VFD, A question for the manufacturers....

[Reed Gray]

I keep thinking back to a demonstration that our club had, and the lathe was a Nova DVR. The turner was unfamiliar with the lathe. He put a piece between centers and started the lathe up. It was at high speed, and he hit the off button. He fired it up again, and hit the ramp down button, which if you are familiar with the DVR, is very slow to respond. The piece came off the lathe, going up in the air. No injuries. Yes, he should have checked start up speeds first, but he didn't. The question I have, is would it be possible with all the electronic gadgets out there to make a variable speed lathe that automatically goes back to 0 rpm when you turn it off? It could be a huge safety thing, especially in class room situations where there are many people using the lathes, and you don't know who used it last, and like most of us at one time or another, have left it at a higher speed when you stopped the last project, and just don't get around to adjusting the lathe speed down.

Yes, a dial indicator would not give a speed range, but for me, I am used to that as I have never owned a lathe that had a read out. Since that is some thing that most lathe companies are adding to their lathes, it should be fairly simple. Not really an inconvenience because the twist knob can go up quickly, and we all comment on "I just turn the speed up till it vibrates, and then back it off a bit" for how we choose speeds.

robo hippy

[Mike Cruz]

Maybe not a horrible idea... I know my PM90 has a feature that it must be in the START postition for the switch to work. Now, for it to be in the START position, that means the handle (not a digital knob) must be rotated to that position...which you can only do with the lathe running (Reeves drive) or while turning the spindle by hand with the hand wheel and rotating the handle at the same time. Since I'm a one man shop, not a school, I deactived that "safety" mechanism. I have a poteniometer to control the speed digitally when I want, and I must say that the lathe responds immediately, so I'm surprised to hear that on the new lathes there is a "lag" time. Also, my VFD is programmed for soft starts. I set it to get to maximum speed (whatever the lathe is set to run at) in 4 seconds, I think. So, there is a little time to realize when you've turned it on, but that the speed is too high.

I assume you are talking about the VFDs that are on new lathes and not aftermarket (like mine). It would be interesting if the VFDs on the new lathes were user programmable...

[Clint Baxter]

The DVR is one that is slow on the speed changes, but that is not common to all the newer lathes. I have one and like it a lot, but that is one thing that is an annoyance, the lag time in speed changes. The lathe does do immediate changes to its preset speedsand i do use that for the majority of my speed changes. There just aren't enough of those presets however. That is one of the advantages on the new 20" Nova, with 10 preset speeds whereas the 16" DVR has only five. the DVR will return to the default speed of 500 rpm if you turn off the power switch instead of just powering it down via the keypad.

As such, I'm sure it is a possibility to set up these VFDs to return to a pre-determined speed each time they're shut off. I I would assume it is just as much a possibility to make this a feature that could also be deactivated for those of us who don't need or don't wish the feature.

I do like the idea but admit, it could be annoying on the Nova, with it's slow speed changes. However, you got to admit, the DVR may be slow, but it beats changing belts any day.

Clint

[Bob Hamilton]

As Clint said, the DVR does default to 500 rpm if it is switched off at the power switch rather than simply stopped from the keypad. I don't think I would want a lathe that reverted to low rpm every time I stopped to inspect my progress.

Bob

[Reed Gray]

I thought the specs on the DVR had been changed so that the off speed was at 200 rpm.

The thing with the dial compared to switches, is that ramp speed is almost instant. The 10 pre set speeds on the new DVR is better than 5, and with the pre sets, you could just push the button. One simple step. Main reason for bringing this up is trying to figure out if it is a safety feature that would be worth while on lathes. As a production turner for years, it would take no time to adjust to the 'new' feature.

robo hippy

[Ralph Lindberg]

I thought the specs on the DVR had been changed so that the off speed was at 200 rpm.

The thing with the dial compared to switches, is that ramp speed is almost instant. The 10 pre set speeds on the new DVR is better than 5, and with the pre sets, you could just push the button. One simple step. Main reason for bringing this up is trying to figure out if it is a safety feature that would be worth while on lathes. As a production turner for years, it would take no time to adjust to the 'new' feature.

robo hippy

Every DVR I have worked with defaulted to 500 RPM. The newer DVRs and all DVR-XP's have 5 preset speeds (older DVRs don't, the club's didn't, until I upgraded the mother board during a fix).
If it is set-up for 5 preset speeds (or 10 with the new one) many people do not know how to quickly change speeds.

To date not one demonstrator has wanted to learn how to access the presets.

[Dick Strauss]

Reed,
Most aftermarket VFDs have a ramp setting for starting and stopping. I set mine to take 2-3 seconds (I think 2 sec is the default) depending on the machine and the loading. This allows for enough time to slow the machine down if it starts going too fast. It is also a good idea to have it slowly ramp down when stopping to prevent faceplates with heavy work from unscrewing themselves on the lathe. I agree that manufacturers should allow users to change settings as long as it won't harm the lathe and force manufacturers to fix abused lathes under warranty (I don't think it should void the warranty assuming you don't go outside of a manfacturer defined reasonable range). In other words, if you constantly run your lathe motor at 300Hz because you don't know better and the bearings wear prematurely, I don't think the manufacturers should be responsible for user stupidity.

I guess I can see why the manufacturers lock the setting to keep people from ruining the lathes during the warranty period.

I also use both an emergency stop and foward/off/reverse switch. It takes a little more thought and reminds me to check the speed as well.

Mike,
You can change the speed of reeves drives without turning on the machine. You need to turn the lathe spindle with one hand by the handwheel/chuck/mounted piece while shifting the speed of the reeves mechanism. It isn't easy at first but becomes second nature after a while.

Take care,
Dick

[Mike Cruz]

Sorry, Dick, maybe I wasn't clear enough, but yeah, I know you CAN do it by hand, but it time consuming and can be a little less than fun. A LOT easier to just disconnect that mechanism... Especially when you are starting and stopping often. But thanks for the tip. I'd rather you tell me something I already know than keep it to yourself in fear of offending me...thus keeping life's little secrets from helping people out. Again, thanks.

[Dick Strauss]

Mike,
I definitely didn't mean any offense and no offense was taken. The reeves drive machines usually say something like "do not change unless the machine is running". People take this too literally. I thought maybe I'd save someone a minute of dismounting their chuck, adjusting the speed, and remounting everything.

[Mike Cruz]

Likewise, no offense taken... I was just 'splainin' myself. No worries. Again, I'd rather you state something (no matter how obvious it might seem) than not say anything at all. I like to think I'm pretty observant and figure things out and don't need to be told the plain as day things that are staring me in the face...but my wife will roll her eyes and tell you differently! :D I've had the fridge door open, a gallon of milk not foot from my nose, and asked my wife where's the milk...I can't find it! :o Again, no worries. Tell me which end of the bowl gouge to use...I might know, but I won't be offended. ;)

[neil mackay]

The question I have, is would it be possible with all the electronic gadgets out there to make a variable speed lathe that automatically goes back to 0 rpm when you turn it off?

The short answer is yes, the long one is it will probably cost considerably more and it will be more complex to progam. As an example of price it could well rival the actual price of the DVR.