GD&T write up

Clock Base:

                 For the first part of the design there are 3 main Categories required to make a working part. We need the bottom to remain Flat, the sides to remain rectangular and for the holes to be positioned correctly.

Flatness:

           This is defined by placing the bottom of the part onto a known flat object (Such as a machinist stone). From here the part will be measured from how much it protrudes from the machinist stone. We then will measure the maximum deviation from the lowest spot on the part to the highest. This deviation has to be within the tolerance given in the GD&T bracket.

Rectangularity:

           Although Rectangularity is not an aspect of GD&T it is simply a combination of the parallel and perpendicular aspect of the part. Datum B is flush to the machinist block. Similar to flatness we measure the maximum height and minimum height that is allowed for that part this value must be within the tolerance block of the specified GD&T. Then for the perpendicularity of the part we keep datum b on the machinist block then grab a known 90-degree angle and apply it flush to the main part. We only allow half the allowed gap between the known 90-degree gauge and the part. It is only half due to the fact that with the gauge we are only looking at one side of the 2-sided tolerance thus we half that value.

Position:

           For the final GD&T part we allow a certain amount of circular difference on the point where the hole is drilled. The reason why the hole is drilled within a circular tolerance instead of the nominal square tolerance is due to the fact that more allowable tolerances are found within a circular tolerance for drilled parts.

Pen Holder:

           For the pen holder there were a total of 5 GD&T requirements placed on the part. This includes the Perpendicularity, Parallelism, Cylindricity, Flatness, and Position of said part.

Parallelism:

           First we have the parallelism of the parts sides to Datum A. This Aspect is important due to the need to have a straight looking pen holder for aesthetic reasons. The reason why the aesthetics of a part matter is due to customer satisfaction. Customers will not want to pay for a part that is produced but doesn’t have a strait pen holder. The way this is measured is by laying the part on a flat machinist stone and measuring the high and low spots and making sure the difference between those two points is within the specified GD&T allowance.

Perpendicularity:

           The Perpendicularity is important to make sure the top of the part doesn’t have a point where the pen prefers to lay i.e. a low spot. This is measured by laying the part on the datum A side and measure half of the allowable tolerance with a 90-degree gauge.

Cylindricity:

The internal hole must be round, straight, and consistent along its length so that a pen can slide in smoothly without binding. Cylindricity is used because it controls the entire 3D form of the bore, roundness, straightness, and taper all in one control. This is more appropriate than simple diameter tolerances, which do not protect form.

Flatness:

The bottom face of the Pen Holder must sit flush against the Clock Base. Any rocking or unevenness would cause the part to loosen over time or appear crooked. Flatness is applied directly to the bottom surface without reference to a datum, ensuring the surface itself stays within a tight tolerance zone.

Position:

For the final GD&T part we allow a certain amount of circular difference on the point where the hole is drilled. The reason why the whole drilled within a circular tolerance instead of the nominal square tolerance is due to the fact that more allowable tolerances are found within a circular tolerance for drilled parts.

Pencil Holder:

           For the pencil holder there were a total of 5 GD&T requirements placed on the part. This includes the Perpendicularity, Parallelism, Cylindricity, Flatness, and Position of said part.

Parallelism:

The outer cylindrical surface must appear straight and uniform for both aesthetic and functional reasons. A visibly tapered or bowed cylinder would be noticeable to the user. Parallelism is applied to the outer diameter relative to Datum A, ensuring the surface does not deviate beyond the allowed tolerance zone. This protects the straightness of the part while still allowing normal machining variation.

Perpendicularity:

The top face of the Pencil Holder must be perpendicular to the cylindrical axis so that the pencil sits evenly and does not lean or favor one side. Perpendicularity is referenced to Datum A, which is the primary cylindrical datum. This ensures the top face is controlled relative to the true axis of the part, not just a machined surface. This is measured by laying the part on the datum A side and measure half of the allowable tolerance with a 90-degree gauge.

Cylindricity:

The internal hole must be round, straight, and consistent along its length so that a pencil can slide in smoothly without binding. Cylindricity is used because it controls the entire 3D form of the bore, roundness, straightness, and taper, all in one control. This is more appropriate than simple diameter tolerances, which do not protect form.

Flatness:

The bottom face of the Pencil Holder must sit flush against the Clock Base. Any rocking or unevenness would cause the part to loosen over time or appear crooked. Flatness is applied directly to the bottom surface without reference to a datum, ensuring the surface itself stays within a tight tolerance zone.

Position:

The threaded hole must be accurately located so the Pencil Holder screws into the Clock Base without cross‑threading or misalignment. A positional tolerance is applied to the tapped hole using a circular tolerance zone.