The size of the fence post, and therefore the boundary that we cannot violate, is 5 diameter. We do this by specifying our holes a basic 50 apart and with a virtual condition that is equal to the size of the fence post. We want to make sure that the combination of size tolerance and location tolerance always protects a hole (or a boundary) such that the fence post will always fit in the hole. Our considered holes will have both size tolerance and location tolerance. That just means the holes that are not the datum hole. The holes that are not the datum hole are referred to as the 'Considered holes' or the 'Measured holes'. We will re-visit our datum hole later, after we learn everything there is to know about the other two holes. Therefore the post will fit snug in the hole and we will forget about it for now. This is also the exact size of the post that goes in the datum hole. So the virtual condition of our datum hole is 5.1-0.1=5.0.

The virtual condition size is the smallest hole minus the perpendicularity error. In this case, the hole will leave a space for the post that is equal to the virtual condition size of the hole. Because we want to forget about the tolerances on our datum hole for now and focus on the other holes, we will consider our datum hole to be at its smallest allowable size and at its maximum allowable perpendicularity error. Our datum hole has size tolerance and perpendicularity tolerance. Once again we will make the far left hole our datum and locate our other holes relative to our datum hole. Now we just need to dig our holes and slide the fence section into our holes. The Related Actual Mating Envelope is the largest perfect cylinder that is exactly perpendicular to datum and still fits within the datum hole. Datum is the axis of the Related Actual Mating Envelope of the datum hole.

The axis of the unrelated actual mating envelope cannot be datum because this axis is not necessarily perpendicular to datum. The axis of the unrelated actual mating envelope of the datum hole must fall within this tolerance cylinder. The perpendicularity control says that there is a tolerance cylinder that is 0.1 diameter that is exactly perpendicular to datum. The datum hole has a perpendicularity control that controls the orientation of the datum hole. The datum hole is not necessarily perpendicular to datum. Our datum callouts in the feature control frame for the Tolerance Of Position tells us that datum must be perpendicular to datum. The hole on the right will be located relative to datum axis. In order to understand our tolerance of position control, we must thoroughly understand our datum.įor now, focus on the datum hole. Note the addition of a basic dimension and a tolerance of position control. In the figure below, the hole on the right is located relative to the hole on the left. In previous chapters we talked about the orientation of the holes, but we never talked about the location of the holes. For our discussion of Tolerance Of Position, we will first look at our holes that we are digging for fence posts to keep our dog in our yard.

Datum simulator