Hard machining some Multifix toolholders

What up?

I bought a mixed set of toolholders when I coughed up for a Multifix toolholder clone a few years back. 

These were bought from Create Tools who appear to actually manufacture some or all of the components. It's never clear if that's actually the case with many of these Chinese companies however, it's obvious that many of the companies selling them on are simply trading companies, no matter how hard they work at pretending they make them themselves.

Having not actually used the things, I stupidly included 2 of the boring bar holders AH2085, rather than specifying them all as AD2090 which have the simple rectangular slot.

Problem is that none of my boring bars require the trough feature, as in fact they all have a flat base. 

And?

This issue clearly requires remediation - by way of machining. It looks to me as if I should be able to open the slots out to take a std 20mm x 20mm tool. This sketch sort of helps to explain what I mean - if you can understand it. I've simply superimposed the 2 profiles and it's shown as I would mount a toolholder in the machine ie "slot up".

It would look like this in the flesh:

Sounds simple enough. But hold on, this thing is (should be) hardened. No problem if I'm using carbide tooling and don't get carried away on the speeds and feeds front. But what are we dealing with here?

Tough talk:

Luckily I have a Leeb hardness tester that may give me some idea. Although these aren't deadly accurate, they are a bit more elegant than running a file across the surface. The principle of operation is observing the coefficient of restitution of a ball bearing fired at the surface. By listening to the multiple bounces, it's possible to make a half accurate estimate of hardness. 

Here's what I found - around 20-30HRC, which is indeed harder than mild steel or tempered tool steel. So I will need to take my time and be prepared for some sparks.

I couldn't decide initially whether to use CNC / CAM to machine these 2 holders. Either way, it seemed sensible to get a feel for recommended settings. To my understanding, you should run almost as fast as you can (surface speed) and take fairly light cuts (feed per tooth). 

Let's have a look at some hard milling F&S starting values and take it from there.

Let's get cracking:

Yes, I couldn't see the point in programming this up when I could simply feed the tool manually with the MPG. It's a simple matter to calculate the coordinates for the tool, so manual feed it is.

Job done. Now some tidying up with diamond needle files and Bob's your auntie.

Looks good to me. 

Good. Now I can make better use of the toolholders without needing to swap tools endlessly, which rather defeats the point of having quick change tooling....