Yesterday a friend of mine told me he was surprised to learn that not all CNC mills run linear scales on the axes to allow the actual table position to be known. He was even more suprised to find that some mills like my Tree run the encoder with a belt between it and the ball screw. I informed him that seemed to work pretty well though many VMCs would be more likely to have the servo motor mounted on the end of the ball screw and so eliminate the belt and that linear scales looks to be a "high end" type of thing to find on a mill.

I went to the Haas site and found that on the VF1 with a MSRP of $47K the linear scales are a $10K option. I told him that my impression was that probably wasn't purchased by many people as the rotary encoders are "good enough" for most work. It looked like Fadal and Sharp also had the linear scales as an option, not a standard feature.

Does Haas actually sell many linear encoders upgrades? It seems like many people might instead take that extra 20-25% and buy a nicer base machine that had a bit more accuracy to start with.

cheers,
Michael

I called Haas engineering department when I was investigating a VF1 purchase about the glass scale option.

At that point in time ... My goodness... it was 2003 !!!

The reply was the positioning and repeatability advertised accuracy for both the encoder and scale were the same value.

I do not know if that has changed... and I have not regretted leaving the scale option off the machine.

"so far" there has been no issue with either in our use of the machine (micro engraving with positioning tolerances).

I was looking at the encoder counts per unit in the Haas parameters the other day. It is some oddball number like 138,000 counts per inch or something. But it seems to be quite a bit more resolution than the minimum commanded axis movement. That is a good thing though, that means it is not struggling along trying to give or take a whole .0001"

Still, I would think as the machine wears in use, that the scale is going to provide greater accuracy over long distances. Now whether the scales actually last long enough to outlive the mechanicals, that is the question.

If the work I am quoting has to be that close, I don't want it.

I did give the wear aspect consideration... the work area for this particular component is very small... I felt like if/when issues with location did appear, simply moving to another work coordinate would solve the issue. So far.... we are not there yet.

I also agree with you on the life of the scales and the aspect of them remaining trouble-free ...