Old 3d Printer Into a CNC for Under $30!!!

I have always loved 3d printing but after I got my newest one, I found myself never using my old Longer Lk4 3D printer. I was thinking what I should do with it and first I thought I should just upgrade it as a fun project but soon realized that would cost more than a new printer. So, it sat there even longer until I came across a project that needed a CNC. I looked online and found a CNC for around $150 and almost bought it when I remembered I still had an old 3d printer. I started looking around to see what I had around that I could use with it and found my old rotary tool. Then, I thought if I am never going to use the printer again why not use it as a CNC and save $120. So, after some CAD design some headaches and way too many test prints I designed something that worked.

In this instructable you will learn how to convert an old 3D printer into a budget CNC machine for under $30

Basic overview

• We will take an old 3d printer running the marlin firmware (I will be using a Longer Lk4)
• We will use open-source CNC software to generate Gcode that the printer can read
• Custom design a mount that fits your 3D printer
• Engrave or cut our first thing

What you will need

• A comfortable understanding on how 3d printers operate
• A 3D printer that runs Marlin (most hobby printers do)
• A cheap WEN rotary tool (WEN 2307 Variable Speed Rotary Tool Kit with 100-Piece Accessories,Blue,Medium - Power Rotary Tools - Amazon.com)
• A basic understanding of 3D design (if you are not using a Longer Lk4)
• Standard M3 hardware, I used (iexcell 1500 Pcs M3 x 4/5/6/8/10/12/14/16/18/20/25/30/35 Stainless Steel 304 Hex Socket Head Cap Screws Blots Nuts Washers Assortment Kit: Amazon.com: Industrial & Scientific)
• The bits that come with the rotary tool
• Access to a 3d printer that can print the parts you need.

To get the 3D printer to work as a CNC there will need to be a few minor modifications. First you will need to remove the hot end assembly. First take out all the screws that secure the hot end to the mounting plate but be careful not to loosen your V wheels screws. Once you have everything off of the mounting bracket make sure that the hot end is still plugged in along with the cooling fans. You will need to keep them plugged in, so the printer doesn't give an error and stop your job.

We need a mount that is going to fit our printers mounting plate so let's design one. If you are using a Longer Lk4 then go straight to Thingiverse and download the Lk4 backplate.

1. Go to Thingiverse and download the blank backplate (Rotary tool mount for 3d printer by puzzleman32 - Thingiverse)
2. Import the file to your cad software (I am using Onshape)
3. Measure your backplate
4. Make a new sketch on the back and put mounting holes where needed for your printer.
5. Copy the sketch into a new workspace and extrude it around 5 mm
6. Modify and print until it fits your printer perfectly.
7. Add the sketch to your backplate then print the backplate and the front plate

Now simply use the M3 screws to mount the backplate to the printers mounting plate. Then, put the rotary tool in with the button facing out and use the M3 screws to secure the front plate. Now take turns tightening each of the screws until the rotary tool can't wobble.

I like to use Openbuilds CAM because it is open-source and free but other toolpath generators should also work. Openbuilds is also good because it supports importing images and not only SVG files. So to set your CNC up follow these steps.

1. go to OpenBuilds CAM Gcode Creator - Public Beta
2. It should pop up with a application setting menu do not close it
3. if you don't get the menu then click on the settings tab then click settings
4. Skip to step 5 then put in the size of your wood or whatever you are cutting so the machine doesn't try to cut something bigger than it can handle
5. save the setting and go back to this menu whenever you are changing the size of what you are cutting
6. Insert a DXF, SVG, or image
7. Now let's create a toolpath so select every line you want to cut/engrave then click add on the right side. (The image shows my engraving settings)
8. In the menu change all the parameters to what fits your job
9. Click generate Gcode then save Gcode then you are almost ready for your first job.

This step is hugely up to what machine you are using but I will show you on my Lk4 and you can apply it to whatever printer you have.

1. Put some sort of waste material down on the bed so if you cut too deep it doesn't ruin your bed.
2. Secure what you are going to cut to the waste board
3. Turn on the printer and make sure that it thinks that it is at 0 on all axis's
4. Unlock the steppers and move the rotary tool to the bottom left coroner of the piece.
5. Now go through and level it as if you were leveling a normal 3D printer but only level your thing you are cutting
6. Return your tool to the bottom left corner and tell your printer to move the z axis up 5 mm

Turn the tool on to the desired speed and start the print job as you normally would.

Here are some tips

• You might need to stop and let the rotary too cool down if there is a long job
• Cut outside or in a ventilated area because it is messy and can release fumes
• Tape your hot end to your frame and cover it so it doesn't get dirty (the price you pay for not changing the firmware)
• always use safety glasses when using
• If you have a filament run out sensor cut a small section of filament and put it in, so you don't get an error
• when its cold outside I cut in my window well so I can watch from inside