Now that you have the gantry sides (Parts Q and R) bolted to the Gantry Bottom Support (Part P), it's time to finish up the y-axis frame by adding the Y-Axis Rail Support. Consisting of two pieces of MDF bolted together, these two pieces will provide stability and rigidity to your CNC machine.
The y-axis frame you're building performs two functions. It rolls along rails mounted on the sides of the table, allowing the machine's router to move forward and backward. It also provides a "minitable" that allows the z-axis frame (covered in Chapter 13) to move side to side.
The y-axis frame consists of six pieces of MDF:
Part O | Y-Axis Rail Support (front) |
Part P | Y-Axis Gantry Bottom Support |
Part Q | Y-Axis Gantry Side (completed in Chapter 10) |
Part R | Y-Axis Gantry Side (completed in Chapter 10) |
Part S | Y-Axis Rail Reinforcement (back) |
Part E | Y-Axis Gantry Bottom Nut |
In this chapter, you'll be cutting, drilling, and mounting Parts O and S-these two pieces are bolted together and mounted above the tabletop and between the two gantry sides. Figure 12-1 shows Part O outlined (Part S is bolted to the back of Part O and not visible in the figure).
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
Please read through this entire chapter first before you begin cutting and drilling. Remember, measure twice (or more) and cut once.
If you've completed all the work on your CNC machine up to Chapter 11, you should have a partial assembly like the one shown in Figure 12-2.
Refer back to Chapter 11 for the distance you measured between the two gantry sides. You're going to use this same measurement as the length for cutting Part O. The CNC plans provide a length of 26 11/16" (26 and 11/16 inches) and a height of 8". Substitute your measurement for the inside distance between Parts Q and R that you wrote down in Chapter 11. Cut Part S to the dimensions specified in the CNC plans.
Part O needs to be chamfered to hold the angled aluminum rail that will be bolted to the top and bottom edges. Figure 12-3 shows one of Part O's edges marked for chamfering and the router chamfer bit set to the proper depth. (You can see Part O with its edges chamfered in Figure 12-4.)
Next, measure and mark all the holes for drilling on Part O. For the 7/16" cross dowel holes on the left and right sides of Part O, we suggest drilling 1/8" pilot holes. Figure 12-4 shows Parts O and S clamped together (and you can see the pilot holes drilled in Part O). Notice that Part S is centered on Part O; try to be as exact as possible before clamping the two pieces together.
Tip
It's also beneficial to label the surfaces of Parts O and S that are touching so that when you bolt the two pieces together later, the holes will line up perfectly. If you forget to do this and you accidentally flip Part S over, you can always put the two pieces together and look to see if the pilot holes match up with Part O.
Part S will be bolted to Part O, so you can drill the ten pilot holes through both parts to help ensure the bolt holes will match up exactly. Figure 12-5 shows the ten pilot holes drilled into Part O and through Part S (on the back).
You'll be using 1" bolts to hold Parts O and S together. When a bolt and nut are tightened, both the bolt head and the nut must be below the surface of Parts O and S. To do this, you'll need to counterbore the surface of both pieces. Figure 12-6 shows a few of the counterbore holes drilled using a 1" Forstner bit. The approximate depth drilled into Part O is between 1/4" and 3/8"-you'll need to experiment with your counterbore bit to determine the proper depth for ensuring that the bolt head is below the surface of Part O.
Perform the same actions on Part S; counterbore 10 holes an approximate depth of 1/4" to 3/8" so that the nut sits below the surface of Part S. Figure 12-7 shows a few of the holes counterbored for Part S.
Next, use a 1/4" drill bit to drill holes (for the 1" bolts) in all 20 of the counterbore holes (on Parts O and S). Figure 12-8 shows these holes being drilled into Part O.
Next, use a 7/16" bit to drill the holes on the left and right sides of Part O that will hold the cross dowels. Also drill the 1/4" holes into Part O's edges where the bolts will be inserted and screwed into the cross dowels. Figure 12-9 shows the cross dowel holes being drilled.
