Monday, March 7, 2011

Monty Remon’s Diamond Tool Holder

An internet search for diamond tool holders reveals that this method of grinding and mounting tool bits has been around for years and that several designs are manufactured for the industry and retail at considerable (inhibiting) sums.
I like many must have puzzled over the geometry and the tool holder machining to get the magic angles at the sharp end. I was lucky my solution came in a flash and I made the prototype in five minutes. I just worked back from the bit in a straight line (keep it simple), the tool holder was a piece of 5/16 square door handle furniture mounted in a Taig tool post, jacked up 3/32" then the end drilled through 1/8" diam., at 10degs 'ish and then a saw cut 1/3 down and long enough to get a far as the clamping bolts. It took a further 15 minutes to try and grind a tool bit. My non-standard Taig tool post was reduced in height by 1/4" to allow for the tool bit geometry and a 1/4" packing washer fitted to the top to keep the clamping bolt happy and the large corner reliefs allow the tool access to the work piece. The theory that the vertical clamping force would lock the inclined tool bit proved true.
OK so that was the tangential system sorted but the 'diamond' part needed internet help from those in the know. I found figures of 30 degs tool bit grinding angle and mounting in two planes at 12/12degs., to be common. Much head scratching and drawing yielded the result that the tool bit should be inclined at 16 degs., in the tool holder to give the req'd angles with the holder/ tool post clamped at 45 degs to the work face. (Could it be this simple?)
I came up with a system to accurately drill and broach 1/8" square hole in a tool holder at the 16 degs., and achieve a 30 deg., face on the tool bit. Basically two tool holders are made at the same time, with part of each forming the drilling broaching /guide for the other.
The broaching tool was a length of 1/8 sq., tool steel set in a flanged brass turning, the drill chuck transmits the cutting force via the flange to the broaching bit. A diamond disc in a Dremel was used to make notches on the end of the cutter.
The 5/16 bars were bolted together and packed up 3/4" one end then clamped to the side of a 1x2x3 block for drilling and broaching. Flipped over and the process repeated. The parts were unbolted and the small clamping bolt holes drilled and tapped, then separated with a saw and slotted. Grinding the angle on the end and fitting the clamping bolt and washer completes the tool holder.
Bit sharpening the correct angle is achieved by using the tool holder. If 7/8" diam wheels are fitted as per the drawing and a roughly ground (30 degs.,) piece of 1/8x1/8 tool steel is clamped with 1/16" protruding from the bottom, then rolling the assy., to and fro on a diamond stone will give the correct angle.
A couple of points. Flatting the surfaces of the bars with a fine file prior to bolting together and broaching would seem advisable and and it would help with stability in the tool post, but you could of course start with thicker stock and mill it down but it would seem that 5/16" bar fills the bill.
If the axel hole is omitted from one of the parts then the slot could be extended to the mid clamping point and the inboard tool post bolt used to clamp the bit as in my prototype effort.
How well does it work? It performs just like in the videos. I was only surprised at how good it felt to slowly hand feed the tool and see the metal come off, what a good finish!