Calling Bill Boehme -Question on constant torque monitoring

[Roger Chandler]

Hi Bill,

On the Grizzly Go698 thread there was a post from someone who just bought a Laguna 18x47 lathe, and they asked about the Laguna version vs. the Grizzly version, and the reply was that Laguna's has "constant torque monitoring."

My question: is this a sales gimmick, and if not, how do they go about accomplishing this on their VFD? Would this explain the "pulsing/hunting" at low rpm on the Grizzly machine, if theirs did not have it?

Your time and expertise are greatly appreciated. By the way Bill, Laguna says on their video about their version of this lathe that they have an "encoder in the motor" for constant torque monitoring. Could this be the difference between the two, and the reason for the hunt at low rpm?

 

[Bill Boehme]

Hi Bill,

On the Grizzly Go698 thread there was a post from someone who just bought a Laguna 18x47 lathe, and they asked about the Laguna version vs. the Grizzly version, and the reply was that Laguna's has "constant torque monitoring."

My question: is this a sales gimmick, and if not, how do they go about accomplishing this on their VFD? Would this explain the "pulsing/hunting" at low rpm on the Grizzly machine, if theirs did not have it?

Your time and expertise are greatly appreciated. By the way Bill, Laguna says on their video about their version of this lathe that they have an "encoder in the motor" for constant torque monitoring. Could this be the difference between the two, and the reason for the hunt at low rpm?

Sorry about the slow response. I was in the hospital yesterday for a cardiac catherization and I am limited on my activities for a few days. They said no "surfing" for a while.

Using an encoder to provide motor speed feedback to the controller is certainly the ultimate in motor speed control. At the same time, I think that their marketing weenies have exercised more than a bit of literary license in the way that they have interpreted what their engineers might have described to them. Unless they have installed a load cell or strain gauge in the drive train, the best that they could possibly do is make a ballpark guess at torque since they have no way of knowing the moment of inertia of the load and can only estimate how much torque is used to overcome the resistance from the cutting tool. Furthermore, attempting to stabilize a control system using force (or torque) feedback is an invitation to frustration. Torque feedback is as noisy as heck and by the time that it is filtered enough to be usable, the phase lag makes it unusable. Besides that, monitoring torque is pointless -- if the speed can be regulated, then that is all that is important. While marketing hype like that is not uncommon, it is a turn-off to me.

 

[Roger Chandler]

Once again, great information Bill

Sorry about the slow response. I was in the hospital yesterday for a cardiac catherization and I am limited on my activities for a few days. They said no "surfing" for a while.

Using an encoder to provide motor speed feedback to the controller is certainly the ultimate in motor speed control. At the same time, I think that their marketing weenies have exercised more than a bit of literary license in the way that they have interpreted what their engineers might have described to them. Unless they have installed a load cell or strain gauge in the drive train, the best that they could possibly do is make a ballpark guess at torque since they have no way of knowing the moment of inertia of the load and can only estimate how much torque is used to overcome the resistance from the cutting tool. Furthermore, attempting to stabilize a control system using force (or torque) feedback is an invitation to frustration. Torque feedback is as noisy as heck and by the time that it is filtered enough to be usable, the phase lag makes it unusable. Besides that, monitoring torque is pointless -- if the speed can be regulated, then that is all that is important. While marketing hype like that is not uncommon, it is a turn-off to me.

Dear Bill,

Thank you once again for your expertise that helps the rest of us who are not trained as you are in the electronics field. You save us from being misled by claims and hype that go with sales.

I hope you will take it easy, and go slow as to getting back on track with your turnings. I hope that the medical folks who are attending to you will find the issues you are facing to be minor ones. I hope also that you will not need a pacemaker, defibrilator device, as some of those get interference with the electronics and motors on lathes and chainsaws.

One member of our local club had to have one implanted, and had to sell all his turning tools including his Jet 16/42 evs lathe.

Great to hear from you, and we will mention you in our prayers!🙂

 

[Bill Boehme]

Thank you very much, Roger. I had a triple bypass eleven years ago. The cardiologist said that this exam showed that my coronary arteries look to be in perfect shape which is really good news. I was not looking forward to the prospect of being "field dressed" again.

As far as the marketing hype for the Laguna, it is fairly benign. The owner can use it to brag to his buddies about this "feature" so that they can wish that their lathe also had "it". Tool envy, being what it is, is not something to be ignored by marketeers.

 

[Roger Chandler]

Thank you very much, Roger. I had a triple bypass eleven years ago. The cardiologist said that this exam showed that my coronary arteries look to be in perfect shape which is really good news. I was not looking forward to the prospect of being "field dressed" again.

As far as the marketing hype for the Laguna, it is fairly benign. The owner can use it to brag to his buddies about this "feature" so that they can wish that their lathe also had "it". Tool envy, being what it is, is not something to be ignored by marketeers.

Bill,

touche'

 

[Bernie Weishapl]

Bill glad things went well for you. Take it easy and don't rush things.