Position - Controlling Threads on Features
ฝัง
- เผยแพร่เมื่อ 13 ก.พ. 2021
- Knowing the proper methods for specifying and inspecting threaded holes can eliminate confusion and may even make a difference in your next ISO audit. Check out our video, where Brandon explains this in detail.
Interested in learning more about GD&T? Check out more of our free GD&T resources here:
download.gdandtbasics.com/you...
11:03 utilizing this method when drawing up a print is soooo much better, thank you! I’ve also found that a less “busy” print is easier for this inspection software we have that automatically balloons/bubbles drawings to actually balloon/bubble the print with less error; it’s never perfect, you still have to check it but it’s generally more spot on when the print isn’t filled with redundant features.
For some reason a lot of our government jobs have drawings that do NOT follow this method at all. They also ALWAYS want basic dimensions reported which makes no sense. I can understand our machinists wanting to know the values to see what adjustments would need to be done since they’re actually making the part and just giving them the True Position value isn’t helpful, but why the customer needs them doesn’t make any sense to me 🤷🏻♀️
Brandon is a great instructor with a strong background in quality control and GD&T basics (ASME Y14.5) from the ASME Standards. The Major Diameter noted is a very fast and effective check for "Zero Defect" applications on hardware components like electric cover plates and octagonal junction box parts. Flexible GD&T rules are often effective if a "SIMPLE-quick Verification" supports a quality plan. Every part is defined by functional planning. Excellent Video! Thanks for your efforts!
T J (Tom) Vanderloop, Author, Mechanical Designer, & Consultant; ATEA, AWS & SME Membership/Leadership.
Teşekkür ederim. 👏👏👏👏
Instead of that flexible hole location gauge shall we check thorugh cylindrical probe in CMM...?
With the flexible thread, the p.d. must be measured before the thread is split, correct ?
How are these gages calibrated after the thread is split and does material fatigue cause the p.d. to be v-shaped, as opposed to concentric ?
I've seen the tangs break on these. What is recommended shelf life before purchasing new flex plugs ?
Would you say precision of thread location measurement follow this order if inspected in their method, where pitch dia being more precise and major dia being least precise?
pitch dia > minor dia> major dia
Sharath,
Thanks for your comment.
Locating using the pitch diameter is going to result in a measurement that is closest to how the part will assemble since the pitch diameter should engage and locate in the actual assembly. Also keep in mind that physically trying to measure the location of the minor diameter on a male thread will be much more difficult than measuring the location of the Major Diameter. On the flip side, it would be much more difficult to measure the Major Diameter on female threads than it would be to measure the Minor Diameter.
Hope this helps!
-Your GD&T Basics Team
Soooo how would you apply MMC to this?!?? Or better yet, how could you even measure what the actual PCD is to determine if you've got any bonus? Are the jo plugs manufactured to a certain tolerance or min/max in PCD per thread size?
It is best to avoid applying MMC to threaded features. Not only is it hard to determine, especially when using the pitch diameter, but its also not how the feature truly functions. The thread will always dictate the location when it is fully seated. For that reason it would not match the function of the part to allow the size of the thread to allow any bonus positional tolerance. MMC is best used when the size of the feature directly affects the ability of the part to assemble or not.
@@Gdandtbasicsahhh....well I understand the reasoning behind why its best not to apply MMC to threads from a manufacturing standpoint, but I only ask because at my job we get prints all the time with threaded features that call out location with MMC and so everyone (myself, GD&T SMEs, and the rest of our engineers and inspectors alike) are stuck because no one knows to apply this on the plate. It's so frustrating because we have no control over the drawings, some are as old as the 70s, others are only a few years old.....why bother adding it to begin with on the print if it can't be inspected?!
Does this also apply to externally threaded features? Are similar gauges also available for external features like studs?
Yes, this does also apply to external threads and utilizes a "ring" style gage (this is not a "typical" ring gage used to gage threads).
Hope this helps!
@@Gdandtbasics Are "ring" style these standards like flex thread pin gages.
if datum B is derived from datum A, datum C is derived from datum A and B, so why are you referencing a cylinder of diameter 0.16 additionally to datum B and C?
Hi brothers, I ask one doubt to all, how to calculate the MMC to threads for true position.
To find the MMC for a threaded feature, we must refer to the specification sheet for that fastener. If its a common fastener, often times we can search the Machinery's Handbook for the MMC values.
Lets say the holes do not have threads. Do you have to measure the hole as a cylinder or can a circle be used instead?
By default, Position is a 3D control, meaning that it is a Location and Orientation control of an axis when applied to a cylinder. It can be measured as 2D (out of necessity), but this means that we're switching from an axis to a center point. Orientation is no longer controlled.
Hope this helps!
What exactly did you mean by "Qualifying the DATUM?" Are you saying you must have some sort of GD&T form control on the DATUM surfaces in order to have them as DATUMs?
By "Qualifying the Datum Feature" we are referring to "Datum Feature Control". The ASME Y14.5 standard states that we should add a Form control to the Primary Datum Feature and Orientation and/or Location to the Secondary and Tertiary Datum Features.
Hope this helps!
@@GdandtbasicsNot exactly. ASME Y14.5-2009 (section A.2) states that form tolerances "should be considered" for the primary datum feature, and orientation controls "should be considered" to relate the secondary datum feature to the primary datum feature. To clarify, although having these controls is almost always a good idea, they are ultimately optional.