Threading the turret locknut - buttockus tightus!!

Finally, after fighting and beating the Fusion 360 post processor, I am in a position to machine and thread the nut. 

First, drill out 16mm diameter:

Face off and chamfer:

Bore out to 17.0mm:

Close enough!

Here's the insert for a 1.5mm internal thread. You can buy LH and RH inserts but the so-called "LH" inserts are simply intended for use with the spindle in reverse and the tool cutting behind the axis. So this is a "RH" insert.

Yes, it's pretty tight. The insert is 16mm diameter from the tip to the back of the bar. The bore is 17mm and the final diameter of the thread root is 18mm, so not much room for mistakes. Touching off at 17mm here leaves an alleged 1mm clearance at the back.

Sanity checking with an MF18 tap. Looks plausible, certainly.

And off we go...

There's about 2mm clearance between the main body of the boring bar and the workpiece. I set up the thread depth in Fusion to take into account the length of the shank but it's good to see I hadn't cocked up the measurements.

It took less than a minute in the end and the finishing tap went straight in. If anything, it was slightly oversize but not by much. I've got plenty of threads to work with and the male thread is 100% threaded by the looks of it.

Bottom line is that it spins on nicely without undue slop.

Now, refit to the chuck and get it running true, so I can create the finished nut which isn't simply a threaded hex bar. I got lucky here, as the runout was minimal first time round.

At this point my concerns about swarf getting to the ballscrew and magnetic linear encoder proved valid. The tiny bits of swarf from my previous steel machining (the spindle nose 5C cartridge) had got everywhere inside, not least the magnetic strip. This caused loss of encoder signal and a loss of axis position. You can see some of the swarf on the stainless steel strip below:

I've cleaned it up now and taped over the open holes but ultimately will need to make a proper cover for the top of the cross slide.

Next - turn down the turret nut to the correct dimensions and refit the turret.