Quill Control

I'm working through a CNC conversion on a SuperMax manual knee mill. The control side of things is now mostly setup and I'm now working through the steel side. I have noticed that there are some companies which sell ball screw kits for the quill. I understand ball screws are a must for X and Y, but I'm lost on why these kits exist for quill control. It makes more sense to be to direct drive it or have a pulley setup. I feel like I'm missing part of the equation. What am I missing?

I'm lost on why these kits exist for quill control. It makes more sense to be to direct drive it or have a pulley setup.

Although it looks tempting to just add a pulley setup, (which has been done in the past) you may find that the original set up which was for manual use is not as accurate as you want and may also have a great deal of backlash.


Rick G

If your just profiling and drilling holes and nothing else you don't need much accuracy on Z. However if you want to do anything that needs the Z axis to be accurate you need a ball screw. My BP with an Anilam 3 axis conversion has a ball screw kit on the Z and even with that the connection point is weak so +- 0.005 is a good day on my Z axis. Any more than that and I know the screw is loose that connects the ball screw to the quill.

JT

Ok, I follow.

So what about direct drive/pulley drive the quill, but have a gas shock or air cylinder constantly trying to push up the quill? I would think it would remove any backlash. Thoughts?

I assume you mean connect a pulley to the pinon shaft originally used to raise and lower the quill while drilling or boring? I suspect the result would not be as good as you envision, but I've not tried anything like that so I can only draw on general machine experience. I would in that situation just use the manual handle to position the Z and use the quill lock and run as a 2 axis CNC.

Is a SuperMax similar to a Bridgeport Series 1 mill?

JT

The first mill I converted I replaced the fine feed handle with a pulley and belt to a stepper. This allowed me to disengage the stepper drive and use the machine in "manual" mode using the original handle.
With this there is a lot of backlash which I used backlash compensation to help with.
As John said this is fine for drilling and profile. It does make accurate Z height setting difficult and somewhat at the mercy of the cutter pulling the Z height one way or the other.
The problem I ran into with the spring was having a spring that had enough strength and travel and this also reduced the downward force available to drill with.
This machine is still in use at another shop.

Having said that the next mill I converted I made up a ball screw setup for the quill and never looked back.

Rick G