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Author Topic: Rigid tapping with servo spindle  (Read 8241 times)

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Rigid tapping with servo spindle
« on: November 19, 2008, 02:15:15 PM »
Hello Guys,
Just wondering if this is at all possible with mach3?

I was kind of thinking it may be possible if we treated the spindle (servo) as a separate rotational axis it could be done.

Just a thought
imagine you have a theoretical 1 turn per inch tap, and you wanted to tap a 1" deep hole, and the tap is 1" above the surface of the hole.

If you change your spindle to be A axis, and make it rotational.

Then you could code something like this:
F10 (tapping feed rate)
G01 X-1 C720 (this will move the z axis two inches down and turn the spindle 720 degrees or two turns)
G01 X1 C-720 (this will move the x axis two inches up and turn the spindle 720 degrees or two turns in the other direction)

I think this might be a way of being able to rigid tap with a servoed spindle.

Any thoughts?
regards
Fernando

Offline Graham Waterworth

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Re: Rigid tapping with servo spindle
« Reply #1 on: November 19, 2008, 02:23:38 PM »
The problem is pitch control during acceleration and declaration, you can not read an encoder fast enough with the current set up.  To get the accuracy needed you need 2000 ppr minimum

It may be possible with the SS later.

Graham
Without engineers the world stops
Re: Rigid tapping with servo spindle
« Reply #2 on: November 19, 2008, 02:33:45 PM »
Thanks Graham,

Well the thing is, if you treat the spindle as an Axis, you wouldnt have to worry about that.

Both movements would be automatically syncronized to finish at the bottom of the hole, just like any other XY move, except this time its a Z A movement.

Im not saying that the tapping would be lightning fast, but it would be possible.

Maybe just write a wizard to calculate the number of turns given a tap size and pitch and hole depth.

Regards
Fernando

Offline Graham Waterworth

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Re: Rigid tapping with servo spindle
« Reply #3 on: November 19, 2008, 02:43:13 PM »
If you are talking about small taps I can see it working as the load on the spindle will be very low so the torque lag will be low, course larger taps I can see been a problem as Mach is not in control of the pitch the servo units are and they don't know what each other are doing.

I am not saying it will not work, I just think it is flawed and as such is not reliable.

Graham
Without engineers the world stops

vmax549

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Re: Rigid tapping with servo spindle
« Reply #4 on: November 20, 2008, 12:26:09 AM »
IT works just fine with a servo or stepper IF you use a swapped axis approach. You will have to hand code the cycle .

(;-) TP
Re: Rigid tapping with servo spindle
« Reply #5 on: November 20, 2008, 08:04:21 AM »
Hey TP,
have you had any success doing this?
Best regards
Fernando

vmax549

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Re: Rigid tapping with servo spindle
« Reply #6 on: November 20, 2008, 09:40:18 PM »
Yes we tested the approach. With a servo spindle it will work if you do the swap axis Z>A then code a tap cycle and the return the swapped axis . Other have done similar things by adding a tapping drive to the spindle that when engaged uses a similar approach using the rotary axis to drive the spindle during tapping.

Thing is with all of them it takes a non standard approach to the programming (;-)

(;-) TP
Re: Rigid tapping with servo spindle
« Reply #7 on: December 15, 2008, 10:53:11 AM »
Hello,
Just found this video in youtube, not quite as fast as some VMC but it does the job for sure.
http://www.youtube.com/watch?v=l8QRMYt7vEE

I couldnt embed the video but the link is up there
<a href="http://www.youtube.com/watch?v=l8QRMYt7vEE" target="_blank" class="new_win">http://www.youtube.com/watch?v=l8QRMYt7vEE</a>



Best regards
Fernando
« Last Edit: December 15, 2008, 10:57:08 AM by fer_mayrl »

vmax549

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Re: Rigid tapping with servo spindle
« Reply #8 on: December 15, 2008, 11:43:21 AM »
THat is an OLD video AND it is not rigid tapping  and it at 100 rpm (;-) You have to use a T/C tap holder. I now tap regularly at 400rpm in the SRT cycle from #4 to 5/8".  A good VFD and dynamic braking is required. AND it does a very good job.

(;-) TP

Offline simpson36

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Re: Rigid tapping with servo spindle
« Reply #9 on: December 18, 2008, 10:21:55 AM »
I recenntly aquired a Tapmatic head. The SPD series is specifically designed for use on a mill and uses a standard boring cycle (it self reverses).  No clutch, so make sure you know the depth you need.

Works fantastic!

Anothe approach is to fab up a simple slip joint with a retun spring so you just down Z less than the thread pitch until the tap touches the hole and then stop Z movement and keep the spindle turning. The tap will draw itself into the hole and all you need to do then is reverse the spindle at the 'bottom'.

I know this is a bit of a red-neck approach, but it does work and it doesn't ruin good parts by ripping the threads out as with an uncoordinated rigid attempt.