Drag knife / vinyl cutter adapter for Bambu X1

Drag knife / vinyl cutter adapter for Bambu Lab X1

(Above: a video on how to install this retrofit!)

Have you been wishing you had a vinyl cutter, but you couldn't justify spending another $200 on yet another CNC machine when you already have a perfectly good three-axis CNC machine in your living room already?  Did your printer wake up in the middle of the night recently from Bambu's cloud bumbling, and leave you wishing “wow, I really wish that instead of a hot nozzle, my printer was wielding a knife instead”?  Are you fundamentally incapable of leaving well enough alone?  Well have I ever got the model for you: a chunk of plastic that you can print yourself that (temporarily) replaces your Bambu's extruder assembly with a drag knife holder.

WARNING

If you build this thing, you are literally putting a sharp blade that you got from Amazon inside of a $1,500 printer that does not have a working E-stop button.  That is a stupid idea!  This model comes with NO WARRANTY, EXPRESS OR IMPLIED.  If you build this model, you do so at your own risk. 

That means: if you slice the inside of your machine, that is your fault.  If you slice your finger, that is your fault.  If you break your machine and void your warranty, that is your fault.  If the requisite incredibly stupid heater hack burns your machine down, that is your fault.  Keep a close eye on your machine when you're using this.

Obviously this is not endorsed by Bambu Lab or anything like that.  I assume they will be pretty upset when they find out that I did this.  Don't tell them my printer's serial number, please.

What you need to build this

Ok, I wasn't able to dissuade you, which is good, because this is actually a pretty cool gadget and once you get it up and running it's quite easy to use.  If you're going to build this, you need:

• Three M3x4mm heat-set brass inserts.  Here's an Amazon link to what I bought.
• Three M3x16mm screws.
• A Graphtec CB-09 knockoff cutter holder.  Here's an Amazon link to what I bought.
• Some cutter blades.  I used 45 degree blades.  Here's an Amazon link to what I bought.
• A cutting mat that can be cut to fit your hotbed.  Here's an Amazon link to what I bought.
• Hey, if you're going to go to all this work, you might as well cut some stuff; here's the vinyl I bought.
• If you want to be totally cheesy about this, you can leave a hotend and extruder dangling off the top of your toolhead – suit yourself.  (We'll talk about that in a bit.)  But if you want to do this a little more reasonably, here are some Bambu-specific electronic parts to get:
  • A spare thermistor + heater kit to fake the printer out with.  Here's an Amazon link that I can't really vouch for because I haven't tried this one in particular, but whatever.
  • A Molex PicoBlade-compatible crimp kit (in particular, a 5-pin 1.25mm PicoBlade connector) to fake the printer's cutter sensor out.  Here's the kit that I have.
  • Two 100 ohm resistors.  I dunno, get them wherever.  I used some 0603s from a bag of parts I have lying around.  This is probably fine if you use Amazon, but I get mine from Digikey.
• While you're printing this, you might as well print a PTFE cable release tool to make your life a little easier. I printed this one. 

Assembly and installation

Installation is pretty easy the second time (it should take only a few minutes), and takes a little bit of thinking the first time.  See the video (or embedded above) for some help.  Here's, roughly, how you do it:

1. Print both halves of the design.  I printed mine out of PETG, because it's what I had lying around; I used PLA as a support interface material to make it easier to have the floating overhangs.  An example 3MF file is attached.
2. Heat up your soldering iron good and hot, and insert the heat-set brass inserts into the bottom of it.  Don't be sloppy, get them in good and straight, and heat ‘em up enough that you’re not going to pull them out with torque.
3. Test fit your (empty) drag knife holder between the two parts – insert it in the middle, make sure it fits, and then gently tighten the three screws down.  It doesn't require a lot of force to hold it in place.  Be gentle.
4. Perform a bed calibration.
5. Power down your printer, and remove the toolhead cover.  Follow the directions on the Bambu Lab web site to disconnect the cables for the extruder and the hot-end.  If you don't have a heat source, I just picked the silicone glue off with a tweezers (which you're going to need anyway to weed your vinyl…).
6. You do not need to remove the hot end in order to remove the extruder – remove the screws shown in step 6, with the hot end still attached.
7. Remove the filament cutter by gently unhooking it from the lever.
8. Using the screws that you removed from the extruder, attach the adapter to your printer.
9. Install the cutter into the drag knife, and adjust it such that it is sticking out somewhat (1mm or so when depressed).  Cut depth will be controlled by the automatic bed leveling and Z axis adjustment, so it is less critical to adjust the cutter height than it would be using this cutter with a plotter.
10. Install the drag knife cutter into the adapter, and then tighten the three screws down.
11. Reinstall the screw for the filament cutter lever.

