Philosophy of CMM Software and CMM

[zancky]

hi Hawat,
I have got a special real case:
a valve housing that can not be assembled if the mean diameter is out of tolerance and, "icrendibile visu", the roundness is smaller then 0.03 mm:mg:!!
it can not be controlled by any go-nogo plug gage!
(for those who think lower roundness is better and for anyone involved in ISO and ASME we need a drawing symbol to state a minimum ovality!)

 

[True Position]

Now that's a special case! Do you need ovality or would tri-lobed work?

 

[zancky]

Now that's a special case! Do you need ovality or would tri-lobed work?

the part is a valve housing (let's think about a closed tube/pipe on the bottom and a flange at the opening and small wall thickness). the customer needs to insert a magnetic plug on the bottom with interference (there is a final station in order to roll outside housing wall to fix the plug). if the interference is given by the two diameter (bottom of the housing and plug diameter) the friction is so strong that will deform the total valve length. So in order to have no clearance between plug and housing inside diameter we are "using" the roundness. "lobed" will be perfect but it is a press drawing part.

 

[zancky]

I have got a new issue: roundness.

drawing requirement about roundness in every standard is about circle and doesn't need any other reference/datum.

into the real world cylinder and cylindricity are self-reference features not circle and so not roundness. In some cases we need a reference/datum axis in order to determine the circle/diameter ( let's think about a circle created by the revolution of an inside/outside rib) and so the roundness (e.g unwritten assumption)

working with CMM usually we look for some (from 1 to 2) reference axis into the parts in order to align the CMM system axis before performing the measure. Cometime the requirement is a hole diamter therefore we can apply the cylinder feature first on the parts to be measured.

something different happens working with roundness machine o dial bore gaes with which the "alignement" process may be performed by looking for the minimum roundness error

I would like to know Your opinion/experience and I have attached 2 file for example


thanks

 

[True Position]

I am sorry to say, my math skills have been lost due to lack of use. Is your concern that since you align to the cylinder on the CMM the software will correct for any errors in the hole/pin's axis compared to a roundness checker which would just trace an oval pattern on a mis-aligned hole/pin and report how round/out of round the oval was? (Or potentially report an oval as round.)

 

[zancky]

I am sorry to say, my math skills have been lost due to lack of use. Is your concern that since you align to the cylinder on the CMM the software will correct for any errors in the hole/pin's axis compared to a roundness checker which would just trace an oval pattern on a mis-aligned hole/pin and report how round/out of round the oval was? (Or potentially report an oval as round.)

sorry but it was difficult to me to explain.
I would like to point out that
- In the real world sometime a diameter and a roundness requirements on the drawing may be just a question how You align the part and it may be there is no indication on the drawing how to proceed.
- CMM can give a affordable result respect to round tester if you find a reference axis
- My friend procedure always minimizes the actual roundness: in my example an oval cylinder has 0 roundness measure

hope it is clearer

 

[Stimpy]

Learn mode in MCosmos is awesome. I've written thousands of programs, 99.9% of which were written in Learn mode. Works great, easy to use. I've never had any issues.

 

[tribalarm]

I too find Learn Mode really easy to use and haven't had an issue with it.

I also program directly in edit mode but find this a lot more time consuming.

Along with the fact if you use Mitutoyos Offline programming then you HAVE to program through learn mode.

The automatic feature recognition on Calypso is different to this but Mitutoyo Cosmos has the same auto recognition, just start measuring a feature and it will perform the same as Calypso, ie work out what element you are trying to measure, rather than selecting from the menu.