I've never heard anyone call it a speed hump, but apparently it's quite common?
you take them off and use a disc grinder or a wheel grinder to sharpen them..
That's kind of a confusing question. Perhaps it would be best to just explain how a door frame is built and you can answer your own question. The two sides of a door frame have a number of 2x4 studs fit together to form a main support column for the door header. This may be 2 or 3 slapped together to form a column that is 2 or 3 2x4s wide. Across the top of the door frame is a 4x4 or greater header (solid beam) that spans across the doorway from one support column to the other. This is then all built integral to the rest of the wall framing to support the door opening. If you wanted to widen the doorway, you would have to move one or both of the support columns to the side. But, then the header beam would not be fully supported by the columns and you would have to replace it with a longer header. That is, you can't just extent the header by adding a piece of wood on the end. It needs to be one solid piece to function properly. Can you now answer your own question?
be a scientistjk a water treatment plant operator is a good one
For rotary type mowers, I use a hand held high speed grinder with a 12mm diameter cylinder about 4 cm long. Wear a face shield and gloves. When I do this i usually do a oil change and replace the spark plug also. I tip the mower on it's side after draining the oil and fuel and grind the blade. The amount of material removed is minimal compared to the rock chips so I do not worry about balance. When I have time I replace the blade and install a new one for about $10.
