Back in Chapter 1, we introduced you to the general concept of the CNC machine. You learned about the various axes that are used to get the machine's router bit to the material for cutting and drilling. And in Chapter 2, you got a brief overview of the CNC machine you'll be building.
Up to this point, you've been reading and learning about some of the methods you'll be using to cut, join, and build your CNC machine. In this chapter, however, it's time to get your hands dirty (just a little bit, we promise). You're going to begin building the first component for your CNC machine.
You're going to cut some MDF and use the information you learned in Chapters 4 and Chapter 5 to build the x-axis. We don't want to overwhelm you, so we're going to break up the assembly of the x-axis into multiple chapters. Read through this chapter for an overview of what you'll need to accomplish by chapter's end-maybe even reread it. (You're in no rush, right?) Let's get started.
For your x-axis, you're going to need to cut a total of four pieces of MDF. We will be using a combination of actual part names as well as part letters when describing an MDF part. This will, hopefully, make the instructions a little easier to read (and much less annoying since we won't have to reference each part by its full name).
The MDF parts you will be cutting are as follows:
Part Y | X-Axis Table (top half of table-2'×4') |
Part Z | X-Axis Table (bottom half of table-2'×4') |
Part T | X-Axis Table Leg |
Part U | X-Axis Table Leg |
Note
Please refer to the MDF Parts Layout 1 and MDF Parts Layout 2 PDF files available for download at www.buildyourcnc.com/book.aspxwww.buildyourcnc.com/book.aspx
Again, we highly encourage you to read through this entire chapter first before you begin cutting. Once you're ready to begin, we'll start with the X-Axis Table (Parts Y and Z).
Figure 7-1 shows an image of the final CNC machine's MDF parts all assembled. The table is the largest component of the machine, measuring 24"×48". This surface area consists of two pieces of MDF, both 24"×48", bolted together to provide a strong surface and reduce warping. (The tabletop also has angled rails bolted to the two long sides of the MDF-this will be covered in Chapter 8.)
For this chapter, we're going to focus on only the tabletop; the table's legs (Parts T and U) will be covered in Chapter 8.
Caution
The part layouts found in the MDF Parts Layout 1 and MDF Parts Layout 2 PDFs are not to scale; refer to the MDF Plans and Cut List file for actual dimensions.
If you've purchased a large 48"×96" piece of MDF, you'll need to cut that sheet into four equal parts each measuring 24"×48". If your hardware/lumber supplier provides MDF in quarter sheets (24"×48"), like the ones shown in Figure 7-2, this will reduce the amount of cutting you'll have to perform. The cost of four quarter-sheets may be a little higher than a single 48"×96" sheet, but you'll save some time in not having to measure and cut a larger sheet.
Note
Because the saw blade has a thickness (typically 1/8"), anytime you cut your MDF you'll be losing a small amount of material. If you mark a line in pencil and cut down that line as accurately as possible, the piece you are cutting will be shy (short) about 1/16". Try to maintain a consistent method when cutting-will you try to cut exactly down the center of the line, to the left, or to the right? Whatever your decision, use it with every cut you make. Overall, this design will allow for small deviations caused by the thickness of the cutting blade.
Note
At our hardware store, we were able to purchase quarter-sheets of MDF for $7.95 each. A larger sheet of MDF with dimensions of 49"×97" was sold for $25.98. Besides the price difference of around $6.00, the larger sheet was also oversized a little beyond the 48"×96" mentioned earlier. Sometimes the edges of the larger sheets of MDF are a little dented or broken, so the larger MDF sheets come slightly oversized so you can cut away the damaged portions. Keep this in mind when cutting the large MDF sheet into four parts-each of those four smaller sheets needs to be 24"×48".
Once you have two sheets of MDF with dimensions of 24"×48", consult the MDF Plans and Cut List PDF file for help in laying out the pieces for drilling. You'll be referencing the pages labeled "Bottom Half of Table" and "Top Half of Table" for the measurements used in drilling and chamfering the two pieces. (If you're not familiar with chamfering yet, we'll explain that shortly.)
Figure 7-3 shows a portion of the Bottom Half of Table sheet and Figure 7-4 shows a portion of the Top Half of Table sheet.
Because you will be bolting the top and bottom halves of the table together, it will be easier work if you clamp the two pieces together, mark the spots to be drilled on the top sheet of MDF, and then drill pilot holes (1/8") through the top and bottom sheets at the same time. Both the top and bottom halves will have larger holes drilled in identical places, so by clamping the two pieces together and drilling pilot holes, you can be assured that when you bolt the two pieces together, all the holes will match up.
After you've marked the top half of the table and drilled all the pilot holes, it's time to chamfer the edges. What is a chamfered edge? Look at Figure 7-5.
The chamfering is done using your router and a special bit (called a chamfer bit). It allows you to cut away material at an angle-in this case, a 45 degree angle. Refer back to Figures 7-3 and 7-4 and you can see a profile of each piece. Viewed from the side, there is a small 45 degree surface. This angled surface will allow you to attach a piece of angled aluminum rail to the sides of the table; you'll learn more about this in Chapter 8.
Caution
Use a router with extreme caution. Consult your router's documentation for proper usage and safety. Use safety goggles and remember to always move the router in the same direction that the bit spins.
Chamfer the top edges on the top half as indicated by the CNC plans, and chamfer the bottom edges of the bottom half, also as indicated in the CNC plans. (This entails using the 45 degree chamfer bit to remove half of the 3/4" sides of Parts Y and Z. It doesn't have to be exact, but try to be as accurate in your chamfering as possible.)
If these two pieces were clamped together now, the side of the tabletop would look like Figure 7-6.
Once you've chamfered the edges, it's time to make the table's rails.
The last task for this chapter is the cutting of two pieces of angled aluminum rail. You can use either 1" or 1 1/4" rail for the sides; for our tables, we selected 1 1/4" rail and cut two pieces, each 48" in length. Figure 7-7 shows one piece of rail cut.
Tip
If you use 1" rails for the x-axis tabletop, this is the only time you'll be able to use the 1" angled aluminum rail; when the rail is mounted to the tabletop, its edges won't protrude above or below the tabletop surface, allowing you to use a 90 degree square later when mounting the gantry sides (see Chapters 10 through 12). We didn't have any 1" rails at the time, so we went with 1 1/4", which also works fine but does create a raised lip just slightly above the tabletop's surface.
Take the two 48" pieces of rail and set them aside for now.
At this point, you should have the following items completed:
Part Y with dimensions of 24"×48"
Part Y chamfered along the top of the 48" edges
Part Z with dimensions of 24"×48"
Part Z chamfered along the bottom of the 48" edges
Two 1 1/4" rails cut to 48" length (1" rail can be substituted)
Parts Y and Z marked and 1/8" pilot holes drilled