Parallelism Feature of Size - Rules for DRF
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- เผยแพร่เมื่อ 4 ต.ค. 2024
- In this question and answer video, Brandon demonstrates the proper way to apply parallelism constraints to features of size. He provides some helpful hints for CMM inspection of basic dimensions.
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Great video, Thank you so much to share your knowledge, regards from Mexico
Your drawing having a 0.00 datum at the Bottom Right Hand Corner freaks me out!! Bottom Left Corner is what it should be. This is a second clip of your's that I have noticed.
Haha, I know what you mean from an X,Y graphical perspective. However, we should mention Datums are about function only - not right or left. There is no default datum location other than where the functional surfaces/features are. Yes in this example it is very simple and doesn’t really matter, however, if this part mated on the right side, the datum needs to be put on that side. Just thought we should clarify!
@@Gdandtbasics I am also aware that GD&T eliminates all that - meaning where the origin is but there is an unspoken consistency if you google several examples of drawings and it always is on the Bottom Left Hand corner but I am glad I could amuse you with my comment. Great videos you've been posting! BTW, this was back in the days when you would have the datum or starting points as per the assembly or design sequence but GD&T eliminated the myth.
How do you use Axis Parallelism (or straightness) on conical features? Specifically, a hole that has multiple taper angles and nominal diameters at different depths.
Parallelism can be applied to a conical feature just like it would be applied to a cylindrical feature. When applied to the feature of size, it will control the parallelism of the axis of that feature to the datum reference frame. To your point about a hole with multiple tapers and diameters at different depts, each different "section" or diameter/taper would be a different feature of size and would be controlled with their own feature control frame. However, keep in mind parallelism wont control location, so if coaxiality is what you're actually after, we suggest runout or position instead.
@@Gdandtbasics Would you need to use the taper symbol on the holes? I'm not sure I understand how to attach the FCF to a conical FOS otherwise. Currently, I use a section view with angles, and this reflects the design intent and is the easiest to interpret.
Can we use one of the axis of the hole as priamry datum, and apply parallelism to the other axis of the hole respect to the primary datum? If yes, only primary datum wouldn't be enough to control all six freedom, how should we pick the secondary datum or even a tertiary datum needed?
Yes you absolutely could use one hole as a primary datum feature and control the other hole with parallelism with respect to datum A. In this case since we are using parallelism, we have controlled 2 Translations and 2 Rotations. So you are indeed correct that we have not controlled all 6 DOF however, for parallelism we are only concerned with orientation of the axis to the other axis, and NOT translation and NOT rotation about the datum axis. So that would be perfectly fine to only reference datum A in this scenario if youre ONLY concerned with orientation.
@@Gdandtbasics Thanks for the feedback. What if we still concern with all the three rotational movements between the two axis, and wanted to use the parallelism to control, is that legal based on ASME? I take your picture for example but the two holes become threaded holes in my case. Both two holes will be assembled with a hollowed clylindrical shaft valving , imagine we have a clylindrical filling gun to fill these two shaft valving one by one, during the filling we must keep the parts stay flat (means not clockwise or counterclockwise movement allowed) and also need enough room for the filling gun so it will not interfere with the shaft valvings.
Is it legal to use parallelism to control with, use one of axis as primary datum A(have controled 2 Translations and 2 Rotations) , the bottom surface as datum B to control the third rotation? Or any disadvantages for indroducing the datum B?