Chips with Probe Basic Lathe Coversational!

Despite the AliExpress tracking info showing the ballscrew sitting at the China consignment hub, look what turned up a few days ago.

Yes, SFU3205 (single ballnut, 32mm OD, 5mm pitch). It even came with a transfer tube(?) to allow you to remove the ballnut without sowing the ball bearings across the length and breadth of the workshop.

Thusmost:

Anyway, time to drill the pilot hole in the stock for the bearing bracket. Centre drill, then 8mm drill, then 25.5mm drill.

There. Ready for the boring operations.

Then set up the first boring operation in the PBL Conversational screen (open out from 25.5mm to 50mm):

At this stage I was thinking I should check the spindle speed. This machine originally had a 1500 / 3000rpm motor and if you wanted the max spindle speed of 1600rpm, you needed the motor to be running at 3000rpm (that's the no-load, synchronous speed - slightly lower when under load).

The motor fitted to the machine is a 4 pole (ie 1500rpm) 3kW induction motor. That's a bit OTT but I had it kicking about and it saved having to buy another one. HWIW, it originally powered an air compressor on an electric urban bus to power the brakes and air suspension.

If I'm running this motor much above its 1500rpm base speed, it's going to be well down on power. And in the Linuxcnc .INI file, there's a spindle scaling factor that translates / scales the 0-10Vdc output from the Mesa 7i76 board to actual spindle speed. I've disable the I (and D) term in the PID controller so that the motor speed is a direct function of the analogue control voltage from the 7i76's digital potentiometer.

The only simple way to independently measure the spindle speed is using the "Machtach" device that I procured, built and installed on the machine some years ago. 

This uses an optical sensor to detect markers on the spindle nose and calculate the rpm. Those markers are still present on the spindle nose and the device itself seems to work once powered up.

True, there's an encoder on the spindle that reports back the actual speed but I'm not 100% convinced it's set up correctly - I suspect it is but now would be a good time to check.

You may notice that the motor pulley is rather larger than the original - it's actually the biggest I could fit under the cover. That's because I swapped it out when upgrading the motor. 

This was before, with the original, smaller pulley:

And after, with the oversized pulley:

The result is that I can actually get over 1500rpm at the spindle from this setup, with the motor operating below base speed ie not field weakened. And the scale factor is bang on - I'd clearly frigged it to get the exact correct values. And the reported spindle speed displayed (from the encoder) is sot on.

On with cutting chips, then. The operation is broken down into 2 steps - bore through at 50mm, then counterbore at 62mm. If I ran both operations together, I believe the conversational feature would merge them and avoid duplication (air cutting). However, this is the first time out for Chris Polanski's "Intuiturn" conversational macros, so one step at a time etc.

That seems to be going well so far: 

Oooof, even with the rear and top chip guards fitted, this was a painful business. Blue hot chips are flying out in all directions. Rather than stop the process, I grabbed a handy cardboard box and hid behind it.

That was almost manageable, containing perhaps 90% of the hot chips. And a good result. In fact, I must have screwed up the touch off step a bit, as the bore came out almost 0.4mm undersize. Easily managed by a final (manual) pass.

Good result.

So there we have it - the first use of the (Internal Turning) conversational macros. I need to fit a more sensible chip guard that will enclose the front of the machine, so I don't get burned and the workshop isn't sprayed in tiny chips.

Arguably it would be sensible to connect up the coolant pump but the same thing goes - I need a guard to contain the mess, so it's simpler to just run dry for now.