VFD upgrade

killswitch505

killswitch505

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Howdy from New Mexico!!! I've been a member for a while do a lot of lurking only posted a few times. I've decided to do a VFD upgrade on G4016 lathe. with the hopes of getting better results and not as much stress while threading to a shoulder also maybe some cleaner threads by going from single to 3 phase. So naturally I've a few questions that i haven't been able to find by searching or I didn't want to bump an old thread wanting to get more in depth.

• gear changing, I thread at my lowest speed (70 rpm) 90% of the time. I'm almost always Threading up to a shoulder. Say if I want 30 rpm would I set the speed at 70 and adjust with the VFD from there? I've read a few places where guy just leave their lathes at say 700 rpm because that's the fastest they usually turn their machines and leave it in one speed. That seems to me like it would would or could cause excessive wear on that particular gear set. My thoughts are to switch gears to get to the closest rpm range that I can a fine tune it from there to hopefully get more gear life.

• dynamic braking and ramp start, I picked up a brake resistor for my drive. I've read where guys install them and like using them and I've read where guys think they tear stuff up due to back lash. I'm sure I will end up play around with the settings but I was thinking maybe a stop it on a 3-4 second curve and maybe at 5-10 second start?

•this is a little off subject and I know I could have done some research but if I'm posting I might as well ask. I'm installing a coolant system. I'm coping a diy I found on YouTube 5 gallon bucket and fish pump. some of y'all might have seen it. My question is what are y'all using as far as water soluble oil? I did a bit of research on this and pick up what had the best reviews on amazon, Sta-lube anti corrosive soluble oil it's a CRC company I've used a lot of their products and like what I've used. I'm not opposed to using something better. Also I was wondering if y'all are using anything to keep the water from getting funky and nasty I've seen where people are using chlorine tablets I can not see where that can be good at all I've also seen where guys don't use anything at all. I was thinking maybe a UV light like they use in hot tubs. Am I wasting my time worrying about this?

Thank you in advance

Dennis
 
I can't comment on your VFD questions because I don't have a lathe with a VFD. On the subject of coolant I use Rustlick 5050 in my milling machine mixed at 35 to 1. I haven't had any issues with rust and I don't use additives. Still smells the same as the day I put it in.

Tom S.
 
Thanks for the reply Tom I will have to check that out if I don't like the results with the crc stuff
 
Hi Dennis, can't comment on water-based coolant, can comment on VFDs.
Running in a high gear and setting the VFD to get a low spindle speed has a couple of disadvantages, reduced torque at the spindle is one as you don't get the multiplication the gears would give (the motor power is torque x RPM, torque is related to motor current which has a maximum the VFD can supply, another limit the motor can take before the Magic Smoke escapes - so half speed, max current gives half the motor HP)The other is that the motor is likely cooled by an integral fan and the airflow drops with the square of the speed - half speed, a quarter of the cooling... If you plan to run at low VFD frequencies add an external fan/blower to keep the Magic Smoke inside!

Dave H. (the other one)
 
British Steel said:
the motor is likely cooled by an integral fan and the airflow drops with the square of the speed - half speed, a quarter of the cooling... If you plan to run at low VFD frequencies add an external fan/blower to keep the Magic Smoke inside!
Click to expand...
When I read this it looked wrong to me. I remember being told it was the cube of speed. So I looked it up and apparently we're both wrong.
http://www.rotron.com/techcorner/fan-laws.aspx
The most common change made to a fan is that of altering its rotational speed. For a given speed change percentage:

  • Flow change is directly proportional.
  • Pressure changes by the square of the proportion.
  • Power changes by the cube of the proportion.
Click to expand...
That being said, I definitely agree about adding dedicated cooling if running for long periods at low speed.
 
killswitch505 said:
• gear changing, I thread at my lowest speed (70 rpm) 90% of the time. I'm almost always Threading up to a shoulder. Say if I want 30 rpm would I set the speed at 70 and adjust with the VFD from there? I've read a few places where guy just leave their lathes at say 700 rpm because that's the fastest they usually turn their machines and leave it in one speed. That seems to me like it would would or could cause excessive wear on that particular gear set. My thoughts are to switch gears to get to the closest rpm range that I can a fine tune it from there to hopefully get more gear life.

• dynamic braking and ramp start, I picked up a brake resistor for my drive. I've read where guys install them and like using them and I've read where guys think they tear stuff up due to back lash. I'm sure I will end up play around with the settings but I was thinking maybe a stop it on a 3-4 second curve and maybe at 5-10 second start?
Click to expand...

A machinist friend converted his Grizzly G4003G lathe to VFD with brake resistor. If I recall he has this set to stop in about 1 sec. This does not seem abrupt. I think 3-4 sec is not much different than the time to stop before he did the VFD upgrade. Ramp start may be 2 sec.

A friend of the friend liked his VFD upgrade, he asked my friend to help him with a VFD upgrade including brake resistor. This fellow machines precision gun/rifle barrels so also does a lot of threading to a shoulder and wanted the ability to get slower speed and more control of stopping the thread. If I recall, his lathe was set to similar stop/start times when we left.

The start/stop times are adjustable in the VFD settings. I would try various times. You will soon find settings which feel right for your needs.
 
We can get maybe a rpm or less with ours not in back gear vs slow speeds possible.

Set lathe for natural speed most commonly used and use vfd to vary from there.

For threading shift lathe to lowest speed and further down with vfd.

Add a stop pedal or brake bar so easy stopping with foot

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 
The 4016 being a gear head, speed changes are pretty easy - my lathe has 6 speeds each in backgear and direct, other than backgear in/out can shift while running so I tend to use the VFD for fine adjustment, jogging and when I need to go overspeed (2500 on a lathe designed to do 1500) - it DOES go to 2 RPM with the VFD wound right down, but there's not a huge amount of torque and it seems to 'cog' a bit, I only use it for toolpost grinding / milling where another tool does the hard work!

What I have found useful is a slider pot on the cross-slide controlling VFD frequency that ramps up as the tool approaches centre, useful to maintain "near-constant" surface speed, which helps get an uniform finish and helps with parting off.
 
Now that is a clever idea!

Like an automatic speed control for easy setup.



Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 
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