Figure 12-10 shows the 1/4" holes drilled into the edges of Part O.
Next, cut two lengths of angled aluminum rail to match the length of Part O. Figure 12-11 shows the rail placed on top of Part O but not yet bolted down.
Now it's time to bolt all the pieces together and attach them to your CNC machine.
Insert ten 1" bolts and washers into the counterbored holes on Part O, as shown in Figure 12-12. Push these bolts into Part O and through Part S.
Attach ten nuts to the ten bolts inserted into Part O and through Part S. Figure 12-13 shows a nut tightened down; note that it sits slightly below the surface in the counterbored hole.
Next, use ten 3" bolts (five per side) and ten cross dowels to attach Part O/S to the gantry sides, as shown in Figure 12-14.
Note
Figure 12-14 shows Part S and the nuts used to secure it to Part O. It doesn't matter which way you attach Part O/S, but the direction Part O is facing will be the front of the CNC machine. Keep this in mind for future reference.
Place the aluminum rails on the top and bottom of Part O/S, as shown in Figure 12-15. We used painter's tape to hold the two pieces in place.
Mark the aluminum for drilling; you'll be drilling two holes into the aluminum so that 2" bolts can be inserted and screwed into two cross dowels, one on each end of the rail. Drill the holes into the rail and bolt them to Part O/S. Figure 12-16 shows the rails bolted to the frame.
And that's it for the y-axis frame! You're now approximately two-thirds done with your CNC machine. Take a break and have some fun sliding the frame forward and backward along the tabletop's rails.
After you've bolted on Part O/S, you may find that the y-axis frame grips the tabletop rails either too tightly or too loosely. Here are a few suggestions for ensuring that the BRAs roll smoothly on the rails.
BRAs are too tight on the rails, part 1: This can be caused by the gantry sides and their matching BRAs pressing too tightly against the x-axis rails they will ride on. To alleviate this problem, you can insert washers in the gaps between the gantry sides and Part O and/or Part P to move the gantry sides further out (and by further, we're talking about maybe a 1/16" distance). This will, in turn, move the BRAs slightly away from the rail, reducing pressure and providing a smoother motion. You'll have to experiment with different washer placements.
BRAs are too tight on the rails, part 2: This can also occur if Part O and Part P are cut too short in length. Once again, you can insert washers in the gaps between the gantry sides and Part O and/or Part P to move the gantry sides further out. But if Parts O and P are cut too short, no amount of washers will really help, and you may be forced to remeasure the distance between the gantry sides and recut Parts O and P.
BRAs are too loose on the rails: If you cut the length of Parts O and P too long, the gantry sides will not hold the BRAs securely to the rail. Grab the y-axis frame and wiggle it a bit-do you hear rattling from the BRAs? One solution is to trim Parts O and P down just a bit-maybe just a 1/32" or 1/16" on each side. This will pull the gantry sides in closer, and the BRAs will more securely ride the rails. (Of course, if the BRAs then become too tight, refer to the preceding two points for using washers to fix this problem.)
At this point, you should have the following items completed:
Parts O and S drilled
Parts O and S bolted together
Two pieces of angled aluminum rail cut, drilled, and mounted to Part O/S
Part O/S with rails mounted to the y-axis frame
For the work performed in this chapter, you will use
1/4" bolts; 1" length; quantity: 10
1/4" nuts; quantity: 10
1/4" bolts; 3" length; quantity: 10
1/4" bolts; 2" length; quantity: 4
Cross dowels; quantity: 14
Chapter 13 is where you're going to begin building the z-axis assembly. This assembly will move side to side along the y-axis frame's rails and provide the machine's router with the ability to move up and down with respect to the tabletop surface. You'll be building some more BRAs, cutting rail, and drilling . . . so let's get started.