Re: [CAD_CAM_EDM_DRO] more ball screw/CNC retrofit questions
Posted by
Jon Elson
on 2002-05-03 22:41:32 UTC
no falloff wrote:
There are rolled screws for positioning, with various levels of accuracy.
There are ground screws, and precision ground screws with accuracy as
high as your wallet will take you. And, there are plain ballnuts and anti-
backlash ballnuts.
line up accurately is no small job. I made my own yoke for the ballnuts in the center
of the saddle, and it was a big job, and I had to shim things because I wasn't able to
measure the parts accurately enough. Unless you want a long, slow, irritating process,
I'd recommend buying a complete set.
second. That is WAY too slow for any positioning servo system. You could use it
as a manual error check to spot lost steps and keep an eye on backlash, though.
however, so one worry is cleared up. Tight anti-backlash ballscrews/nuts of
sufficient precision fix the accuracy and repeatability problems, assuming the
machine ways are in good shape. If you will be taking heavy cuts or need
high rapid-feed rates, then a servo is very desirable. If you will be doing
high precision work, or making expensive workpieces where a lost step
could cost you thousands of $ or weeks of work, then a servo is also a
good choice.
Jon
>Yes. There are rolled screws for power transmission (no accuracy spec at all)
> I'm a bit new to this, and I'm still trying to figure out exactly what I ultimately want to do so please bare with me.
>
> Are there different types of ball screws?
There are rolled screws for positioning, with various levels of accuracy.
There are ground screws, and precision ground screws with accuracy as
high as your wallet will take you. And, there are plain ballnuts and anti-
backlash ballnuts.
> What should I be looking for if I want to try to find ball screws to retrofit my lathe or Bridgeport to CNC? I see Bridgeport retrofit kits that have the X and Y axis ball nuts as one unit and are likewise fairly expensive. Is this necessary or would it be relatively easy to use two independent (less expensive) units? Such as the ones that seem to be common on ebay?You can go this way, but they won't be drop-in replacements. making all the components
line up accurately is no small job. I made my own yoke for the ballnuts in the center
of the saddle, and it was a big job, and I had to shim things because I wasn't able to
measure the parts accurately enough. Unless you want a long, slow, irritating process,
I'd recommend buying a complete set.
> Lastly. Can high rez. DRO quills be used to supply the feedback that is lacked in a stepper motor type system?No. These are really modified digital calipers, and only update the display about twice a
second. That is WAY too slow for any positioning servo system. You could use it
as a manual error check to spot lost steps and keep an eye on backlash, though.
> Is there such thing as a comparator either in the controller or PC software for this? Likewise, am I just better off with servos to achieve higher accuracy/repeatability?Servos do not strictly improve accuracy or repeatability. They don't lose steps,
however, so one worry is cleared up. Tight anti-backlash ballscrews/nuts of
sufficient precision fix the accuracy and repeatability problems, assuming the
machine ways are in good shape. If you will be taking heavy cuts or need
high rapid-feed rates, then a servo is very desirable. If you will be doing
high precision work, or making expensive workpieces where a lost step
could cost you thousands of $ or weeks of work, then a servo is also a
good choice.
Jon
Discussion Thread
no falloff
2002-05-03 18:00:40 UTC
more ball screw/CNC retrofit questions
Jon Elson
2002-05-03 22:41:32 UTC
Re: [CAD_CAM_EDM_DRO] more ball screw/CNC retrofit questions