Have you ever heard the term jobber drill bit and wondered why is it called so? You are not alone.
Years ago, when I was first starting out as a toolmaker, I thought that all drill bits were the same, except for the sizes. As I gained more and more experience, I discovered that there’s basically a drill bit for everything.
That said, while the applications of each drill bit are pretty obvious, what confused me the most was the jobber drill bit and its jobber length. I thought there may be more people confused like me and so in this article, I’ll explain what jobber bits are and how they’re measured.
So, let’s get into it!
What Is a Jobber Drill Bit?
A jobber drill bit is a general-purpose twist drill bit with a straight shank. The term jobber length refers to flute length (which is the length of the twisted part of the drill bit). The flute length of a jobber bit can go from 8 to 14 times the diameter of the bit.
For example, if a jobber-length drill bit has a diameter of ¼″, its length would be 2 ¾ inches which is 11 times the diameter.
Jobber Bit Uses
Jobber-lengths are excellent for general purpose applications since they can handle a wide variety of jobs. They usually come with a point angle of 118° or 135°. Jobber bits can be used for drilling wood and metal and they are very versatile.
Keep in mind that the term jobber has nothing to do with the material it is made (HSS vs cobalt vs carbide) or coating (titanium vs black oxide). These bits come in a plethora of styles to tackle different applications. You can find heavy duty-split point bits, para-flute jobber bits, cobalt bits, and high helix bits.Tip Although you can use a jobber bit on wood, my recommendation is to use a spade bit or brad point bit for drilling wood.
Why is it Called a Jobber Bit?
What is the actual meaning of jobber bit? Let me take you on a short trip down history lane.
The term Jobber was most commonly used from 1850 to 1950. It refers to the middleman between manufacturers and retailers (any person or company that buys from the manufacturers and sells to retailers).
What does that have to do with drill bits, you ask?
Well, during that period, manufacturers used to sell general-purpose drill bits that aren’t designed for specific purposes like today. These bits were of medium length, making them suitable for a wide variety of applications. A “jack of all trades, master of none”, if you may. Such drill bits were called “jobber bits”. In other words, a jobber drill bit was what’s known today as a “general-purpose” bit.
As time passed and drill bits got more specialized, jobbers started to lose their charm as the only kid on the block (they are still the most commonly used bits, though). Today, the term “jobber” refers to the bit’s length rather than its purpose.
Wanna Get Technical?
What I detailed above regarding the length to diameter ratio is what you’d call a crude rule of thumb. If you want to check the exact definitions of the “jobber length”, take a look at ANSI/ASME B94.11M-1993.
Jobber Drill Bit Size Chart
Different systems are used to measure these drill bits, including letter sizes, fractional sizes, wire gauge sizes, and metric sizes. Here’s a table that explains the flute length and overall length of a jobber drill bit using fractional sizes:
|Fractional Sizes||Flute Length (Inches)||Overall Length (Inches)|
Jobber vs Mechanics Drill Bit
Compared to a jobber drill bit, a mechanics drill bit has a shorter flute length and overall length, making it more resistant to breakage and shearing. So, while jobber drill bits are suitable for soft materials like wood, composite, and soft metal, mechanics bits can take on harder materials and hard metal drilling.
Screw Machine Bits
The screw machine bits are even shorter and are also called stub drill bits. These bits usually have a flute length of 4 to 7 times the diameter of the bit.
Here is an approximate average length of these drill bits for quick reference.
- Screw Machine Bits: The flute length is approximately 5 times the cutting diameter of the bit.
- Mechanics Length Bit: On average, the flute length is 8 times the bit diameter.
- Jobber-length Bit: The length of the flute is 10 times larger than the diamter.
* This is a very rough estimate. The exact length depends on the cutting diameter of the bit and also the manufacturer.
Which Bit Should You Use?
As for which you should use, the answer is easy. The stubbier the drill bit, the stronger the bit and less chance of breakage.
If you need to drill soft materials like plastic, aluminum, etc. get a jobber bit. On the other hand, if your project includes drilling harder materials, use a mechanics drill bit or screw machine bit if the flute length is sufficient for your job.
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