Lathe - Variable speed versus Not

[zeeprogrammer]

I was doing a little dreaming of the day I can purchase a new lathe. This will happen when I retire or move to a new home...whichever is first.

I was looking at the G0602 and noticed a new offering...the G0752.

They are virtually identical except the G0602 has 1 of 6 speeds (150 to 2400 in steps) while the G0752 has variable speed (100 to 2000 and you can change speed while running). And the G0752 is about $350 more. Otherwise...all the same specs.

So my question is...what are the benefits/advantages of variable speed versus not (other than price).

P.S. It's now clear to me how the speeds are selected/changed on the G0602. I could use some clarification on that as well.

Thanks.

[philjoe5]

Zee,
Speeds are changed with belts and cone pulleys on the G0602.  When I bought mine 7 years ago the variable speed wasn't offered.  It's definitely worth the extra money because:
1.  You can run a spindle speed less than 150 rpm (G0602) which is useful for threading and essential for most parting
2.  If you're cutting different metal stock, steel, ally, brass, it's easier to adjust the cutting speeds
3.  With variable speed, you can rapidly hog off stock, then take a finishing pass at a slower speed, therefore, feed rate

Cheers,
Phil

[Jo]

I keep hoping that a certain gentleman will invite me up to have a play with his varispeed lathe  but clearly he doesn't think I will find it of any real value as despite all my  hints he refuses my advances (towards his lathe ) so he clearly lacks confidence and I promise I will be gentle with him his lathe 

More importantly the question should be: what is has the greatest advantage power feeds on the cross slide  , 2 or 3 channel DROs  or variable speed headstock  .

My personal view is don't waste money on fancy motor control, which is likely to go wrong, when a DRO is worth it weight in gold on lathe or milling machine And of course you really need independent variable power cross feed where the feed rate varies with diameter not the spindle speed 

Jo

[steamer]

I have a variable frequency drive on my Southbend, and a Variable speed mechanical drive via Salisbury clutch style expanding pulley and special belt on my Logan.

I have found the VFD to be completely free of all issues, while I regularly need to mess with the other mechanical drive.

I love my VFD as I can thread to a shoulder, and near the end....slow the spindle down to a crawl and stop at the point I want to stop....on the other drive, you have to turn it off in time for it to coast down to zero...

I don't know if this lathe you're looking at is a VFD or a DC drive.....but if it's Chinese circuits...I'd probably leave it alone, save my sheckles and put a real VFD on with an appropriate control box.    My VFD is fed from single phase.

Dave

[zeeprogrammer]

Thanks Phil. Yeah I'm more concerned with low speed rather than high speed.

Thanks Jo. A DRO is a given regardless of which way I (eventually) go. Hence not a question.

I don't know anything about power cross feed. A little searching leads me to understand it's great for facing and a post that talked a little about parting (if one has the courage).

Being pure hobby for me, it's not clear the benefits are worth it.

Are there other benefits?

Just saw your post Dave. Thanks. Are there good lathes in the $1000 to $1500 range with VFD? (I can't justify spending more on what will be pure hobby.) I probably wouldn't go the route of modding something like that.

BTW...regarding the DRO...I've been looking at magnetic (hall effect) rotary encoders. There's some interesting devices out there. One that provides up to 16384 counts per revolution...another that provides 1024 counts as well as quadrature and even brushless motor control signals. Anybody playing with these? AS5048, AS5040. There's also an AS5306 that can be used as a linear encoder.

[steamer]

I don't know Zee....The drive I have is about a $450 purchase, and a complete bolt on retrofit of the existing motor with a new control box.   ( you need to use a 3 phase motor)

But that was it.   Any standard lathe could easily be converted.

Dave

[Arbalest]

I guess I'm a bit old fashioned but I still prefer gearboxes and belts/pulleys. We had a variety of Harrison M300 lathes where I used to work (fantastic machines!) and even the latest brand new version didn't have any variable speed drive, just a traditional gear box for changing speeds. I can see the advantages for CNC etc but it becomes a little less clear for Manual machines, especially as VFD's still seem expensive to me. Far eastern machines also have a pretty poor track record for their circuit boards, a friend of mine has had three replacements on his mill. It would always worry me what I would do if the circuit board blew some years down the line. I guess the bottom line though is cost, cheaper to make a circuit board than a gearbox.

[AOG]

BTW...regarding the DRO...I've been looking at magnetic (hall effect) rotary encoders. There's some interesting devices out there. One that provides up to 16384 counts per revolution...another that provides 1024 counts as well as quadrature and even brushless motor control signals. Anybody playing with these? AS5048, AS5040. There's also an AS5306 that can be used as a linear encoder.

Are you thinking of some sort of rack and pinon on the carriage or sensing the rotation of the dials?  In ether case how would you deal with the backlash ?

