Thursday, 9 January 2014

CNC - First real cut

 Here's the first real run with the CNC with a diamond engraving bit in the dremel.

I put a grid of silicon door bumper pads (about 7mm dia) on the bed as way to stop the acrylic work-piece from sliding.  I also used a pair of moly magnets from an old server HDD, one stick to the underside with double sided foam tape.  These things have enormous amount of magnetic pull, and with the other one directly above it, it clamped the work-piece to the bed without risk of distorting it.  Works a treat!

I used CamBam to generate the g-code, but I reckon I had the feed rate too high.  The dremel bit seemed to twitch when it got to the end of each it was under too much side load.  This did cause the letters to have a small bump at the start/end point of each character.

This run was 1.0mm deep, 0.5mm each Z step, and 200mm/min feed rate.  I might be a bit ambitious with these settings :-)

It also doesn't help when the dremel collett seemed to swing the bit off-centre upwards of 0.25mm each way (a combined runout of 0.5mm).

The CNC router upgrade may be sooner that I had planned, but in its current state, a reasonably OK setup for learning with.

Next test..cutting a profile and drilling some holes.  If I don't update this for a while, it's most likely gone all horribly wrong...but that's just me being optimistic :-)


Wednesday, 8 January 2014

Converting an A3 printer into CNC machine - In Summary

In short, it's been an awesome project to do, and I would do it again in a heartbeat.  I've still got some tidying up with cable routing, etc, but it has had it's first run with a pen zip-tied to the Z-axis.  The results are pretty good, and the accuracy is nice to see. (

There will be some enhancements and improvements:

  • Upgrade the rails and linear bearings to 12mm,
  • Expand the Z carrier to accommodate a 52mm CNC spindle,
  • Put in a 400W CNC spindle
  • Make the lights on the dash go blinky blink :-)
I would also like to drop in a 4x20 character LCD screen and get some output from the Arduino...some sort of job status maybe?

So on behalf of Dasher (she's been sitting here listening to me typing this blog) and myself, thanks for reading.  Feel free to leave feedback or ask questions.  Dasher won't give a fat rats bum about feedback or questions, but I'll do my best to get back you as soon as.

In the meantime, please check out the video of the first run, and I'll update the blog when I do something a bit more exciting than an electronic sketchograph.


Converting an A3 printer into CNC machine - Pt5

This was a time consuming part...sorting out the electrics to make sure that;

  • It didn't look ugly,
  • They worked,
  • Easily got at and unplugged, in case it didn't work
  • It wasn't going to get hung up, damaged, shorted, cooked something
  • They kept working.
An ideal area for the electrics was what used to be occupied by the old power supply (woefully under powered for this task) and all the messy bits of the printer, such as an ink scraper that had what can be best desrcibed as a biohazard in its little collection pot!

As you can see, plenty of room for the boards, a 200W PSU, some room underneath for excess wiring storage and a power bar.  I also hooked up a small jumper cable for a power switch to the earth + green wire from the ATX plug.

I tied 3 wires each of the red (5V), yellow (12V), 2 wires each of black (x 2) and wired them onto the power bar.  There's plenty left on the PSU loom of I want to do something like wire in the UV light strips I have when I was modding CPU cases :-)

Next thing was to make up some tidy, yet practical plugs for the CNC shield.  This thing is in a tight space, so I don't really want to be messing around with single header pin sockets.  So here's a good tip..and made life so much easier..

Get some of these..

Thread 2 bits of heatshrink onto them..

Heat the big bit first until it wraps nicely around the plug ends, then seal off the scruffy end with the smaller bit of heatshrink. Viola!

Now you can plug/unplug them as a group, they don't flex as much when you try to plug them in, and they stay in the right order.

 So here's the Arduino Uno, with the Protoneer CNC shield plugged in on top, and a small proto board I made up to connect the steppers to the CNC shield.

I made up another plug for the emergency stop, hold, resume and abort pins (hidden behind the plugs in the photo)  I was able to use the original printer control panel buttons and attach them to the CNC pins.

It was just a matter of working out the connections with a multimeter, and making the life changing decision on which button should do what.  I figured the E-Stop button should be the biggest one...'cause it's easier to hit in a panic.

I've already used it twice when I messed up my endstop switches!

