Vertical milling machine

[Noel]

Hello all, I'm contemplating on buying a JET JVM836. Does anyone out there own one and is happy with it or should I avoid it. I'm a hobbyist and will not use it for commercial production work. Would like to hear pros and cons or alternate recommendations. Thanks.
Noel

[doug]

noel

I'm going to buy a jet myself. but your
numbers are different than mine. I am going
to get 2hp 3phase. The only thing i know is
there made in Tiwain,most "knee" vertical
mills are pretty much the same. You can't do any havey machining on thoughs light machines. but you can do light work on a 2hp or 3hp. also 3phase is cheaper to operate.

doug

[Noel]

After reading your reply, I think I'll avoid the JVM836 Doug. My next coice is the JTM-1. I already have 3 phase power for my lathe. What are your thoughts on the JTM-1? Noel

[doug]

Noel

I have looked at them in person. There is
a Jet Outlet where I live. The real question
is how long will the bearings hold out. For
a home workshop I think you would want less
gagets. Its expensive to get anything fixed.
As to your question,I am going to buy a
jtm-1. I would like a 3 hp but can't afford
it. I would'nt worry,most machines are run
16 to 20 hours aday. Your not going to do
that.

Doug

[SGW]

I saw a JVM-836 a couple of weeks ago. It looks pretty good.

I have the JVM-840, which I bought about 16 years ago. It's no longer offered; the 830 or 836 seems to be the replacement.
The only complaint I have, after 16 years, is that the table is pretty soft and dents easily. Otherwise, it's been a very good machine. I think you'd be happy with the 836.

I might suggest that you get the 3-phase motor and a variable-frequency-drive for speed control. Even though my 840 has a two-speed motor (like the 836), lowest standard spindle speed is 192 rpm. With a decent-sized slitting saw that works out to 200 fpm cutting speed, which is pretty lively (about 2x what it ought to be, in fact). I got a surplus TECO-Westinghouse VFD a couple of months ago, and it's great. I can now get down to as low as 30 rpm.

See http://www.dealerselectric.com/ or http://www.vfds.com/vfdprice.htm, for instance.

[SGW]

P.S. I serioulsy doubt if you could possibly need more than a 1 hp motor on the JVM-836. It just isn't that big a machine.

Even a 1/2hp motor would probably be enough for anything you'd put on an 836. The motor on my JVM-840 is rated 1/2 hp at its lower speed, and I've never felt the need for more power.

[JimH]

I have the JVM-836. I am very happy with it, given it does not have a quill power downfeed and is limited to 5 speeds (with a max of 1550). Mine has the 1.5 HP motor (11/220 single phase). In a conversation with Jet they will void warrenty if a static phase converter (VFD) is used. The motor is not inverter rated.
I have had the motor go out on it (for unknown reason) and Jet had a replacement at my door in 2 days. (I won't go into what FedEx did to the replacement motor, as Jet had to send me a second replacement, again in 2 days).
I am currently considering a new lathe (to replace my Atlas Clausing) and Jet is at the top of my list. I suggest talking to Alley Supply Co in Nevada (look in HSM for ad). They have good prices, including shipping. They also like to talk about machines, features, and trade offs.
Jim

[SGW]

You can't use a VFD with a single-phase motor anyway.

[Noel]

JimH, do you know what caused the motor to burn up? Also, you got me curious now. What did Fedex do to your replacement motor?
SGW, thanks for you input. I was not aware that you couldn't use VFDs on single phase motors. While I already have a rotary phase converter for my lathe which I sized to also accomodate a mill in the future, I was planning to use a VFD to vary the speed of a three phase step pulley mill. I now wonder if Jet will allow this.

[SGW]

No, a single phase motor and a VFD wouldn't get along very well because of the starting circuit required in a single phase motor. Typically, the starting circuit drops out when the motor gets up to 80% of its full speed or something, so if you slowed down a single phase motor by any significant amount the starting circuit would stay engaged, not likely to be a good thing for longevity.

A three phase motor doesn't have that problem because the phase shift among the three phases makes the motor self-starting.

I see no reason why you couldn't use a VFD on your mill if it has a three phase motor. I've got one on my Jet mill; it works fine. Friends have VFDs on an assortment of machinery and have had no problems. I'm well past any warranty period so I don't have that to think about, but as best I can tell there is no particular reason why using a VFD on a three phase motor should be a problem, anyway. I imagine if you ran the motor bog-slow for an extended period, heavily loaded, it might complain, but you're not going to do that. Or if you cranked it up to some outrageously high speed well past its design limits you might have problems, but I can't imagine you're going to do that either.

[JimH]

Oops. I meant that if I was to replace the burned out single phase motor with a Jet 3 phase motor, could I use a VFD. They said Jet 3 phase motors are not rated for use with a VFD. If you read their ads and warrenty, they say "warrenty is void if used with a static phase converter".

I never did figure out why the first motor quit. I believe the the starting switch locked on, which popped the the capacitor. It did not smoke or get hot. Someday I'll figure it out, but for now, I don't care.

FedEx dropped the motor multiple times. The end cover was smashed against the fan (which was bent). The electrical connection box was smashed. The capacitors in the connection box were no longer round cylinders, they were eliptical. The exposed shaft had a good ding on the end of it.

Jim

[SGW]

A VFD is not the same thing at all as a static phase converter. A static phase conveter is basically just a capacitor that creates enough of a phase shift to get the motor spinning; then it drops out and the 3-phase motor continues to run on single phase power.
A VFD, on the other hand, produces a very good approximation of "real" 3-phase power, albeit of variable frequency, but there is no reason the motor should care about that, within reason.