The cutter is now mechanically installed.  You now need to connect enough cables to keep the printer happy about the filament cutter and the heater.  You have two general approaches for this:

Floating extruder

If you wish to do no further modifications, you can simply leave the extruder and hot end on top of the toolhead, and use the existing electrical components to keep the printer happy.  You need to babysit the printer if you are going to do this: the extruder can fall off of the top of the toolhead (especially during homing) and make chaos.  To do this:

1. Unhook the hotend cables from the cable guide on the extruder.
2. Connect the five-pin extruder sensor connector to the toolhead.
3. Connect the two-pin thermistor connector to the toolhead.
4. Connect the two-pin heater connector to the toolhead.
5. You can leave the four-pin fan connector disconnected (and I recommend doing so, since this will prevent the printer from trying to heat the nozzle above 100°C).
6. Route the cables out the top of the toolhead, and reinstall the toolhead cover.
7. Place the extruder assembly precariously on top of the toolhead.

Electrical components only

If having a toolhead sticking out seems all too precarious for you, you can connect just the electrical components needed to make the printer happy.  Even if it does not plan to provide any heat, the printer needs a heater connected, a thermistor connected, and a sensor for the filament cutter.  To do this:

1. Connect a spare heater to the toolhead.
2. Connect a spare thermistor to the toolhead.  Lightly wrap them together such that the thermistor is touching the heater.  This should prevent the printer from attempting to melt down whatever the heater happens to touch.
3. Take a 5 pin PicoBlade connector, and insert wires into pins 1, 2, and 4.  (Pin 1 is where the white wire was on the original extruder sensor connector.)
4. Connect a 100 ohm resistor between pins 1 and 2, and another 100 ohm resistor between pins 2 and 4.  Apply heat shrink to seal the assembly off.
5. Connect the 5 pin PicoBlade connector to the extruder connector on the toolhead.

Cutting vinyl!

Ok, time for the fun part – slicing some vinyl!  I use Inkscape to generate DXF files, and the dxf2gcode software to generate toolpaths for a vinyl cutter.  Don't be tempted to do silly things like exporting STLs and having a slicer slice for you – that won't work, because a drag knife has a nonzero turning radius.  Here's how I set up dxf2gcode to print for my drag knife adapter.

First, launch dxf2gcode, and set it to drag knife mode.

Go to dxf2gcode's “Configuration…” box, and set up some reasonable defaults.

• In “General settings”, set:
  • Machine type (default): drag_knife
  • Configuration values use the unit: mm (if it was set to ‘in’ before, restart the app after)
• In “Machine settings”, set:
  • Retraction coordinate: 10mm
  • Safety margin: 3mm
  • Workpiece origin coordinate: 0mm
  • Slice depth: -0.08mm
  • Final mill depth: -0.20mm
  • G1 feed rate (2D plane): 600 mm/min
  • Third axis feed rate: 150 mm/min
• In “Output settings”, set:
  • Uncheck the box “Cutter compensation is done by machine”
  • Retract to drag depth if angle exceeds: 25°
• In the “Tools table”, remove all tools but “tool 1”, and set tool 1 to have a diameter of 1.6mm, a speed of 600, and a start_radius of 0.0.
• Click “Apply”, then “Close”.

Go to dxf2gcode's “Postprocessor configuration…” box, and set it up to generate reasonable G-code for the Bambu.  The following is a starting suggestion.

Now, load your DXF into dxf2gcode.  Go to “Move Workpiece Zero”, and then set the offset to 20mm x 20mm; make sure that the nearest cut is a good distance above and to the right of the center (the gray circle), lest your printer crash into the filament cutter.

Go to “Export” and click “Optimize and export shapes”; save your file.  Rename it to a .gcode file, and copy it to your printer's SD card (either by FTP, or the old fashioned way).  It's good to eyeball the contents of the gcode file to make sure that there aren't X or Y coordinates that are too obviously wrong (i.e., <30mm).

Finally, insert your cutting mat, and tape it down to a build plate.  Add some vinyl, and print the gcode file from the printer's interface!  From there, you can use a relatively normal vinyl transfer process to apply your new decals.

Tips and tricks, and things to improve on

I've found this process to be pretty reliable, shockingly, once I got it working.  Keep an eye on your printer while this is happening – if any of the sensors fail, it will rapid-traverse over to the poop chute, slinging a knife around with it!  Resuming from that configuration will result in the knife gouging your nozzle wiper.

I've found a little bit of trouble around shape quality with small shapes.  The core problem, as far as I understand, is that the drag cutter has a positive turn radius.  dxf2gcode tries to compensate for this (this is what the ‘tool diameter’ does), but it doesn't seem to reliably land the knife in the right direction when it starts a cut.  I think the way that one probably wants to do this is by ramping the knife into the workpiece, and making two passes on each object to cut… probably in the future I will investigate how to do this if I want to cut smaller decals, but for now, most of what I'm cutting is large enough that this isn't a problem.  I recently tried turning the cutter diameter to be way higher than I think it should be (it should be 0.45mm radius, I ended up having to set it to 1.6mm radius…), and the G-code that I've attached includes that modification, which appears to work much better.

Feedback

I spent, like, 60 hours designing and building this and writing it up.  It's way too many, but if you like it, that will make it have been worth it.  So if you find this useful, please let me know!  I would especially like to hear from you if you have suggestions for improving the cut quality.