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Other Safeties Use them or Not?

thestelster

Ultra Member
Premium Member
On that topic, what is the deal with vfd's and brakes ? I thought I read you need a special type of VFD, or maybe an external resistor for the VFD to handle the sudden stop of the brake. Is that correct ?
On my VFD's, they do have a certain amount of braking you can set internally, but if you have a heavy load, i.e. a big chuck, it won't help. You have to get an external resistor. I plan on getting these resistors for my lathe and mill. They would be greatly advantageous when performing metric threads on the lathe (where you can't disengage the half-nuts), or power tapping on the mill.

And I would think if you had a emergency stop button utilizing the external resistor for maximum braking, that would be the safest. I read, depending on the load and resistor, you can stop the spindle in less than one revolution.
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
On that topic, what is the deal with vfd's and brakes ? I thought I read you need a special type of VFD, or maybe an external resistor for the VFD to handle the sudden stop of the brake. Is that correct ?

I agree with @thestelster on this. I dunno about what others say about stopping in 1 revolution though. Maybe at 70rpm but call me a Doubting Thomas at 2500.
 

thestelster

Ultra Member
Premium Member
DIY lathe foot brake.
That's pretty cool. Though I use the space under the lathe as storage. A couple of moving dollies that holds my lathe chucks, and the compound slide, and milling attachment. Plus, that foot pedal would always be right in my way when I have to lean over the lathe to get close when working on small parts.
 

phaxtris

(Ryan)
Premium Member
Premium Member
I have the internal braking set up on my lathe VFD, I think they all do that to an extent, but I thought there was something you needed to do when you attach an external brake
 

thestelster

Ultra Member
Premium Member
I have the internal braking set up on my lathe VFD, I think they all do that to an extent, but I thought there was something you needed to do when you attach an external brake
You have to enable DC braking in your settings, and on my VFD, you can control the wait time, frequency setting, deceleration force and times, and a couple of other parameters.
 

phaxtris

(Ryan)
Premium Member
Premium Member
You have to enable DC braking in your settings, and on my VFD, you can control the wait time, frequency setting, deceleration force and times, and a couple of other parameters.

Yea I understand that, I do have it set up in my VFD, I am talking about external braking, like a foot brake
 

thestelster

Ultra Member
Premium Member
Yea I understand that, I do have it set up in my VFD, I am talking about external braking, like a foot brake
Oh, sorry, I misunderstood. I would think that if you plan on incorporating a foot brake, that it should also trigger an emergency stop signal to cut all power and signal outputs from the VFD. I'm pretty sure all or most VFD's have a safe stop function.
 

phaxtris

(Ryan)
Premium Member
Premium Member
Oh, sorry, I misunderstood. I would think that if you plan on incorporating a foot brake, that it should also trigger an emergency stop signal to cut all power and signal outputs from the VFD. I'm pretty sure all or most VFD's have a safe stop function.

Yea I just thought I read you needed to incorporate some kind of special circuitry or a resistor, or something to deal with the excess current when the foot brake is actuated, I think it's more than just incorporating a trigger switch to the VFD

I may be wrong, but I believe I read that somewhere, that it's more than just telling the VFD the stop is actuated
 
Most VFD's offer limited braking because they do not have enough heat absorption built in. How the braking works is that the motor is treated like a generator and resistors are the load applied within limits.

DC injection also requires heat removal which is why it is not as effective. As a locking to hold a motor in the stationary position they are great.

As to tapping, if its CNC run a tapping mill cutter for better results and a larger size range as you are milling the thread. If tapping manually use a taping head, here HP & Torque is the limiting factor in size of the tap.

As to stopping the lathe go to the Grizzly site and download the manual for your lathe (closest model) if not find one with a brake. Take a look how they install it.

Most aren't that big as they are on the motor side where torque input is small compared to spindle output.

I love leveraging technology but don't over complicate simple applications.
 

JustaDB

Ultra Member
Do I use safeties? It depends. If they get in the way of what I'm trying to do w/ the tool, no. If they're not a PITA, they stay.
 
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