electronic lead screw

[RJSakowski]

If you stop the lead screw at the gutter, how will you pick up the same lead for the next pass on the thread?

Good point, thank yout! The lead screw has to remain on in order to maintain the relationship with the spindle. Back to disengaging the half nuts.

 

[homebrewed]

Based on some work I did in the long past, you may be able to further improve your optical switch'es resolution with a lens to focus the light to a smaller point at the interrupt point. I was using a HeNe laser at that time so its diameter at the focal point was a few multiples of the wavelength -- 635nm. White light won't be as good as that, but a decent diode laser module could get you pretty close.

As an aside, 635nm is 25 micro-inches.....

 

[RJSakowski]

Based on some work I did in the long past, you may be able to further improve your optical switch'es resolution with a lens to focus the light to a smaller point at the interrupt point. I was using a HeNe laser at that time so its diameter at the focal point was a few multiples of the wavelength -- 635nm. White light won't be as good as that, but a decent diode laser module could get you pretty close.

As an aside, 635nm is 25 micro-inches.....

I installed optical homing on my Tormach 770 to improve homing repeatability some years ago. I used an Omron OPB829DZ optointerupter, combined with regulated emitter LED current, comparison to a regulated reference voltage via an LM311 comparator, and well designed optics. This provides consistent positioning to within +/- .0001", the resolution of my Tormach DRO.

 

[Qtron]

Optical switching with good accuracy... can a DRO be programmed for that function? Or, does this
really have to be a separate wired-in item?

There's good technology out there (LVDT comes to mind) for microinch triggered switches, if that is really necessary. The half-nut
might not be as fast to disengage as an electric clutch, or motor brake solution.

The proximity sensor shown is on our router at work,
It is very low cost, its within 0.1 mm, BUT, has a repeatability of 0.01 mm !!
LVDT's have come a long way since first conceived, but wont match this on the same price/accuracy page.
I like the idea of a spindle motor brake, as synchronicity can be maintained with the LS.
One vid i saw (seen so many, hard to remember) has the operator cut a first pass, stop, reverse the lathe then, run fwd again & cut the second pass etc, no 1/2 nut disengaged.
He did have a stepper on the cross-slide to slighly retract during 'rewind'.
Excellent system. It may have been Wade'O Design on youtube. No answers forthcoming on enquiries placed to his website, sadly.

 

[RJSakowski]

Tormach's Path Pilot controller has the ability, once homing has been set, to electronically stop the at the homing and far limit positions at the same position exactly with no overshoot, even when approaching at full rapid speed (130 ipm). To do so, it has to be decellerating as it approaches the limit position based upon feedback regarding its current position vs. target position.

 

[Qtron]

My DRO's are not capable of outputing a signal at some preset position.

The advantage of optical switching is that I already have the design done. The mechanical part would need to be modified but the circuit board is already done. I don't believe that I would have to disengage the half nut. I could simply cut the pulses to the driver. It might coast for a few steps but it should be fairly repeatable. A full step is .00021" on my lathe.

Whats a "Tormach's Path Pilot controller " whats its primary function? -web link?
Going back a few pages in this thread, Have you any idea why Briney Eye, Jon, was alarmed (.. Eek! ..) when he discovered Clough was doing sums on the fly in his code?- ( as vs Jon, & i guess many arduino users, doing the math's first, then kicking off the stepper etc.)
is there a distinct advantange to Clough's approach? - a sudden spindle speed drop, or?

 

[RJSakowski]

Tormach makes several "personal" CNC machines. Several years ago, they replaced the Mach 3 controller with a proprietary controller based on Linux CNC and called PathPilot. My 770 came with Mach 3 controller and if I ran full bore up to the limit switch, it would overshoot and hit a hard stop.

With PathPilot, once you home the machine , you will not ever actually hit the limit switches (the home position is set about .050" shy of the limit switch). PathPilot also programs in a far limit, the default position based on the machine parameters but user programmable so the machine works to electronic limit positions.

You can download the manual here: https://www.tormach.com/support/wpdmpro/um10349-pcnc1100-manual-0916a-web/ Some people running non Tormach machines are using PathPilot. Since it is based on Linux CNC, it has to be open source. The communication is through a special board called a Mesa, IIRC.

I thought that Clough used a rather peculiar way of syncing the lead screw to the spindle. He explains his logic in his second video, around 26 min. in.

 

[Qtron]

Tormach makes several "personal" CNC machines. Several years ago, they replaced the Mach 3 controller with a proprietary controller based on Linux CNC and called PathPilot. My 770 came with Mach 3 controller and if I ran full bore up to the limit switch, it would overshoot and hit a hard stop.

With PathPilot, once you home the machine , you will not ever actually hit the limit switches (the home position is set about .050" shy of the limit switch). PathPilot also programs in a far limit, the default position based on the machine parameters but user programmable so the machine works to electronic limit positions.

You can download the manual here: https://www.tormach.com/support/wpdmpro/um10349-pcnc1100-manual-0916a-web/ Some people running non Tormach machines are using PathPilot. Since it is based on Linux CNC, it has to be open source. The communication is through a special board called a Mesa, IIRC.

I thought that Clough used a rather peculiar way of syncing the lead screw to the spindle. He explains his logic in his second video, around 26 min. in.

Using mobile ph ATM, this forum's protocols wont allow upload of a ph file, but anyway I note from your kindly provided link to Tormach user manual, they use 3 phase steppers! Must be an advantage with them, or are they simply a lower cost device?
I presume the 770 is not cheap!
Maybe Mach 4 has solved the 'head butting' issues of Mach 3 as u defined, RJ.
Will replay vid 2 re Clough, THANKS!, but largely the Q re Jon's approach, vs Cloughs remains unclarified.
Certainly the arduino is cheaper, easier to prog, (still no joy re mine not talking to the TI ide properly- I've asked Clough), and of course, the big appeal is Jon's touch screen, plus, and still the big unknown, the better torque achieved by fully utilizing the lathes gearbox (I don't mean change gears), an added complication of his ELS setup , but a worthwhile trade-off.

 

[GreatOldOne]

If you stop the lead screw at the gutter, how will you pick up the same lead for the next pass on the thread?

As per the video someone posted previously. Disengage the leadscrew when you hit the relief. Stop the lathe. Back the tool out, reverse the lathe and start it up. When the thread dial comes back to the mark you where using, re-engage the halfnuts. Run the lathe back to the beginning of the thread and stop the lathe. Push the tool back in, and put your cut on. Lathe back into forward, start. Rinse and repeat.

if you don’t have thread dial, you’ll need to keep the half nuts engaged, and try and stop the lathe in the relief - but the rest of the procedure stays the same.

 

[Qtron]

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