On that note..if you have no previous CNC experience, please get your endstop switches sorted before playing.  Nothing is more distressing than seeing your creation attempt to wind the ends off your machine.  I'm only using the smaller Nema17 steppers @ 4.8kg/cm torque.  On a 6mm, 1.5mm pitch threaded rod, that's a lot of grunt.

Next...the final words.

Converting an A3 printer into CNC machine - Pt4

The Z Axis:

This was always going to create a challenge, mainly because of the limited space.  In fact, this one took a day to work out.

Basically, I put a 25mm sq section aluminium tube between 2 lengths of 25mm angle, and bolted and screwed 2 short bearing drawer slides between each piece (as seen in my rough sketchup drawing)  To allow the centre piece to move and clear the end pieces, I simply packed them out with a washer at each end.  Each end has 4 8G self stapping hex head screws to make sure it all stays square.  This arrangement allows for a very compact Z axis, and the centre section is the exact right size to take the dremel flexishaft handle that I have.

If I ever (and I reckon "ever" might be sooner than I wish) have to put a proper small CNC motor in there..I simply replace the 25mm sq section with a 25x50mm rectangle section, cut a new piece of acrylic to accommodate the extra width, and I can bolt it straight on (he says...casually!)

Here is the top half with the top bearing retainer and screw rod nut.  The bearing is a standard 6mm deep groove shielded bearing held in place with 2 pieces of acrylic.  The lower one has a hole to match the OD of the bearing, and the upper piece is drilled a bit smaller to keep the bearing from lifting out.

I also made an acrylic nut to hold the MDF insert in place.  I drilled out a larger piece of 6mm acrylic with a 10mm bit, heated the inside edge of the hole, and basically tapped a thread using the insert.  Then trim it to the right size and you are away.  You can excerpt a fair bit of pressure on it without cracking.

The steel bracket was then used to mount the insert to the centre section.

The lower end is where I mounted the stepper, and I made up a couple of small proto boards to hold the ribbon cable to power the stepper and take the wiring from a small momentary switch.  The switch is activated by a small tab (a suitably cut bit of 25mm angle) on the bottom of the screw rod mount, and acts as the Z endstop.

I soldered 4 lots of 3 wires from the ribbon cable for power to the stepper (see the next part for the other end), and laid it out so it would roll around as the Y axis moved, very much like the original print head ribbon cable. worked for the why not make it the same.

I also dropped in a balun retrieved from the printer just in case I got line noise.  Not sure if it needs it, but with the stepper being capable of drawing 2.5A, seems like a good idea.

I used the trusty MDF inserts to clamp the dremel handle inside the centre tube.  I drilled 2 x 10mm holes on one side, and directly opposite each hole, drilled 8mm holes.  That way I can screw in an insert from the inside out, using the 8mm holes as a place to feed the 6mm hex key needed to screw the inserts through.  Then I cut a saddle out of 6mm acrylic for the thin end of the handle, and a custom bent (hit it with a hammer) saddle from the 40mm aluminium angle.

The inserts give the 6mm bolts something to push against when screwed up tight against the dremel handle.

Nearly there....the electronics!

Converting an A3 printer into CNC machine - Pt3

The Y Axis:

The original print head carriage got a hack and slash so I could re-use the shaft runners.  These aren't linear bearings...more like a bronze bush.  I plan to replace them with linear bearings because there is a small amount of lateral movement in them.  However, since the shaft is only supporting the back side of the Z carrier platform, it's not such a this stage.

I used some 40x40x1mm aluminium angle to make up a stepper mount, the mounting bracket of an 8mm smooth rod (recovered from another printer I pulled to bits) and the threaded rod mounts.  I had a bunch of LMUU8 linear bearing + mounts from ebay, which I put to use with the 8mm rod.  I had thought about a vertical Y axis arrangment, but there wasn't much point since the gap down through the top platform is only a couple of inches, and there is heaps of space to tuck the second rod into the front edge.  My thinking is that is also spreads the Z axis load across both shafts and keeps the moving mass a bit lower down.  I'm not a physicist/engineer/mathematician, and that argument probably flies in the face of all good CNC designs..but works.

Everything was screwed down with 8G hex head self tapping screws.  Having quite a few flat and level surfaces to measure from helped with the alignment..although some was done with the old "eye-o-meter".

