Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Dom on March 05, 2010, 05:39:07 AM
-
Does mach 3 support rigid tapping and if so what features must I enable in the configuration and also what do I need in terms of hardware/electronics to make it possible ?
-
Short answer is no.
You can however do rigid tapping if you have a servo or stepper as a spindle, you would then use SwapAxis to swap the spindle to an A axis and programme that way.
A lot of people do semi rigid tapping using a floating holder.
Hood
-
What do you mean exactly by "SwapAxis?"
-
If you have a Servo for a spindle you can set up an A axis in ports and pins and then have a macro to swap the A axis for the spindle. That will mean that when you command an A axis move it will actually send pulses out to the spindle. Because the spindle is now getting treated as an axis the moves will be in sync between A and Z so you can rigid tap.
Hood
-
I was under the impression that if you added an optical sensor to count spindle rotations then mach3 would rigid tap, however if you say thats not the case I'll accept that I was misinformed. However the question remains if mach3 cant rigid tap would I need or want a sensor to count spindle revs at all ? Is it necessary to have one to tap with a floating tapping holder or would the sole benefit be just to get an rpm readout on screen in mach ?
-
In Mill the Index pulse is used to read RPM, not sure but possibly closed loop VFD spindle control may also use it although I am unsure how good that is. If you use G95 (Feed per rev) on mill then you would need the Index for RPM, most use feed per minute on a mill though.
On a lathe the Index pulse is needed for threading as well as for G95, G95 is normally the mode you would use on a lathe.
If using a floating holder to tap, whether mill or lathe then it would still be a good idea to have a RPM readout as it will help with your calculations for the code..
Hood
-
Dom
The problem with rigid tapping lies with slowing down to zero, reversing and coming back out maintaining position
This is doable with a servo motor but there is probably a reason Mach cant do the threading cycle
Phil
-
This guy claims to be doing it with a servo spindle and not using swap axis.
http://www.youtube.com/watch?v=19aSV9JeU10
-
He is not using swap axis but he is just setting Mach up to have the C axis with the same pins as he has for the spindle. So as long as he doesnt call a RPM at the same time as he calls the C axis he is fine. So basically he is doing a swapaxis() without doing the actual swapping and with none of the safety features of the swapaxis() ;)
There are a few motion controllers that support rigid tapping, one is the kFlop and another is the CSMIO/IP-S and also the IP-A. I use the IP-A on the Chiron and it does an excellent job of rigid tapping, even peck tapping.
http://www.youtube.com/watch?v=d87kv3GSqvY
Hood
-
Yes but so far NONE have done RT with a VFD ,encoder setup. Hoods setup uses a servo spindle on the CHinron.
With a servo spindle(expensive) you can simply use 2 sets of specs on the spindle axis( Spindle/C) and call the one you need.
The spindle will NOT get confused this way as it just does whatever you tell it to do.
Mach3 cannot do RT (VFD/encoder) from the LPT version because it is a buffered system. To do true RT from a VFD/encoder it has to run LIVE in realtime.
With a VFD and Braking resistors you can get very good control with SRT (semi rigid tapping) with a floating tool holder. With the VFD using braking and DC injection you can stop the spindle very quickly on the down stroke. Use the G84 cycle with this and you have a very good SRT system. I have even used it to do blind holes.
The G95 does NOT work well in Mill when trying to use an index signal. It does work well without using the index signal to sync the feeds. Mach cannot track the signal through a spindle start /restart. It will crash your G84 cycle every time.
Just a thought, (;-) TP
-
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
-
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
-
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.
-
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
-
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
-
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
-
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.
-
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
-
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.
-
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
-
Those were NOT your standard VFDs they were Vectored VFDs where the VFD is connected to the encoder directly. I have access to a Mazak that runs it.
Those vectored VFDs are virtually a servo drive that uses a 3ph motor, very expensive and were later replaced by true ac servo drives. The last Vectored drive that was replaced here was well over $5k just for a rebuilt unit.(;-) OUCH. The servo drive drives were only $3k.
IF mach through a controller can do synchronous tapping it will serve in most cases but it it NOT rigid tapping where it can stop on a dime.
IF you google Route66 rigid tapping you will see a version that does Synchronous tapping well with a controller that supports it. But as you see it is NOT doing blind hole tapping just through hole. It cannot do true RT as it cannot stop on a dime either.
In most cases with a compression tapping head and through hole tapping you can do just about as well without the encoder enterface Just G84 it . If you do a LOT of tapping the same size you CAN get down to a 1-2 thread depth tolerance.
