In this final instalment, I am going to finish the KReduCNC build, taking you through its operation by creating a part. Before we start I want to go over some of the upgrades that I have added to my KReduCNC.
The first upgrade I add to any CNC I build is an “Emergency Stop” or Estop as it is commonly referred to. The Estop shown here allows me to quickly shutdown the CNC operation if things go south. Some controllers have inputs designated for the Estop. These allow the hardware to shut down and then send a signal to the software (Mach3) to stop the job. Other controllers have generic inputs that can be assigned in Mach3 as an Estop. This will enable you to quickly stop the job in software. Until you get an actual button wired, you can use the large Mach3 reset button located in the lower left of the application.
One of the more tedious aspects of setting up the CNC to get it ready to mill your part is setting the tip of your bit to the surface of the stock. The depth probe shown here allows you to set the bit by slipping a pad under the bit and hitting a button.
By adding a power switch, it can be used to power down your CNC when it is not in use. This is a safety feature that will also extend the life of your electronics.
If you add a set of homing switches like the ones shown in Figures 4, 5, and 6, you can setup the minimum and maximum travel of your machine. This will help you keep from crashing your machine.
This will also allow Mach3 to check any G-Code you load to make sure it does not machine outside the bounds.
Once you have a set of homing switches installed, a set of fences like those shown here will allow you to easily align your stock consistently and accurately. Once tuned, you can even flip your stock and machine the back side of the stock if needed.
The controller I used in the KReduCNC has a relay built-in. By wiring a set of connectors to this relay, they can be used to turn your spindle on and off automatically.
I want to take you through the operation of the KReduCNC by showing you how I made a set of special tool holders shown here.
Many times when we make a part, we don’t do it in full 3D. It is cut out of a piece of stock following a set of toolpaths that we create with CAM software. This is often referred to as 2.5D.
When I design a part in 2.5D, I use a CAD package like CorelDraw, to layout the part. Another CAD package that works well with 2.5D design is Adobe Illustrator.
Once the part is designed, the part is exported into a format that the CAM software can understand. In this demonstration, I will be using Vcarve Pro, by Vectric. I have found that exporting the part in EPS format works very well with Vcarve.
The job of the CAM software is to create a toolpath for each graphic vector we want to cut or drill. The CAM process is started by importing the exported CAD file into Vcarve. Vcarve has various toolpath options for creating a toolpath. The profile toolpath shown in Figure 11, is the most common. When creating a profile toolpath, you tell the software which graphic vector to use, how deep, which tool, tool speed, inside or outside cut. Another option when creating toolpaths in Vcarve is adding tabs. Tabs allow you to cut all the way through the stock but still leave the stock attached to the stock.
Vcarve will overlay your toolpaths on the drawing (Figure 12) so that you can keep track of what you have done. In addition, as each toolpath is created, you can also view the actual cut part in the simulation view shown in Figure 13.
Once all the parts have been created, the toolpaths are exported as G-Code. G-Code is what Mach3 uses to move the spindle in order to machine the part.
The design calls for a piece of stock 4” wide by 3” tall and 3/8” thick. In addition to the stock you will need a waster board cut to the same size as shown in Figure 14. The waster board is used to keep your bit from hitting your table top when the CNC cuts through the stock.
Clamp the stock and the waster board to the table as shown in Figure 15. You can use any piece of wood with a hole in it as a clamp. The T-slots are designed to hold the head of a 1/4” hex bolt head. Just add a washer and 1/4" wing nut and any piece of plywood or solid wood with a hole in it and you can secure the stock. The clamps shown here are from a laser cut kit that I will be selling on my website. Leave the clamps a little loose and the left edge free as you will be squaring the stock in the next step.
The next step in stock setup is to square up the stock. This is done by placing the edge of the bit up against the side edge of the stock, as shown in Figure 16. The bit should be near the front of the stock. Next, move the spindle straight back to the rear of the stock, as shown in Figure 17. You want the edge of the stock up against the bit. If it’s not, move the stock until it is. Go back and check the front again by moving the spindle forward. If the stock is no longer against the bit, move the stock until it touches the bit. Keep repeating this process until the stock is against the bit at both the front and back of the side edge. If you add the homing switch and fence upgrades this step is pretty much eliminated as the edge of your stock will always be square against the fence.
Add the rest of your clamps, as shown here. Use as many clamps as it takes to secure the stock. The clamps need to keep the stock flat against the table and keep it from moving from side to side. If you look closely, you will notice that the clamps are two pieces of ply. The ply on the bottom of the clamp is slightly shorter than the one at the top. This creates a lip that keeps the stock from sliding. If you are using solid clamps, you can grind a small notch in the clamp to accomplish this.
One thing to bring up here while I am talking about clamps, is that I always use wood clamps on my CNC routers. This is so I don’t ruin the bit if I accidently hit one while machining the part. Believe me, you will hit the clamp from time to time.
To align the spindle with the stock, move the bit so that its center is directly over the front left corner, as shown in Figure 19. Move the spindle down so that the bit is just touching the top surface of the stock. Once the bit is in position, go to Mach3 and zero the X, Y, and Z axis, as shown in Figure 20.
Machining the Part
The first step in machining the part is to load the parts G-Code into Mach3. This is done with the File/Load G-Code menu option. Once the G-Code has been loaded, your Mach3 screen should look like the one shown in Figure 21. The actual code will be displayed in the panel on the upper right side of the screen. Mach3 also shows the actual toolpaths in the upper right panel.
To start the machining process, turn on your spindle and set the rotation speed of the spindle. In this case I set the spindle to about 18,000 RPM. Failure to turn the spindle on before starting the cutting operation could result in a broken bit. Note that the spindle control upgrade will allow Mach3 to turn on the spindle once the job starts.
To start the Job (cutting process), hit the large green button labeled “Cycle Start”.
Finishing the Part
Once started, Mach3 will direct the spindle to cut each of the toolpaths. The finished part will look like the one shown in Figure 22. Well, not exactly. Unless you add some sort of dust collection upgrade the part will be covered in shavings and dust. The first step in finishing the part is to remove the stock and vacuum all the debris. This is a very important step as any debris left on the table will affect how the next piece of stock sets on the table.
The part is still attached to the stock with the small tabs added with the CAM software. Punch the part out of the stock. You can remove the small tabs with various methods. Wire cutters will work, but I prefer a small rotary tool with a sanding or carving bit. Depending on the material you may need to remove flashing from the edges of the part. Most of the time, I use a fine sanding sponge. Once cleaned the part will look like the one shown in Figure 23.
You may have noticed here are some small grooves in the part. These were added as guides to drill some mounting holes. One of the grooves is also used as a guide to cut a slit in the front of the part. The finished part is shown in Figure 24.
There are two of these parts used to hold the tool I will be testing. In addition, these parts were meant for another CNC so I had make a couple of adapters that let me use them on the KReduCNC. All these parts can be seen in Figure 25.
Just for Fun
I mounted the tool holders on the KReduCNC, then added the tool. The tool is a pneumatic air scribe (engraver), shown in Figure 26. The air scribe is used to mark metal and other materials without actual machining. Looking at Figure 27, you can see that it works very well.
This completes the KReduCNC build series. I will post the drawing files for the tool holder on my support page for the KReduCNC. In addition, I will be adding various upgrades to this build as time permits.
In this article, I covered the basic operation of the KKeduCNC by making a tool holder for a pneumatic CP 9361 Scribe.
Making the Tool Holder