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Portable CMM Arm Hexagon vs Faro

ArturoMeltri

Plastic
Joined
Jan 15, 2018
Hello!!

I need your help to decide which portable CMM should I buy.

I'm comparing Hexagon Absolute ARM 85 with Scanner and probe, this portable CMM offers a 0.008mm precision with a Faro FaroArm with Scanner and probe, and this protable CMM offers a 0.009 mm precision.

I don't really know which one should I choose because they are very similar in price and very similar in precision, can someone share with me their experience with any of this two options.

I'm quoting a 2.5 m arm lenght and they are around 65k with Polyworks software.

Thank you!!
 
2.5 Meter arm length @ .008mm accuracy?

You sure that you don't mean .008" accuracy?


If not - then things have changed a bunch since I last checked!


----------------------

Think Snow Eh!
Ox
 
2.5 Meter arm length @ .008mm accuracy?

You sure that you don't mean .008" accuracy?


If not - then things have changed a bunch since I last checked!


----------------------

Think Snow Eh!
Ox

Hello!

I have verified with my Hexagon-Romer dealer and yes, they already have .008 mm precision with the 2.5 m lenght.

Faro told me that in the best situation they can offer .008 mm but normally the arm is 0.01 mm precision.
 
The QA dept of a company I worked for a couple of years ago got a Faro arm and were using it for all kinds of measurements. I worked in a group that designed a lot of large parts with tight tolerances (like 36" dia +/- .002) - the Faro arm caused a lot of arguments and rework because it repeated great but never measured right.

Parts would get rejected and sent for rework and the vendors would measure with mics and disagree with the Faro arm - if the rework was done invariably the parts wouldn't work. It always came back to the Faro arm just measuring wrong. Lots of back and forth between bigwigs and expensive heavy parts being shipped all over and builds being delayed.

Not sure if it was something with the way the QA guys were using it or what, but it sure didn't make me confident in those things.
 
Hexagon vs Faro

Hello!!

I need your help to decide which portable CMM should I buy.

I'm comparing Hexagon Absolute ARM 85 with Scanner and probe, this portable CMM offers a 0.008mm precision with a Faro FaroArm with Scanner and probe, and this protable CMM offers a 0.009 mm precision.

I don't really know which one should I choose because they are very similar in price and very similar in precision, can someone share with me their experience with any of this two options.

I'm quoting a 2.5 m arm lenght and they are around 65k with Polyworks software.

Thank you!!
In my experience the Faro will give accurate readings in the +/- .025-.075mm range. Do not count on it to give accurate diameters; if there is a discrepancy between shop and inspector (on diameters) resolve it with hard gaging. The newest version of their software leaves some things to be desired. GD&T position needs a CAD model, and some types of geometry ( 90* elbow with connectors) can be frustrating.
Any sales rep is going to give you the typical dog and pony show. You have to find out if there are after salep costs, i.e. training, software updates, dealer only calibration, warranties, etc. When my company bought a new Faro and I went over the itemized quote I found that we could get the rolling stand and magnetic base plate for half the cost elsewhere (original manufacturer).
 
They're synonymous in my world.

Accuracy is how close the mean is to the true value. Precise is how closely the data is together. For example, if we throw darts at a dart board and they form a spread out cluster around the bullseye, that is accurate, but not precise. If they all land on double 20, that is precise, but not accurate. If they're all in the bullseye, that is precise and accurate.

Put another way, accuracy measures systematic error, precision measures random error.
 
In my experience the Faro will give accurate readings in the +/- .025-.075mm range. Do not count on it to give accurate diameters; if there is a discrepancy between shop and inspector (on diameters) resolve it with hard gaging. The newest version of their software leaves some things to be desired. GD&T position needs a CAD model, and some types of geometry ( 90* elbow with connectors) can be frustrating.
Any sales rep is going to give you the typical dog and pony show. You have to find out if there are after salep costs, i.e. training, software updates, dealer only calibration, warranties, etc. When my company bought a new Faro and I went over the itemized quote I found that we could get the rolling stand and magnetic base plate for half the cost elsewhere (original manufacturer).

We want to use the Faro or Hexagon to measure some complex forms which can't be measured with Vernier Calipers or Micrometers.

We have some pieces that have 3D surfaces and we can't measure them right now. We trust in our tolerance, machine and when we have this kind of surfaces we use new tools to get the surface finish we need and believe our pieces are ok.

We have made around 10 pieces of this kind in the last month and not a single one was rejected but we want to be sure.

Hexagon made a demo in one of this pieces and the result was great, we had only +.013 mm in the surface and my client give me +.025 tolerance.

So, do you think is a good investment to our company to get this tool? We want to be sure that our pieces are ok when we send them to our client.
 
The QA dept of a company I worked for a couple of years ago got a Faro arm and were using it for all kinds of measurements. I worked in a group that designed a lot of large parts with tight tolerances (like 36" dia +/- .002) - the Faro arm caused a lot of arguments and rework because it repeated great but never measured right.

Parts would get rejected and sent for rework and the vendors would measure with mics and disagree with the Faro arm - if the rework was done invariably the parts wouldn't work. It always came back to the Faro arm just measuring wrong. Lots of back and forth between bigwigs and expensive heavy parts being shipped all over and builds being delayed.

