MMC condition 1

[par1]

I have one hole with 6-6.4 mm dia, which has given the 0.4 mm diametric positional tolerance at MMC.
What would the possible dia of hole?
My understanding says from 5.6 - 6.4 mm hole.

5.6 mm would be the virtual case but if real part has that dimension does quality people will accept that dia ?

 

[TheTick]

The diameter range is dictated by the diameter dimension (6.0-6.4 in your case). The MMC modifier affects the position tolerance, but not the hole size tolerance.

MMC for the hole is 6.0 mm.

 

[looslib]

What the MMC in the positional calout specifies is that at 6.0 dia, the theoritical axis can be off by the .4 of the positional tolerance. Worst case, at LMC, your dia of 6.4 can be positioned off location by zero. You have used up your positional tolerance by the hole tolerance.

I believe this is correct. Corrections are welcome.



"Wildfires are dangerous, hard to control, and economically catastrophic."
"Fixed in the next release" should replace "Product First" as the PTC slogan.

Ben Loosli
CAD/CAM System Analyst
Ingersoll-Rand

 

[par1]

I have a book of Alex Krulikowski (page 55 on a small pocket book if u have one)& in that it says that the virtual condition for that hole is 5.6 mm dia( 6- 0.4, due to the diametric hole tolerance at 0.4 MMC) But, I am thinking that the 5.6 mm is a real case?

My question is if production people will make that hole of 5.6 mm than quality people will approve it or not?

 

[TheTick]

Virtual condition:
What is meant by this is that if the hole is at a position at the extreme edge of its tolerance, the maximum diameter pin that could be expected to fit is 5.6 mm.

 

[par1]

I understand the meaning but the question arises is that the virtual condition is an acceptable case by quality control when they measure the dia using CMM/vernier caliper?

The spec for the given hole is satisfied at dia 5.6 mm or not?

 

[par1]

By the way, The Tick could you just explain me @ the pin you r talking,
Is this the pin which is going to assemble in that hole or the pin which uses to check the dia of hole?

I am kind of novice in this field so might be i'm asking some basic questions?

 

[looslib]

The pin dia has to be 5.6 for the hole to fit over it when the hole is out of position by the maximum tolerance and at MMC.

Since your position may be off by .4 and your hole dia is 6, the max pin that will fit through that hole condition is 6-.4=5.6.


"Wildfires are dangerous, hard to control, and economically catastrophic."
"Fixed in the next release" should replace "Product First" as the PTC slogan.

Ben Loosli
CAD/CAM System Analyst
Ingersoll-Rand

 

[ewh]

You cannot use virtual condition when inspecting the hole. As stated above, it only defines the effective diameter when assembled. The inspected hole must meet the tolerance given (6-6.4mm) to pass.

 

[TheTick]

If you were designing a gage to check the parts, the pin to check the hole position would be 5.6 mm diameter. This is how our gages are designed.

 

[par1]

I need ur help EWH in this topic to make my fundamentals clear.
If the hole has to be within a 6-6.4 range &
1. when the hole is out of position by the maximum tolerance and at MMC of 0.4 mm.
2.if pin is a seperate single piece component

Then why the pin has to be 5.6 mm dia?

THe pin is for assemble or to check the dia?
I will really appreciate if you help me in this matter,

 

[TheTick]

The pin would be part of a gage. The part would be constrained on the gage with respect to the datums. It is a functional gage to check fit. Hole size would have to be checked separately.

 

[ewh]

If you were inspecting the hole size only, it would have to be as called out on the drawing (6-6.4 mm). Since there are geometric constraints involved, the pin size (in a fixture) would reflect the extreme of those constraints.

The hole is 6 at MMC. Subtract the positional tolerance of 0.4 and you have a pin diameter of 5.6 mm. This pin is not meant to inspect hole size only, but size and position together, and must be part of a fixture (to simulate the required datums).

I hope that helps clear it up some. The others posting on this thread may be able to help explain it more clearly.

 

[par1]

Thank you very much EWH,The Tick & Ben.