Wednesday, 8 January 2014

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!

No comments:

Post a Comment