John S.C. did something that I have not yet seen. He applied a ball-screw to the DIY version of the CNC Machine found on the step by step and the book "Build Your Own CNC Machine". Yes, you heard me right! A ball-screw. Why do I sound excited? Read on.
If you are unfamiliar with what a ball screw is, you are in for a treat. A ball-screw is a lead screw mated with a nut that contains ball bearings. The screw has a slightly different thread so the ball bearings can ride within the root of the thread. The root of a thread is the valley, the lowest point between two threads. You might be saying... but the balls in the nut will not turn if they are crammed in there. Well, the nut actually has pipes that allow the balls to flow around and not cause any scraping or binding. The end result, the ball screw is super tight and super easy to move.
John Shows us photos of the specific parts of the machine that was modified. John also provides some suggestions and tip for the builder of their CNC machine. the remaining narrative is by John.
Here is the photo of the barrel nut jig with the steel bushings. The front piece has two barrel nuts to attach it to the top piece rather than gluing it. Then there is a small slot so that the front piece can be adjusted sideways to accurately align the 1/4" hole with the top. The front has two steel bushings which keeps the drill bit aligned - one doesn't work. The front bushing is 1/4" ID by 1/2" OD and the top bushing is 7/16" ID by 3/4" OD. I have a similar jig to drill the barrel nuts for the 1.25" aluminum rail which extends down 3/4" instead of 3/8".
Here is an assembly tip for aligning the barrel nut with the bolt. I found a few cylindrical ceramic magnets in my tool box. I put the barrel nut on the magnets with the slot side on the magnet. When I insert the barrel nut in the hole, the magnets keep it aligned and flush with the surface so that the machine screw aligns perfectly. Also, when you have a barrel nut assembled in the rail, then use a machine screw with two nuts in order to lock down the depth at which the screw is aligned in the other rails.
For an assembly tip, I found that some boards have matching holes. So I bought some inexpensive 1/4" threaded rod and put them through the holes so that it makes it easier to measure the length between boards, rather than using the long clamps. When I saw this, I rebuilt the boards by 2" longer in the back and used two threaded rods to tighten down the bearings on the rail and make it level. So now I need only one board between the threaded rods to hold a ballnut and flange to drive the Y-gantry using an ACME ball screw which I purchased. It has 10 TPI rather than 13 TPI.
Another assembly tip is to drill a hole about the size of the nut, and then use a vise to push the nut into the board. This board can be drilled with larger holes through which the 1/4" machine screws can fit onto the drive board. Thus the board can be shifted to match the position of the drive threaded rod. Large washers can be used to hold the nut in the board. I tried this and it works well, but I still like the ballnut even though the cost is some 50 times more!
A third assembly tip is to use a drill with a 1/2" chuck to test drive the threaded rod back and forth rather than using your fingers.
A fourth assembly tip involves not being able to drill a hole in the side of the MDF board. To get around this problem, the board to be drilled has to be clamped to the table. Then the jig has to be clamped to the board and the table in order for there to be no vibration which prevents drilling.
A fifth tip is to get a Drill Doctor for sharpening the drill bits which really helps and is less expensive than buying new bits.
A sixth tip is to purchase those red and black board clamps with the curled metal holders. They make it easy to drill the holes in the side of the board rather than relying on the dimensions. That is, it is more of a fitted construction rather than making the boards to the dimensions given, even though the dimensions are accurate, but from errors in measurement, transfer punching, pilot hole drilling and jig drilling which tend to have tolerances, the holes can be misaligned. With this method the machine screw aligns with the barrel nut first time through.
Here are two photos of the right angle clamp which holds two boards together such as end-to-end or like on the Y-gantry in the middle. You can see the two holes are available for partial drilling. After drilling an alignment hole, then a transfer punch aligns the hole with the jig. Then the large barrel nut hole is drilled followed by the 1/4" hole. I get such good results that the barrel nut and screw go in the first time now.
These clamps are made of plastic and some people have experienced cracking of the plate. What I did was to insert them on the board and then Superglue them together so that the plastic doesn't bend, which is what causes the cracking.
Here is a photo of the z-axis ball screw and the flange nut. I attached the drill and it goes up and down smoothly. I can even turn it by hand.
I removed one machine screw on each side that holds the bearing rail and replaced it with a threaded rod that keeps everything rigid and makes it easier to assemble.
After cutting a board with the circular saw, the board fell on the cement floor which left a dented corner. So I put some bubble wrap on the floor to cushion the fall. I see you have the anti-backlash flange nut for sale.
The 1/2" collars don't grab the ball screw so I had to use the set screw collars. The diameter is slightly less is the reason.
I still have to install the x-axis ball screw which I can do today. Overall it is looking very good.
There are some interesting possibilities for routing out a linear Fresnel lens for heating a heat pipe. This would create a mold for pouring optically clear plastic that hardens into the lens. Also, on Make magazine there is artwork made using staples. It might be possible to put a staple gun on the machine and convert bitmaps into raised staple drawings. Then another one is using a clay dispenser to create ceramic bowls and sculptures. By mounting a rotating knife on it, leather can be cut to make bags and other products. A fourth stepper motor would turn the knife to align it to the path.