"D" slots profile

[Peter Warcholyk]

Good Morning Folks,

What method(s) can be used to report out the profile on "D" shaped holes?

I have measured 4 "D" slots on my part, 7 points.

Typically, I report out the location of all 7 points, with the "T" value.

I then did a "construct feature set" out of each group of 7 points. (Is this ok to do?)
If I report out the profile, form and location, of the feature set, I get a measured value almost double that of the individual location points.

If I report out the location of the "sets", everything shows up ok.

I'd appreciate your insight on this matter.
Secondary note; when the parts are placed on the checking fixture, the "stab pins" on the fixture enter the "D" slots just fine.

Blessings,
ZydecoPete

[Wes Cisco]

Good Morning Folks,

What method(s) can be used to report out the profile on "D" shaped holes?

I have measured 4 "D" slots on my part, 7 points.

Typically, I report out the location of all 7 points, with the "T" value.

I then did a "construct feature set" out of each group of 7 points. (Is this ok to do?)
If I report out the profile, form and location, of the feature set, I get a measured value almost double that of the individual location points.

If I report out the location of the "sets", everything shows up ok.

I'd appreciate your insight on this matter.
Secondary note; when the parts are placed on the checking fixture, the "stab pins" on the fixture enter the "D" slots just fine.

Blessings,
ZydecoPete

Since the fixture shows the parts good, I would think the demon dimensioning method that shows them good would be the one to use. I missed seeing which version you run, but if you have an autofeature to check the slot, that is what I use, then I can use tp and profile on the autofeature and it works just dandy. HTH

P.S. appologies for not responding earlier.

[craiger_ny]

All I can do to help is bump you to the top.

I am guessing with the profile being double you are getting a zone size (±) hence double what the linear mislocation is perhaps.

[Peter Warcholyk]

Craiger,

Thanks for your response. I forgot to mention, I use 3.7mr3.

I can't use autofeature as this slot is a "D" shape, therefore I measured and dimensioned individual points.

I was wondering if it was "legit" to create feature sets out of the groups of points, and the correct way to tolerance the sets.

I am also guessing that the profile of the sets are being doubled. Would I be ok in also doubling the tolerance, since the fixture shows slots being ok with the "stab pins" ????

Thanks for your assistance folks.

Blessings,
ZydecoPete

[Randy L.]

Could you attach a copy of your report? When you dimension a profile of a feature set, it takes the min and max points and adds them together. Is that what you are seeing? Example pt1= .010, pt2= .012 and pt3= -.005 your profile is .017. Let say your profile tolerance is .040 or +/-.020 (assuming it is a bilateral tolerance).

[John Riggins]

PC-DMIS and reporting profile of Feature Sets

I do not use the deviation values provided by PC-DMIS for form and location of surface profile on feature sets.
I do a graphical analysis and then look at the MIN and MAX values.
I take the greatest absolute value (either positive or negative) and double that to report Surface Profile.
PC-DMIS will take those 2 values (if positive and negative), add them together and report that as DEVIATION, or, if all of the values are either positive or negative it will report the greatest (absolute) as DEVIATION.

[justncredible]

Are the D slots on a pattern? The construct feature set would show if the pattern falls into the diameter called out. So if I am not mistaken would be giving you a postion, better known as "True Position" of the pattern to the datums and whatever value for the center point of the feature set.


Is the "D" slot called out with a radius and flat to the radius center point? Or are the slots called out as slots? Say as a woodchuck slot is called out with a known form for size?

I would need to see a print to understand what the intent is? Unless the slots are called out with a TP for the set, then measure each one by itself and report location per the print. If it has a TP callout then the function of the feature set would be checked as if the cmm is laying the mating part on it, so construct the feature set and report the TP of the entire set. If that is what you are doing, and it reports out, check any modifers such as MMC on the in-process fixture pins, and the MMC in the cmm program.

I just guessing...............

[Peter Warcholyk]

Hello justncredible,

The "D" shaped slots are not in a pattern.
The actual call out on the print is as follows; |0.5|A|B|C|
Part is in metric, and I'm using v3.7mr3.

ZydecoPete

[justncredible]

Does the callout have a 4X or does it have phatom lines to the other slots?

Metric or standard does not matter, they are both just numbers.

The callout has no modifyers?

[Peter Warcholyk]

justncredible,

The callout indicates 4 "holes" |Profile 0.5|A|B|C|. There are no modifiers.

ZydecoPete

[justncredible]

Nice callout, it controls the shape and position, If you have the cad, you could use T's
If not, then use profile of a surface for the form, and TP for the relationship to the datums.

Just the way I would probly do it, maybe others have a better way. I am just a noob. SORRY!

[Scott Appleyard]

Pete, assuming you are using CAD, if you dimension the 'T' values for all the points in your slots, you should see the relative form and position of each slot. A positive 'T' value indicates a stock heavy condition and a negative 'T' value indicates a stock shy condition. If you create a feature set from the points and dimension the profile, make sure you are using the Form and Location option and use half the tolerance stated for upper and lower tolerance. You should notice that if you 'add' the greatest positive and negative 'T' deviations, it should equal the result of the feature set profile dimension. This is indicating the tolerance band width needed to 'contain' all of your points.
Hope this helps!

[Peter Warcholyk]

Scott,

Yes, I have the cad, and I did dimension the individual points with the "T" value.
I do understand the material condition. I was not sure if it was legitimate to construct a feature set, from a "D" shaped slot.
Based on the FCF, I would agree that I should select the "Form and Location", with half the tolerance stated for the upper & lower tolerance.

What did concern me was that some of the individual points in a couple of the slots, (and not all cavities of parts), did show out of spec. The out of spec condition varied from about 0.25mm to 0.45mm.
The interesting part was that when place on the check fixture, the stab pins would still "accept" the part.

Thanks to all for your replies,
ZydecoPete

[Scott Appleyard]

Pete, is the part you are checking a sheet-metal stamping? I assume this from the type of feature you are checking. Is the hole punched, laser cut, hydroformed etc..?
What type of feature are you using to check the points? I assume edge points. In the case of edge points, the measurement in the edge vector direction will be reported for 'T' values. If you need the measurement in the surface vector direction reported, you need to use the 'S' value. I 'm pretty sure you already know this, but it may be a good idea to check your vectors.
Also, what type of probe are you using? Ball or cylinder. I'm pretty sure everyone on the board agrees that cylinder probes are a bad idea.
What size have the pins been made to?
Just some food for thought i guess...

[Peter Warcholyk]

Hello Scott,

The part is actually an injection molded plastic part.
I'm using an edge point as a "relative measure" feature, and then taking points in 7 places within the "D" slot.

I'm using a 1mm ball type styli. All hits / vectors are appear to be just fine.
As to the size of the pins on the checking feature, I'm told that they were made to the "minimun" size.

Pehaps the next time that the part comes up for measurement, I'll use edge points for all of the 7 hits.

Thanks for your input.

Blessings,
ZydecoPete