Horizontal CMM Experience? Looking for info...

I think not being calibrated in 5 years may be a tell tale sign, also if It's pretty old it probably won't have the accuracy of your bridge or your 3rd party. Also, horizontal arm machines tend to be bigger, hence less accurate. There are probably more factors than listed here including temperature compensation etc.
We run 2 horizontal machines here and regularly have sphere checks fail around 0.1 - 0.2mm.
Also do they mount the fixture the same as you on blocks or flat on the bed, is there sag in the fixture naturally?

I mentioned temperature and we're supposed to be trying to get that info. The fixture is sitting on the table, not clamped. It's a huge fixture, so it should sag to meet table.

Thanks for the info, I appreciate it.

As the arm extends further out from the mast, the more "droop" that you get and that is 100% Z axis error. If it hasn't been calibrated in 5 years then they're wasting their time. More than any other machine the horizontal arms need to have a current table comp map because gravity acts on the arm so heavily the further you extend it out. Oh, yeah, I've some experience with a horizontal arm CMMs; I'll never go back to another.

Mike

It seems like such a terrible idea. I didn't believe that it was actually a thing until I saw a picture.

Ok, I'm starting to feel better about life now, thanks for filling me in!

Two questions:
Did you verify that your CMM program was outputting good numbers by checking some dimensions through other inspection means?
Are all three of you using the exact same program?

If yes and yes...and if 2 out of 3 are saying its good, and the 1 saying they are having issues hasn't been calibrated in 5 years...... then I think we have found our issue.

To Milicron Mike 's point....I hate horizontal CMMs due to the exact issues he has laid out. There is a fine science that must be learned & applied in order to measure properly and accurately.

We use a 3rd party company that makes up their own program, chooses their own points and all that jazz. The 3rd party company verified that the fixture was good to the nominal that they picked.

We don't use the same program. They sent me their nominals though. I brought them into our original program and snapped them to our CAD surfaces and they worked... So their program is good, even though it isn't the exact same points as the points we picked.

It's just awkward because it's a big customer and we have to be like: "Hey budz, it's effed on your end, not ours".... and they insist that their all good there....



So why would anyone opt to use a horizontal machine? What are the benefits of having one of those??

Horizontal CMM's can be single or dual arm.

Common origin is crucial when inspecting with master and slave arm.

p.s. Why is this posted in the Off-topic?

Oh boy. "Pizzing" contests aren't good (especially if they're people you're trying to get money from).

I would do is this:
1) Get a copy of your CMM calibration cert. Hopefully you're fully calibrated to a NIST standard. This proves your machine is calibrated & working properly.
2) Write a quick little program to measure something like a tightly toleranced thread ring THAT HAS BEEN CALIBRATED TO A NIST TRACEABLE STANDARD. I'd do it 30 times...each time re-aligning the part before DCC measurement. Collect the data. Run through CPK formula to provide further data that your CMM is repeating on this gage. Once/if satisfied....
3) Request for your fixture back. Measure it 30 times...each time re-aligning the part before DCC measurement. Collect the data. Run through CPK formula to provide further data that your CMM is repeating on your fixture.
4) Last but not least....do a 100% layout inspection of your fixture on the plate. Collect the data in an inspection report. Hopefully all checks out well.
5) Send them: your CMM cal cert, CPK data on your ring gage or whatever you choose, cpk data on your fixture, and accepted layout inspection report.
6) Ask them to prove to you respectfully yet objectively how they can reject two reputable source's data with an un-calibrated piece of junk (i suggest you choose your own working but I'll leave that up to you).

There's a lot there, hopefully i was able to help

DAN_M Man, I've actually been doing this as I've been talking to you guys. I'm doing a basic ball bar setup on one of our machines (we're calibrated every few months or sooner if an oopsie happens)... I'll send them the bar and ask them to run the same program and see their results. Getting the fixture back is kinda tough as it's in a different country. I'm hoping proving the repeatability of the machine along with the calibration records will be enough.

The company trusts their machine and their operator, hopefully not regardless of the numbers I provide. I think he's got them bamboozled pretty hard.