Tony

[kvom]

My lathe is variable speed.  The main advantage as I see it is that it's quick to adjust without stopping when you get chatter or the chip color is off.   When parting off thick stock it's nice to be able to speed up when the tool gets toward the center.  CNC lathes can offer constant SFM, something it's hard to do manually.  We can only approximate.

At low RPM the torque drops off a lot, so I still have a bull gear.

[Jasonb]

Jo are you still hinting that you want to twiddle my knob? you know its broken once thats why im protective of it

I don't understand your comment about cross feed. Most quoted cutting sopeeds are based on periferal speed, on a large facing cut this woul dbe constantly reducing a sthe dia get less. Variable spee dallows you to increase the spindle speed as the dia reduces so keeping a constant cutting speed (actually I do understand, has something to do with a Hardinge)

Zee its not quite clear if that lathe has a DC motor which can suffer with loss of torque at lower speeds, over here the similar lathes have just started to be supplied with 3 phase AC motors with VFDs to get teh variable speed which don't suffer anywhere near as much.

Also be aware that its not 100-2000rpm at the turn of a knob, there are three pairs of pullys which give a range of speeds in each, mine has two sets and the variable gives me 50-950 or 100-1900.

I wrote this the other day as to why I like my variable speed.

" I would not want to be without my variable speed now. Its ideal when cutting threads using a die on the lathe, I can turn down a bit of hex to the required size at say 1000rpm then just back out the tool, bring up the tailstock, turn the speed down to 50rpm at the same time then run the thread down the part before stopping then running in reverse to back the die off at a faster speed then back upto 1000rpm to tidy the end with a file. Far easier than stopping the lathe, fitting a spindle crank, winding that to cut thread and then back it out.

Likewise when drilling a hole in stages, start with a small drill at full speed then just keep changing bits as you work up through the sizes to a big blacksmiths drill no need to keep stopping and moving gear levers or worse change belts"

J

[PStechPaul]

I agree that a VFD (and a three phase motor) would be the way to go, and use the belts and pulleys to get the maximum torque/speed combination. The VFD will allow the same torque at all speeds, but the lathe's components will determine what you get at the spindle. You should be able to buy a 2 HP 3 phase motor and similar VFD for less than the $350 additional for the variable speed lathe.
 
My similar size 9x20 lathe uses a 4 pole single phase 3/4 HP motor, 1790 RPM. With a VFD you can overclock it to get twice the speed, with less torque.
 
Another option I would possibly consider is using a 90V or 180V treadmill motor and controller. You can often find them in 1 or 2 HP for $50 or so. The speed control would not be as precise, but maximum torque might be impressive.
 
Customer reviews for the G0602 seem pretty good:
http://www.amazon.com/Grizzly-G0602-Bench-Metal-22-Inch/product-reviews/B000M67TJ2
One of the reviews of the G0752, not so much:
http://www.amazon.com/review/R1V36CL6OU7ZIA/ref=cm_cr_pr_viewpnt#R1V36CL6OU7ZIA

[Arbalest]

I forgot to mention, the first job I had lined up for my new Lathe when I bought it was to do something I'd not done before - cut a thread on it. The minimum speed of the Lathe was 180 rpm which seemed far too fast for me so the very first job ended up being to turn a new, smaller, motor pulley. I managed to get the speed down to 100 rpm without too much bother. The pulley is still on there now.

[steamer]

I just cut a 11/16-24 thread in stainless with the VFD....it was really nice to turn up to the shoulder at about 20 rpm, then stop exactly where I wanted, retract the tool, switch to reverse and back out at about 500 rpm...never unlocking the half nut......sweeet!


I cut a 1/2-20 thread with a die and did pretty much the same thing here

<a href="https://www.youtube.com/watch?v=WJSs7rsrA7s" target="_blank">http://www.youtube.com/watch?v=WJSs7rsrA7s</a>

[mklotz]

On-the-fly speed adjustment sounds great (facing large pieces, stopping chatter, super fine finish,  etc.) but like some others here I don't trust electronics and doubly so for far eastern electronics.

With a VFD you're not dependent on a long-out-of-business supplier to repair/replace your motor controller board. 

Power crossfeed is a real blessing when facing large pieces.  It's also nice if you intend to mill on the lathe.  That practice is more common abroad than here in the States so it's not a deal breaker for you, Zee.

[steamer]

On-the-fly speed adjustment sounds great (facing large pieces, stopping chatter, super fine finish,  etc.) but like some others here I don't trust electronics and doubly so for far eastern electronics.

With a VFD you're not dependent on a long-out-of-business supplier to repair/replace your motor controller board. 

Power crossfeed is a real blessing when facing large pieces.  It's also nice if you intend to mill on the lathe.  That practice is more common abroad than here in the States so it's not a deal breaker for you, Zee.

Amazingly enough....I completely agree with Marv!....  Don't worry Marv...I won't do it too often.

My VFD has been awesome....wouldn't go with out it now.

Dave