Finish machining the adaptor mating surfaces in position

With the spindle nose adaptor now finally in place and a wonderfully good fit on the spindle nose itself, I have the final(ish) task of finish machining the taper nose that will mate with the various D1-3 chucks.

As measured previously, I have a small amount of radial and axial runout to deal with. The taper is slightly oversize (by design) and I have a few tens of microns to remove. But this could go horribly wrong if I play my cards wrong.

Given that it's a taper I need to finish, there's no manual (MDI or MPG) operation I can use. So it looks as if some hand coded or conversational g-code is called for. I'm not aware of any simple way to gear the X axis to any Z axis moves - doubtless I could do this in LinuxCNC but probably not in Centroid.

Here's the section view, showing the taper dimensions:

The required operation is G90 (turning and taper turning), with the taper radius parameter specified:

In my case, the "R" coordinate is going to be (negative) 2.75mm, bearing in mind that I will be working in units of diameter. In which case, the G90 line should look like this (preceded by a rapid to the start position):

....

N40 G00 X54 Z11         ;rapid to start position

N50 G90 X54 Z0.00 R-2.75 ;taper cutting

....etc

It's a bit confusing until you read the manual carefully. If you don't specify a taper value ("R"), the move is simply an axial feed move followed by a radial feed move. The axial and radial distances are defined by the initial position and the final position.

If you want a taper, the "R" parameter results in an interpolated radial movement as the tool makes the first axial move in Z, followed by the secondary radial feed move. So in my case, there is an 11mm axial move combined with a 2.75mm radial move, which results in a taper of 1.375mm in 11mm (the arctan of 1.375/11 is 7.125 degrees). Note that this radial move needs to be specified as a negative value here. In my case there is no secondary radial feed move, as the start/finish position is at the same radial position as the end of the axial / taper move. It simply makes a taper cut and then returns to the start position.

This is what the Centroid simulator sees when I load this code:

Looks pretty reasonable to me.

I can't stop it beginning life at 0,0 unless I'm missing something here. So I will ignore the rapid move through the stock(!). Apart from that, the start coordinate (X54 Z11) looks right and the end of the feed move (X54 Z0) also looks good. The final rapid move back to the start coordinate (X54 Z11) appears to be as authorised. Looks good to me. 

So the plan is to set Z0 at the very front of the adaptor (having skimmed it for axial runout), position the tool around X54 Z11 and hit go. I will start out at a larger radius and adjust the tool wear in X until it skims the taper. Then keep adjusting the tool wear until I have the correct fit.

Let's see how this goes.....