Tangential Tool Holder

Update: I've since replaced this tangential tool holder with a new version for my new tool post. The new tangential tool holder is described here.

As soon as I heard about this type of toolholder from Mike's Workshop, I was intrigued. There seem to be many different designs around and they all need a milling machine! For a couple of years I'd had it on my list of "one day" projects to do when I had the skills and equipment. Once I'd bought my milling machine, it was always bound to be high on the priority list.

It is possible to buy these toolholders from Eccentric Engineering, but they cost £78+postage and they won't be made for my QCTP. Mine only cost me a few pounds to make, so much better value!

This tool holder is amazing. Being slightly blazé about these things, my first test was to put a piece of 20 mm diameter EN1A into my collet chuck and take a very deep cut. Probably foolishly, I went for a 2 mm radius cut (to take the piece of mild steel down to 16 mm in one go). Amazingly, it coped admirably (although you could hear the lathe was struggling a little and I'm not sure I'd do it again). Cuts of 1 mm radius are effortless and (with a tiny radius ground on the tool-bit) leave a fairly nice finish. I am seriously impressed by this tool.

Manufacture

The tool holder is made from two blocks of mild steel: a fairly simple 50 mm × 50 mm × 25 mm block of mild steel with a 25 mm hole in it for my toolpost (along with the slit, clamping screw and height-adjustment screw) and a much more complicated piece that holds the tool. The two parts are held together by three M6 low-head cap screws. Using low-head screws was probably unnecessary but I wanted to be sure that there was as much space as possible for facing. The slot in the tool holder is designed for an 8 mm or 5/16" HSS toolbit.

Machining the block for the toolpost was trivial (especially since the SX3 will drill a 25 mm hole in a piece of mild steel in one go!). Machining the tool-holder part was much more complicated, not least because I needed to visualise all the angles involved. I don't own a tilting vice, so to get the complex angles required for the toolholder, I clamped the block of steel (a piece of 20 mm × 20 mm steel mild steel I had lying in the scrap bin) into the vice and used a digital angle gauge to tilt it over at 12°. I then used the angle scale on the radial milling vice to get the other 12°. After that, it was easy! To get the face that the three tool clamping screws would bear against if the tool were removed, I just used the digital angle gauge again.

Tool Grinding

In order to use the tool, you need to sharpen an HSS toolbit to the correct angle. This is easy once you've made a relatively simple alignment jig. Mine is described here.

A 3D Model

One of the biggest difficulties of making this toolholder was visualising the various angles that needed to be used to get the tool to be presented in the right manner. To help others get their heads round this, there's a simple model of the toolholder at the bottom of this page. You'll need a relatively modern browser for this to work, but you should be able to drag it around with your mouse to look at it from different angles.

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