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opencomputeproject / Time-Appliance-Project

Develop an end-to-end hypothetical reference model, network architectures, precision time tools, performance objectives and the methods to distribute, operate, monitor time synchronization within data center and much more...
MIT License
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PCIe Bracket V3 dimensions #24

Closed wisxxx closed 1 year ago

wisxxx commented 3 years ago

The vertical hole centers are referenced to the top surface of the short bend section at the upper end of the bracket. This position, being on the outside of the bend, is not as well controlled as the bottom surface. The CEM and off-the-shelf brackets all use the bottom surface as a reference.

The horizontal hole centers are properly referenced to the inside of the bend of the ears.

Also, not specified are:

wisxxx commented 2 years ago

UPDATE: A check of the 3D model setup shows that this is a non- or very low risk issue. Careful management of the Z offsets of the STEP models reduces the bracket / connector centerline offset to something small.

Original;

SMA connectors do not appear centered in the cutouts when the .STP model is combined with a 3D model of the connectors (Amphenol 901-143-6RFX, from SnapEDA) mounted on a 1.57 mm (61.8 mil) thick board. The offset is estimated to be about 0.64 mm.

The connector model dimensions appear match the part drawings. Both models are very close to their correct positions vertically. Mounting the bracket on the top side of of the board puts the connectors below the center of the cutouts.

It may be that the cutouts are oversized to accommodate different SMA connectors. Is that the case?

looking from outside: image

zoom image

mounting detail image

ahmadexp commented 2 years ago

@wisxxx, I really want to thank you for all the amazing reviews you have been doing on the time card.

wisxxx commented 2 years ago

What is the reference feature for the connector centerline dimension? If it is the top surface of the ear, then the extension line is drawn incorrectly.

ctr_dim

wisxxx commented 2 years ago

What is the bracket material thickness? Is it the PCIe CEM standard 20 ga (0.86 +/- 0.08 mm, 34 +/- 3 mils)?

Ref: PCI Express Card Electromechanical Specification, Revision 4.0, Version 0.9, p. 137.

wisxxx commented 2 years ago

To quantify the connector to I/O bracket cutout misalignment: 1.1 mm (43 mils), assuming the 6.83 mm dimension in the drawing is from the top of the mounting ear attaching to the bottom of the nominal 1.57 mm thick board and the connector is the Amphenol 901-143-6RFX shown in the BOM.

The layout shows the distance from the bottom of the board to the connector centerline as 7.93 mm.

vert_layout .

wisxxx commented 1 year ago

Addressed in bracket V4 docs.