ASME Y14.5 defines the Fixed Fastener Case as Where one of the parts to be assembled has restrained fasteners, such as screws in tapped holes or studs, it is termed. Determining positional tolerand of clearance holes that are joined with a fastener is a fundamental skill for anyone using GD&T. For external threads there are pitch micrometers. Position tolerance us easy to calculate and can be completed in a few easy steps. there is not a good one that I am aware of. You still have to find a method to determine what the pitch diameter actually measures. (How silly of me not to add), that only tells you the location. They are very time consuming and require program modification, but IMNSHO they are the best way to attempt at accurate reporting of MMC on a thread with a CMM. On the few rare occasions that I have been ordered to put MMC on the thread on a report I have used the self-centering thread bushings. If it comes down to the MMC determining if the thread is good or bad, I advocate a functional gage. I almost never use pc-dmis to calculate MMC on a thread.
90% of the time I use a cylinder and I make sure that the distance between the first and last hit is a multiple of the pitch and that when more than 2 rows are used the distance between the first and last is also a multiple of the number of rows. I only use a circle when the length of thread and or reach of the tip demands it.
I myself measure the minor diameter of threaded holes using the pitch function of pc-demon. limit defines the boundary at MMC, see h11 limit from the chart (ISO Shaft Tolerances. Some think the only reason MMC is allowed and used on threads is to facilitate the manufacture and control of "Hard functional gages". GD&T, Geometric Dimensioning and Tolerancing,Form Tolerances. Some think MMC should not be applicable to threads because of the self-centering tendency of threaded features. Some of those participating in the discussion where doing so while attending meetings reviewing comments on the proposed draft of the new standard. See our Privacy Policy.For giggles I will toss in here that in the last few days there has been yet another discussion of this on the Yahoo Y14.5 user group. 375 +/-.005 then you subtract what your actual dimension is from. Download it today on iTunes or Google Play. B- is the 11.00 bolt circle so your position must be taken from that feature. Export lathe G-code for chamfers, tapers, & radii with tool nose compensation 28. Circular segment calculator 23. Fraction Converter 24. Tap Drill Calculator for roll form & cut taps 19. Machinability & cutting speed data for over 180 materials 18. CNC Machinist Calculator Pro is a machining calculator designed to make your life easier. Our app is perfect for CNC programmers or operators who need to make quick calculations on the fly.
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