When designing a carbon fiber part that uses screws or fasteners, the design of the hole is a critical detail and effects assembly, appearance and ultimate performance.
Some applications require a simple hole. But many carbon fiber parts need special machining features, like countersinks or counterbores, to make sure you get a nice finish on the surface or that the screws go in properly.
Choosing the wrong type of hole could lead to problems such as:
l Screw heads protruding from the surface
l Component in wrong position
l Not enough space
l Incorrect height assembly
l Further Machining on Receipt of Parts
Engineers need to know the difference between through holes, countersinks and counterbores so they can create clear drawings and avoid unnecessary changes in production.
The simplest type of hole that can be machined is a through hole.
The hole goes all the way through the carbon fiber plate . Usually the diameter is equal from top surface to the bottom surface.
Typical applications of through holes are:
l Nuts and bolts, screws
l Mounting brackets
l Spacers
l Mechanical connections without countersinking of the screw head
like a mounting plate of carbon fiber which is attached to another structure by a plurality of through holes.
When requesting CNC machining, the drawing should clearly define:
l Hole diameter
l Position of hole
l Number of holes
l Hole center to hole center distance
l Required tolerance if the hole is used for alignment
For standard 2D carbon fiber cutting parts, a DXF or DWG file is usually sufficient.
A countersunk hole is a conical depression around the top of a through hole.
The screw head may be a flat head below or flush with the carbon fiber surface.
Countersunk holes are commonly used in cases where:
l Needs smooth surface.
l Screw head must not interfere with other parts.
l The part will contact with some other surface
l Appearance is important
For carbon fiber visible parts, countersunk holes are often used because they maintain a clean surface appearance.
Typical applications include:
l Sim racing steering wheel panels
l RC car chassis plates.
l Equipment covers
l Carbon fiber mounting plates
If a drawing calls for a countersunk hole, it is necessary to specify:
l Through hole diameter
l Countersink diameter
l Countersink angle
l Screw Specifications
A basic note like “countersink hole” may not be sufficient as different screws require different angles and dimensions.
A counterbore is a flat bottomed hole counter sunk around the main hole.
A counterbore is a cylindrical step and a countersink is a conical recess.
Counterbores are normally used when a flat surface is needed to seat a screw head or fastener.
Typical applications include:
l Socket head screws
l Bolts with Cylindrical heads
l Components requiring for hidden fasteners
l Regulation of screw depth in sections
Counterbores are common on carbon fiber CNC parts where the screw head needs to be recessed into the plate either partially or fully
The drawing shall indicate:
l Main hole diameter
l Counterbore Diameter
l Counterbore Depth
l Machining Direction
l Fastener dimensions
Your supplied image shows a typical counterbore feature machined into a carbon fiber sheet, where the recessed area provides space for the screw head.
The main difference is the shape of the recessed area.
| Feature | Countersink | Counterbore |
| Recess shape | Conical | Cylindrical |
| Screw head type | Flat head screw | Socket head screw / bolt |
| Bottom surface | Angled | Flat |
| Main purpose | Flush appearance | Controlled screw depth |
| Common use | Visible panels | Mechanical structures |
And neither is better globally.
The correct choice depends on:
l Type of screw
l Assembly structure.
l Surface requirements
l Space for installation available.
l Final appearance requirements
For Standard holes, a DXF/DWG file may be enough.
However, for special machining features such as countersinks, counterbores or recessed surfaces, a STEP file is preferred because it contains clearer 3D information.
A complete CNC drawing should be:
l Hole diameter
l Hole location
l Hole quantity
l Hole type
l Top diameter
l Angle
l Depth
l Screw specification
l Recess Diameter
l Depth
l Bottom surface requirement:
l Specification for Screw
Providing complete machining information helps the supplier understand not only the hole size, but also how the finished part needs to function during assembly.
Hole design is only the first part of a complete carbon fiber machining project.
Depending on the application, customers may also need:
l Bevels on the edge (edge chamfers)
l Surface markings
l Silk - screen printing
l Installation of a press-fit nut
l Metal parts bonding
l Assembly matching
If cutting is not the only part of the project, submitting all the manufacturing requirements at the same time may reduce communication time and minimize changes after production.
We also provide custom CNC machined carbon fiber parts with additional processes such as drilling, countersinking, chamfering and other custom machining features.
Things to consider before sending a CNC carbon fiber drawing:
l The screw head can be left exposed
l OK for standard mounting connection.
l Surface appearance is not critical.
l Needs a flat surface
l Uses flat head screws.
l The screw head need to sit flush
l A cylindrical screw head needs to be recessed
l A flat seating surface is required
l Screw depth needs to be controlled
A properly designed hole will facilitate the CNC machining process and also ensure that the final carbon fiber part will fit during assembly.
If you have a DXF, DWG, or STEP file for a custom carbon fiber component, we can review the machining requirements and recommend a suitable hole design before production.