Geometric positional tolerance is given of.1 mm with modifier M. The modifier has specific meaning, It add a bonus tolerance. When shaft is at MMC there will b . GD&T bonus tolerance is an important concept for design engineer. This article will explain the Geometric Dimensioning and Tolerancing concept with an. However, there is no bonus tolerance allowed in this condition so the perpendicularity would be much better controlled regardless of the size of the hole.

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For example if you wanted to ensure that a pin always fits into a hole when the hole is at MMC, we could design a pin gauge that mimics the lower limit of the hole. The virtual condition can be controlled with a functional gauge. Functional gauges can be a huge benefit to gonus environments where measuring on the line quickly is critical.

The drawing has a Thanks for spotting it and letting me know! Should be fixed now.

Is this the same typo you were referring bbonus Good Catch- you are right — we changed this example a while back to simplify it and the second drawing never was swapped with the new one. Thanks for the help with pointing this out!

Can this also be translated to a concentricity tolerance? True position tolerajce 0 simply means that at Max Material Condition largest pin or smallest hole your part must be perfectly centered. Ultimately you should target the LMC of the part Smallest pin or largest hole so that you can be out of position more.

Base on the example above, so what are the MMC values of 1. Diameter of the pin 2. Diameter of the hole. The example shows how to calculate the Gauge size, also known as the Virtual condition. The term maximum material condition means the largest external feature or the smallest internal feature. For a pin, its largest size is considered the MMC. The tolerance given in the feature control frame applies to this size. As you get smaller in size, you are allowed to add whatever the differences is between your actual size and the MMC, to your geometric tolerance.

MMC can apply by allowing the parallelism tolerance to increase for a feature of size as the size moves away from the MMC. Thank you very much for your clear explanations! Will it be concidered as produced at mmc?

What if it was called out with straightness at mmc? Will it get bonus tolerance for the sections where the diameter is less than And what if the call out was true position or perpendicularity with mmc? Would there be any bonus tolerance allowed? Thank you very much in advance, simon. The part would actually be both depending on where the measurement was that made it You would usually take the boundary condition of the part which would be the MMC.

According to the envelope principle your part cannot go outside of its MMC envelope, and cannot have any 2 point measurement less than the LMC. Now bring in straightness at MMC.

The design intent is that you are specifying the combination of the worst geometry with the worst size. So if you were to inspect the part, you would need to make 2 measurements.


First is using your straightness gauge set at If the part fits, the straightness is met. Next your part would be measured for size. No 2 point measurement could be above If these pass your part is in spec. The true is that yes, you would get bonus tolerance as your part diverts from MMC, so one side could be less straight than the other. The goal is that it fits into its assembly meaning the straightness and size cannot allow it to exceed a certain limit. This works because straightness is not datum controlled.

Position and Perpendicularity would be fairly similar, only it would depend on the same 2 measurements Position and size would all have to be met independently. This means that if your part is at MMC with a zero Perpendicularity Tolerance your part would need to be perfectly perpendicular. For datum controlled features, the rule typically is that it would be considered as a MMC part — since it could not move anywhere if it was set in a functional gauge.

PlzSir Details for mmc with example more confusion in mmc reading drawing that this is use for hole or pin. Note that with a composite or multiple single segment control the individual segment requirements are verified separately. Thanks for your patience.

Sorry Matt, it took a bit to get back here, so the part has a baseplate and 2 side plates welded to the base 90 deg angle. These 2 side plates are separated by mm and they each have 2 thru holes 50mm This one has a position tol of 2mm with respect to B at MMC mmc is called on the tol and the datum. This again has a composite tol of 0. We are trying to come up with a gauge to check the second hole position relative to B within tol and Is parallel to B within tol. For a feature of size hole, pin, tab, slot etc.

I have seen parts where there is MMC called out for positional tol and some that do not have MMC callout on positional tol. Here if there is mmc on the positional tol, part at But if there is no mmc symbol used on the positional tol box, and the part measured at A minor correction on your statement above. MMC refers to maximum material condition. The best way to think of this is the condition that will make the part heavier i. In your specific example you always have a tolerance zone of 0.

The MMC size of the hole internal is 9. At a diameter of 9. The way this works is all about assembly at the next higher level. You know that at your MMC size and tolerance you are guaranteed a fit if you calculated it correctlyevery size must have tolerance so if your hole is slightly larger it should make sense that you would be able to accommodate an increase in positional tolerance as well and still have everything fit together.

This would be the easiest way to inspect this control. As for how to measure it the old school way: You should be able to rotate your part a full now. Second, get two dial indicators and set them up so that they are diametrically opposed of one another on the controlled surface, for this example lets say put the indicators at 0 and degrees straight up and down.


You need to be able to set up the indicators such that they start at a radius of Now, as you spin your part you get two measurements from your dial indicators and these tell you what the local radius is from the datum axis pay attention to whether you are adding or subtracting from nominal based on dial indicator plunger movement in or out from your nominal Now, add these 2 dimensions together and divide by 2 to get a number we call r0.

Introduction to Bonus Tolerance

Subtract r0 from your measured local radius from the 0 deg indicator and you have your concentricity error Co. Every distance Co must be within the cylindrical tolerance zone defined in your feature control frame. I hope this helps.

If I am measuring an ID hole with a tolerance from. Your limits of size specify just that, limits. The positional tolerance applies to only the hole position, it has no impact on the size.

As for the impact to the design? That really depends on what the design is for, I would wager most applications would be fine with it. Ultimately, the discrepant condition should be written up and flowed down to the customer to evaluate and disposition. MMC or Maximum Material Condition like its counterpart Least Material Condition [LMC] is specifying at which physical condition the stated tolerance in the feature control frame applies to a specified feature. Think of MMC as the condition that results in a heavier part, i.

The amount of bonus tolerance is equal to the amount of departure from the stated MMC or LMC in the feature control frame. The bonus tolerance available is 0. The total tolerance available at 0.

Bonus Tolerance | eMachineShop

Why does this work? Hello, can you put also a presenation with MMC on tolerancce datum? I think that will be common in the near future. To avoid confusing the difference between internal and external features think of MMC as the condition which makes the part heavier i. Your MMC hole size is 4 and you are provided no additional tolerance through bonus.

Now, if vendor only has a 5 drill bit you still get the 1 positional tolerance zone but now you get another 1 for a total of 2.

If the hole comes in at 6 you get the stated 1 plus 2 for a total of 3. No matter what, you always get the 1 and any additional tolerance is the result of the actual hole size drilled into the part.

Why does it work this way?

The goal here is assembly. If you calculate that you can live with a hole of size 4 and tolerance of 1, then it should make sense that as your hole grows in size you would be able to tolerance an increase in the tolerance zone while still protecting assembly.

LMC gd&y in the same way, just in the opposite direction and can be used to protect wall thickness of say a bore in rod. I hope tolerwnce helps! Keep cruising the forums and website.