My two cents. place a part on surface plate and indicator means you are checking parallism and flatness at the same time. if it is good, then it safe to assume flatness is good. if it is out, you have to isolate using the three cones, but you have to flip the plate and measure using an indicator undearneath not like what is shown, and if not it almost like the same thing on the surface plate.
They are separate call outs, but for quick check that is fine. Assuming a rectangle that is perfectly parallel but one side is wavy or flatness is out. if you put the wavy surface down on surface plate then parallel is good, so as the flatness on the flat side. then if you flip the flat surface to the surface plate, and wavy surface on top then you measure the deviation, since you know it was almost zero from the flip, you know you are measuring flatness this time.
Hello, when inspecting the flatness without a datum, why do we have to make three equal height of points as a surface? Couldn't the three points not at the same height?
A great question. 1. Firstly we know Flatness doesn't need datum. 2. Tolerance zone is two parallel perfect planes within all points or elements should remain. 3. Since there is no datum in first principle method need to create a first perfect plane. 4. A perfect plane passes through only three points. 5. Now how to create this plane. The option one is place the surface upright down on the surface plate used as datum simulator. This method automatically create a three highest points touch tangential plane. 6. Now to find the deepest inside point as a flatness value dial must read from the bottom side. This requires a special setup of a surface plate having a hole through from bottom a dial plunger can be pushed. This is very hard and uneasy method. 7. To replicate the same method a three adjustable jack points used to find three points at equal height separated as possible within surface. 8. You are absolutely correct that these points are not top 3 heights points or allows a tangential plane. But when measurement with dial indicator is carried out it must note maximum and minimum readings with plus or minus sign. This difference is called the Flatness. 9. This is the only option remains when conventional method to adopt. 10. If you want mathematically defined perfect Flatness value it is very easy to us CMM, three coordinate measuring machine. Hope you are happy with the answer. Regards
@@accurateasmeiso4262 Thanks for the detailed explanation. So 1.The three points at the same height meant for the surface to be checked, for your example, on the top surface, is that correct? 2.Is there a difference between using CMM and height gauge? Both of them require the three points at the same height?
U r welcome 1. Yes, true. 2. CMM doesn't require three points on same height. In fact part can be placed in any orientation. Software does mathematical calculations for flatness.
I am writing about flatness measurement. When you put 3 equal height datum on bottom, actually you create parallel surface from touching points. So, you do same thing with putting granite surface. I couldn't find the answer which I expected..
Critically asked question, Appreciate. If we make 3 points equal separated maximum with respect to that plane maximum and minimum variation of same surface is measured. Simply from three point plane max and min is band of tolerance. Good question !
Hi Emin, I guess your question is asking putting 3 adjustable pins below the bottom surface to measure is the same as putting it on the granite table right? I think the 3 adjustable pins is not equal height. It is adjusted to a height that make 3 points of the top surface at equal height. So it is different. Hope you can understand what I say here.. 😄
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One of the best video to describe Flatness and Parallelism that I have seen. Thanks.
finally a video that seems logically correct
My two cents. place a part on surface plate and indicator means you are checking parallism and flatness at the same time. if it is good, then it safe to assume flatness is good. if it is out, you have to isolate using the three cones, but you have to flip the plate and measure using an indicator undearneath not like what is shown, and if not it almost like the same thing on the surface plate.
Parallelism and Flatness need to treat separately. Not dependent as said if one is good then another is also.
They are separate call outs, but for quick check that is fine. Assuming a rectangle that is perfectly parallel but one side is wavy or flatness is out. if you put the wavy surface down on surface plate then parallel is good, so as the flatness on the flat side. then if you flip the flat surface to the surface plate, and wavy surface on top then you measure the deviation, since you know it was almost zero from the flip, you know you are measuring flatness this time.
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Hello, when inspecting the flatness without a datum, why do we have to make three equal height of points as a surface? Couldn't the three points not at the same height?
A great question.
1. Firstly we know Flatness doesn't need datum.
2. Tolerance zone is two parallel perfect planes within all points or elements should remain.
3. Since there is no datum in first principle method need to create a first perfect plane.
4. A perfect plane passes through only three points.
5. Now how to create this plane. The option one is place the surface upright down on the surface plate used as datum simulator. This method automatically create a three highest points touch tangential plane.
6. Now to find the deepest inside point as a flatness value dial must read from the bottom side. This requires a special setup of a surface plate having a hole through from bottom a dial plunger can be pushed.
This is very hard and uneasy method.
7. To replicate the same method a three adjustable jack points used to find three points at equal height separated as possible within surface.
8. You are absolutely correct that these points are not top 3 heights points or allows a tangential plane. But when measurement with dial indicator is carried out it must note maximum and minimum readings with plus or minus sign. This difference is called the Flatness.
9. This is the only option remains when conventional method to adopt.
10. If you want mathematically defined perfect Flatness value it is very easy to us CMM, three coordinate measuring machine.
Hope you are happy with the answer.
Regards
@@accurateasmeiso4262 Thanks for the detailed explanation. So
1.The three points at the same height meant for the surface to be checked, for your example, on the top surface, is that correct?
2.Is there a difference between using CMM and height gauge? Both of them require the three points at the same height?
U r welcome
1. Yes, true.
2. CMM doesn't require three points on same height. In fact part can be placed in any orientation.
Software does mathematical calculations for flatness.
I am writing about flatness measurement. When you put 3 equal height datum on bottom, actually you create parallel surface from touching points. So, you do same thing with putting granite surface. I couldn't find the answer which I expected..
Critically asked question, Appreciate. If we make 3 points equal separated maximum with respect to that plane maximum and minimum variation of same surface is measured. Simply from three point plane max and min is band of tolerance. Good question !
Hi Emin,
I guess your question is asking putting 3 adjustable pins below the bottom surface to measure is the same as putting it on the granite table right?
I think the 3 adjustable pins is not equal height. It is adjusted to a height that make 3 points of the top surface at equal height. So it is different. Hope you can understand what I say here.. 😄