I use a compression tapping head WITH a clutch to prevent broken taps on blind hole. NOT the best solution but it works.
(;-) TP
Just a thought, (;-) TP
-
TP, I was talking about modern Mazaks, my neighbour who is in charge of a place with quite a few Integrex reliably informs me that there is rigid tapping in his machines but also their is the synchronous tapping option. The difference he told me is rigid tapping he can tap reliably but if he needs to go in again and adjust depth then unless he has the sync option he is out of luck. Now he is likely totally wrong so I will let you win as obviously he doesnt have a clue what he is talking about :)
Hood
-
With true rigid tapping the spindle SYNCs to the index signal to give it a starting point of reference of rotation that sets teh home on spindle rotation. The drive is setup with parameters JUST like the other axis servos are. The control knows exactly where the spindle rotation is as compared TO the index signal. It can repeat or retap or peck tap a 100 different times and the depth will always be exactly as programmed and the thread pitch will always match up as long as the tap has not moved in the holder.
Around here we have only been working with these type or things for about 45 years now so you are right we might not know what we are doing over here yet.
So ends another discussion, (;-) TP
-
No Terry I already said you win and that my Neighbour doesnt know what he is talking about :) Didnt say what you were the winner of but...
BTW had a look at your route66 thing, better tell them they are falsely advertising, they refer to it as rigid tapping and as you quite rightly say it is most definitely not :)
Hood
-
............ 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
Dear Hood,
I'm interested in the response from CS-Labs, will appreciate the update.
Thanks,
Russ
-
Will do Russ, no reply as yet but as this is likely their first day back it may be a while before they can get a reply out to all that have emailed.
Hood
-
Russ,
got a reply from Wojtek at CS-LAB,
Question asked was
"Hi Wojtek,
can you tell me, is rigid tapping possible with the IP-S & IP-A and the Enc
module when using a VFD to control the spindle? "
The reply was
"Hi,
Yes, sure it is"
Short and sweet but my question was asked prior to all the extra info required by some ;D
I have asked for some info on how closely the Z will be observed or whether that would be dependant on the VFD and its setup.
I have also asked if peck tapping is possible with a VFD.
Hood
-
Thanks Hood.
Wondering if this would require/use the index signal ... or if it is a one shot deal with an inverter.
Also, guess the enc. index would negate the need for the normal spindle speed sensor ?
Thanks again,
Russ
-
Russ,
I would imagine an Index on the encoder would be required, definitely if wanting to do peck tapping (if that is possible with a VFD) and as you suspect if you have the Enc module with an encoder attached the spindle speed is obtained from that, so no need for an additional Index.
Hood
-
HIYA Hood I guess the difference is the some of us have a great deal of 1st hand experience using and testing tapping on a mill and others just rely on 2nd hand info from others. (;-)
But I will let you continue to advise users as to how it really works (;-)
Been there done that, (;-) TP
-
Very gracious of you Terry, much obliged that you have given me your blessings :)
Hood
-
Hopefully without jumping into the frey, I just wanted to point out a detail that is missing on re-tapping the same hole.
In addition to having the spindle at the same starting point (not necessarily azimuth 0 or index, but the actual starting point from which that particular hole was tapped). you need to have the Z at the starting point for that particular hole also.
This is not too bad if you have only a few holes at the same elevation, but can get complicated with a lot of holes at different elevations or a string of holes done with relative moves.
In my 'rigid' tapping macro, the retract amount is also a consideration because I allow any retract value (to clear obstacles in moving to the next hole) as a parameter passed to the macro. Since the retract can be any value, the macro has to determine if the current Z is at the retract height and accommodate that space in the next Z move prior to starting the next tapping motion.
In my setup, I have the choice of homing the spindle before each hole, but I found the cost in time to do this is too great in contrast to the benefit of being able to re-tap old holes. holes tapped too shallow are typically discovered at assembly and in practical terms it is much cheaper to hand tap the hole deeper or spec a shorter fastener (if possible) than to run the part back thru the CNC process.
Whether there is a tool changer and whether the tool holders have drive dog also plays into the 'sync' equation. Assuming the spindle homes before each tool change and the tapping routine returning to the starting azimuth for each tap sequence, the spindle will retain it zero reference during any tapping run regardless of how many holes are tapped. With dogless systems like Tormach, your options would be greatly reduced and you could only reliably re-tap (assuming a spindle home is done after picking up the tool) until the next tool change. When that tool is retrieved again, there is no guarantee the azimuth will be the same , so homing the spindle again will NOT necessarily return the tap to the same starting point.
