Lathe Purchase advise

jtorral · Nov 9, 2018

First of all, this is my first post on the forum and am looking forward to being an active member.

So here is my dilemma.

I have a 12 x 36 lathe with a 3 phase 1.5 HP 10AMP motor getting ready to ship to me next week. After shopping around for a decent RPC, I narrowed my selection to the American Rotary AD-10 phase converter which is 10 HP and will do a startup of up to 28 AMP draw. The cost of the RPC is 950.00 lets just round up to 1k.

Having said that, I can step up to the 13 x 40 version of the 12 x 36 late but with hardened gears in the head and a single phase motor for an additional 1500.00. However, I wouldn't need the RPC.

What makes the decision difficult is that I don't really have a need for the 40" lathe. Don't think I will turn anything that large. But it will only set me back 500.00 for the upgrade.

Would you keep the 12 x 36 or do the 13 x 40 for an additional 500.00?

JT

HuFlungDung · Nov 9, 2018

I think you will never curse having too much capacity. Having to run a RPC is not a plus either, but having a 3 phase motor could be beneficial if you happened to run it from a VFD, because then you'd have some exciting features available like variable speed (nice for facing) and dynamic braking (with a braking resistor).

Bobw · Nov 9, 2018

Why do you need a 10hp phase converter for a 1.5hp motor??

Have you ever had to use a RPC.. They suck... In my experience, they are loud,
obnoxious, power hogs, and its one more thing to turn on and off and one more thing
to break (had a bunch of start caps go out on several of them).

I would jump through many many hoops to not use an RPC ever again in my life, even
going so far as using a water wheel and a line shaft...

A VFD to run that machine wouldn't cost you all that much, and bring some nice control
and flexibility, and they aren't loud power hogging pieces of crap.

On the other hand.. Bigger is always better.

jtorral · Nov 9, 2018

Thanks for the replies.

The reason for the 10 HP RPC for a 1.5 HP motor is the startup surge on the motor draws almost 15 amps. The 5 hp rpc has a max of 7.5 amps

I am looking into a VFD option for cost savings and fine control of speed.

Bobw · Nov 9, 2018

jtorral said:
I am looking into a VFD option for cost savings and fine control of speed.

And you can set up a soft start, so you don't get the big current draw like with a
simple on/off switch.

Bob-J-H · Nov 9, 2018

An RPC will handle that surge. I put a DC motor on my lathe. I don't like hearing the RPC either.

72bwhite · Nov 9, 2018

I run my 3hp lathe off a 7.5 rpc because that's what I had.
funny thing that 7.5 is much louder then my 40hp one
but the 40 is for the qt10 and it grunts for a second when the spindle spins up.

but you would never regret having the ever so slightly larger lathe.

Bobw · Nov 9, 2018

72bwhite said:
but the 40 is for the qt10 and it grunts for a second when the spindle spins up.

Slow the spindle ramp down a bit. My QT20, when I was running RPCs, I had to slow
the ramp all the way down to 5 seconds to even get the spindle to spin.. And
even at 10 seconds, it wouldn't start at all in high gear. My lathe is OLD, she's
a good girl, but she's OLD, and the default was 0.2 seconds I think.. Even if you
spread it out to a half a second, it should drop that spike down a bit, might even
extend the life of your spindle drive a bit.

The day I had 3 phase put in was a glorious day.. I got to run that lathe in high
gear for the first time.. It was AWESOME!!!!!

Jaxian · Nov 9, 2018

Have to say, if your RPC is loud it's a piece of junk. I have two American Rotary RPC's, one a 20hp and one a 75hp. They are about as loud as a microwave. I can't hear them over the enclosure fans on the CNC's much less when they are cutting.

Also a good RPC, say an ADX series, will have a CTR setup. Mine is 6x FLA with no voltage change. It works perfect. Compressor on/off, TSC on off, other machines taking cuts, never a drop.

Also if you buy the right one it's a lifetime warranty.

So really, if you want a RPC, just don't buy a piece of junk or make it yourself and you will be fine.

The same capacity Phase Perfect was 3x the cost and with only a couple year warranty. They are great but not 3x better than a quality RPC.

Just my opinion.

72bwhite · Nov 9, 2018

No need to do that Bob
that's just the only time it draws much, even then the 40 is still quieter then the 7.5
at idle
3phase would be nice but Edison won't do it for my garage.
now a phase perfect would be nice but I'm cheap.

Vladymere gr · Nov 9, 2018

I have a multiple 3 phase devices in my shop. All 2HP or less. One RPC feeding a 3 phase breaker box runs all of my devices. The RPC is home built and is using a 5HP motor. No grunt when devices start and not that loud.

Below is a photo of my RPC set up. Single phase breaker box on the left and RPC stuff on the right.

Vlad

PeteM · Nov 9, 2018

JT - Rotary converter questions aside, I'd consider spending the extra $1500 for the larger lathe. Some reasons:

1) If it has hardened gears and bed, that's a significant plus.

2) Could be better ergonomics - larger dials and the like?

3) Infinitely variable speeds (VFD) will come in handy.

4) The smaller lathe may have 6" chucks, the larger 8". Even if you want to turn something just 6" in diameter, you'll want the larger chuck.

5) Likely a larger through hole. There will be times if you have 1 3/8" you desperately want 1 1/2". And if you have the 1 1/2" . . .

6) Likely heavier castings, wider bed, greater rigidity.

7) While 36" capacity will work for most home shop stuff, you'd be surprised how quickly capacity gets used up. Say you want to put a pretty deep hole in the end of a 30" piece. By the time you put your center rest in place, add a tailstock chuck, and grab a taper length drill -- you're out of space with 36" and still (almost) in business with 40" between centers.

