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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Enclosure finally added to my Tormach PCNC440

Reduction in Sparkly Bits around the House

When I bought my Tormach PCNC440 in 2016 I included the enclosure kit in my order.   On receipt I thought that fitting the enclosure would dominate the size of the workshop so I never got round to fitting it.   It has sat in its shipping box since then.  I have consequently shared quite a bit of my swarf (chips) with long suffering family.

After a recent (particularly heavy) CNC run I had a serious covering of swarf in the machine tray and because I had no enclosure round the mill, I had quite a lot distributed further afield (i.e. into the house).   Domestic peace was becoming an issue. Time to do something about it. 

Out came the enclosure kit, cobwebs dusted off and around three hours later I had the enclosure fitted.  I have to say it looks good and does not overpower the workshop as I thought it would.   My wife is impressed and says it looks a more professional machine and ‘if you had it why didn’t you fit it before now’ ? 

My Tormach PCNC440 with its enclosure fitted
The picture above shows the enclosure mounted on my PCNC440 with the monitor in the original position before fitting the extension arm to the ISO bracket. The keyboard tray uses a domestic drawer rail mounted on the top of the standard Tormach cabinet. My recently fitted dual fogbuster system and my Hall Effect based tool height setter (yellow top) are visible.

The fitting did however create some follow up problems.   

My control monitor had up to now been mounted on the side of the 440 on a standard ISO TV mount.  With the enclosure fitted this meant it was ’round the side’ and difficult to get to.   I debated a new long reach ISO but they are expensive.  Plan B was to make something. I rummaged around in my aluminium stock and with the help of Fusion 360 came up with a seriously overengineered extension arm to add to the existing ISO mount. This would allow the monitor to move forward to be in reach at the front of the mill. 

ISO bracket extension on Tormach PCNC440
My seriously over engineered extension bracket to move the ISO mounting of the monitor more to the front of the 440

This bracket became the first CNC job to run after fitting the enclosure.   I am pleased to say it was the cleanest my workshop floor had ever been after running a job.

Having fitted the new bracket and mounted the monitor, all the cables needed extending.  Fortunately I had had the foresight on my original order to include the extension cable kit.   As a result I only had to extend the power supply lead from the monitor 12V ‘brick’ supply.

The second issue was where to mount my ITTP probe as this had formerly mounted on the side of the 440.   With help of some more Fusion design I modelled a corner mount that picked up on the enclosure fastenings.

After that first heavy machining run I noticed for the first time the slight smell of the mist coolant when opening the enclosure doors.   Before the enclosure was fitted the smell must have dispersed into the general workshop air.   With the enclosure fitted the air was concentrated inside the mill and I only got the smell when sticking my head inside.  While it had never been a problem (as far as I can tell …) I thought I should do something about it.

Sometime ago I installed a ceiling extract duct in the workshop.   This vents to the outside world via a custom roof tile. Normally the system sits with a flared cowling (made from a cut down flower pot) on the ceiling entry duct.  The system normally acts as a background trickle extract.   The cunning plan in the design was to use various pipe components to provide bayonet style connection pins (Nylon screws) to allow extension trunking to be used.   A bit like a BNC RF connector if this is familiar to you.   This would allow me to use an add-on length of expanding flexi trunking to bring the extract nearer to any heavy fumy activity such as welding or oil bath hardening.

With the use of further scrap odds and ends of aluminium, I mounted a pair of support bars across the top of the new 440 enclosure. These would fix the ducting over the enclosure during heaving CNC sessions.   Not a total solution but certainly one that will reduce the general smell of XtremeCut 250C when I stick my head in the enclosure.

Workshop extract system
Extract system showing ceiling mounting intake, trunking adapter and mounting on my Tormach PCNC440.  Note the two Nylon screw protrusions are for a bench mounting clamp when used for welding extraction etc and now used on this new use of the system on the mill.

A good day’s activity with all the issues addressed and domestic bliss hopefully restored.

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CNC Work Reference Centring using Mushrooms

This is probably not original but worth commenting on.   I have a tooling plate on the bed of my Tormach PCNC440.  This has a matrix of M8 holes on 25mm spacing together with intermediate 3.7mm tooling pin holes.

Quite often I have a need to set up my work CNC coordinate system (WCS) such that it is centred on one of the M8 holes. 

If I want to do a quick and dirty centre on one of these holes then I use the Laser Centring tool as mentioned elsewhere on my blog.

If I need to be a bit more precise then I have a mushroom/top hat shaped disc with shank that is a tight fit in the tapped M8 holes.  PathPilot has a number of probing routines and these include finding the centre of a circular object.    Simply push the top hat into the desired hole and then probe the disc for centre.  You can use an active probe such as the Hallmark ITTP.

If you haven’t got an active probe you can use a Haimer.   Simply align the Haimer tip somewhere close to a maximum point on the disc circumference and advance the axis to show a reading on the Haimer.  Rock the opposite axis back and forth and watch the Haimer reading to find the high point on the circumference.   Zero the axis.   Go to the opposite side of the disc and repeat this process and divide the measured diameter by 2 for the disc centre.   Repeat on the opposite axis.

(You can use this Haimer rocking back and forth method to find the diameter high point when cross drilling a circular item to fit grub screws etc).

Hole centring mushrooms
Two examples from my ‘mushroom farm’

The mushrooms are made with a silver steel shank that is skimmed to be a non wobble (how technical is that ..) fit in M8 (~6.8mm) and an aluminium top hat that is superglued in place on the shank.   Once the glue has set the top hat is squared up while held in a collet in the lathe.  This ensures concentricity with the shank.   The disc will now sit flat to the tooling table when the shank is pressed home and perpendicular in the hole.

Clearly the larger the disc diameter the less centring error there will be.

I now have a ‘mushroom farm’ of discs for all manner of hole sizes.  It’s not rocket science but as you well know, I am all for a simple (aka lazy) approach.  Apologies to all the Grannies out there.

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Clough42 Electronic Leadscrew Project Implementation Notes

I have been avidly watching Clough42 on YouTube.  James comes over as a really nice guy and his presentation of his projects is excellent.

My principle interest is the Electronic Leadscrew modification to lathes.  When installed this removes all the hassle of gearboxes and look up tables to be able to cut both Imperial and Metric screw threads and to set X axis movement feed rates.

The concept is simple but his implementation is second to none.  A rotary encoder is fitted to the spindle to count revolutions of the chuck and a stepper motor (or servo hybrid) controls the rotation of the leadscrew.  The resulting feed speed is derived from look up tables.  The whole installation is controlled by a Texas Instruments LaunchPad C2000 microcontroller development board.

I have documented how I implemented this on my Myford Super 7 Big Bore lathe and the pdf can be downloaded below.   There is also a ZIP file of all the Fusion related models for either CNC or 3D printing.

Electronic Leadscrew on Myford Super 7

Minor edits added to v3 relating to programming the servo controller

Electronic Leadscrew on Myford Super 7 v3

Electronic Leadscrew Fusion 360 Files

Updates : –

Painted control panel for Clough42 Electronic Leadscrew
Finally got the Clough42 Electronic Leadscrew control panel box painted and rather pleased with the result.

Since installing the ELS I have incorporated thrust bearings on the leadscrew mounting.   This impacts on the coupling to the stepper motor.

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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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