I think everyone agrees that blind holes are the Gorilla in hard tapping. In practical terms it is often doable to simply drill the hole an amount deeper than the required threads to accommodate the variation posed by tapping heads, VFD's and perhaps even the occasional programmer screw-up, but it is undeniable that exact control of the Z depth is the holy grail and the only method (other than thread milling) to provide safe 'bottoming' type tapping. My tapping macro stores the current acceleration parameters and then maxes them out for the tap operation and then restores them to the original settings. My experience has shown that normal acceleration settings (and mine are already much higher than most) are not adequate for rigid tapping with small taps. 'Stop-on-a-dime' performance has been mentioned. Taps smaller than 1/4" or M6 need 'Stop-on-an Insect' performance . . . and a small insect at that.
Love the clutch idea, but it seems that would defeat any ability to go back to that hole for a re-tap. To prevent broken taps (my nemesis, incidentally), my plan is to use the torque control I/O on the servo drives to set the max torque below a certain threshold depending on the tap size. In this way, the drive would stop prior to snapping off the tap and would fault the system allowing for a change to a new tap without having to then dig the old tap out of a hole. This method would also protect against a spiral tap from becoming a permanent part of the workpiece if it snaps off due to being bottomed in a blind hole.
A lot of the above comments would not apply to the high end machines being debated, but considering the typical machine running MACH software, I'm hoping the information may be useful to the few who have servo powered spindles. :)
-
Well I got a reply from CS-Lab regarding using a VFD for tapping, the depth will not be so precise as using a servo and may overshoot a bit. That will depend of the acceleration/deceleration of the VFD, so the faster the better obviously.
Regarding peck tapping, CS-Lab say it is no problem with a VFD and works in the same way as I can do with the servo, and it works exceptionally well. So looks like the only thing with VFD tapping and the CSMIO is you will have to learn your overshoot, obviously this will change slightly with different materials and how sharp/dull the tap is but it should work well enough for most that do not have a servo.
Hood
-
Just as an FYI, I found a significant improvement in thread quality (and less broken taps) by adding a pause at the end (bottom) of the tap cut.
Some Systems have this and some don't, but if you have the option, try putting dome delay to let the torque settle down before the reverse juice kicks in. Even 1/4 of a second can make a significant difference even with an AC servo.
Also, in my experience, even with ball screws, it takes longer for the spindle to accelerate than for the Z axis to start moving. Also the spindle accell is effected by tap size and material being cut, sharpness of the tap, etc.) while the Z movement is not. Compensation for this can be found in putting a delta between the Spindle and Z axis to give the spindle some bias in acceleration.
-
With my setup it seems to work exceptionally well and so far I have had no problems with snapped taps, have only gone as small as M3 taps in 316.
I did some videos a while back when rigid tapping was first implemented in the IP-A and IP-S.
Here they are.
http://www.youtube.com/watch?v=GNL2XdsJz2E
http://www.youtube.com/watch?v=2DE4sAgLPX8
http://www.youtube.com/watch?v=A29bYyWzrlo
http://www.youtube.com/watch?v=UbNizRlRT1g
http://www.youtube.com/watch?v=d87kv3GSqvY
As you will see, in some of them I have deliberately set the spindle accel very slow for them, others I have my normal acceleration.
Hood
-
I do enjoy the 'Hoodisms'. You phrase " . . . . 'ONLY' gone as small as M3 in 316 . . . ." as if this is still in the realm of easily doable. If I had to hard tap M3 in 316, I'd need a couple shots of Jack Daniels first . . :D Plus I would stick to the 50% thread hole size as a minimum. Just thinking about 316 makes my eye start twitchin'. ;)
And that tool changer . . . man, I'll never get tired of watching that thing! Hopeless. Deer in the headlights :-[ Anyway, did you find any advantage to using the slow accel on the spindle or were you just testing? The mill seemed to do fine both slow and fast, but if you had 100 holes to tap, there would be a massive difference in the part cycle time.
Theoretically, if you have the Z accel higher than the spindle and a fast computer, Mach should be able to coordinate the Z movement to the spindle regardless of the spindle acceleration, slow or fast. What I would be wary of is the tapping speeds you are going to transition thru and the period of time spent there.
Tapping tends to be SFM critical (in my experience) so I prefer the tap to cut at the correct speed and stop quickly to minimize the possibility of binding if and when it passes thru an SFM that is nasty bad for the particular size/material being cut. Also, I am a speed freak when it comes to CNC and I am not one to wait around while a spindle (or anything else) comes up to speed. I tend to think in terms of MRR for general machining and Seconds Per Hole for drill/ream/tap and anything else to do with holes.