8) Between the VFD and the larger size, likely a lower RPM. Sometimes handy for threading to a shoulder, winding springs, etc.

If none of that applies, you can probably buy a $400 VFD that will run your 1.5 hp motor. Or, a 5hp rotary converter. Beside the cost and slightly larger space requirement the one downside to the larger lathe might be a lower top speed. Of possible concern if most of your work is really small.

Danny VanVoorn · Nov 9, 2018

HuFlungDung said:
I think you will never curse having too much capacity. Having to run a RPC is not a plus either, but having a 3 phase motor could be beneficial if you happened to run it from a VFD, because then you'd have some exciting features available like variable speed (nice for facing) and dynamic braking (with a braking resistor).

I don't understand how variable spindle speeds on a lathe are a benefit? It's like an urban myth that hasn't been proven or even thought through but people seem to buy it!
Unless you have variable feed rate also then the surface speed only changes if you can change a feed gear, not practical on the fly. Now a lathe like a Hardinge with both variable feed and speed can be dialed in to hold a constant surface feed rate.
Dan

PeteM · Nov 9, 2018

Danny VanVoorn said:
I don't understand how variable spindle speeds on a lathe are a benefit? . . . Dan

While not a game changer, it can be handy in a number of ways:

1) The speed steps between many lathes are pretty far apart. For production work (multiples) it allows the right speed. For one-offs it lets one tune the speed to avoid chatter, resonances, or just get to a place it sounds and feels (and cuts) right. A change in speed can also sometimes be the difference between a c-chip and long strings.

2) Lots of times you want a lower low speed, and not necessarily with a ton of torque. VFD can cut the low speed in half or more.

3) The previous poster mentioned facing. It's handy enough to roughly keep a somewhat constant speed (and thus change the effective feed) as one goes from very high speeds at the periphery to near zero at the center. Could easily cut the time of a cut in half, assuming you started with a max good or safe FPM at the periphery and just left it in place throughout the cut. 500 SFPM at the periphery of a decent sized disk ends up near zero by the time you're down to a nub at the center.

steve45 · Nov 9, 2018

Danny VanVoorn said:
I don't understand how variable spindle speeds on a lathe are a benefit? It's like an urban myth that hasn't been proven or even thought through but people seem to buy it!
Unless you have variable feed rate also then the surface speed only changes if you can change a feed gear, not practical on the fly. Now a lathe like a Hardinge with both variable feed and speed can be dialed in to hold a constant surface feed rate.
Dan

Ummm... No. The slower the spindle speed, the slower the surface speed. Yes, the ratio of revolutions to feed rate is the same, but the speed of the surface is simply the RPM x circumference. I have a Tachulator on my lathe that allows me to input a radius and read surface speed.

HuFlungDung · Nov 9, 2018

Danny VanVoorn said:
I don't understand how variable spindle speeds on a lathe are a benefit? It's like an urban myth that hasn't been proven or even thought through but people seem to buy it!
Unless you have variable feed rate also then the surface speed only changes if you can change a feed gear, not practical on the fly. Now a lathe like a Hardinge with both variable feed and speed can be dialed in to hold a constant surface feed rate.
Dan

The faster the spindle rotates, the faster the feed rod revolves without changing gears at all. You don't want to change the feed (in inches per rev) when you speed it up and an ordinary lathe does this for you.

Mr-Mike · Nov 10, 2018

-AR makes an excellent product. If you have a noisy one, lube the bearings and tighten-up the screws on the body. Also, don't use the fittings, pull the armature and hit the bearings directly. This things are whisper quite
-I have a 5hp AR model. I recently picked up a 3hp Lagun. Figured I would try run it. The 5 starts and runs it all day long no problem (even though the max start rating is 2.5hp)
-I don't see how running a 50/60 hz motor at 20hz or 40 for that matter, provides maximum torque consistently - no thanks VFD...
-Pretty sure your talking about Chinese crap. Stay away is my advice.

HuFlungDung · Nov 10, 2018

Mr-Mike said:
-AR makes an excellent product. If you have a noisy one, lube the bearings and tighten-up the screws on the body. Also, don't use the fittings, pull the armature and hit the bearings directly. This things are whisper quite
-I have a 5hp AR model. I recently picked up a 3hp Lagun. Figured I would try run it. The 5 starts and runs it all day long no problem (even though the max start rating is 2.5hp)
-I don't see how running a 50/60 hz motor at 20hz or 40 for that matter, provides maximum torque consistently - no thanks VFD...
-Pretty sure your talking about Chinese crap. Stay away is my advice.

That's true, you lose torque with a non-vector drive VFD when running much below the motor's rated speed. But, you've still got all the gears available provided in the lathe headstock, so you've got plenty of ranges to work in. And not every cut is a monster cut, so you can often make do with less than full motor hp on a cut. You can also overspeed the motor in a given gear, so you've got full hp available above 60hz. While the torque still drops off above 60hz, for the most part, you're machining at smaller diameters and this requires less torque. I imagine there would be a learning period while one learns what power is available in every gear.

I don't even have a manual lathe with a VFD, but I can see the advantages. If I was serious about it, I'd put an encoder feedback vector drive VFD. That will provide constant motor torque down to a very low frequency. I did this to a cnc mill retrofit I did years ago. Made low rpm tapping doable without stalling the spindle all the time.

Lathe Purchase advise

Plastic

Diamond

Diamond

Plastic

Diamond

Hot Rolled

Titanium

Diamond

Stainless

Titanium

Hot Rolled

Attachments

Diamond

Titanium

Diamond

Stainless

Diamond

Aluminum

Diamond

Similar threads