How To Make Your Own CNC Milling Machine – Part 3
One of the first options I decided to Make to my CNC Milling Machine was a Ballscrew upgrade. I decided to upgrade the Acme Thread Leadscrews to BallScrews. A Ballscrew (sometimes spelled Ball Screw) is a type of linear actuator that translates rotary motion into linear motion. It uses ball bearing in a helical groove to transfer the motion with very little friction. Because of this low friction fit, ballscrews have less backlash or slop than Acme leadscrews and allow you greater repeatability.
Where to get them?
Before we get started, I just wanted to say that replacing the leadscrews with ballscrews is a completely optional upgrade. The supplied leadscrews are very good for manual machining and will also work well as a CNC mill. However, ballscrews are more accurate and are designed to have less backlash than a leadscrew is capable of maintaining. Adding the three ballscrews to the machine costs about $200 dollars. I got mine from a seller on ebay: Linearmotionbearings2008 Ebay Store. The nice thing about getting the ballscrew from the ebay seller was that he offers a machining service and will machine the ends of the ballscrews to your specifications. Since he has done this machining many times he already knew the sizes needed, which made the purchase even easier.
There are also several other sources for ballscrews including Roton, NSK and Nook Industries. There are also a variety of sources to order ballscrews online. Roton Products Inc. http://roton.com is one source I have used in the past. Roton provides good service and reasonable prices. Another good source is Automation Technologies Inc, http://www.automationtechnologiesinc.com. This company also offers many other parts to build CNC machines.
I started with a CAD drawing from the Hossmachine DVD as the basis for my Ballscrew mounts but I made some modifications which I hope will be improvements. I used Vectric Aspire to convert the DXF drawings to gcode. Then on the Z axis ballscrew mount I added some curved surfaces to match the shape of the Ball nut. The ballscrew mounts replace the leadscrew mounts on the Grizzly G0704 milling machine. They are designed to slip over the edge of the Ballscrew nut and bolt onto the flange with 1/4-20 screws. The previous version was easier to make but I felt the curves were cleaner and used less material.
On the X axis ballscrew I added a slot to allow the Zerk fitting (for lubrication) to have easier access through the top of the cross slide. I did not make any changes to the Y axis mount but I may make a slightly different version when I see how thing fit.
Making a CNC Milling machine requires a lot of metal working. Most people will use a manual milling machine to do the metal work. I was lucky to have access to a CNC machining center so that is how I made my ballscrew mounts. Using the machining center was faster and I believe gave me better parts. I machined the parts from T6061 aluminum stock.
Machining the X & Y Mounts
The picture on the right shows the X and Y mounts just after I machined them from 7/8″ aluminum stock. The parts still need to be tapped and deburred. Tabs were used to hold the parts in place in the stock while machining. I cut the parts free later with a metal cutting band saw but you could use a hack saw.