Brown & Sharpe Reflex Z Axis Question

I recently acquired a Brown & Sharpe Reflex CMM. I never had or used a CMM before so everything is new to me! After getting it set up, I checked the precision of the x, y, and z axes using gauge blocks. I ran the machine in "height gauge" mode. I performed the measurement with blocks of different sizes. What I observed was the Z axis results always had approximately 0.078in added to the values. The other axes did not exhibit this.

I ran the probe set up procedure several times and got the same result. The machine also came with a second
(Renishaw TP1) probe and I got the same result with the different probe. I posted a table of the measurements in this thread to illustrate what is happening.


Since this mode of measurement only takes two points and subtracts them, how is it coming up with this additional value?

Anybody have any idea what is causing this and what I could try to correct it?

Thanks,
Alan

After reading the training manual closer, I think the problem is a bug in the software. The method I had been using was to measure two points and let it calculate the change in distance along the axis. For some reason it worked well for x and y, but not z. There is another method where you measure the first point, set it as the datum, then measure the second point. Using this approach, the z axis also gave accurate results! For posterity and in case anyone else runs into this, I've posted the menu pic illustrating how to set the first point as the datum.

I have no idea what is specifically going on, but those error values are suspiciously close to 2mm equivalent. I would wonder if somehow the Height Gage mode operates the Z-axis under some different set of parameters, perhaps in relation to use of a 4mm probe. If you can't figure it out from the inputs you get here, maybe Hexagon can offer some guidance.

After seeing your second post, I wonder if you are performing an alignment step prior to measuring the gage blocks(?). I have used a Zeiss Eclipse machine (manually, years ago), and this step is one that I always thought was a consistent requirement on any CMM. The alignment step essentially assigns datums to the part surfaces and/or the surface plate on which the test part is placed.