The 40mm angle is the perfect height to rest one edge on base of the Y carriage chassis.  It also ensures that it is parallel to the rest of the top assembly, and provides a great mounting point for both the Y axis screw rod and the endstop microswitch.

Again with the 25mm angle, I made up a screw rod bearing mount.  The acrylic is retaining a 6mm flange bearing.  The small pieces of white plastic are from one of the discarded printer parts (one of the flap hinges) and just the right size for bearing bushes.  Yes...I should double-nut the bushes, it's on my "enhancements to do" list.

The nut for the screw rod is a self tapping MDF machine insert.  It's ugly, but it works!  Because of the flange at one end, it butts up against the face to the mount, ensuring it is straight.  The length also removes all discernible backlash, and therefore no requirement for an anti-backlash nut setup.

The 2 small self tapping screws are there to anchor the insert from rotating.

I do plan to pull everything back off at a later stage and tidy up my rough-as-guts hacksaw cuts, remove barcode labels and pen please don't give me any grief about it :-)

And finally...the business end!

The 40mm angle has a bit of flex in it, so I braced it with a couple of 50mm tri-corner steel brackets, which made the whole thing rock solid.  In theory, the steppers shouldn't be subject to any linear pressure since the bearing at the other end should be stopping that.  The brackets helped with the torsional twist (although if you have the bearing, carrier nut and stepper all aligned should be as smooth as a baby's bum!)

Here's a close shot of the bearing arrangement that the Z axis rides on.  The 8mm rod and bearing was close enough to be a good point for mounting the Y+ endstop switch.

Next..the Z axis!

Converting an A3 printer into CNC machine - Pt2

The X Axis:

I decided to go with ball bearing drawer runners for the X axis platform.  They are compact, smooth, and virtually no play in them.  I mounted them between 2 lengths of 25x25x1mm aluminium angle...

This arrangement semi seals the runners to reduce the ingress of shavings and other mess into the ball bearing guides and carrier.

I did have to bend the end-stop tabs down so they could clear the screw heads used to attach the inner track to the inside rail.

This is where keeping the printer screws is a very good idea.  I was able to use the self tapping pan-head screws which were a perfect fit between the "U" chance of moving up or down.

Aligning them was dead easy...use a set square on the front edge of the printer base plate and simply line the rails up and screw them down.  I used flat head 8G x 12mm self tapping screws (pre drilling the pilot holes)  I put 3 down each side, but the centre screws seemed to pull the rails down and bound up the runners too much.  One at each end is adequate to hold everything in place.

There are a couple of places in the printer base plate that are pressed with ribs (obviously for strengthening) but you can put the rails close enough to the left/right edges to get full length support.

I drilled and tapped 4 x M4 machine screws along each side into a sheet of 6mm acrylic for the milling platform.  There wasn't quite enough rigidity in the acrylic to stop the edges rocking when pressing down on the platform, so I also screwed 2 lengths of 25mm square section aluminium across each end...which firmed it up just nicely.

I needed to cut out a small section at the end of the back square channel to clear a micoroswitch that I mounted for the axis + endstop.  This was a lesson learned when I crashed the channel into the switch and nearly tore the thing apart...bit of  heart stopper!

Next....the Y axis.

Converting an A3 printer into CNC machine - Pt1


This is a retrospective blog on my conversion of an old HP 2500C A3 printer into a CNC machine.  It's retrospective because the original plan was to just pull it to bits for parts!  If I had known (or planned) that it would become a CNC machine, I would have blogged as I went.

So what started as a deconstruction turned into a reconstruction once it became apparent that the bare bones chassis of the printer would be the perfect starting point for a desktop CNC machine.

The printer is approximately 12 years old, and I hadn't used it since it stripped off a few teeth from any one of many gears inside the beast.  You can pick these printers up off places like Ebay and Amazon for around $150-$200.  They had mixed reviews in their day, and the cartridges were hideously expensive.  The thing weighs around 30kg (66 lb) so it would be ideal for a small boat anchor.

The tear down:

It took a few hours to pull apart, and the panelwork did its usual thing of holding on for dear life via the hidden lock tabs, screws and various other clips.  Everything is held together with T-6 and T-20 star screws.  I was able to use most of them during the reconstruction.

So after trimming 3/4 of the weight out of it (including a nice collection of 7 motors), I was ready to start.