[SomeWhatLost]

stepping on the PDB foot pedal while the machine is cutting = bad

just thought you all should know, just in case you were planing on doing the same thing...

broke my TTS-R8 adapter collet, and my 1/4 bit...

(technically, I was not running the mill... let my brother use it... anyway, I am just happy it wasn't me)

[SCzEngrgGroup]

Wow! I'm surprised they didn't provide an interlock to prevent the PDB from being activated when the spindle is turning. That's a serious safety hazard. Did the drawbar unscrew and drop the tool and collet?

Regards,
Ray L.

[BAMCNC.COM]

I almost did that the other day, wow would that be scary.

[kevinro]

I did this about 2 weeks ago. Talked to Tormach, and sure enough there is no interlock on the Pdb. In my case, the spindle flange nut that pinches the pdb was spun up into the top of the drawbar. At the same time the toolholder dropped out and hit the vise. Luckily I was in a rather tall rapid step over to the next cut or it would have been a real mess. Took me by surprise for sure. I had walked up to the machine to check on the operation and my foot caught the pedal.

Fixing it took about 30 minutes. Appears no worse for it. Tormach says they fail test this scenario and the machine survives just fine, but the tooling is another matter.

Feature request already submitted.


Sent from my GT-P5113 using Tapatalk HD

[wbleeker]

The other day I thought that this may happen, my solution kick, the pedal sideways and use the hand operated switch.
Will

[SomeWhatLost]

who needs an interlock ? seems simple enough to just not step on said pedal while machine is running... or so I thought...

the collet stayed in place, didn't unscrew or drop out or anything... just cracked a bit off...

my spindle flange nut was spun up into the top also, kind of odd, wonder why it did that?

[kevinro]

who needs an interlock ? seems simple enough to just not step on said pedal while machine is running... or so I thought...

the collet stayed in place, didn't unscrew or drop out or anything... just cracked a bit off...

my spindle flange nut was spun up into the top also, kind of odd, wonder why it did that?

When the PDB piston lowers, it grabs the flanged nut on the spindle. The amount of force is pretty substantial. With the spindle turning, it just unscrews itself until it hits the mechanical stop that is the belleville springs. Once that hits, friction between the top of the draw bar and the nut from the piston is overcome and the spindle and nut turn together. The result looked pretty scary when I opened mine up. Thought it had done some very serious damage. However, turns out that all parts survived.

It also turns out to be a minor blessing as I realized I had an early PDB with only 3 sets of springs. Ordered 4 new sets and a new draw bar. I can now cut with a 1/2 bit without pullout. Wouldn't have noticed if it wasn't for this mistake.

[SCzEngrgGroup]

It's surprising Tormach didn't interlock that. Not so much to prevent damage to the machine, but to protect the user from flying tools and collets. It's easy to do - the VFD should be capable of providing an output signal that goes true whenever the spindle is in Run mode. That's what I use on the new "micro" power drawbars I've just designed, when a VFD is present. If not, I provide a spindle sensor integrated into the drawbar to serve the same function. Safety first!

Regards,
Ray L.

[nitewatchman]

It's surprising Tormach didn't interlock that. Not so much to prevent damage to the machine, but to protect the user from flying tools and collets. It's easy to do - the VFD should be capable of providing an output signal that goes true whenever the spindle is in Run mode. That's what I use on the new "micro" power drawbars I've just designed, when a VFD is present. If not, I provide a spindle sensor integrated into the drawbar to serve the same function. Safety first!

Regards,
Ray L.

Interlock would not make any difference at 5140 RPM's. The PDB Cylinder would clamp the spindle nut and spin it against the Belville Washers before the VFD can even attempt to stop the spindle.

I did the same thing with the foot pedal at 3600RPM's sounded like the world ended but there was no apparent damage other than dropping the tool and bonking the tip on a small drill.

nitewatchman

[MichaelHenry]

Interlock would not make any difference at 5140 RPM's. The PDB Cylinder would clamp the spindle nut and spin it against the Belville Washers before the VFD can even attempt to stop the spindle.

I did the same thing with the foot pedal at 3600RPM's sounded like the world ended but there was no apparent damage other than dropping the tool and bonking the tip on a small drill.

nitewatchman

Wouldn't it make more sense for the interlock to disable the PDB release when the spindle is running?

