Posts Tagged MPCNC
Flushed with success from engraving a hard drive platter for the 21HB5A tube, I bandsawed an acrylic square from a scrap sheet and unleashed the diamond drag bit on it:
That’s side-lit against a dark blue background. The long scratch and assorted dirt come from its protracted stay in the scrap pile.
If you look closely, you’ll see a few slightly wider loops, which came from a false start at Z=-0.1 mm.
Engraving at -0.5 mm looked pretty good:
Despite an angular resolution of 2°, the curves came out entirely smooth enough. The gritty scratchiness resulted in a pile of chaff covering the engraved area; perhaps some oil or lube or whatever would help.
Rescaling the pattern to fit a CD platter worked fine, too:
Polycarbonate seems to deform slightly, rather than scratch, leaving the final product with no chaff at all:
In this case, the doubled lines come from the reflection off the aluminized lower surface holding all the data.
That CD should be unreadable by now …
The three collet pen holders I got a while ago came with ink cartridges:
So I bought three bucks worth of a dozen pens to get pretty colors, whereupon I discovered they didn’t fit into the collet. Turns out the locating flanges aren’t in the same place along the cartridges:
The flanges on the top cartridge have been shaved down perilously close to the ink, but it now fits into the collet.
Bonus: a dozen fairly stiff springs that are sure to come in handy for something!
That’s with a 0.1 mm cut depth, sidelit with an LED flashlight.
Feeding those nine digits into the Guilloché pattern generator script should get you the same pattern; set the paper size to 109 mm and use Pen=0 to suppress the legend.
The same pattern at 0.3 mm cut depth looks about the same:
It’s slightly more prominent in real life, but not by enough to make a big difference. I should try a graduated series of tests, of course, which will require harvesting a few more platters from dead drives.
Either side will look great under a 21HB5A tube, although the disks are fingerprint and dust magnets beyond compare.
Drawn at Z=-0.1 mm on scrap acrylic with the diamond engraver in the modified collet holder:
The badly rounded corner comes from a Z touch off in facepalm mode; the poor diamond must have been trying to dig a 2 mm trench through the acrylic.
Then again at Z=-0.5 mm:
At half a millimeter, the holder applies well over 100 g of downforce. There’s no way to know how much lateral force the tip applies to the holder, but it’s obvious the parallel beams on the MPCNC drag knife adapter lack lateral stability:
Bending beams still seem much better than a linear bearing, though.
Of course, the diamond engraving points have a 3 mm shaft that doesn’t fit in the 2.5 mm Collet Pen Holder, but making a hole bigger isn’t much of a problem …
Commence by drilling out the collet closer nut:
The hole didn’t start out on center and I didn’t improve it in the least. A touch of the lathe bit and a little file work eased off the razor edge around the snout.
The knurled ridges at the top are larger than the threaded body, which requires a shim around the threads to fit them into the lathe chuck. Start by cutting a slightly larger ID brass tube to the length of the threaded section:
I finally got a Round Tuit and ground opposing angles on the cutoff tool ends, so I can choose which side of the cut goes through first. In this case, the left side cuts cleanly and the scrap end carries the thinned slot into the chip tray.
Grab the tube in a pair of machinist vises and hacksaw a slot:
Apply a nibbler to embiggen the slot enough to leave an opening when it’s squashed around the threads:
Put a nut on the collet threads in an attempt to keep them neatly lined up while drilling:
Drill the hole to a bit over 3 mm in small steps, because it’s not the most stable setup you’ve ever used. Eventually, the diamond point just slips right in:
Reassemble in reverse order and It Just Works:
Now, to scratch up some acrylic!
The Mighty Thor provided the new-ish Squidwrench logo in various digital formats, not including DXF, but
dxf2gcode can process PDF files (and a few others), and the cutting / weeding / transfer ended well:
That’s the same 14 mil gold vinyl you saw in the Crown test.
Alas, I re-covered the pattern with the transfer film when I ran the mug through the dishwasher, in the mistaken belief the film would protect the vinyl. Come to find out the film adheres better to the vinyl than to the mug: it pulled loose during washing and peeled most of the logo off the mug.
Setting the drag knife to cut hot pink 9 mil = 0.25 mm vinyl film produced another logo:
It’s now survived several trips through the dishwasher with no protection, so I’ll call it a win.
dxf2gcode to use a cutting depth = 1.0 mm for about 400 g of downforce, which seems to work, although the vinyl surface showed some marks from the flat nose around the drag knife blade.
The USB camera provides a convenient way to set the “workpiece origin” before cutting:
Because the camera sits 130 mm beyond the blade in the +Y direction, it can’t see the swathe along the front of the MPCNC. Hard and soft limits in bCNC / GRBL keep you (well, me) from smashing the gantry into the rails, but it’s a nuisance when you forget to tape the vinyl far enough from the front.
That’s a PNG converted from the SVG original, because WordPress regards SVG and DXF files as security risks.
Run the DXF through
dxf2gcode (from the Ubuntu repository) to produce G-Code suitable for my MPCNC’s GRBL controller, tape a sheet of paper to a sacrificial acrylic sheet, fire up bCNC, set the origins, and run the G-Code:
As expected, the cut paper pulled off the acrylic, because it’s not glued down; I have some Cricut adhesive cutting mats which are definitely in the nature of fine tuning. In any event, the paper showed I could get from a DXF image to drag knife cutting action.
This being a crown, gaudy gold vinyl seemed appropriate:
The weeding process removes everything that’s not the crown; I used a razor knife to cut a square and remove the vinyl around the crown. A good needle-nose tweezer works wonders!
Apply transfer film to the weeded crown and peel it from its backing paper:
Stick it on something desperately in need of decoration and peel off the transfer film:
The tricky part is setting the drag knife cutting depth to match the vinyl sheet thickness (14 mil = 0.36 mm), so the blade cuts the vinyl without cutting through the backing paper. This seems best done with manual trial cuts on scrap vinyl, pressing the drag knife holder down firmly by hand and tweaking the depth adjustment for a clean cut.
The G-Code cuts at 400 mm/min = 6.7 mm/s, perhaps a bit on the slow side.