The CNC machine you’ll be building calls for using four sheets of 2'×4' MDF. You have two options Here:
1. Buy a single 4'×8' sheet and trim it yourself into four 2'×4' sheets.
2. Ask the seller to cut the 4'×8' sheet into four 2'×4' sheets.
2. Ask the seller to cut the 4'×8' sheet into four 2'×4' sheets.
Most hardware/lumber stores do not like to cut MDF due to the dust it creates, but some will—it
never hurts to ask. But make certain to ask them to trim them to 2'×4' sizes, especially if the single sheets come with a little extra material on the edges.
never hurts to ask. But make certain to ask them to trim them to 2'×4' sizes, especially if the single sheets come with a little extra material on the edges.
You may luck out and find a seller that sells quarter-size MDF sheets, precut to the 2'×4' size (see Figure 3-4). You may pay a little more per quarter-sheet, however. Trust us—it’s probably worth the extra dollar or so per quarter-sheet, and the cuts will likely be extremely accurate and easier to carry (MDF is heavy).
Figure 3-4. Try to find MDF in quarter-sheets with 2'×4' dimensions.
The quarter-sheets in Figure 3-4 were priced at $7.95 per sheet when the photo was taken. Multiply that by four sheets and you get approximately $32.00. Compare that to a single 4'×8' sheet sold at the same location for $26.00. Not having to carry and cut that big heavy sheet: Priceless. OK, maybe not—but definitely at least worth the extra $6.00 if you can find the quarter-sheets. Also, keep in mind that pricing will very likely fluctuate from location to location; the prices we quote in the book may not match exactly what you pay.
Limit Your Cuts
Take a look at Figure 3-5. It shows a listing of the parts you’ll be cutting along with their dimensions. Notice that some of the parts have identical measurements—either in width or length.
Figure 3-5. Try to group your parts so you’ll make as few cuts as possible.
You can download the entire listing in spreadsheet format at www.buildyourcnc.com/book.aspx. After downloading the file, open it and you’ll see some of the part names match up with Figure 3-6. Figure 3-6 shows one of the two PDF files that contain the measurements and part layouts for two of the 2'×4' MDF sheets. These part layouts are designed to help you make fewer cuts, as well as to help make certain that paired parts (such as the two gantry side pieces) are identical in size because they’re cut together along one or more edges. You can download the part layout files at www.buildyourcnc.com/book.aspx. Keep in mind that there are only two of them because two of the four 2'×4' sheets will be used to make the CNC machine’s tabletop and require no cutting.
Figure 3-6. The CNC machine parts are grouped to reduce the amount of cuts you’ll need to make.
Time Your Cuts
This may not make sense now, but trust us—try and cut only the parts you need, when you need them. Look back at Figure 3-6. The two parts in the lower-left corner are the Y-Axis Rail Support and the Gantry Bottom Support. These two parts need to be identical in length, but this length won’t really be known until you reach the point where you’ll assemble the Y-Axis Gantry. See the dotted line running vertically to the right of these two parts? That cut can be made to separate these two parts from the rest of the MDF sheet, but it’s not the final cut that’s indicated by the solid line on the right side of both parts. Download and examine carefully the part layout files mentioned in the previous section. You should see that each 2'×4' sheet is further divided into sections that can be set aside until the parts they will provide are needed.
But we hear you yelling “Hey, Figure 3-3 shows all the parts already cut out!” Yes, it does. But what you can’t see in Figure 3-3 is the frustration we encountered when we figured out (later, after this photo was taken) that we really shouldn’t have cut out the Y-Axis Rail Support and Gantry Bottom Support until we needed them!
We’d also like to share with you another one of our big mistakes in the hopes that you avoid it. You’ll be using two 2'×4' sheets of MDF to make the CNC machine tabletop. These two pieces will be chamfered (see Chapter 7) and bolted together, and should be flush along all the edges. Well, in our eagerness to get ahead, we chamfered both sheets, measured and drilled the top sheet, squared it up, clamped it along the left and right sides of the bottom sheet, and drilled the holes. And guess what happened? The bottom sheet, which we assumed was exactly 2'×4', was actually 1/4" wider than the top sheet, but we didn’t notice that until we bolted the two sheets together—the chamfered edges didn’t match up! (Not a huge mistake, but it slowed us down since we had to unbolt the sheets, trim the bottom sheet, rechamfer it, etc.)
The lesson to be learned here is to measure all your parts and make certain they match up with the dimensions found in the actual CNC machine plans.
It never hurts to double or even triple-check your measurements against the part layout sheets and the actual CNC machine plans!
