Here we go, but first we have to get on the same page about driver bits and the centrotec chucks and system. My comments are based on my understandings of how the system works, plus my 20 years experience as a Journeyman tool and die maker and tool designer.
What actually drives the bits is the internal hex that is formed in the motor / drive shaft of the drill it’s self. Because of that, you could stick any ¼ hex drive bit into a Festool drill, with no chuck at all. Makes for a real short profile, but while the bit will drive well (keep in mind the bit drives from the engagement of the FLATS- not the corners) there is nothing to keep the bit retained in the drill when no chuck is used. As I understand it, and as it appears in the current design the centrotec chuck has two functions. The first is as a retention system for the bit which holds the bit in securely, but releases it quickly and easily without any tools or torqueing actions. The second function it provides is a longer engagement of the outside of the bit or driver shaft, keeping the bit or driver straighter in a system that does not clamp onto the bit. It also helps with concentricity of the bit, which is more important in drilling than in driving.
For the purposes of this specific application, concentricity of the bit is not important, as the bit can actually float in the drill, but will be positively driven by the hex drive. Some will probably argue that driver concentricity is important (concentricity being the “trueness of the driver bit as it spins”) but keep three things in mind. 1- we drive fasteners at slow speeds, not full out open, 2- the shaft of the driver is supported concentrically at both end when you drive, the drill aligning the hex end and the fastener entering the wood acting like a stabilizer or live center at the other end, and 3- what do you think the chances are that with a hand held screwdriver (in use for 100s of years) that you would drive the tool perfectly centered in your hand.
What needs to happen to convert Kreg driver bits to work perfectly well with you centrotec chuck?
You need to get the outside dimension of the corners of the hex small enough to pass through the round opening in the centrotec chuck. You need to shorten the hex length of the driver so that the shoulder where the hex meets the round shaft of the bit will fit below the ball detent in the centrotec chuck, thus retaining it in the drill assembly. You need to not disturb the hex flats if at all possible, because that is what drives the bit and transmits power.
In my tool and die days, I would have just put the driver bit in a collet on a tool and cutter grinder and taken down the corners of the hex to the proper diameter to fit in the centrotec chuck, which is believe around letter size N or .302”. Since I don’t have access to that equipment anymore I made do with what I had, and did this on my Worksharp 3000.
[attachimg=#]
The pictures show the worksharp, with a wooden block and a hole drilled in the block that just fits the round part of the Kreg bit. By aligning the corners of the hex with the side of the block that is flush to the drilled hole, and using shims to set the height to the surface of the disk (I use playing cards for lots of things) the “corners” of the hex cab slowly and precisely and repeatability be ground down until they fit just properly into the centrotec chuck and pass through without too much play. Once you get the proper shim thickness, all you have to do is align each corner down to the bottom of the block and grind them off. This is very consistent. The pictures should make it obvious. One you have the right shim thickness, it takes less than a minute to grind all six corners of the driver. These corners do not do anything in the function of the tool, so if they are not all exactly the same, it doesn’t matter. This process is very accurate though, and your results should be pretty much the same every time.
[attachimg=#]
[attachimg=#]
You can use the centrotec chuck as a sizing gauge. Remember, you want to take of as little as possible, evenly from all corners and have the bit just slide through the bore of the chuck. If you set this up correctly, you CAN NOT even touch the hex flats, so you don’t have to worry about that.
Once the modified hex fits through the centrotec chuck nicely, all you have to do is cut off the bottom part of the hex on the Kreg bits. Cut at the very center of the radius between the two hex sections. The bits are hardened, so you will need a dermal with a cut off wheel or any abrasive cut off wheel for steel. I use a 4 ½ grinder with a cutting wheel.
Sand the sharp corner of the end of where you cut and that’s it.
Place the centrotec chuck on your drill, pull the green collar back, and the hex will slip through the chuck and into the hex in the drill shaft. Release the green collar and the ball detent will pop back into position past the end of the hex, touching the round shaft of the driver, retaining the bit. Try to pull it out. You need to re-press the green collar back to get the bit to release from the drill.
Done deal.
I bought 5 sets of Kreg bits from Amazon for $25, and made the block, found my shim size, ground 10 hexes to fit and cut the ends of in less than 30 minutes. I should have enough to last me my lifetime, but if I ever need to make more, I’ll keep my block and my calibrated playing card, and I will be able to do these in just a minute or two. For non pocket hole square drive, I just use the wire detent bits in the Festool holder.
[attachimg=#]
[attachimg=#]
I took the pictures after I finished the run of bits, thats why there are already cut to length. I ground the hexes full length, it makes it more stable. Also the abrasive git was 120. Worked perfectly.
I hope this helps someone.
Jay
