Boring out the spindle nose adaptor body

I made a start on this some months ago on the Bantam but it struggled to overcome the cutting load. This was with the motor in high range ie ~1:1 ratio, yet I needed something like 500rpm. The right solution would have been to change the gear ratio, along with the corresponding settings in LinuxCNC but TBH I couldn't be arsed - and I thought I had a chuck for the Tree when I acquired that dodgy Kitagawa chuck. Now I have a better solution that will allow me to learn about the Tree.

Let's get it mounted in the newly fitted 4-jaw:

It's fairly concentric - or at least good enough, given that I am about to do some roughing out:

New pulley for the motor:

But first, I need to fit a smaller pulley on the motor. Currently I have a 300mm pulley on the motor and 160mm on the motor. That would give the best part of 6000rpm, which would be fine for a small collet chuck but way over the top for a 6" chuck with a max speed rating of 2000rpm. Instead, I'll fit a 118mm pulley on the motor, giving a 3:4 reduction. With a 3000rpm motor, this would theoretically deliver a top speed of 2250rpm, which is better. And when I am down around the 500-1000rpm range, the 4kW motor might stand a chance of cutting some decent chips.

Here's the current setup:

I also have a small pulley behind, although perhaps that was a bit on the small side. I simply chose the smallest that was available for a 28mm shaft.

That's better. The 300mm pulley is still on the motor, but this time it's at the back. The shorter belt worked out well. I calculated the required length quite simply from the difference between the pitch diameters (multiplied by 0.5 x Pi). Good. Now we are finally ready for action.

Let's make some chips then!

The new 20mm boring bar is rather longer than I need, so I will chop it down a bit. Besides, I bought 2 with that in mind. I need about 80mm stickout on this job, so I'll chop off about 50mm.

It's not hardened, so the bandsaw copes fine:

Ready for action:

Off we go:

Quick skim passes in X and Z, then measure it up so I can tell the machine where the tool tip is.

Let's do it:

No video, it didn't happen:

One consequence of taking girlie cuts is that the final finishing pass resulted in some squealing and a slightly patterned finish. If I'm going to do this with indexable tools, I should use a ground / honed insert I suppose. But it's not a functional surface, so I can live with it for now.

A final observation - running the machine with the hydraulic pump off results in a shitty surface finish and hellish chatter. I think we can conclude that although there may be some residual pressure on the turret, it's not enough to ensure rigidity of the tool. That probably shouldn't be a surprise but I was wondering and now I know.