[cobrakai]

Hi guys,
New member here. I just picked up a lightly used PCNC1100 mill and I'm trying to get the power drawbar working. I aligned the cylinder with the drawbar, have about 1/8" gap between the air cylinder bolt and drawbar, everything is nice and level, and I have 100-110psi going to it.

When I press the release, the cylinder just lifts and tips up to the left. It doesn't even compress the Belleville washers at all. I am getting about 1" of stroke on the cylinder but it pushes itself out of the way. I took it apart and I notice quite a bit of wiggle where the drawbar mounting plate is supposed to pivot on the eccentric mount. The metal is extremely thin in this area for some reason... it looks like a flawed design. As I understand it, the mechanism is designed to start to tilt, then bind on the pivot mount and that is where the holding force comes from.

Has anyone else had this issue? What should I do? This really looks like a manufacturing or design flaw to me but my searches aren't showing much.

[nitewatchman]

Any chance you have a photo? There should be a Flanged Retainer on the top of the rotating spindle. When the PDB is actuated the piston rod should extend and strike the end of the draw bolt. The cylinder will then rise until the top of the cylinder mounting plate contacts the bottom of the Flanged Retainer and its motion upwards is stopped, about 1/4" or so. The cylinder rod continues to extend opening the collet until the Belville Washers are collapsed and the cylinder stalls.

If the cylinder can rise by 1" and I am understanding your description correctly, the Flanged Retainer appears to be missing. The upward travel is NOT controlled or stopped by the cylinder tilting sideways and binding on the eccentric bolt. Looking at the two photos from the Tormach website, the Flanged Retainer is in the parts photo in the bottom row second from the right. In the assembled photo it can be seen directly above the mounting plate and below the Belville Washers.

If by chance the PDB has be actuated with the spindle turning it will instantly lock the assembly and stop the spindle. In the process, if the spindle is rotating at high speed it can strip the threads from the inside of the Flanged Retainer. Perhaps this has happened before you received the machine and the Flanged Retainer has been replaced with the standard retainer that comes on the machine. This would create the condition you describe and prevent the drawbar from working. I have this on first hand knowledge.

My PDB and ATC work very well together and it sure beats cranking a wrench.

nitewatchman

[TurboStep]

From you description it sounds like something is missing. I took a photo of my PDB for comparison - this is taken from the right side.
The design is not intended to apply pressure via the pivot. The PDB bracket should sit under the flange of a large black T-shaped nut. When the PDB is activated it pushes up on this nut and down on the drawbar. Is this nut present?
I wouldn't try to operate it unless it's working correctly otherwise you may damage something as there are some large forces at work.
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Edit: nitewatchman was faster!!!

Attachment 198706

[cobrakai]

I am such an idiot! Thanks for the responses. I had the flanged retainer tightened in the wrong direction, up to the base of the washers rather than down, and the whole concept of how it was supposed to work went right over my head. I blame it on a long day of work and the anticipation

I simply spun it the other direction and it now works perfectly! I probably ovalized that pivot hole a little bit by tweaking it upwards like that, but it still functions just fine.


ON ANOTHER NOTE:
I made this little video before we figured this out, so ignore that last part (doh). I included some video of me incrementally jogging the axes using the pendant. There is one frequency on each motor where the resonance is very loud, shaking the whole base and machine. Above and below this speed it sounds fine. Is that normal? Does the LeadShine upgrade kit eliminate this vibration?

PCNC1100 Tests - YouTube

[tbaker2500]

Yup, that's mid-band resonance. My understanding is the series 3 steppers reduce this significantly. (I have a series 1 setup)
You can read more about it in Tormach's Series 3 whitepaper: Direct Document and Software Download | Tormach LLC providers of personal small CNC machines, CNC tooling, and many more CNC items.
It gets into detail around page 11.

[nitewatchman]

I changed my Series II out to the Series III LeadShine drives and motors and there is a dramatic improvement or reduction in resonance and noise across all speeds. The max traverse rates are a little higher also.

I also run a Fenner Belt on my machine spindle which reduces noises and vibration of the spindle drive belt significantly on my machine. There has been much debate here over the merits of the belt but for me there is a significant improvement over the stock belt and the premium aftermarket belts I tried. They just don't bounce and roar as much. There is a whistle at lower speeds but I find this much less objectionable.

nitewatchman

[cobrakai]

Thanks for the extra input.

I have one other issue, that is 3 of my ~10 TTS holders are not fully pulled into contact with the bottom face of the spindle. I have adjusted the drawbar tension correctly and the other tool holders pull up nice and snug. However these 3 (all set screw holders) have about .005" gap between the spindle and top flat surface on the holder. There is no debris I can see, and the dimensions seem okay although I'm just using vernier calipers to measure those. My first guess was that the diameter was too large, causing the TTS collet to bind before pulling completely upward.

Has anyone had this one before?

Other than that, the machine is awesome! I got my ATC working perfectly and it's so cool to watch. I haven't even thought about the 4th axis yet since I can't even operate the basic 3 axis yet.

[TurboStep]

I fully agree with nitewatchman, the difference with the motor upgrade is dramatic.
I've had a similar problem with the holders. The recess in the top of the holders for the end of the R8 collet wasn't deep enough, particularly on the ER20 holders. Tormach sent me a replacement R8 collet which was just a little bit shorter and I've had no further problems since. This is now their standard collet length.
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[cobrakai]

Oh really? I took out my collet and a able to push the tool all the way into the shoulder. It's just that it doesn't move enough when retracting into the spindle. It's the correct flattened type too. I could read the part number on it if that matters.

By the way, I sprayed some grease into my Z axis motor brake and wow, the noise is easily 50-60% quieter. I still get the resonance but none of this rattle noise.

[TurboStep]

Oh really?

Yes really!
I did have similar problems (note the use of the word "similar" - I'm not in front of your machine so you'll have to decide yourself if this is your problem or not).
Here is a quote from the mail from Tormach from 26th August 2011:
"The measurement for the protrusion on the spindle is done at the factory with a special gauge, and doesn’t necessarily correlate to the actual collet protrusion. This is something we discovered while investigating the very issue you mention, which let to us offering the shorter version of the collet. Regarding the collet, we have ordered a full shipment of the slightly shorter collets, this will soon become the only collet we sell, so no worries about using a “modified” collet that you won’t be able to get replacements for.

I don’t have the tolerance limits of the spindle taper… that would be pretty hard to measure anyway.

....

The depth of the relief spec on all the holders should be 2mm +/-.2mm."

Yes REALLY!
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