If your CAD part has its z zero on the bottom, which coincides with the granite surface of the CMM, How do you take hits on that surface in DCC mode? In manual mode its simple to probe the granite around the part and call that z zero. Once you switch to DCC mode, I cant figure out a way to instruct the machine to take hits on a plane extended out from the part bottom. I have worked around this in the past by moving the z on the cad model but the part I am measuring now doesn't lend itself to that method. It is basically a large cone with no plane at the top. The part is too large to fixture on its side. Thanks in advance.
I'm just wondering what 's about the flatness of the underside of the part in front of granite flatness... Even if the granite is not calibrated, I think that it's quality is better than a classical machined surface (IMO).
I have a Global S 7107 made in 2021
The flatness of the granite across the entire face was w/in .015". The flatness in 1ft X 1ft areas was approx. 0.003"
If I need to measure the bottom of a part, I will usually mount it up on blocks use a star-probe
I'm just wondering what 's about the flatness of the underside of the part in front of granite flatness... Even if the granite is not calibrated, I think that it's quality is better than a classical machined surface (IMO).
I have a Global S 7107 made in 2021
The flatness of the granite across the entire face was w/in .015". The flatness in 1ft X 1ft areas was approx. 0.003"
If I need to measure the bottom of a part, I will usually mount it up on blocks use a star-probe
yes, the newer machines are NOT made to the 'standards' they used to be made to. Once the controllers were able to be used to map the machine into spec, they no longer had to BUILD them to spec. My almost 40 year old Validator has a very flat table (like, <0.001" total for the entire machine)
Matthew D. Hoedeman respectfully I would love to challenge your statement. Do you have any evidence to support newer machines are manufactured with the reference surface being uncertifiable to surface plate reference specifications? I strongly believe that in order for these machines to function as designed, the air bearing surfaces for bridge CMM's must at some point comply with ISO/IEC 17025 specifications. Why would whomever manufacturing the surface plates stop at just the bearing ways? They'd almost have to manufacture the parallel surfaces with the same equipment, no?!
The only instances I've ever heard of where the granite was 'certified' on a CMM was for those that have a granite plate that isn't a solid part of the machine, but just a plate that 'floats' on the table of the machine, not one that the bridge actually rides on. My global has 2 different elevations that the bridge rides on, not a single plane of stone. Back in the day, when they (B&S) made the slabs, they had to make them in pairs as they used the 2 slabs to hone each other flat. Can't do that now (like with my Global), and sure can't do that with the machines that have the 'up' step of granite that also acts at the Y axis way surface. Yes, they are close, but look at Dan's post, his stone is WAY out of any kind of spec, and that is only 2 years old! Also, since they went to the 3-point bridge support, this allows much more 'un-flatness' to be workable for the table since the table maps take care of it. I'm pretty sure Dan's machine isn't certifiable to surface plate standards since it is 0.015" over all and 0.003" in 12x12" area.
