Figure 10-1 shows an image of the final CNC machine's MDF parts all assembled with the Y-Axis Gantry Sides circled.

For this chapter, we're going to focus on cutting and drilling these two pieces.

Figure 10-1. Parts Q and R make up the gantry sides of the CNC machine.

Figure 10-2 shows Part R cut to the proper dimensions of 17 3/4"×7". Part Q is cut to the same dimensions, and both pieces have been marked for drilling. Refer to the CNC plans PDF file for the locations and measurements of the holes to be drilled.

We've mentioned this earlier in the book, but when drilling holes, it is sometimes helpful to use a center punch, as shown in Figure 10-3. You can create a small dimple in the MDF to help you center the drill bit with more precision.

Figure 10-2. Part R cut and marked for drilling

Figure 10-3. Use a center punch to create small holes to assist with drilling.

Next, clamp parts Q and R together, as shown in Figure 10-4. You can drill the two parts separately, but clamping them together saves time and can help to ensure that when the two parts are mounted, their respective holes will match up.

Figure 10-4. Clamp parts Q and R together before drilling.

You're going to drill a total of 16 1/4" holes in the gantry sides before they are mounted. (The larger holes shown in Figure 10-1 will hold bearings and will be drilled into each gantry side shortly.) Figure 10-5 shows all 16 1/4" holes drilled into Parts Q and R.

Next, you're going to drill the larger hole into each gantry side that will hold a bearing. Refer back to Chapter 9 for instructions on drilling the shoulder and large hole that will hold a bearing. The holes for the bearings need to be drilled as accurately as possible. For that reason, here is an alternative method for drilling these holes with a drill press that differs slightly from the method used in Chapter 9.

First, keep the two pieces clamped together as shown in Figure 10-5. Use a 1" Forstner bit to drill a single hole through both pieces, as shown in Figure 10-6.

Figure 10-5. All of the 1/4" holes have been drilled in Parts Q and R.

Figure 10-6. Drill a 1" hole through Parts Q and R.

Next, while keeping the two pieces clamped together, counterbore the larger hole on Part Q, as shown in Figure 10-7. The diameter of the larger hole is 1 1/8". Drill to approximately 3/8" depth. Once again, the easiest method for doing this is to use a Forstner bit.

Figure 10-7. Drill a 1 1/8" hole into Part Q.

After drilling the larger hole into Part Q, flip the clamped pieces over. Put the 1" Forstner bit back in the drill (or drill press) and, without turning the drill press on, lower the 1" bit until it goes into the 1" hole in Part R. Clamp Parts Q and R to your drill press table. This will allow you to remove the 1" Forstner bit, insert the 1 1/8" Forstner bit, and drill the second larger hole centered perfectly in part R.

Figure 10-8 shows Parts Q and R with the bearings inserted into the holes. A 1/2" rod has been inserted through the bearings to show that the holes match up.

Now set Parts Q and R aside for a moment, and let's build two BRAs, one for each gantry side.

Figure 10-8. A 1/2" rod inserted to check that the 1 1/8" holes are lined up properly

Each gantry side will have a BRA mounted to it. Refer to Chapter 4 for details on building BRAs; for this chapter, you're going to cut two 7" lengths of angled aluminum rail. Figure 10-9 shows the two pieces cut.

Figure 10-9. Cut two 7" lengths of angled rail for the BRAs.

Next, you'll need to use your pilot hole template (see Chapter 4) to drill 1/8" pilot holes at the ends of each piece of rail. Figure 10-10 shows the pilot holes being drilled into the rails using the small metal template.

Figure 10-10. Drilling pilot holes into the BRA rails

Next, use the 17/64" bit to drill holes for tapping. Figure 10-11 shows the holes drilled and ready to be tapped.

Figure 10-11. The larger holes are drilled into the rails and ready to be tapped.

Finally, use the tap to add the threads to the two pieces of rail. Figure 10-12 shows the tap inserted into one of the pieces of rail. Go slowly, and make sure that the tap bit is "biting" into the hole as straightly as possible.

Figure 10-12. Use the tap to add threads to the holes.

Figure 10-13 shows the bolt-bearing-nut assemblies screwed into the rails. You now have two 7" BRAs, ready to be attached to the gantry sides.

Figure 10-13. Add bolt-bearing-nut assemblies to the rails to complete your BRAs.