Here is a scratch built
machine (from the plans or book
) that exhibits great workmanship, but more importantly, how some of the construction of the CNC machine was done. William L. used sound techniques to make sure the machine would be constructed as intended, knowing that some of the machine would have various size differences within the sub assemblies that would make some of the measurements within the plans not work.
It is important to note that the video process for constructing a CNC machine on this site should be watched as a minimum requirement for constructing the CNC machine from the plans or the book. This will provide you with a good understanding of a few techniques to make sure that the measurements for certain parts will work. It is obvious that William watched these videos and completely understands these techniques and order of making the right cuts from measurements made during the construction.
One such example: even though there are measurements in the plans for, say, the y-axis rail support (the bridge of the gantry), this measurement may be either too long or too short, depending on the table width, the bearing rail assembly (BRA) final effective measurement, and the method of attaching the BRA to the gantry sides. It makes more sense to make the y-axis rail support last and deriving the measurement by dry fitting all of the parts around the y-axis rail support.
You can see in the photos where William did just this by using long 1/4" all thread rods to keep everything in place while these measurements could be made. On the z-axis, you can see that he also used a precise digital level to make sure the top and bottom bearing holders are perfectly parallel and the back and front parts would exhibit the same measurement.
He used this technique on the gantry sides to find the measurement for the part under the CNC machine that spans the gantry side and holds the x-axis nut. This is also the measurement for the y-axis rails.
The method that the machine uses to move the axis back and forth uses a nut and a screw. In this case, William is using an 1/2" allthread rod which has the same TPI as a standard 1/2" screw. William decided to put the nut right into the wood. This is a somewhat advanced method of woodworking to get the nut to fit in the wood perfectly. This method makes sure that the nut will not turn, causing increased backlash. Drilling a hole in the wood at the minor diameter of the outside of the nut and using a file to create the flat edges would create this area for the nut. Another method would be to create a hole just a tiny bit smaller than the nut and use pressure to insert the nut and add a bit of epoxy to keep the nut in place.
To reinforce this nut, William used a large washer and drilled two holes in the washer for screws and nuts to mount into the wood.
Instead of making the machine full length, William decided to reduce the length to fit the needs of his application. The length is one of the easiest features of the scratch built CNC machine to modify. Just cut the table portion as short as you need. The lead screw, aluminum rail and bolt holes will be the only modifications needed. It is not recommended to go any longer than 48" however, since the table will sag since no support can be added below the table unless the gantry sides length increased and the table thickened with a system of ribs similar to a torsion box.
Drilling holes on the edge of the wood to intersect with the cross dowel holes is difficult without a jig unless you have incredible dexterity. William chose to use two different jigs, a handmade jig that is similar to the jig in the book, and a doweling jig by general tools. The handmade jig is a bit different to the book's recommendation as it contains drill bushings. The drill bushings make drilling a bit more accurate, insures a straight drill and protects the material within which the bushing is placed. The doweling jig that William used adjusts so that the hole will be centered along the edge and has a long hole to make sure the drilling is perpendicular to the wood at all times.
Check out Williams method to create perfect holes for the BRAs. He uses a lathe and a piece of round stock of wood. He creates a slot in the stock to slide the aluminum angle into and that keeps the aluminum angle steady and centered for that hole for the drilling and tapping.
Here are a few words from William on his experience building the CNC machine: I received your book "Build Your Own CNC Machine" from my son on Christmas 2011. I fell in love with the project, and have read the book many times, and found it very easy to follow. I am 73, and since I retired I have been woodturning and making my own tools & equipment. I have a nice studio with all the tools that I needed to make this project. I have followed the book instructions except mine is 28"x24" because of the little space that I have left in my studio, and I was going to use it to make designs on my woodturning projects, which would be about 18"x18" cutting area, which is sufficient for my work. I made it more streamlined by rounding the corners and used oak on the pieces E,M,B, parts, and cut out to fit the nut, for the lead screw, and glued it into place, and on top of that I put large washers and two bolts & nuts. I found these peaces not strong enough, and I put an extra wood screw on part M & B so that it would not twist out of place. I used 1/4 threading rods and nuts to align everything level and precise measurements before cutting these last pieces.
The whole project was a labour of love, and I tried to keep the cost down, and I came very close to your estimation. We have all our own ways of doing things, and we all can share and learn from that. I have mention in my last e-mail to you, all the changes that I have made in this project, I hope for good reasons, or whatever I had available to make those changes. I have used my doweling jig for all my 1/4 inch edge drilling, which was easy to drill. The wood lathe came in handy for tapping the threads for the railing, my hands are not as steady as I use to be, so that worked very well for me. To drill the hole for the 1-1/8" bearing, after I drilled it 3/8" deep, I made a bushing on the lathe with a 5/8" center whole which I used to drill the center hole right through. I also made the legs 3/4" higher and joint the legs with a peace of 3/4" material which I had laying around the shop for a while. I find it stronger and together as a unit. I may poly the unit later. The next one I am building will be made out of waterproof and formaldehyde free material. It is called Medex waterproof MDF.