[Welder2022]

I just acquired a VMC 15 with 10 hp spindle and rigid tap. 2 spd belt spindle drive. I am trying to tap some 1" structural steel plate 3/4-10 thru.
I am drilling .672 thru and c/sinking before tapping. I am using the g84.1 rigid tap cycle; no problem with this. I am using a rigid tap holder with a Hss starting tap at 100 rpm and new semi synthetic coolant. I did some test holes in 1/2" plate no problem. First part from the 1" plate: first hole no problem. 2nd hole, the spindle stopped turning halfway down but the Z kept moving and broke the tap. I am thinking the belt slipped and the encoder didn't know it. Anybody else had this probem?
And so, if this is indeed the issue, can I expect to be able to do this job with new belts? Or is this beyond the machine capability?

[megacanam]

if torque is indeed the issue, have you ever thought of thread milling them? I have not tapped anything that big, but I am also looking into thread milling due to the number of taps i have broken.

[Welder2022]

Yes I have changed to thread mill the parts, that works fine but is killing me on cycle time. My question still remains, what size/depth of tap can I expect to be able to run on this machine?

[megacanam]

Yes I have changed to thread mill the parts, that works fine but is killing me on cycle time. My question still remains, what size/depth of tap can I expect to be able to run on this machine?

Im running on single phase and the largest I have tapped was 1/2-13. But I ran a OSG A-Tap .75 deep in 4140 with no problem for 336 holes and still looks new. Here is the part no in 3/4-10 EXOTAP A TAP Taps - OSG

My problem is with 1/4-20 taps, I must have broken 6 of them now, Im like you... I hand tap them faster and better then the Fadal.

[jbranting]

I use 3/4-10 taps in mine with 10 hp. I do 50 RPM and use cutting fluid. I also peck tap in anything over 1/2" deep that is steel.

[David Michael]

The bottom line, with the 10 HP motor you have about 37 to 55 ft of torque to work with.

Not all spindle drives are the same, the Baldor drive is one of the top performers, Mitsubishi was the least.
At the original Fadal, I worked with most of the drive manufactures and developed the rigid tap control feature back in 1991.
You can put a AC clamp-on meter to measure how much current is actually going out to the motor. You should see about 30 amps before it stalls. The rule of thumb is 3 amps per Horse Power.

With the VMC15, it is a cogged belt so it never slips the motor can just stall.
The High/Low 10K drive is mechanically good going down but relies on the hydraulic support when reversing so the idler doesn't kick out and cause slippage. Checking the oil in the idler line is important. With the 10k you have twice the torque since it has a 2 to 1 reduction to the spindle.

Always try to run the rpm as high as the surface speed will allow; just going from 100 rpm to 200 rpm improves the motor torque efficiency.

In our job shop days with similar material, we would run the hole diameter as large as possible to reduce the torque requirement.
We had some nasty titanium that we couldn't even drill the hole without melting the drill and we had a couple of hundred parts to drill. Lucky we found we could anneal the titanium, drill the holes then heat treat them again.

Hope this helps...

[carbidecraters]

David thank you for stopping in here from time to time. Its good to hear from you. I have a questions about retrofitting rigid tapping. Is it just spindle motor, encoder, encoder cable, drive, software and the spindle board with rigid tap eeproms. Is it that simple?

[Welder2022]

The bottom line, with the 10 HP motor you have about 37 to 55 ft of torque to work with.

Not all spindle drives are the same, the Baldor drive is one of the top performers, Mitsubishi was the least.
At the original Fadal, I worked with most of the drive manufactures and developed the rigid tap control feature back in 1991.
You can put a AC clamp-on meter to measure how much current is actually going out to the motor. You should see about 30 amps before it stalls. The rule of thumb is 3 amps per Horse Power.

With the VMC15, it is a cogged belt so it never slips the motor can just stall.
The High/Low 10K drive is mechanically good going down but relies on the hydraulic support when reversing so the idler doesn't kick out and cause slippage. Checking the oil in the idler line is important. With the 10k you have twice the torque since it has a 2 to 1 reduction to the spindle.

Always try to run the rpm as high as the surface speed will allow; just going from 100 rpm to 200 rpm improves the motor torque efficiency.

In our job shop days with similar material, we would run the hole diameter as large as possible to reduce the torque requirement.
We had some nasty titanium that we couldn't even drill the hole without melting the drill and we had a couple of hundred parts to drill. Lucky we found we could anneal the titanium, drill the holes then heat treat them again.

Hope this helps...

