Perpendicularity Callout

[millsd4]

I've got a cylinder with a perpendicularity callout to a flange bonded on one end of the tube. Tube is 72 inches long, and callout tolerance is 0.250mm to datum A.
Datum A points to the outside surface of the cylinder on the far end. Just wondering how to find out what the callout is asking for, if its saying that the tube must have an axial runout no larger then 0.250mm over the whole length of the tube or if it is a localised measurement. Would it be better to have a angle tolerance?

 

[dingy2]

The perpendicular call out of 0.25 mm (or 10 thou) is from the bottom of the tube to the top.

This is not checked using with circular or total runout. If I had a CMM, it would be pretty easy but I have a feeling that you might not have that equipment so I will relay the measuring method using toolroom equipment.

You have a granite table. Obtain a angle plate and place it gently on the granite table. There is a surface that is perpendicular to the angle plate. Clamp datum A on this surface so that the tube should be parallel to the table. If the part is too heavy and tends to fall over, support the angle plate.

Take a dial indicator on a height gauge and zero off on the tube centre line (highest reading) closest to datum A. Go to the other end and take the reading close to the end. Record the reading (let say it is 3 thou) rotate the part 90 degrees on the angle plate and do it take the angle again. Let's say that it is 4 thou here.

Using a bit of math, it looks like the tube is out .005 (square root of .004 squared + .003 squared).

That is how one would confirm this requirment.

Dave D.

http://www.qmsi.ca

 

[ringster]

Let me see if I have this correct. You are using Y14.5,yes?

You state that the callout of datum A is one end of the OD. That would mean that the datum would be the axis of the cylinder.

Having once obtained that you must check the flange for a perpendicularity to the axis as stated, .250mm.

I wil admit that sounds rather tight, however that is apparently what the drawing is attempting to impose.

That is how I figure it, anyhow.

 

[millsd4]

Actuly, we do own a cmm, but it;s only a 6' Romer Portable. My software will calulate the perpendicularity but my main question was:

I am using Verisurf software and it has no problem calculating the perpendicularity. In order to come up with a Deviation amount, I need the distance from the plane that the deviation should be measured.

It will calculate the angle, and the amount it is out, but I need to know at what distance to get the deviation. With the way that they have setup datum a, do I set the distance at the tube diameter, or at the tube end (total length)??

 

[ringster]

The perpendicularity would be the distance between 2 perpencdicular planes that would extend for the diameter of the part. You would have to convert the angle of the end surface to see what that spacing would be for the extent of the diameter.

This is how it works in theory. Im not familiar with the equipment you are using.

 

[millsd4]

so let me get this right. I have used my cmm arm to measure the end Plane. Also used it to measure my cylinder. The software can use the hole axis for perpendicularity. So I take these two items (89.722 degrees), and calculate the deviation at the distance (tube diameter)(inside or outside?)

 

[dingy2]

I think that you are saying that the flange on one end is datum A. That was my assumption when I first responded to this post.

Take 3 points on the flange shown at datum A to create a plane.

Now take a number of points around the bottom of the cylinder parallel to the plane to create an axis. The larger the number of points, the more accurate the result. If your CMM has GD&T in its programme, set up the axis to 90 degrees to the flange (datum A plane). Now go to the top of the cylinder and take a large number of points around the circumference of the cylinder. Your CMM should tell you how far the centre of the axis at the top is out relative to the bottom. It value cannot be larger than 0.25 mm.

Good luck!

Dave D.

http://www.qmsi.ca

 

[ringster]

Could you provide a sketch? It should be helpful.

 

[ctopher]

A sketch will be helpful.

Maybe a projected tolerance zone could help?

http://me.queensu.ca/courses/MECH314/documents/Lecture27-GDT-15-2007.ppt#415,14,Projected

Tolerance Zone indicated with a Surface Line(CSA)

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion

 

[Edwards0012]

The perpendicularity callout is a zone tolerance of the perpendicularity of the flange on the tube to the axis of Datum A. You take the basic location of the flange and project a line 1/2 the callout window one direction and 1/2 the other and that is your target window for the OD.

Axis center will need to be calculated and then you can determine the angle of the flange. If it measured at 89.722° then you can use some trig and find how far out it is at the OD of the flange and determine if it is within the perpendicularity window.

http://www.tec-ease.com/tips/august-98.htm

 

[millsd4]

Ive attached a quick sketch I made in paint. Hope it helps.

 

[ringster]

If this is as shown on the dwg, I would suggest you ask for a redifinition of the requirements. What is the imposed standard for the controls?

 

[dingy2]

Thanks for the sketch since it does change things.

With a CMM create an axis on the OD by taking a number of points around the circumference at one end of the OD and get the best fit centre. Do the same thing at the other end and now you have the best fit axis.

Dial in 90 degrees on the CMM for the plane. Now take a number of points making sure that you go to the extremities of the surface. The maximum difference in your case is 0.25 mm. If the actual value is above this, the surface is nonconforming.

Dave D.

http://www.qmsi.ca

 

[millsd4]

What i did was use the cmm arm to build a cylinder using the inside of the tube(controlled surface) since it is a composite part the outside surface is unfinished. The program then input a axis in the center of my cylinder and i created the plane on the flange. The software i use is so versitile it will actuly calculate the deviation in perpendicularity as long as you put the distance it should find the deviation at.

For example, what the software does it make 2 axis, one at nominal and one at actual. Then you input the distance at which you want to find the deviation and it will calculate the distance between the 2 axis at that location. the problem being, the way the customer toleranced the drawing i dont know what distance i should have the deviation calculated at, ive been told 2 differnt things by the engineers here, one said it is the entire length of the tube, the other said you calculate the distance as the tube diameter.