How Long is a Jobber-Length Drill Bit?

I'm really surprised so many people are informed on this topic. I thought manufacturing has left our shores and machinists were a dying breed. Bonus question - what's the benefit of high helix drills?

Up until 1988 the standards for all U.S. metal cutting tools, including Jobbers length drills were set and maintained by the Metal Cutting Tool Institue, a trade association of the U.S. manufacturers, published in the the Metal Cutting Tool Handbook. That's what we at Vermont American Corporation and the other U.S. mfrs ground our cutting tool products to. In 1988 they merged with the Cutting Tool Manufacturer's Assoc. to become USCTI, see:uscti.com/u_pages/about/about.asp
Called Handbook of Specifications, the jobbers dril section is avaiable to non-members for $35.00.

I'm just glad I was able to grasp the hole picture here. It was not a really deep post, but one that held my interest. Thanks for not veering off center.

A jobber length drill bit is short enough so that the end point won't deflect in the work when held in the drill press chuck, and thus an accurate, straight hole can be achived with the minimum number of steps. Using a longer bit requires starting with a small diamter drill and then stepping up in drill size to the final diameter to prevent the deflection of the drill bits from causing a "crooked" hole. The name "jobber" comes from this reduction in machining time.

In reality with drill bit sets the length is often standardized to fit the case and the "correct" length is immaterial to the manufacturer and the end user. Sadly hole boring tool design has progressed very little over the last 100 years save for better alloys and lengths are seldom appropriate to the task at hand. Even the hardness is an average of requirements between hardness for boring and brittleness. Factor in issues with heat tempering the work piece while during the boring operation or for other materials like plastics the melting of the material.

Based on practical experience, a "jobber" length drill bit fits into the index without being so short as to not be properly contained and without being so long that the drill index does not close. Stubby drills are shorter than that, and drills to long for the index are "long". This follows the observations about l/d ratios, and explains the apparent inconsistancy observed. The reason is mostly related to the stiffness and the need to avoid flexing during use, which will lead to buckling when excessive feed pressure is applied. So the reality is it came backwards from the application side, instead of forward from engineering. How about that?

I think Titus meant "boring" as in drill bit and boring a hole. Get it?

Thanks for your comments. Find the dimensions for standard jobber-length drill bits at: www.seltools.com/HSS_Drill_Bits/HSS_Drill_Bits.pdf for #60 through 1/2-inch. This table provides overall length, flute (twist) length, and diameter information in inches and millimeters. I couldn't find an online table of that information for drill bits #61 and higher, although Machinery's Handbook lists that data.
Also, see pages 46 through 48 at: www.scribd.com/doc/18135634/Hbook for general dimensional information. --Jon Titus

yes it was boring...but informational.

What is improtant as well is contrasting this with the split point and stub drill bits.

I have always admired your work since those Bug books. I would have been nice if you posted the length for the most popular drill bits, for example no.7 and so on