Proposed Y-Axis Ballscrew Mounting Assembly & Cover.

In the picture above you can see my proposed design for the Y access Ballscrew mounts and general cover. It was clear that I would want to provide a strong barrier of protection from coolant and chips interfering with the ballscrew nut and support assemblies. At this stage I had already selected the types of limit switch and homing sensor that I was going to use. Even though these were IP68 rated, I wanted to include all these sensors inside the assembly to keep them as free a clear from contamination interference as well. I was also planning to use linear glass scales in this build which combined with running the MESA 7i95 Controller and DMM Servo's would give me Fully enclosed positional feedback for maximum precision and backlash management. This works by feeding back the actual real time position of the servo using the highly accurate glass scale to allow the control system to make positional adjustments to where the servo thinks it is, to where it is physically is space.

Listed below are some of the design considerations that I decided I would want in the design of these assembly mounts....

• Easy access to the servo, coupler, fixed and floating ballscrew supports and the ballnut connection. Simple diagnostic and adjustment to the limit switches, homing and glass scale connections.
• Enclosed limit and homing switches.
• Extra cable shielding protection.
• Managed drainage for inevitable entry of coolant into the assembly.
• Provision for Way-Covers to minimise swarf and coolant ingress.
• Neat, tidy and risk-free cable management.
• Simple to access and remove the entire assembly for maintenance.
• I knew this full assembly would be heavy, so I wanted to consider the ease of removing the whole assembly as well.
• Viton Rubber seal to be used on appropriate joints to minimise coolant ingress through potential pooling. Viton is a type of rubber that is resistant to damage from coolant fluid.
• Provision for simple micro adjustments of the ballscrew positions for fine tuning and dialling in the whole machine.
• Incorporate an extremely precise and rigid servo motor mount.

These assemblies were on of the time consuming to design actually. I spent a lot of time trying a variety of solutions and approaches to put a tick in all of the boxes above. I planned to build the entire assemblies out of Aluminium cast tool plate with the exception of the ballscrew, supports and servos ofcourse. Originally, I had planned to make the entire assemblies myself. The build had evolved into something with the potential to be very rigid and accurate, so I thought it extremely important that the servo mount and screw supports were made with very tight tolerances. I was fortunate enough to have a friend of mine volunteer to make these components for me on his CNC Milling Machine. I would have struggled I think to drill the 80mm diameter servo holes and place the mounts with such accuracy that I could achieve almost perfect concentricity with the ballscrew and motor shaft. That’s not to say that I would not have been able to do it with the relatively simple tools I had at my disposal, but the importance of getting it right for the success of the project, it seemed too obvious that the best way to go was to have these made properly. I would cut, drill, tap and assembly all of the other components in these assemblies, however.

Unfortunately I was due to have some terrifying flashbacks of time in hell already served, as I had another twenty holes to drill in granite.

Blank Drill Jig for the right side of the Y-Axis.

Drilling jig with holes for the drill guide of the Y Axis Ballscrew assembly mount.

If you decide to take on such a project, I will highly recommend that you complete a full design in CAD, so that you can take advantage of the ability to drill holes in granite whilst they are not permanently bolted to other parts. If I had completed the design of these mount assemblies before I mounted them to the granite surface plate, I could have drilled them laid flat with a pillar drill and this would be much easier. Unfortunately I was left with only one option and that was to drill them by hand with a power hand drill. Do not underestimate how much time and energy it takes to do this. The noise and vibration of drilling for long periods of time makes your bones hurt and it gave me a terrible headache, even having worn ear protection. It took two solid eight hour days to drill these twenty holes. I had also bruised all my chest and the ribs were sore from applying pressure to the drill constantly. I had considered somehow clamping a drill press sideways, but I decided it wasn't worth the risk of putting undue stress of the granite while drilling holes. This far into the project with a fractured side of granite would have been highly dis-heartening.

A simple wooden jig used to help align the core drill square and perpendicular to the granite.

Holes drilled and inserts mounted in one side of the assembly.

Holes drilled in the left side of the Y granite upright.

It is also a very messy job drilling granite.

Continue to Y-Axis Ballscrew Mount Assembly Part 2 >