True Position Checking such as Bolt Hole Position w.r.t Center Bore on Wheels

Kanagu · May 16, 2011

Dear All,

Am having some of basic doubt regarding Ture position inspection.

I know that it can be inspect with CMM.

My doubts are

Ex.: Bolt Hole position w.r.t center Bore on Wheels)
1) Can we use position gauge for inspection of true position.
2) If position gauge can use, wheather MMC will affect the gauge design. How the Product MMC will incoprate with Position gauge.
3) Wheather tolerance is allowed for PCD on which holes are place, that holes are having True postion.

Few more doubts are there but i have clear basic first.

Urs Kanagu
Thanks in Advance

Paul F. Jackson · May 16, 2011

The gauging must reflect the specification and the specification should reflect the function.

For any of us to comment on what your gauging should look like we must see your specifications (a complete rendering of the datum features and the specified tolerances from them)

Questions that I would have from a question like yours are:

Are the lug nut friction surfaces coned or flat?

Is the wheel's bearing hub ID a (slip or pilot fit), (a clearance fit where the coned lug nuts actually center the wheel), or (are is the pilot and the lug nuts competing for the centering translation constraint)?

Without looking at the function and specification... the answers to your questions will reflect the readers vision and experience with something other than what you are looking at.

Paul

True Position · May 16, 2011

A properly made position fixture have has the features at MMC and maximum out of position. This makes any part which passes the fixture in spec.

falconer65 · May 16, 2011

Paul F. Jackson said:
The gauging must reflect the specification and the specification should reflect the function.

Paul

I agree with this wholeheartedly. If more work is done at design level it prevents a lot of pain further down the line. Too often I see prints with true positioning that do not reflect manufacturing, assembly , measuring, or gaging reality.

Erik

David DeLong · May 16, 2011

The drawings with positional tolerances should reflect the assembly or function of the part and gaging is based on the drawing.

If, as Paul states, the function is such that the mating part locates or centers on the holes in the pattern, then RFS is used (no MMC). If the part assembles in the holes rather than centering on them, then MMC is used.

Gauging is more appropriate than a CMM with positional tolerances since all requirements are confirmed simultaneously. The checking fixture is the mating part made in the worst possible condition.

True Position · May 16, 2011

David DeLong said:
The drawings with positional tolerances should reflect the assembly or function of the part and gaging is based on the drawing.

If, as Paul states, the function is such that the mating part locates or centers on the holes in the pattern, then RFS is used (no MMC). If the part assembles in the holes rather than centering on them, then MMC is used.

Gauging is more appropriate than a CMM with positional tolerances since all requirements are confirmed simultaneously. The checking fixture is the mating part made in the worst possible condition.

Some CMMs can deal with the simultaneous position problem and properly apply the MMC bonuses to the datums, giving the datums some freedom to shift/rotate and not incorrectly just adding more bonus tolerance.

David DeLong · May 16, 2011

True Position said:
Some CMMs can deal with the simultaneous position problem and properly apply the MMC bonuses to the datums, giving the datums some freedom to shift/rotate and not incorrectly just adding more bonus tolerance.

I have heard that some CMMS can deal with MMC on datums as well as in the positional tolerance but that is not what I meant by simultaneous.

Whenever one places or stakes a positional pin in a hole, the hole is confirmed the full depth of the hole rather than in one slice. I realize that a CMM can check the hole full depth but is it really performed out there? I don't think so. I just bet the hole is confirmed in position in one slice only.

Also the datum holes at MMC are located with a cylindrical pin which would contact the smallest ID of the hole which could be on the top, bottom or the centre. A CMM, one might take a number of readings half way down the thickness of the material in the hole. Is that the same as using a cylindrical pin on the checking fixture? Not really.

True Position · May 16, 2011

David DeLong said:
I have heard that some CMMS can deal with MMC on datums as well as in the positional tolerance but that is not what I meant by simultaneous.

Whenever one places or stakes a positional pin in a hole, the hole is confirmed the full depth of the hole rather than in one slice. I realize that a CMM can check the hole full depth but is it really performed out there? I don't think so. I just bet the hole is confirmed in position in one slice only.

Also the datum holes at MMC are located with a cylindrical pin which would contact the smallest ID of the hole which could be on the top, bottom or the centre. A CMM, one might take a number of readings half way down the thickness of the material in the hole. Is that the same as using a cylindrical pin on the checking fixture? Not really.

The CMM software I know actually uses a functional fit for datum features to simulate the misalignment you're talking about. You would need to scan helixes along the pin/hole features but they are calculated correctly.

This is getting a bit off topic. To the OP, the problem comes down to your position gage and it's design, it's possible to design them to take MMC into account but that had to be done at the APQP stage.

Kanagu · May 17, 2011

Thanks for ur replies..

Herewith am attaching the disc drawing with spec.
I had also attached the Position Gauge rough sketch.

Pls look after those and advise me for the above Doubts.

Urs kanagu

Paul F. Jackson · May 17, 2011

No MMC!

The axis of each of the 4X pattern of holes have to be within their constant value cylindrical tolerance zone no matter what their size is. You should fit the rotation of the 4X pattern so that no one hole is used to clock the pattern but the rotational deviations about are minimized. Then each individual clearance hole [C] serves as a datum feature to control the location of the coned lug nut mating surface.

Functionally if is a slip fit to the bearing hub... both and the four coned surfaces fight to stop translation about the hubs pilot diameter. If has more clearance than the 4X pattern [C] position tolerance then the coned lug nut surfaces stop translation as a pattern.

Paul

True Position Checking such as Bolt Hole Position w.r.t Center Bore on Wheels

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