Speaking of seconds per hole, I can't tell from the videos if you have a pause in the tap sequence between directions.
Considering that the accuracy of the Z stop is the Gorilla for VFD rigid tapping, did you find and difference in accuracy or consistency between fast and slow spindle accel? It would be interesting to see the results of tapping a row of blind holes with fast accel and the next row with slow accel and compare the depth and consistency and quality of the resulting threads. Then do the same with and without a pause between directions.
No hurry on that. You know, whenever you have some free time . . :P
-
I was only slowing down the spindles accel in response to questions asked by Terry in the thread we were discussing this in at the time.
There is no pause at the end and actually Mach itself is not controlling the tapping, it is done totally in the CSMIO and is called via M84 instead of G84.
The spindle in these vids is dual speed, ie feed out is set to double the in-feed rpm, can be set to what you want but double seems to work well for me.
Just to avoid confusion, my spindle is a servo and is controlled by the CSMIO as a servo ie +/- 10v control to the drive and it adheres to the acel I have set in motor tuning, the Z is synchronised to the actual encoders counts and it seems to work very well, the spindles encoder is 32,768 pulses per rev so the CSMIO is getting plenty of positional data to keep things on track.
Hood
-
Oh and regarding 316, I think nothing of it as it is what I use day in day out being that the vast majority of my work is done for fishing boats. When I do 5083 Alu I think of it as cutting air. Just wish I could get my hands on a faster spindle motor :D
Hood
-
I was only slowing down the spindles accel in response to questions asked by Terry in the thread we were discussing this in at the time.
I was reading that stuff and I thought it was actual and not theoretical.
There is no pause at the end and actually Mach itself is not controlling the tapping, it is done totally in the CSMIO and is called via M84 instead of G84.
It was my impression that Mach did not implement rigid tapping at all.
The spindle in these vids is dual speed, ie feed out is set to double the in-feed rpm, can be set to what you want but double seems to work well for me.
Now there is an interesting idea. Why didn't I think of that?
Just to avoid confusion, my spindle is a servo and is controlled by the CSMIO as a servo ie +/- 10v control to the drive and it adheres to the acel I have set in motor tuning, the Z is synchronized to the actual encoders counts and it seems to work very well, the spindles encoder is 32,768 pulses per rev so the CSMIO is getting plenty of positional data to keep things on track.
I guess I better revisit that site. It was my impression the CSMIO was a motion controller. From this description, it is also a servo drive? I may give this device a close look for the new mill I will start work on in a couple weeks. The Kflop is a powerful tool, but getting it to do things takes a huge investment in time.
Oh and regarding 316, I think nothing of it as it is what I use day in day out being that the vast majority of my work is done for fishing boats.
Yes, I remember. And you work on big stuff with big machines. That's why I was surprised to see M3. Figured the only use you'd have for that might be as a toothpick :)
-
It was my impression that Mach did not implement rigid tapping at all.
Mach will go through the motions of rigid tapping if you call a G84 but it requires that you have a floating holder and that your spindle speeds are close to that commanded as it is just going through the motions and not looking at what is happening. Mach4 will be different but ..... well enough said ;D
.
I guess I better revisit that site. It was my impression the CSMIO was a motion controller. From this description, it is also a servo drive? I may give this device a close look for the new mill I will start work on in a couple weeks.
It is just a controller, it is controlling the servo drive/amplifier with +/- 10v and takes in feedback from the encoders so that it can do the PID. The position in Mach is also updated from the encoder position by the IP-A controller that I am using, the IP-S is the Step/Dir one and it does not take axes feedback other than spindle encoder for use in tapping or threading.
The Kflop is a powerful tool, but getting it to do things takes a huge investment in time.
That has always been the drawback of the kflop for me, it is also however the big selling point to others. If you are fluent in C or whatever it uses then you can likely do most things, if you are not then you are relying on others for even basic things or you need to learn programming quick.
The CSMIO products are not so open in this regard but they have thought of nearly everything that is considered normal for machine tool control and implemented it for you.
Yes, I remember. And you work on big stuff with big machines. That's why I was surprised to see M3. Figured the only use you'd have for that might be as a toothpick :)
I do all sorts, do work for a couple of companies that supply products to oil companies some of which are tiny electronic devices :)
Big machines can do tiny work where wee machine usually cant do big work ;)
Hood