About a couple of years ago I refurbished a North Bros 1003 bench drill and I’ve been meaning to do a post about how it works.
The North Brothers Manufacturing Company were based in Philadelphia and became famous for their Yankee branded tools, particularly the iconic ratcheting screwdriver without which no handyman’s toolkit is complete.
The original ratchet screw driver was invented by Zachary T Furbish of Portland Maine in 1895, and he joined North Bros a couple of years later when the company he was working at – Forest City Screwdriver and Drill Company – was acquired by the firm.
Furbish was a prolific inventor who went on to file around 30 patents for inventions relating to tools and their associated manufacturing processes. We know from his subsequent patents – all of which were assigned to North Bros – that he moved to Philadelphia after joining the company.
Furbish seems to have inspired North Bros to focus their attention on tools, having previously sold kitchen equipment, and although he died in 1906, he seems to have handed on the baton to another enterprising inventor in the company, George O Leopold, who created the remarkable Yankee automatic bench drill in 1913.
The publishers of Popular Science Monthly and Popular Mechanics have generously made their entire back catalogue available via google books, so we can get a reasonable survey of North Bros’s efforts to sell their wonder drill. The earliest advert is from 1915 and the last in 1929, which gives us a rough idea of the production dates.
The marketing men make a lot of the “automatic” mechanism and, fair enough, since the drill does automatically descend without a separately operated down-feed and it also automatically switches to “friction mode” at the extremes of travel or when the drill jams.
It is not true, however, that “the moment the drill begins to cut, the feed automatically changes to Ratchet movement” as the North Bros marketing men claimed in August 1919. Putting the drill in ratchet mode in fact requires the user to twist the small lever on the feed mechanism to the left, and this is no doubt what – in the same advert – the tall pointing man is explaining to the short fellow in the strange hat.
Realism had returned by 1926 and there is a clear description of what the drill does, although sadly the hat/pointing demonstrators are no longer there.
You may notice the handy little spanner hanging from the bottom of the screw that attaches the drill to the bench in the 1916 advert. Inevitably all of these were lost within 15 minutes of unpacking the drill, and apparently North Bros lost their’s too since it is never to be seen again in later adverts!
How it works
North Bros took out a number of patents to protect their bench drills, listed below. Most of the innovations are described in US1103783
There are a several ingenious features on the drill. I’ve paraphrased North Bros own word’s (from the patents they took out to protect the drill) in an attempt to summarise the sophisticated features it provides.
The beveled gear wheel meshes with a pinion mounted on the spindle (17, in the drawing above).
The spindle is splined throughout its length and the bevelled pinion has a key adapted to the spline so that it can drive the spindle
A locking bolt (19) has a projection which enters the spline in the spindle to prevent the spindle from rotating when you want to open or close the chuck.
The lock is turned on or off by twisting the lever (21) from vertical to horizontal.
The head of the drill consists of two cast parts, a carrier (18) that sits on the feed screw (10), and the upper part of the head is a sliding bearing (12) which is held to the spindle by a screw (13) and washer (14) and is adapted to slide on the vertical guide (15) which is mounted on the upper portion of the frame and has a stop (16) to limit the upward movement of the sliding bearing.
The top of the feed screw is a ratchet wheel (17) which engages a pawl (20).
A spring is located between the pawl and the inner side of the socket it is mounted in which forces the pawl to engage with the ratchet mechanism.
The tooth of the pawl is bevelled on one side so that it can be turned to the right or the left to drive the ratchet wheel in either direction. In the mid position (when the lever is vertical) the arm rides up a cam on the carrier and will lift the pawl out of engagement with the teeth.
If the pawl is set to feed the stem forward or backwards, at each revolution of the spindle the screw stem is fed the distance equal to a tooth in the ratchet wheel.
(when the pawl is disengaged, the screw stem is fed the distance equal to a tooth in the larger main beveled gear wheel and this means the drill can be advanced rapidly to or from the work piece).
There is a segment located in a transverse slot in the spindle that receives a small roller, and the upper end of the roller rests against the segment. The roller has two purposes, first it transmits the end pressure of the feed screw to the to the spindle through the segment and second it acts as a cam to reciprocate the carrier:
The feed screw is locked to the spindle by a ball bearing mounted in a socket in the spindle (27) and in the socket back of the ball is a spring – the ball is adapted to two notches in the feed screw (on opposite sides).
Under normal conditions the spindle turns with the feed screw, but if the drill should bind in the material then the spindle becomes uncoupled from the drive screw as the friction will be enough to push the ball bearing out of the inside slot of the drive and the drill will not go further until it reengages (and this prevents damage to the drill or bit).
Automatic feed shifter
When the drill is in ratchet mode and travelling downwards (lever pointing to the left, when facing the drill) the lever will eventually come into contact with the projection 24 and is shifted to the position illustrated in Fig. 8, causing the arm to ride on the upper wall of the notch (20) (which acts as a cam) withdrawing the pawl from engagement with the ratchet wheel 17, stopping the longitudinal movement of the spindle but not interfering with the rotation thereof.
When it is wished to reverse the ratchet movement, the lever (21) is turned to the position illustrated in Fig. 9, so that the, upper projection (25) of the shifter will be in the path of the lever and, by reversing the rotation of the driving handle the movement of the spindle and screw will be reversed and the ratchet feed will take place on the upward movement.
When the lever comes in contact with the projection 25, it is caused to rotate on the lower wall of the notch on the carrier and the pawl will be withdrawn from the ratchet wheel.
(note it is not obvious why you would ever want to do this – if you place the lever vertically then the ratchet disengages and you can withdraw the drill much faster).
Finally there is the chuck, similar to the spring loaded 3 jaw chuck you find in some old Miller Falls hand drills, but with the addition of slots in the carrier that receive the 3 jaws and stop them moving from side to side. This is also patented:
|US1103746A||1914-07-14||relieving the guide block of pressure|