Mechanical Design
Screws
There are self-tapping screws that makes their own taps.
There are counter-sunk screws. It has a chamfer on the underside. It allows the screw to be flush with the surface. It also completely centers the screw.
A lag screw has a hexagonal head and can be tightened / loosened using a wrench.
Cap screws has a few variations. One of which has Allen, or socket heads, and can be turned using an Allen key. Note that there can be other shapes too. Use the right screwdriver for the right screw. One particular type is a torx screw and has a star shaped socket.
Set screws does not have a head. It just have an Allen socket at the top. They often go all the way into the part, which is the reason why they don’t have a head.
Easy-Out
In the case of head detaching from a screw stuck in a part. Use an easy-out which has opposite tapping.
Bolts
The shank is the cylindrical part between the head and the tapped threads. The shake diameter is denoted as S. The thread has a thread diameter, often times it is the same size as the shank diameter. The root diameter is the inner diameter (without threads). The head width is the height of the hexagonal head.
If we need to drill a hole for threading, the hole must be the size of the root, not thread.
Sex/Stripper bolts are used in joints because the outer shaft is smooth.
Nuts
A hex nut is a regular nut with hexagonal shape. A wing nut can be adjusted by hand because of its “wings”.
Lock nuts has nylon on the inside to lock the bolt.
Deep nuts are long and is useful when we need bolts coming from both sides.
Washers
They are used to protect the parts. If the hole is a bit too big, a big washer can be used to fix.
They are also used to disperse the stress due to the tightness of the bolts to avoid getting the part damaged.
Pins & Clips
A snap ring goes on a shaft with a small groove. Flat punch and pipe cutters are also useful for clipping things.
Use rivet to fasten two pieces of parts together if you don’t have access to the other side of the hole.
Chemicals
Adhesives
Obviously, glue are useful, but often times they aren’t enough if the surface doesn’t like adhesive. Silicon will work better. For lamination, paint works really well because it sticks to metal and holds the parts together using surface tension.
To tighten bolts, there are loctite. Loctites can come in blue or red, they are used for different types materials.
Use tapping fluid to tap threads.
Use WD-40 to reduce friction.
Shafts
To make connections on shafts, there are a few constraints:
- Axial constraint - Locking the shaft along the axis direction.
- Shoulder
- Cotter pin
- Retaining Ring
- Squeezed shaft
Connections
Support
Anytime a shaft is being supported, there are two types of supported.
Cantilever holds one side and span holds both sides. The span configuration can hold much more torque.
For a sandwich connection, which is often used to hold laminations together and squeezed together, make sure that the top layer is chamfered, and only the bottom layer is threaded. All layers in between should be clear.
Post-Processing
Make sure to use personal protection equipment when doing post processing.
- Sandblasting
- Filet
- Deburr edges and holes
To put finish on surface, you can spray paint, powder coat, or polish.
Reminders
- Glue does not stick to non-porous material like metal or glass
- You cannot spot-weld aluminium
- Iron rusts if it is not painted / powder coated
- Prototype should be able to be disassembled, adjustable, and modular
- Shop will get more busy later in the term
- Water jet breaks down when its overused