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- Thread starter DavidR8
- Start date
TorontoBuilder
Ultra Member
I dont wanna get banned or executed by one of his fanboys so I'll hold my tongueThe greatest man alive today? Then we agree
to dissipate the back current during braking of heavy load on the lathe so you dont fry a VFD
When I had my mill running on 3-phase the internal braking resistor was not large enough for the energy produced when I stopped the mill. I had to set the braking very low to avoid tripping the vfd
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I have installed dozens in to the hundreds of vfds and inverter systems. Only time I have ever used an external break was on winch systems to support loads or mill grinders. If the vfd is sized properly and programmed for the load there should be no need to have an external brake. Are guys stopping the motor with the vfd or a mechanical brake? This problem sounds more like a line reactor issue than braking.
I think @TorontoBuilder nailed it. But given your followup question, I think it would help to provide a few more details.
The need for external braking is a mid-size lathe concern for lathes in the 10 to 14 inch swing size. It may also apply to some smaller and bigger lathes.
These lathes don't always include a foot brake. But they always have a huge gear, shaft, chuck, and rotating part mass that does not wind up very quickly and NEVER stops fast enough in an emergency.
This does not apply to mills or small lathes or big lathes or a hundred other machines. It might apply to a big shaper with a big flywheel though, and I'm sure there are others.
The bottom line is that a VFD cannot stop the inertia of a large rotating mass fast enough in an emergency situation. The need is for an external resistor to handle the large back current associated with a fast emergency stop.
This isn't about holding a load on a winch, it isn't even about stopping the lathe. It's about stopping it FAST in an EMERGENCY.
It takes about 10 seconds (WAG) to wind up my lathe at its highest speed with a heavy chuck and a big part. And maybe 4 times that to stop it. If something goes wrong, I don't want to wait 30 seconds or more while my lathe is winching in a critical body part or thrashing my ways to shreds with a part that bent in my jaws.
I want two stops for my system. A normal stop that applies normal stopping forces, and an emergency stop that almost breaks the gears to stop as fast as possible.
I think you would instantly understand if you stood in front of my lathe with a big part in my big chuck running at high speed.
I echo @Susquatch sentimements.
The 3-jaw chuck on my 12x36 probably weighs 20 lbs. Add the drive train and a 5 lb part and spin it all up to 1200 rpm and that's a lot of rotational inertia.
I'd like that to come to a stop in under two seconds. I expect that requires a pretty significant amount of force and will absolutely require an external braking resistor.
The 3-jaw chuck on my 12x36 probably weighs 20 lbs. Add the drive train and a 5 lb part and spin it all up to 1200 rpm and that's a lot of rotational inertia.
I'd like that to come to a stop in under two seconds. I expect that requires a pretty significant amount of force and will absolutely require an external braking resistor.
My go-to CDN supplier of motors and drive is https://www.emotorsdirect.ca/motors
TorontoBuilder
Ultra Member
For those people lacking imagination, google can find you gruesome videos of why it is beneficial to have the ability to rapidly stop your lathe. Or for someone else to do it while you're being pounded into ground round.
I've read many a safety thread where commenters claimed this type of thing only happens in 3rd world countries and/or to the dumbest darwin award winners, but this is a fallacy I guess they tell themselves so they can approach their lathes without too much butt pucker.
The reality is that lathes are inherently dangerous, so operators should enact as many controls as they can to protect their safety.
A lathe or shop accident can happen to anyone, even well respected, skilled and knowledgeable workers. Look how many youtube stars are missing digits.
Accidents will likely be the result of your getting lax on precautions of a lapse of concentration from fatigue...
In Alberta the appeals court just ruled against a calgary firm whose employee died while polishing a piece on a manual lathe. The company failed to protect workers and their actions were partly responsible for the death of their employee.
calgary.ctvnews.ca
I've read many a safety thread where commenters claimed this type of thing only happens in 3rd world countries and/or to the dumbest darwin award winners, but this is a fallacy I guess they tell themselves so they can approach their lathes without too much butt pucker.
The reality is that lathes are inherently dangerous, so operators should enact as many controls as they can to protect their safety.
A lathe or shop accident can happen to anyone, even well respected, skilled and knowledgeable workers. Look how many youtube stars are missing digits.
Accidents will likely be the result of your getting lax on precautions of a lapse of concentration from fatigue...
In Alberta the appeals court just ruled against a calgary firm whose employee died while polishing a piece on a manual lathe. The company failed to protect workers and their actions were partly responsible for the death of their employee.
Calgary company convicted in fatal 2019 workplace incident loses appeal
A Calgary company that appealed its convictions and associated fine for its role in the death of one of its workers has been denied by the court.
BaitMaster
Ultra Member
@djberta I’m in a similar camp as a pro industrial/automation electrician…. I can’t even count the number of VFD’s I’ve had to do with…..
But…. From my experience fixing machine tools and other extremely high inertia loads on OEM equipment (not my design) I have run into braking resistors more than a handful of times. It’s not unheard of, and has the benefits the fellas listed above. Basically takes the extra dc bus voltage and fires it through the resistor.
But…. From my experience fixing machine tools and other extremely high inertia loads on OEM equipment (not my design) I have run into braking resistors more than a handful of times. It’s not unheard of, and has the benefits the fellas listed above. Basically takes the extra dc bus voltage and fires it through the resistor.