Distance Dimensioning

[rochcnc]

Ok.I'm going from a plane face to a hole/cylinder.
which is better-more accurate.2d or 3d.
I'm suer that 3d would be the most accurate.
Am I right on saying that 2d will give you x,y or z dimensions.
3d gives the true location?
A little help would be appreciated.

[russd]

3d is going from center to center. I believe you want 2d perpendicular to your plane. Then I guess it depends where your circle is in relation to your plane. Just a start though.

[rochcnc]

its going from a plane deep in a c-bore to circles on ends of part
and that is a location call out +/-.001.
I still believe 3d is the way to go.

[Matthew D. Hoedeman]

2D distance will always be an "as seen" distance from a specific workplane orientation. You can then "fine it down" in the dist-dim window (to an axis or to a feature, etc.) ANY "distance" that can not be seen from that workplane will NOT be in the calculation, no matter WHAT you do.

Example. Take a point on the table. Take a point on top of a block that's on the table. Using a Y workplane, you will "see" ONLY Z difference and X difference. If using the Z workplane, you will "see" only X & Y, and if using an X workplane, you only "see" Y & Z.

3D distance is from an XYZ location to an XYZ location, shortest distance, through 3D space.

Using a plane and ANYTHING other than a POINT can jump up and bite you in the rear end. A cylinder's XYZ point WILL CHANGE from measurement to measurement along the axis of the cylinder. Same for a line. A Sphere is a good check, point-to-plane.

[Chally72]

Ok.I'm going from a plane face to a hole/cylinder.

Am I right on saying that 2d will give you x,y or z dimensions.

No. 2D is exactly what it says. 2 Dimensions. So a 2D dimension would be XY, XZ, or YZ, depending on your workplane. Your workplane is very important in determining what answer you get when you ask for a 2D dimension.

A 3D distance from plane to a circle would give you a distance from the center of the plane to the center of the circle. Kinda like taking a string and holding it in the center of each feature, and measuring the length of string. If you are working to any kind of blueprint, you should be using 2D dimensions. A 3D dimension is not related to any workplanes.

Do you have any sort of inspection background? Have you used calipers? How do you caliper the width of a 123 block? You clamp the calipers square to the edges to get the distance between them. You don't angle the calipers so they are holding at different heights on the surface and are not measuring the parts square. The same principles apply to every measurement you make on a CMM. You must be sure that you have set your part alignment and workplanes up correctly before taking any measurements, or you will get bogus numbers.

[John Riggins]

If you want the distance perpendicular to the plane, do this:

Distance, 3D, circle 1st, plane 2nd. (I am assuming that the circle is perpendicular to the plane).
You will get the distance from the centroid of the plane to the center of the circle. This distance will be perpendicular to the plane.

[dph51]

Ok.I'm going from a plane face to a hole/cylinder.
which is better-more accurate.2d or 3d.
I'm suer that 3d would be the most accurate.
Am I right on saying that 2d will give you x,y or z dimensions.
3d gives the true location?
A little help would be appreciated.

Q. which is better-more accurate.2d or 3d.
A. I'm suer that 3d would be the most accurate.
Q. Am I right on saying that 2d will give you x,y or z dimensions.
3d gives the true location?

A little help would be appreciated.


A little sketch would be helpful to understand what it is that you are trying to accomplish. Distance or location? What workplane are the features in?

[rochcnc]

Looks like both are correct.
However,I did find that using 2d vs. 3d there is up to a .003
difference in the location.
It can't possibly be that hard to understand this. From the alignment,the original you should be able to go from that.Rotation,rezeroing,etc...not a chance.
This isn't that difficult of a part. and as far as the answer.....3d is the correct answer in this case. Seeing as how they say this in the notes:"Centerline thru dia bores must be parallel to face-A-(top of part) w/in .002 and perp to centerline thru Bore dias(which are the c-bores and faces) w/in .004. Bores must be conc w/in .004". Thus the location from the face to the centerline would be calculated in 3d.

Who agrees?

[Chally72]

Looks like both are correct.
However,I did find that using 2d vs. 3d there is up to a .003
difference in the location.
................
Who agrees?

Not me.

[bob mappes]

Looks like both are correct.
However,I did find that using 2d vs. 3d there is up to a .003
difference in the location.
It can't possibly be that hard to understand this. From the alignment,the original you should be able to go from that.Rotation,rezeroing,etc...not a chance.
This isn't that difficult of a part. and as far as the answer.....3d is the correct answer in this case. Seeing as how they say this in the notes:"Centerline thru dia bores must be parallel to face-A-(top of part) w/in .002 and perp to centerline thru Bore dias(which are the c-bores and faces) w/in .004. Bores must be conc w/in .004". Thus the location from the face to the centerline would be calculated in 3d.

Who agrees?

I would tend to disagree until I at least saw a drawing and your code before actually committing to answer either way.

[John Riggins]

Looks like both are correct.
However,I did find that using 2d vs. 3d there is up to a .003
difference in the location.
It can't possibly be that hard to understand this. From the alignment,the original you should be able to go from that.Rotation,rezeroing,etc...not a chance.
This isn't that difficult of a part. and as far as the answer.....3d is the correct answer in this case. Seeing as how they say this in the notes:"Centerline thru dia bores must be parallel to face-A-(top of part) w/in .002 and perp to centerline thru Bore dias(which are the c-bores and faces) w/in .004. Bores must be conc w/in .004". Thus the location from the face to the centerline would be calculated in 3d.

Who agrees?

If you are doing 3D you need to understand that the 2nd choice you make can be critical. The distance will be perpendicular to it.

[John Kingston]

I would tend to disagree until I at least saw a drawing and your code before actually committing to answer either way.

I'll jump up on my soapbox and agree with Bob. There are a number of issues that come into play here and you need to make sure you (and those trying to help you) understand them. There is a really cool method of verifying this. It is called SURFACE PLATE MEASUREMENT. Have you tried measuring that way? Measure to the edge of the hole. Record the result.
Put a pin in and measure it right at the surface. record the result.
Measure that same distance away from the surface that the hole is in. Record the result.

Are they different? Do they match the CMM results? Why (or why aren't) they different? Why or why don't they match the CMM results?

Food for thought. Understanding what is happening is everything.

<Jumps off soapbox>
<logs out>
<Heads for home for a beer>