Attendance
LEGO project demos!
Cool things of the week:
Peppermill Remote, Jamming Gear from the TEI Conference
Screw it or Glue it? On Fastening and Joining Parts
Non-permanent joints: fasteners, screws, nuts
- Practical, quick, lots of options
- Disassemble-ability is important for prototyping and learning
Permanent joints: welding, rivets
- Hard to teach welding w/o equipment
- You can’t really take apart these things without a helluva lot of effort
Non-permanent joints
Screws/Bolts
- Identified by major diameter and threads per inch, followed by length
- ¼-20 x 5/8” has ¼” diameter, 20 threads per inch, and is 5/8 inch long
- UNC vs. UNF
- Screws smaller than ¼” use numbers as designators
- Ex. A 2-56 screw has a major diameter of .086” and 56 threads per inch
- Metric screws are called out with an M, their diameter, their pitch, then length. Ex: M3x0.5-10
- Screw Selector
Taps
- Some screws are self tapping
- Some materials don’t need to be tapped (wood, some plastics), you can drive a screw right into them
- For all others, proper technique will save you a lot of time and broken taps!
- Types of Taps, Tap Drill Chart
10 Step Tapping Procedure
- Put your safety glasses on and clear your workspace
- Use a center punch to make a mark where you want to drill
- Clamp the piece of metal down to your worktable. Use the correct tap drill bit size for your screw, and drill a hole.
- Clear off any metal chips or burrs from the hole with a deburring tool
- Spray or squirt some tapping fluid or WD-40 on the hole
- Install the tap in the tap handle just like you would insert a drill bit into a drill
- Place the end of the tap in the hole you just drilled, and position the tap perpendicular to the material. The tap must stay perpendicular to the material surface the whole time or it will break. Carefully turn the tap handle clockwise one or two turns until you feel the little teeth on the tap start to bite into the aluminum. From this point on, turn the handle 1/2 turn clockwise then 1/4 turn counter-clockwise. This backing up is necessary to cut the aluminum in small pieces so the chips don’t build up, plug up the tap, and cause it to break. Taps are made of material that is very strong, but very brittle. They will break surprisingly easily if you twist too hard. Don’t try to correct for misalignment once you’ve started to tap the hole.
- Once you’ve gotten to the bottom of the hole, or through the material, unscrew the tap all the way back to remove it.
- Wipe, rinse, or blow away any metal chips and excess tapping fluid
- Try screwing the screw into the hole. Ta da! It should twist in easily.
Counterbores vs. Countersinks, Drive styles, Head styles
Other types of screws McMaster, Fastener type chart
Others: All thread, shoulder screws, set screws, self-drilling/self-tapping, binding posts
Nuts
Whenever possible design through holes so you can use nuts instead of tapping!
*In general, the screw should extend a couple threads past the end of the nut
Washers
Reasons to use them:
- Avoid marring base material
- Spread screw fastening force over larger area
- Spacer to avoid stressing the inside corner of the screw head
- Indicate bolt is tight enough
- Lock washers keep screw loaded and resist vibrations
Nails, Staples, Velcro, Magnets
Pins - use for alignment and connection (clevis, hitch, cotter)
Retaining Rings
Permanent Joints
Adhesives: Epoxy, wood glue, plastic glue (Weld-on), Loctite, Superglue, hot glue, tape
Rivets
Welding: Joining two similar metals by melting them, sometimes with a filler. Check out classes at the Madagascar Institute, the Education Alliance, and 3rd Ward to learn more.
- Brazing: uses filler rod, melting temp above 800 deg F, can join dissimilar metals
- Soldering: uses lead-tin (or lead free) solder, melting point below 800, reserved mostly for electrical components