Former Blog Articles

Former Blog Articles

Welcome to the first entry of the MAYA BLOG.  We are going to release an article each week.  We are going to focus on different aspects of our industry, starting with a look into GD&T as it relates to custom gaging.  Must of you know GD&T and how it relates to machining parts, but have you considered it from a measurement standpoint? 
Throughout the Coronavirus Pandemic we will touch on one GD&T feature each week, provide some insights, thoughts, and techniques on how to look at a feature from the gage’s point of view.

Blog 1 – True Position – When to use RFS, MMC & what does it mean?
One of the most common misinterpretations of GD&T when building a gage is the use of True Position.  We get asked very often to quote a gage as a ‘must go’ or ‘quick functional check’ or even ‘most cost effective way possible’.  But what if the check reads:

Feature Control Frame RFS

Sweep Unit Example
This check, literally taken, is the true position of a feature from A, B, C datums all of which are regardless of feature size.  To the gage builder, this means we can have no float or slop in the fixture & no ‘bonus tolerance’ is allowed.  Therefore, we have to secure the part / feature.  For a bore that might be a tapered plug, ball arbor, or similar.  When checking the feature, we have to do so with a sweep unit or digital probes at quadrants to report the position relative to the datums.  This is not the ‘quickest, must-go, most cost effective’ way per the request.  What do we have to do to adhere to the request?  (Disclaimer: you must know your process & if modifiers like MMC is permitted based on tolerancing requirements)  The feature would need to be modified it to look like this: 

Feature Control Fame with
MMC Modifiers
Must-Go Gage Example
By adding these MMC (Maximum Material Condition) modifiers to these specific datums/features, this allows us to build a gage that can be ‘must go’ or ‘functional’ per the original request.  This is because we use the positional tolerance and penalize the datum feature, giving us the ability to use a ‘must go’. So next time you are interested in a quick & cost-effective way to check true position, be sure to consider adding MMC modifiers and how that affects the manufacturing of your part.
Have an RFQ?  Please click HERE and submit on our convenient RFQ for on our site!
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 Blog 2 - Roundness or Out of Roundness?

Another interesting GD&T symbol / callout is roundness or circularity.  At first glance without a full understanding of the callout, one might think to check this would not be too difficult.  Maybe you think it can be checked like runout?  Put the part in vee blocks or between centers, probe on the feature & turn.  Unfortunately, that will not give you roundness.  Roundness is independent of any datum and needs to be checked as such.  So no other outside influences allowed.  

To properly measure roundness in a gage for production purposes is more involved than one might think.  Here's some of what you need & why:

- Digital Probe.  Indicators won't work here, you need something that will output the results to a secondary PC.
- PC/PLC.  Something with computing power is required.
- Rotary encoder or similar device.  As the probe is traversing a surface (or stylus) you must know the radial position of that contact point!
- Extremely high precision tooling.  The gage must create an excellent starting position OR be able to track & compensate for inherent error in any build.

(The image below is a good representation of 'plotting the points' to see if any part of the feature falls outside of the limits.)
This sounds costly, and it is.  And 99% of the time it is not what the engineer desires to be checked next to the production line!  A CMM, Roundness machine can perform these checks.  Usually on the production floor what 'Roundness' is often reinterpreted is 'Out of Roundness' or 'Ovality'.  This is the difference or variation between the X & Y diameter measurements of that feature.  Simply put, you can have a bore gage measure an ID at one axis, rotate by hand 90° & measure again.  The difference is your 'out of roundness'.  Looks like this: (X Dia 1 - Y Dia 2) = Ovality.  Another way to think of Out of Roundess is a hula-hoop (see image below).  If you squish a hula-hoop on one side it becomes oblong, or oval.  That is what we are checking with X&Y coordinates.

So keep in mind what the intent for the check is & where the check is being performed.  You can have big cost savings by checking Ovality instead of Roundness!



There are a lot of things to consider when reopening if you've been shut down for a period of time.  Gages are fine tuned instruments that need to be carefully maintained when utilizing them for the first time.  Typically if a gage has been sitting for over a week, it may not react well without some minor PM.  Some things to consider:
- Was the gage cleaned/PM'd before the shut down?
- Is this an environment where coolant or oil residue could have built up on the gage?
- Are there moving parts in the gage?
- Were the masters stored properly? 

Common problems associated with running a gage after it's been stagnant:

- Sticky probes that may not reach a full intended stroke.
- Pneumatic devices that are not extending / moving properly.
- Rotating / moving parts in a gage sluggish, no full range of motion, causing for timeouts.

We can help!  Our gage technicians can come to your facility, PM (preventative maintain) the gage, advise of any problems that may arise when you are at capacity, and provide you peace of mind.  

We are offering an incentive to book your gage technician early before we are booked up!  Click on the link below to be redirected to our service request page.  A member of our team will be in touch after you complete the request form.


Have an RFQ?  Please click HERE and submit on our convenient RFQ for on our site!

Want to chat?  Please send us an email: