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Author Topic: Rigid Tapping  (Read 25098 times)

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Offline Hood

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Re: Rigid Tapping
« Reply #10 on: January 04, 2014, 03:26:02 PM »
Terry as I have said to you before my spindle is controlled by an analogue voltage so in theory it should be the same as a VFD. The CS-Lab website says that rigid tapping is possible with the CSMIO/IP-A and CSMIO/IP-S when using the Encoder module. There is no mention of it having to be a servo, I will however ask them and I will update here with their answer.
Hood

Offline Hood

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Re: Rigid Tapping
« Reply #11 on: January 04, 2014, 03:30:21 PM »
Terry from this it would seem the Kflop can do rigid tapping with a VFD controlled spindle, or thats the way I read it .

"A requirement for Rigid Tapping is that the Spindle has encoder feedback and is possible to move in a fairly controlled manner.  The Z axis motion is "geared" to the measured Spindle Encoder Position throughout the cycle."

Hood
Re: Rigid Tapping
« Reply #12 on: January 04, 2014, 05:30:33 PM »
 I did some ridgid tapping on Fadal 6030 once.  Scary watching a 5/8-11 tap accelerate towards a big cast iron part and plunge right in to a depth of 2 inches and stop, then accelerate back out again!

I've also done tapping with tension compression tool holders on an old knee mill with a Bandit cnc and no encoders and it actually worked quite well.  I just started shallow and watched if the tap was extending or retracting on the way in.  If it was extending the feed was too slow, if it was retracting the feed was too high.

I got lucky recently and picked up two Tormach auto-reversing tapping heads for a very nice price. One is up to 1/4", the other is 1/4" to 1/2".  They look pretty good, I hope they work well.

Offline BR549

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Re: Rigid Tapping
« Reply #13 on: January 04, 2014, 10:12:30 PM »
Hiya Hood the ONLY example I have seen with Kflop was with either a servo or stepper drive spindle and with those I can do it without any outside controller. 

IF you have seen an example please let me know.  I do know it can be done with the correct vector driven VFD ,encoder and realtime software controller.

(;-) TP

Offline BR549

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Re: Rigid Tapping
« Reply #14 on: January 04, 2014, 10:52:50 PM »
OK let me define what I consider to be rigid tapping . The Z must stop exactly where I define it to stop as a servo driven spindle can do because it has the accelration/deacceleration values to work with to plan the moves.

The best you can do with VFD and encoder is the Z follows the spindle to a stop. THAT is not rigid tapping that would be semi rigid tapping . Try that with a close blind hole at 100 rpm then 1000 rpm. The VFD will overrun the end point everytime as it has NO control over stopping other than stop as fast as it can. The controller has NO idea what that value may be and it can only follow the spindle to a stop then restart on reverse.

Just a thought, (;-) TP

Offline Hood

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Re: Rigid Tapping
« Reply #15 on: January 05, 2014, 05:02:13 AM »
Oh now TP, we will likely go round in circles for a long long time as I know how stubborn I am and I think you to be just as much ;)
Anyway what you are describing I would say is synchronous tapping as opposed to rigid tapping ;)
Hood
Re: Rigid Tapping
« Reply #16 on: January 05, 2014, 09:30:55 AM »
While I would agree that an inexpensive VFD and encoder might be set up such that the Z follows it to a random stop position, that is simply not true of many VFD drives out there. A good VFD can produce 100% of rated torque in braking and stop exactly where you want it to.  Lots of them are used in positioning applications.

Offline BR549

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Re: Rigid Tapping
« Reply #17 on: January 05, 2014, 11:24:50 AM »
Actually only very expensive vectored VFD drives can do positioning well. Most cannot do positioning well but can do velocity mode very well.

But the expensive vectored drives are just as expensive as servo drives so there is no real gain.

Rigid tapping has true postional stopping of Z on command.

Synchronous tapping is what you have with a VFD and encoder. The Spindle is synced to the Z axis and normaly runs in FPR mode. AND probably for most applications it would be fine for though holes. BUT not for blind holes.

Been there done that one, (;-) TP
Re: Rigid Tapping
« Reply #18 on: January 05, 2014, 11:39:33 AM »
I'll muddy the waters by throwing out another definition:  Rigid Tapping means simply using a tap rigidly mounted to the spindle.  It says nothing about how precisely you can stop.  It simply implies (requires!) that the axial motion be precisely coordinated with the rotary motion, to avoid breaking the tool.  This can be done with any kind of spindle drive, and a spindle encoder.  Without the encoder, or other means of providing precise coordination, you must use a "forgiving", non-rigid, tool holder, like a tension/compression holder, or a tapping head.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Re: Rigid Tapping
« Reply #19 on: January 05, 2014, 11:49:56 AM »
Bloody hell TP, you better not tell the Mazak  guys that their synchronous tapping is really just  a VFD that doesnt do rigid tapping ;)
We can go round this for weeks and weeks, I will say one thing, you will say another. I will find something to prove my point, you will find something to disprove it and so it will go on. Lots of machines out there that do rigid tapping and have VFDs, most modern ones have servos but a few years back that was not the case and they called it rigid tapping.

Hood