Not sure if it was something with the way the QA guys were using it or what, but it sure didn't make me confident in those things.

What you say is true, some of my partners which are in production are a little bit concern about this tool, because they don´t trust them.

We want to use this tool to measure 3D Surfaces which can't be measure with any other manual tool.

What do you think about using this tool to measuare 3D Surfaces, if you were in my position what would you do?

My boss is giving me the money to invest it in this measuring tool, but I'm worried because I don´t want to cause any of the problems you told us.

My workers are working great and if we reject a lot of their pieces which are ok but the Faro or Hexagon says are wrong we are going to have differences and fights,
 
So they they did the demo on a part you can't check? Sounds like you need to get them back and have them run it on something big that you can check. you can get pretty creative measuring a lathe.
 
What you say is true, some of my partners which are in production are a little bit concern about this tool, because they don´t trust them.

We want to use this tool to measure 3D Surfaces which can't be measure with any other manual tool.

What do you think about using this tool to measuare 3D Surfaces, if you were in my position what would you do?

My boss is giving me the money to invest it in this measuring tool, but I'm worried because I don´t want to cause any of the problems you told us.

My workers are working great and if we reject a lot of their pieces which are ok but the Faro or Hexagon says are wrong we are going to have differences and fights,

What kind of tolerances are you trying to hold on your surfacing? I wasn't in QA so I don't really know a lot about how the arms are setup or used, but I remember the general attitude was that if you had a feature that was +/- .003 or tighter you should push hard to get QA to not use the Faro arm for it as it probably won't be right.
 
Any measurement tool should be proven to be acceptable for the intended use by performing a gauge r&r.

If you can have samples ready the sales person shouldn't balk at helping you program the arm software to perform one as part of the demo.

Any CMM is only as useful as the program. Missing a rotation or leveling can through off the results.
 
The FARO can not, in a million years, measure 8 microns accurately, the manufacturer grossly overstates the capabilities. They're OK for, say sheet metal work, or sand castings, but not precise measurements.

FARO arms can typically repeat to 0.002", with extreme care, Romer arms about 0.001".
 
I've worked with a Romer arm. Here are some of the main points that I've come across.

1) When taking a measurement, the accuracy of your reading is at least 2x the positional accuracy of the machine. When you set your zero/datum, that accuracy of that can float +/-.008mm. When taking the reading of the feature that you are measuring to, that is also only accurate to +/-.008mm. So your total accuracy on a distance measurement for example ends up being +/- .016mm.

2) If using this to verify a part is in tolerance, you should pinch the tolerance in by the .016mm uncertainty. Additionally any parts that are within .016mm of the edge of tolerance zone, may get flagged by the arm as being out of tolerance.

3) If you are measuring parts that are flimsy, part deflection can be a major factor. We check majority of our parts on CMM. Even with a fairly thin part with non-rigid fixturing, the probe gets accurate readings due to very low measurement force. When checking the same parts on Romer arm, we ran into a lot of trouble due to part deflection.

4) The probing is only available down to 3mm diameter from Romer, so smaller features can't be checked. I've read that Faro offers smaller tapered probes for checking small features. (Boggles my mind that Romer arms don't allow you to define custom probe tip diameters)

5) Manual probe arm is a poor option to check hole locations if you're dealing with tolerances tighter than +/-.250mm imo. You can nest it in the top edge/countersink of a hole but accuracy is poor especially if hole is threaded

Might be worth checking out the XM series from Keyence as well. This system has a lighter wireless probe head that runs off of line of sight to the head of the machine. Workspace is conical shaped spanning out to 2 feet or so at the widest point. I think the table movable with an encoder that keeps the total accuracy within .008mm and expands the maximum size of the part you are measuring. System just added model comparison, so you can import a solid model, align a part and compare to the model as you can with romer/faro arms.
 
I've worked with a Romer arm. Here are some of the main points that I've come across.

1) When taking a measurement, the accuracy of your reading is at least 2x the positional accuracy of the machine. When you set your zero/datum, that accuracy of that can float +/-.008mm. When taking the reading of the feature that you are measuring to, that is also only accurate to +/-.008mm. So your total accuracy on a distance measurement for example ends up being +/- .016mm.

If your arm is secure in its mounting to a common base for a fixtured part, would that not eliminate that stack-up in tolerance?
 
If your arm is secure in its mounting to a common base for a fixtured part, would that not eliminate that stack-up in tolerance?

Even if they share a common base and the arm/part are fixtured completely rigid, there is still uncertainty whenever you take a reading with the arm. When you set the zero on a part that is a reading and there is uncertainty. One time you may go to take your zero and the arm with nail the reading dead nuts to what the part actually is. Another time when you take the zero, it could be +/- whatever the accuracy of the arm is. That compounded with the accuracy of the point you measure to gives you the stack-up in tolerance.
 
^ The old gold faro arm i use to use could use anything as a probe, think like the carbide stem off a shattered ruby probe ground to a blunt point. Just ran it through the calibration ball hits and we were good to go, for what we were doing it ended up being a far more useful probe than a stupid shiny red ball ever was.
 








 
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