Looking at this, it's exactly what I'm missing in my knowlege. I'm from central Europe, finishing master's degree in mechatronics and I've never felt more useless. I would like to start my career as design engineer, but we've never seen a lot of blueprints on my faculty. We did some drawings, but almost none GM&T. Now I have a feeling I will have to work as CNC machinist for at least half a year to understand what is going on (and watching this kind of videos too).

Thanks a lot!

So I'm working on a drawing where every dimension is basic. thickness , widths, radius's etc, there are no diameters, the profile tolerance block is (in metric) |1.5 | A|B|C| the tolerance on the print (in metric) is 0 place + - 1 , 1 place + - .2 , example , I have a wall thickness called out at 3.6 mm , what would the tolerance on that thickness ?

@jaycrook1076

2 жыл бұрын

Potentially 2.1mm to 5.1mm thick. The wall to the left or top gets +/-0.75mm. The adjacent wall also gets +/-0.75mm. Your question is ambiguous though.

So the question is, is it easier to use a caliper or a granite block + height gauge setup. Isn't a caliper easier?

@Gdandtbasics

2 жыл бұрын

It’s more than just “what’s easier?”. With coordinate dimensioning we’re only supposed to use “calipers” for the measurement and that is because there is no geometric tolerance referenced back to a Datum. This means that we’re not allowed to use the granite table/height gage method because the granite table would be a Datum Simulator. The coordinate dimension would not be locating the surface and must be treated as a Feature of Size measurement (two-point measurements, surface to surface). Switching to Profile with Datum References means that the surface is now located/oriented to a Datum and we must use Datum Simulators for the inspection. So, you have to ask yourself; do you want the surface to be located/oriented to Datums or treated as a FOS? - Brandon

@ramprabeshkumar8325

2 жыл бұрын

GD&T PLEASE SIR HINDI TEACHING

@w.n.lian.3065

2 жыл бұрын

Thanks for ur explanation. It is really important to distinguish what situations that u should measure datum feature or datum feature simulator!

do we need to measure the basic dimensions of 3.75 and 0.875 in measurement report? or we only need to make sure 0.005 are meet in measurement report? i ask this because basic dimension can no need be shown in profile control.

@Gdandtbasics

Жыл бұрын

Basic Dimensions are not directly measured and reported during an inspection. They are dimensions without tolerances that describe the true profile. You only NEED to report that the total deviation from true profile is less than 0.005 inches. However, when you report the total deviation, the supporting data may be allowed to show how much deviation occurred in the 3.75 and .875 values.

What is the tolerance of the basic radius 4x R.250

@Gdandtbasics

Жыл бұрын

The radii do not have a direct tolerance specific to them. They are captured within the profile tolerance of .005 inches. So any element along that radius may deviate in or out by .0025 inches.

I don't get the whole 10:45 mearsuring from datum feature not datum simulator vs the 3-2-1 rule. In my mind it defies the purpose of datum specification and interpretation. If your datum C is a bit angled and pointed wall is also then you'll get different results depending on where you put the micrometers "head"or whatever its called in english. If it ends up at MMC (which in this case means the point simulating the datum) it's gonna define a different value that at other places. And then if the part functions in a way that datum feature C is flush with a wall of another parts (and locked in space according to 3-2-1) then you'd want the measurements to qualify the part based on the tolerances obtained from it's true position in space which is based on datum feature simulator C...

@eartheartbaratheon791

Жыл бұрын

I mean...if the cross secton of the part (parallel to the datum B) for the dimension 3.75 ends up being a trapeze (short edge at the top) then if I place my micrometer and take measurements at the top of the part its going to be different than taking them at the bottom (because I do not simulate a common plane for all the points on datum C from which I could be taking the measurements). And then even if the part supposedly passes the requirement, when it's going to work with another part at datum C as a tertiary datum (has been assembled by first adhering to datum A, then tangent at datum B and only then tangent at datum C) the real conditions will be measured from the most recessed points on datum feature C which turn out to be higher values.

@eartheartbaratheon791

Жыл бұрын

Well fuck me. The latter part of the video with basic dimensions pretty much sums up my way of thinking of how to measure things. But still, how can I define the tolerance zone proprly for the general dimensioning? It feels dependant on the placement of measuring tools chuck or whatever.

@Gdandtbasics

Жыл бұрын

​@@eartheartbaratheon791 Thanks for the comments and questions! You picked up on the very good arguments as to why it's important to use basic dimensions and geometric tolerances to locate a profile. As you saw, with simple size dimensions being used to locate a profile there is ambiguity and issues because you can’t utilize the datum reference frame. This is the big flaw with traditional coordinate dimensioning. HOWEVER, if we do utilize the datum reference frame by using the profile symbol and basic dimensions, we get to measure with respect to the datum simulators. (i.e., granite tables, angle plates and height gages.)

12:30 Why are you getting the angle from there? Isnt the angle tolerance defined by the tolerance of its dimensioning? If you take the angle tolerance just like that of a dimension thats not even mentioned on the drawing doesnt it become overdefined?

@Gdandtbasics

Жыл бұрын

Great question! The only reason we use the title block in this scenario is because there is not an angular dimension with a tolerance on it in the drawing view. So we must default to the size/angular dimensions listed in the "unless otherwise specified" area of the title block. The size dimensions shown on the drawing are not dictating an angular tolerance between these two surfaces so we are not over defining anything.

@fracapolligummala3548

Жыл бұрын

​@@Gdandtbasics I dont understand why the size dimensions dont dictate the angle tolerances. We have a fully defined datum reference frame, all datum features are defined in flatness and perpendicularity to each other. So when I have a position dimension of 3.750 +- 0.25 that dictates how far points of the surface in question can be away from datum C then it automatically dictates angle tolerances over its worst case, doesnt it?

@eartheartbaratheon791

Жыл бұрын

@@fracapolligummala3548 I think it does specify a region where all the points on this surface must lie for the part to be functional as far as the surface - base C location is concerned. However we're talking here about the feature (window) and its form, which can be further narrowed down if we needed to. It's pretty much the dimensioning vs geometric tolerancing differentiation. The +-1 deg may very well be wider than the region specified by the location dimention and then it's disregarded but it may happeen that it's narrower and then it controls the form without the need of making the dimension unreasonably tight. And I think the angular lines shown lateer on should be skewed inwards not outwards. Then it makes sense. but if they're pointed outwards it looks like any angle to the face would automatically not conform the the size dimensions tolerance like you said. But I'd like to get a calirification to be sure...

@fracapolligummala3548

Жыл бұрын

@@eartheartbaratheon791 Applying a general tolerance to a not called out dimension sound off though. Where for example is the pivot point of this angle suppose to lay? Is it on the true position? The true position of what? The upper or the lower edge? Or any point along the line? Doing this sounds problematic.

@eartheartbaratheon791

Жыл бұрын

@@fracapolligummala3548 Isn't it an implied angle of 90 deg? You have the position of each side of the rectangular window given by a symmetrical tolerance zone. Each side is supposed to be perpendicular to a neighbouring side by implication and the general angular tolerance perteins to that as well. I'm only concerned by the exact location of the tolerance zone since I think it would end up in various places depending on where the contact points of measuring device land (base C wall can and will be a little sloped so the 3.750 value could end up a little farther or closer since we're not supposed to measure from datum but datum feature, which I can't grasp).