It is supplied with an industry standard backing plate which is held in place with four M6 cap head screws.  The supplied backing plate is not suitable for mounting on the microARC .

A 3D model of the microARC is available as a Fusion file and this with some careful measurement allowed me to model a mounting plate for the Xin Dian to fit onto the microARC face.

As a secondary activity I edited the Fusion file to provide a simple sub-mounting plate for the Xin Dian vice on my PCNC440 tooling plate.

Details of both these mounting plates are contained in the PDF link below.

xin dian vice mounting plates

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Milling vice stop for non grooved vice jaws

Another Job Ticked Off

There are a number of lower cost CNC milling vices (vises) available on the market that do not have jaw geometry with grooves for tooling fixtures and vice stops.   Admittedly their jaws could be machined to add this facility but many of these vices have hardened jaws which presents more of a problem.

My CNC vice came from the UK supplier ARCeurotrade and is from their ARC Versatile SG Iron Milling Vices range.   I have the 100mm wide jaw version and the jaws are  just over 11mm (7/16″) thick.

I have a simple plate that acts as a stop  that is flush with the end of the jaws.  This makes use of existing holes in the vice body but often I need to have a stop internal to the jaw footprint.  Juggling then results with all manner of Heath Robinson solutions.

My design is simple and clamps onto the thickness of the jaws.   

There are two M3 clamping screws and there is enough adjustment on these to allow a parallel to also be gripped should it be needed.

CNC vice stop showing clamping onto the vice jaw and also when used with a parallel
CNC vice stop showing clamping onto the vice jaw and also when used with a parallel

I allowed for two positions for the stop rod and the rod is held with a grub screw in each.   There is a central burr clearance neck on the rod so the grub screw does not damage the surface of the rod and make removal difficult.  Clearly the rod could be simplified to have just a single fixed position.

The rod can have rounded ends or it can have ball bearings glued into a cavity on each end of the rod.   The ball bearings would give a higher resilience to damage.

So nothing really complicated or rocket science with just an hour or so of workshop pleasure.   The size can be adjusted to suit your vice jaws and the material can be whatever is in the junk box.

Here is a link to the 2D drawings that were created in Fusion 360.

CNC vice stop Drawing v3

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