Mike

[Sp-4renegade]

I have the 1100 series 3. I know mine locks out. I even double checked it this morning. As long as the spindle turns the PDB is locked out both the foot pedal and the hand switch. It also locks out in manual if the spindle is turning.

[SCzEngrgGroup]

I have the 1100 series 3. I know mine locks out. I even double checked it this morning. As long as the spindle turns the PDB is locked out both the foot pedal and the hand switch. It also locks out in manual if the spindle is turning.

That is exactly how it SHOULD be, and exactly what I was suggesting. So, the question is, why was the OP's system NOT inter-locked like that? He should call Tormach and ask. That is certainly something I would want to fix ASAP.

Regards,
Ray L.

[BAMCNC.COM]

I don't have the balls to test mine, lol

[Sp-4renegade]

I don't have the balls to test mine, lol

Loosen the belt so the spindle wont turn. Then you can test it.

[BAMCNC.COM]

Good thinking, will do it today.

[TurboStep]

Couldn't wait, I just had to try it. I don't have a foot pedal but I expect that the behaviour would be the same with the hand controls. I have a series II + PDB (no ATC).
I removed the belt, started the motor and pressed the release button. The PDB released and the motor cut out and freewheeled to a stop i.e. without using the VFD breaking feature.
The VFD does however have a output to indicate when the motor is being powered. This appears to be used by the ATC which may be why some have reported that the PWB locks out when the spindle is running. Check out the Tormach document UM10081_TTS_ATC_PCNC1100_1212B.pdf. Page 8 shows a photo of the Power Drawbar Control Circuit board with the VFD interconnect on the right. Note the comment "If you purchased a Power Draw Bar before June, 2011, you may need to change the Power Draw Bar control circuit board." If I'm not mistaken, this should be connected directly to the VFD pins T1 (0V Common) and B3 (Digital output - Zero speed) as shown on page 11. I tested this output and it does indicate when the motor is being powered. The PWB control board has a small IC next to the connector which looks like an opto-isolator but I couldn't get a good enough view inside the housing to really confirm this.
I don't have this connection because I don't have the ATC. It would be very tempting to try it out, but then I ask myself why Tormach didn't simply supply a cable with the PDB if it really is this simple?
Step

[rlockwood]

An interlock should be present to prevent the PDB from actuating at all- Tormach is asking for a lawsuit with this one. If they truly stated that they "tested that failure scenario and the machine survived." Its absolute negligence.

[TurboStep]

I couldn't resist...
Just to be very clear, this is not a recommendation. Don't play around with this stuff unless you know what you're doing.
I connected the VFD Interconnect as described in the ATC Operators Manual, and to no great surprise, it works.
If I press the PDB button while the spindle is running it doesn't respond. If I keep it pressed and stop the spindle using Mach3 the PDB releases only after the motor has stopped. However, if I press the PDB button and stop the motor by opening the motor door the PDB activates while the motor is still running down, but this is not the usual way that I operate the mill!
The question still remains why Tormach didn't provide this 1$ cable with the PDB as standard???
Maybe it's time to look for a foot pedal.
Step

[David C. Allen]

Turbo, My guess is that you have the "wall wort" that provides power to the Power Draw Bar Controller. When you open the motor door you open the safety interlock, so some power is removed in the control cabinet but the power draw bar is still under power from the "wall wort". When you add the ATC the power draw bar receives it's power from the control cabinet and the "wall wort" is discarded.

David

[Hirudin]

I'm using a foot pedal that has a mechanical "push to unlock" lever which prevents the foot pedal from being activated accidentally (or, at least it makes it much less likely). Of course, this lock wouldn't help in a scenario of absentmindedly activating the switch when the spindle is running. SCzEngrgGroup's suggestion sounds like a possible solution to that issue.

McMaster-Carr

It's surprising Tormach didn't interlock that. Not so much to prevent damage to the machine, but to protect the user from flying tools and collets. It's easy to do - the VFD should be capable of providing an output signal that goes true whenever the spindle is in Run mode. That's what I use on the new "micro" power drawbars I've just designed, when a VFD is present. If not, I provide a spindle sensor integrated into the drawbar to serve the same function. Safety first!

Regards,
Ray L.

Good to know! I think I'll (eventually) incorporate this into my own design.