TECHNICAL BULLETINS

6061 aluminum is a structural grade aluminum and has a dull (mill) finish. 3003 is an architectural grade and has a mirror like polished finish and commonly used for truck tool boxes and the like. The 3003 alloy is so soft that the chips from drilling or sawing get stuck to the drill flutes or saw blade teeth and requires much coolant to prevent heat buildup. The harder the material the easier it is to drill or cut (to a point, of course). Same with steel, the harder alloys will be easier to drill and cut for the same reason, to a point. Harder alloy steels and hardened steel are completely different. Tool steel, like 4140, is available as a pre-hard or annealed and drills and cuts much cleaner than hot rolled steel. However, the annealed is easier to work with because of its’ softer property state. Cold rolled steel is cleaner cutting than hot rolled steel because there are less imperfections due to being cold drawn as opposed to hot drawn. What defines a hard alloy or hardened steel is mostly the carbon content as well as some other factors such as different elements that are added in the process. Hot rolled structural steel has about 0.5% carbon and 4140 alloy steel has between 0.8% – 1.2% carbon and makes it much better to work with. Carbide and carbon are not related.

You can’t use 3003 aluminum for a floor because it’s too soft and will not last. Also, the shiny finish will show every scratch and look like junk within two weeks. To cover holes in the motor room it’s better to use the 6061 for large holes if there is no support under then and the smaller pieces can be done in 3003.

If you’re drilling case hardened steel you have to use either a carbide tip drill or solid carbide drill. The term “case hardened” means that the steel is heat treated to a specific depth around the circumference in round bars or perimeter in square or rectangular bars. For example, a typical case hardened steel bar can be heat treated to a depth of 0.050”. The best way to understand this is to envision a hardened “skin” around the steel, and the skin can be a pre-determined thickness. A full hardened steel bar is where the heat treat process allows the entire inner depth of the steel to become hardened. This is common in tools such as drill bits, reamers, end mills and the like. When drilling through case hardened steel with a carbide tip drill, first penetrate the hardened layer, then, use a regular high speed steel drill to continue through the soft portion (center section) of the steel until you reach the hardened surface on the other side and again, use the carbide tip drill to penetrate the hardened layer on the other side. You’ll know you’re drilling hardened material when the chips are gritty and the drill sounds like grinding. Use an oil based lubricant, not water based. Even though a carbide tip drill will be able to drill through the softer steel, it will get stuck in the hole because the softer steel chips will load up on the drill causing the drill to break in the hole. A carbide tip drill does not have flutes to allow the soft, stringy chips to follow up and out, however, a solid carbide drill does and can be used to complete the entire job.

You could use a regular high speed drill, but have to flood the coolant which makes a real mess. Otherwise, you can use a cobalt drill or TiN coated drill with is Titanium Nitrate coating and helps prevent heat buildup on the drill. If the drill bit is overheated it causes two things to occur. The drill bit becomes annealed, meaning it changes from a hardened steel to a softer steel and the steel you’re trying to drill becomes hardened. Then, you’ve got problems. With stainless steel, by the time this transfer occurs you will have already discolored the finish so bad that it will require polishing to remove the heat stain. In regular steels there’s usually no finish to discolor, however, in both cases you will then have to use a carbide drill to complete the job. Regardless what type drill you decide to use, drill at a very slow rpm and use an oil lubricant.