Query on Concentricity Inspection

R

raghuvir

hello,
i am new to the forum, we have a machined part which has a concentricity requirement between pitch circle diameter holes and a reference OD diameter of the part. Can someone explain how this can be measured. We have so far checked only positional tolerances of PCD holes with ref to a diameter.

thanks on advance
rags
 
T

True Position

Are you talking about the GD&T tolerance of concentricity or are you looking for the pitch runout?
 
D

David DeLong

hello,
iam new to the forum, we have a machined part which has a concentricity requirement between pitch circle dia holes and a reference OD dia of the part. Can someone explain how this can be measured. We have so far checked only positiobnal tolerances of PCD holes with ref to a dia.

thanks on advance
rags

Concentricity to ASME Y14.5-2009 & 94 editions is the median point of 2 diameters that share the same centre line while ISO standard is the centre of the round feature relative to datum centre. We have 2 diameters sharing the same centre. In both cases, we have 2 or more diameters sharing the same centre line.

You stated a concentricity of a pitch circle to a reference OD. Concentricity does not apply in this situation but positional is appropriate in a regardless of feature (RFS) mode. You would need a primary datum (usually a face), secondary datum (round feature creating the centre line) and, if the part is not symmetrical, a tertiary datum (to orient the part). You measured the part the way I would have measured it.
 
T

True Position

Concentricity to ASME Y14.5-2009 & 94 editions is the median point of 2 diameters that share the same centre line while ISO standard is the centre of the round feature relative to datum centre. We have 2 diameters sharing the same centre. In both cases, we have 2 or more diameters sharing the same centre line.

You stated a concentricity of a pitch circle to a reference OD. Concentricity does not apply in this situation but positional is appropriate in a regardless of feature (RFS) mode. You would need a primary datum (usually a face), secondary datum (round feature creating the centre line) and, if the part is not symmetrical, a tertiary datum (to orient the part). You measured the part the way I would have measured it.

If instead of concentricity the actual dimensions in question are runout (which is widely called concentricity) the usual method requires a locking thread or spine ring. Position is a factor, but form also matters.
 
D

David DeLong

If instead of concentricity the actual dimensions in question are runout (which is widely called concentricity) the usual method requires a locking thread or spine ring. Position is a factor, but form also matters.

Sorry True Position but circular runout, total runout and concentricity reflect actual cylindrical features that share the same centre line. A bolt circle is not an actual cylindrical feature but an imaginary circle.

I guess a good rule of thumb is if one can place datum feature of the part in a chuck then the feature could be checked or confirmed for circular or total runout and even concentricity.

I have a web page dedicated to explaining concentricity to the ASME standard at http://www.qmsi.ca/concentricity.html
 

Kales Veggie

People: The Vital Few
hello,
i am new to the forum, we have a machined part which has a concentricity requirement between pitch circle diameter holes and a reference OD diameter of the part. Can someone explain how this can be measured. We have so far checked only positional tolerances of PCD holes with ref to a diameter.

thanks on advance
rags

Do you have a CMM? (measure both circular features and let the CMM calculate it)

Do you have roundness tester that fits your part? (most roundness testers allow you to measure two diameters sequentially and either let the machine calculate roundness.

Do you have V-block that fits your part? You can mount two digital indicators and substract the two value electronically and record the max.

(You read read the other posts about the detailed technical aspects)
 
T

True Position

Sorry True Position but circular runout, total runout and concentricity reflect actual cylindrical features that share the same centre line. A bolt circle is not an actual cylindrical feature but an imaginary circle.

I guess a good rule of thumb is if one can place datum feature of the part in a chuck then the feature could be checked or confirmed for circular or total runout and even concentricity.

I have a web page dedicated to explaining concentricity to the ASME standard at http://www.qmsi.ca/concentricity.html

Sorry, I figured out my confusion. I read the original post as looking for the 'concentricity' of the pitch diameter such as that of a spline or thread to another feature not the pitch circle of a bolt pattern to another feature. Often you hear people use those terms as equivalents on production floor.

If it's a bolt pattern I agree with you.
 

Stijloor

Leader
Super Moderator
(snip) Do you have V-block that fits your part? You can mount two digital indicators and subtract the two value electronically and record the max.

V-Block? May be possible, but the angle of the "V" will impact the measurement results when the part is lobed.....

Stijloor.
 
R

raghuvir

Thanks for all the replies,
iam attaching the drawing for your comments and views ( ref co-ordinate 4D and 5F), i'am a bit surprised that the print calls for concentrity between bolt holes and reference dia as against positional tolerance in normal cases.

We checked the part on a cmm and the concentricity was out of spec by 0.2mm,( the holes were drilled locating the ref dia B) .

Could this be due to out of roundness of the drilled hole, will reaming the holes solve the problem?
advice
thanks
rags
 

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