In Chapter 14, you cut a few of the parts required to build the z-axis. In this chapter, you're going to drill some holes in a few of those pieces, take a few measurements, and cut the remaining parts required for the z-axis.
As you read this chapter, keep in mind that a few of the parts you'll use for assembling the z-axis may not match exactly with the measurements we provide. This is not necessarily a mistake on your part; slight variations in cutting the MDF can cause some measurements to fluctuate as much as 1/16". Just be patient and keep moving forward, and your z-axis will begin to take shape.
Before you can assemble your z-axis, you're going to need to drill some holes so the various pieces you have cut can be bolted together. Just go slow, consult the CNC machine plans so you can properly mark the spots on your MDF pieces where you'll be drilling, and then select the properly sized drill bit for your drill.
The MDF parts you will be drilling in this chapter are
Part F | Z-Axis Rail Support |
Part W | Z-Axis Bearing Support |
Part X | Z-Axis Bearing Support |
Note
Refer to the MDF Plans and Cut List PDF file for cutting and drilling dimensions of all MDF parts-this file can be downloaded at www.buildyourcnc.com/book.aspx
We'll begin drilling with Part F.
Figure 15-1 shows the undrilled Part F. Back in Chapter 14 we suggested that you mark the piece for drilling before chamfering the edges. If you have not marked Part F for drilling, go ahead and consult your plans and mark the four points where you'll be drilling. You will be using a 7/16" drill bit to drill four holes that will hold four cross dowels.
Figure 15-2 shows Part F after being drilled. The center of each hole is 3/4" from the shorter end of Part F and 1" from the chamfered edge's widest point.
Notice in Figure 15-2 that the plans also call for 1/4" holes to be drilled into the sides of Part F, too. These holes should extend about 1/4" past the 7/16" holes that were drilled for the cross dowels; this will allow the 1/4" bolts to be screwed into and through the cross dowels.
Figure 15-3 shows how we're going to drill into Part F horizontally; all that's left is to clamp the piece down so it doesn't move. Go slow and make certain to keep the drilling as level and straight as possible. We used a small "bubble level" built into our drill to help with drilling accuracy.
Drill all four holes and then set Part F aside for now. Our next step is going to be drilling Parts W and X.
Take a look at Figure 15-4 and you'll see a closeup of Part W with all the drill marks in pencil.
Now take a look at Figure 15-5. This is a portion of the plans for Part W and shows that some of the holes should be drilled with a Forstner (counterbore) bit. This will allow the bolt heads to be below the surface of the MDF.
All of the smaller holes shown in Figure 15-5 are 1/4" holes. But before you drill those, we suggest that you drill the larger counterbore holes first. Figure 15-6 shows Part W partially completed-the larger counterbore holes have been drilled, and all that's left is for us to drill the 1/4" holes. Notice that the drill bit we used left a small dimple in the center of each hole; we'll use this dimple to help us center the 1/4" drill bit. (One of the single 1/4" holes has already been drilled in the upper-left corner.)
Note
We recommend drilling a test counterbore hole in a piece of scrap MDF to help you determine the proper depth to drill. For our Part W, we found that a depth of 1/4" was sufficient to allow the bolt head to sit just below the surface. Don't drill too deeply with the counterbore bit.
If you consult the plans carefully, you'll notice that Part X is an exact mirror of Part W. Take a look at Figure 15-7 and you can see that Parts W and X are drilled almost identically, but the counterbore holes are on the outward-facing surfaces (refer back to Figure 14-8 and you can see the counterbore holes on Parts W and X face away from the center of the z-axis.)
That's all the drilling for now. Up next, we need to mount the bearing-rail assemblies (BRAs) we made in Chapter 7 to the sides of Parts W and X.
Grab the two BRAs you made back in Chapter 7 and flip over Part X to the side with no counterbore holes. Figure 15-8 shows how we've bolted down a BRA using standard 1/4" bolts.
You might find it easier to bolt down the BRA by removing the four bolt-bearing-nut assemblies. Tighten the 1/4" bolts down a little at a time and don't overtighten. When done, put the bolt-bearing-nut assemblies back on. Do this for Parts W and X. Figure 15-9 shows the BRAs added to Parts W and X.
And that's it for Chapter 15. You're almost done with the z-axis!
At this point, you should have the following items completed:
Part F with eight holes drilled; four on surface for cross dowels and two on each end
Part W drilled (along with countersunk holes) with BRA mounted
Part X drilled (along with countersunk holes) with BRA mounted
For the work performed in this chapter, you will use
1/4" bolts; 1" length; quantity: 8 (for attaching BRAs)
1/4" nuts; quantity: 8
You're going to complete the z-axis assembly in Chapter 16. This will involve assembling Parts F, W, and X. But don't worry-it's not hard to do. And when you're done, you'll have 90 percent of your CNC machine completed!