Science/Engineering/Technical forums

Yes the bit should be non-standard for it to work; the bit needs to be a curve of constant width with 3 apexes [that is, 3 'sided' to acheive a square hole] (with cutting edges formed at the apexes) and the gear is an eccentric arrangement, one gear set on another ('epi-cycle'-like).

Not a clue where you'd get one from... China !?!

You can still buy them from Watts Brothers. They are still in business, at least were up to a couple years ago for sure.

The one in the video is not made in china, made in Japan. And Dijet does not sell outside of japan so it really does not matter.

There was also a thread on this over on homeshopmachinist with some pics of one of the guy's, its where I got the patent info:
http://bbs.homeshopmachinist.net/showthread.php?t=51350

I recall reading how to make this tool some years ago. The book was the lifetime experiences of some Dutch chap who was trained about 1900 and his trade school instructor made one on the last day of class to entertain his departing students.

The principle is easy enough, just a triangular shaped tool with slightly rounded sides and a hardened steel template which was clamped to the work. The cutting tool was loosely mounted and just rattled around inside the template. I am sure you could use the same technique to mill holes of any polygon (maybe not triangle?) shape.

That's one way, but this looks a little more controlled in a CNC machine. I'm pretty sure it is an actively-eccentrically driven curve of constant width.

chrismb wrote:That's one way, but this looks a little more controlled in a CNC machine. I'm pretty sure it is an actively-eccentrically driven curve of constant width.

I think it still has the template. It seems the template must have one more 'corner' than the cutter and I suspect the cutter must have an odd number of apex. Each sides of the cutter is an arc centred on the opposite apex. The apex of the cutter engages in a corner of the template at which point the cutter 'walks' around to the next corner cutting as it goes. At least that how I figure it.

One drawback with these as a opposed to broaching is that the holes are slighter bigger at the bottom, obviously OK on thin(ish) materials. An advantage is that they can do blind holes which is a bit more difficult with a broach without debris being lodged at the bottom of the hole.

I think I should try to make one the only real challenge being how to heat treat the tool steel. Maybe.... when I get a round tuit.

I got a Vulcan oven to do most heat treating, it works very well up to its limit of about 1050C or so. This means you can't do some kinds of tool steel with it, but those it can do it gets perfectly. For the super hot stuff it looks like you need something like an induction heater in vacuum, maybe with a helium inlet for quenching, then tempering is usually easily done with your basic NiChrome oven type. Any oven that goes above about 1000 C is going to be expensive and hard to find at all out there - for that you need some more-exotic heater material, and it usually needs a particular atmosphere to live in.