Wednesday, December 30, 2009

Files and the Gentle Art of Centrotecing

Since writing this entry, I rolled a video to show how to do it.  It ultimately has the same content as this posting (so people reading through translators will prefer this entry), but if you rather watch, here's the video version of this post.

The haulidays have kept me away from the shop so light on the useless insight... but I have a few other posts coming.  (Yes, "haulidays" because after the "holidays" you spend your time hauling your now fatter shadow)

I have a Festool C12 drill/driver.  Actually, 2, but that's a long story.  It's a 12V wonder with enough torque to winch your car out of a ditch if you're lucky enough to have its Systainer in the glove compartment at the time.

The problem is that I don't have any Centrotec drill bits or drivers.  Up until 2 weeks ago, there were only metric drill bits for this puppy, but this isn't about drillin'.  The drivers are what I really wanted.  I use the Centrotec Bit Holder to hold wire detent stubby drivers that conveniently stow on the magnetic handle of the C12, but they aren't the Centrotec driver bits made for the C12.

The differences between a regular long ball-detent driver bit and a Centrotec driver bit are:
- the Centrotec edges on the hex shank are softer ('standard' hex shank won't fit the hole)
- the Centrotec ball-detent is about 3/8" (er, 9mm) further up the shank.

The ball-detent position could smell of being non-standard for the sake of selling your stuff, but actually it is because the ball is in the Centrotec chuck while the base of the bit shank sits in the output shaft of the C12.

Tonight, I took 2 McFeely's Robertson drive bits (we 'mericans call those "square drive" bits and have no idea who Robertson is), chucked them in the drill press (individually...) and hit them with a flat bastard mill file to soften the hex edges.  Once they could be easily inserted through the Centrotec chuck, I marked the location of the ball detent based on its location in the bit holder, chucked again and ground out a fairly accurate, if ugly, copy of the Festool detent.

Photo below shows the Festool bit holder by the Kreg #2 long-ass driver to show how I marked the detent.  This photo also shows clearly how the 'standard' ball detent is much lower on the shank than the Centrotec detent.

Result?  These two sit perfectly in the chuck with no play and I cannot pull them out without releasing the ball.  Total time? 10 minutes including wasted time finding a file that went out for a ball of chalk.

In the photo below, left to right, the C12, the Festool bit holder, McFeely's #1 modified, McFeely's #2 modified, McFeely's #2 unmodified, and the bastards who did it.

I decided I should do the long-ass Kreg #2 driver that came with the pocket hole kit.  This puppy is apparently made with diamonds as it was a beast to grind.  I eventually pulled out the Dremel with a grind stone to work off most of it then used a rounded file to make it nice.  Again, this inserts and seats with perfection in the Centrotec chuck.

Photo is of the Kreg #2 chucked for milling:

Next up will be to buy 3 TORX (not shouting, it's how it is spelled) driver bits and grind away.

Highly recommended.


  • Dyami said...

    Nice post. FYI, they're called Robertson because square drive bits were invented and patented by a guy named Robertson. He actually had meetings with Henry Ford to use the square drive bits in the model T, but both Ford and Robertson had big egos and they couldn't make it work. So Ford continued with the inferior Philips.

  • HalfInchShy said...

    Thanks, Dyami... I think the Philips was developed expressly for assembly line work so the screwdriver would cam out before tightening the screw too much. Maybe it was successful at that, but once we moved on to power drivers, I don't see why US (er, we) continue to use Philips. Everybody makes screwdrivers that now try working around the cam-out feature of the Philips.

    I like the Robertson drive; I also like the TORX. Never did much with Pozidrive although I believe they were designed to be a backward compatible format.

    I much prefer TORX, though I do complain that it is difficult to get a decent drive bit for a power driver that doesn't distort after use. Those fine edges don't handle the torque as well as a square hunk of steel.

    Oh, of the screwdrivers made to work around the Philips cam-out, I really like the Wera drivers. The laser etching of the tip makes it hold bits without a magnet attracting everything else and the grip stops it from camming out. Nice.

  • Unknown said...

    Hello Paul-Marcel (or devrais-je dire "Salut Paul-Marcel"? :) )

    Wanted to ask, once you make these changes to the original driver bit (adding the new ball detent and rounding the edges below the new detent), can you still use the bit in a non-Centrotec driver?


  • HalfInchShy said...

    Hi, Peter,

    Yes, definitely you can still use them in a non-Centrotec driver. The ball-detent is in a different location than other drivers (due to how the bit directly engages into the motor shaft in a Centrotec drill). The rounded edges simply make it insert easier in non-Centrotec holders. I use mine in some bit extenders that are from Dewalt and Milwaukee with no problems.