A Forstner Bit Quest

Way back in 1885 Benjamin Forstner applied to the US Patent Office for a patent for a drill bit that to this day bears his name.  The Forster bit was unique, because rather than being guided by an auger screw in the center of the cutter, this bit is guided by its almost continuous rim.

The original design is quite a bit different than it's modern cousins in that most new "Forstner-style" bits have been redesigned to make them easier to mass produce.  How you say?  Well, for one thing the original bits had almost zero center point, while today's bits have a pronounced point.  Now, I have to admit that in most cases this larger point comes in handy.  Imagine having a 1" hole to drill, and after marking the spot on your workpiece where you want your hole how are you going to center the bit on your mark?  now, on the other side of this debate is the fact that if you need to drill a recess that doesn't pass all the way through the wood (think of this as a round mortise) most of today's bits are going to require a shallow bore, unless you're OK with the point poking through your workpiece.

As for the rim, in the old days the rim was almost a continuous rim with just two small breaks where the lifting cutters can be sharpened.  The new design has two very large gaps in the rim that allows mechanical grinding and sharpening.  This is fine for most drilling operations, but where it does create a huge difference is whenever you drill into the wood at an angle or drill overlapping holes in an effort to produce a slot mortise.

The other thing that has changed, and really it's for the best, is that on bits over about 1" they've changed the smooth rim to more of a saw-tooth design.  The smooth rim runs very hot due to friction, and it wasn't uncommon for these bits to lose their temper in normal use.  Not a good prize.

On that point, I was recently looking to make some slot mortises on my drill press when I remembers a unique Forstenr-inspired bit from Vermont American.  Two features set this bit apart from all the others:
  1. It has a single lifting flute, which means it has just a single gap in the rim.   This made this bit a pleasure to use in angled entry and overlapping boring operations.
  2. The second unique feature may sound like a drawback, bit it isn't: They are about 1/3 the length of other bits of a similar size.  True, they can't drill as deeply, but they are very rigid.  Again, this helps immensely in those angled and overlapping situations.
This bit was touted about 20 years ago in an issue or two of Woodsmith magazine, and I used some to great effect.  Since my original set is long gone I hit the web to grab a new set... and that's where the problem began.

Apparently VA no longer makes this style of bit, but instead has adopted the modern design.  DANG!  The odd thing is that they didn't even change the part #.

I did a search of eBay and found someone who is selling 9 sets for four of these bits, so 'll be snatching-up a set of two.  Click this link to see if any of the stubby Vermont American Forstner Bit sets are still available on eBay

No comments:

Post a Comment

You Aint Seen Nothin' Yet!

If you happened to land on this page via a Google search, you aint seen nothin' yet! Click the title at the top of this page to see this blog in it's entirety.