Re: What is the weak link in machine precision?

Hi!
I"m reaching way back to a machine tool technology program I took...
But I think moving the knee is NOT the best way to do it for long term accuracy. In order
to move the knee gibs have to be unlocked and the weight of the knee causes the table to
"sag" and put a lot of pressure on the vertical table slides.
You'd be better off fitting the quill with a drive for the Z axis if your mill lends itself at all
to that.

Ball screws will hold their accuracy a lot longer (though well made and well lapped acme
screws can be as accurate in the short term), and Ball screws take less torque to move.

Regarding the electronics end.... Don't know.. I'm here to learn that part myself :-)

Paul F.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "zipdrive2k" <zipdrive2k@y...> wrote:
> I am wanting to retro-fit a knee mill for prototyping aluminum and
> some steel tooling dies. Many of the parts are complex surfaces and
> require 3 axis simutanious machining. I need to keep the machine
> accurcy in the 0.001" to 0.003" range. Quill will be locked and knee
> will be moved for z-axis. Extreem speed is not a requirement.
>
> I am assuming that the software will be running closed loop and the
> culmitave error will be less than the mechanical error of the machine
> elements. Yes / No? Replacing the acme threaded rods with ball
> screws (0.0006"/ft) seems to be the first step. Z-axis ways - anyone
> experence excessive wear or degration in performance by using the
> knee in constant motion? I (again) assume that the ways need to be
> chromed to help resist wear, or do they not wear for the first 2000
> hrs of use (or some other vage number)?
>
> Anyone with measured performance on their machines?
>
> Thanks.