Thanks for the info. I thought I had a 2 spd belt system but since you say it's a cogged belt, how can the spindle stop and the Z keep moving if it's in a rigid tap cycle? Does the control allow that or is there something else going on? Per my original post, I drilled oversize to begin with because of the depth. I certainly don't mind running the tap faster if that will get me more torque but I guess I was thinking backward; lower rpm more torque.
Next time I will run faster and peck tap with lube and air blast.

[David Michael]

David thank you for stopping in here from time to time. Its good to hear from you. I have a questions about retrofitting rigid tapping. Is it just spindle motor, encoder, encoder cable, drive, software and the spindle board with rigid tap eeproms. Is it that simple?

Yes that's about it... pretty simple!
BTW with our new NXGEN control upgrade, we've improved the RT so you can now RT while in JOG by simply Jogging the Z axis up or down and the spindle will follow using the last thread pitch. It's great when trying to remove a stuck tap or just tapping while in JOG mode... David

[David Michael]

"Or is this beyond the machine" - you're in the upper range, remember you have about 37 to 55 ft lbs of torque. The HT machine has about 165 ft lbs.

I would suggest removing the head cover and verify you have a cogged belt. We had some variations with some of the early VMC15 drive systems that we not cogged belts.
Also watch the belt and make sure it isn't loose and jumping a cog or two. Now a days, you can video the belt drive system with your phone for better insight.

It could be a genuine stall and with the 10 pitch thread the Motor Overload fault tolerance just isn't able to catch it in time?

In a stall condition, you should be seeing the spindle load meter climbing up; torque and amperage are interrelated.

One thought, it might help to try milling instead of tapping and verify the motor is indeed pulling 20 to 30 amps during a heavy cut.
In the old days we build some neat dynos for testing performance... David

[Welder2022]

David thanks for your expert help. A part of my question probably should have been is the rigid tap cycle operating in "closed loop" where the Z axis feed would adjust according to motor encoder (C axis) position or is it in "open loop" where a command is sent to both spindle motor and Z motor without regard to their actual positions?
I say this because the spindle kept moving at least a half inch after the spindle stopped and before I could hit the E-stop.

[David Michael]

David thanks for your expert help. A part of my question probably should have been is the rigid tap cycle operating in "closed loop" where the Z axis feed would adjust according to motor encoder (C axis) position or is it in "open loop" where a command is sent to both spindle motor and Z motor without regard to their actual positions?
I say this because the spindle kept moving at least a half inch after the spindle stopped and before I could hit the E-stop.

The internal operation of Rigid Tap is the same as moving the X and Y axes except for RT the control is making a Z and C move.
Like XY the ZC moves synchronized. They both receive pulsed stepped commands to create motion.
The size of the (ZC) pulse and frequency of the pulses are determined by the required motion speed. This is pretty much standard with most CNC servos.

During motion, all CNCs have allowable servo tracking tolerances. The control generates a fault when the tracking error is exceeded.
In you case being able to adjust the tolerance (having less) so it faults sooner. Its a balance when setting these values, to small that the system shuts down causing nuisance trips. I've personally tested many machines (Fanuc, Haas...) and the servos are very similar.

Unfortunately, the Fadal control has fixed values and these settings are not accessible.

With our new NXGEN control besides doing the ZC moves technique we're also "slaving" the Z to the C axis. By slaving the Z axis, it just follows the C axis, so if the spindle stalls the Z just waits. That will be available sometime in 2017.

FYI, one thing you can do with your Fadal spindle that is handy and very few know about it...

Program G84.2 in a block.
This initializes the servo spindle as the C-axis, with the current location at 0.

Now program G90 G1 F1500 C-90.
The spindle will rotate 90 degrees and hold position.

We use to use scraping tools to create sharp corners in a part by rotating to the corner angle then do stroking into the corner, some thing like this:

C90.
Z-
Z+
XY
Z-
Z+
XY

(repeat until moving into the corner)

You can also program the C-axis in G91 incremental.

M3, M4, M5 will cancel the C-axis.

We first did Rigid Taping back in 1979 with the Fadal VMC45 when very few machines had a servo spindle. We did all kinds of neat things with it as it was a full 6 axis machine and at the time we also had one of the best Job Shops in the LA area back when the aerospace projects were strong. My Uncle Larry (the L in Fadal) ran the Job Shop at the time, he has always been a gifted machinist!

Hope this helps... David

[Welder2022]

David I think that in any case a half inch Z travel with stalled spindle while in rigid tap mode is way out of any kind of tolerance. The only way I can see that this could happen is if the spindle belt slipped under the high torque load. That means the spindle motor wasn't stalled. So, I will examine the belt.
At the time of the stall, there was some kind of error msg on the control but I wasn't able to record it. How can I access the alarm history on the CNC88hs?
Btw, that 22 year old piece of American iron ran max spindle ALL DAY yesterday putting parts on the floor so I can't complain too much......