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

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?

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

John,

Yes I put a stepper with a 10 to 1 gearbox on the knee using the stock setup.
I only use the W (knee) for positioning work so the slow speed is not a problem and with the mass backlash is not an issue.

Rick G

Hmm... I was thinking of having an air power cylinder that is constantly trying to pull the quill up. Then have the motor driving it direct drive or pulley. I would think that would eliminate the backlash? The motor would then always be working against that tension.

?

BigJohnT wrote:

Is a SuperMax similar to a Bridgeport Series 1 mill?

Yes, pretty much.