View Full Version : Lathe accuracy

08-21-2004, 08:06 PM
I have been reading in another forum on some hard to believe claims on lathe accuracy. The lathe in question being a Monarch 10EE.

I have never seen a Monarch lathe and don't know if any were even imported here as I have never seen one for sale secondhand either but why would such a supposedly incredibly accurate and expensive lathe be made when I assume grinding would be a much cheaper and faster option to produce the same results.

See Ya

08-21-2004, 08:40 PM
Ringer: I've been involved in some of those discussions and yes, you can believe the accuracies mentioned. The Hardinge HLVH is in a similar class but with a little less mass.

Monarch has been in Ohio since 1909 and even after changing hands, splitting up, etc. AFAIK the manual lathe division is still somewhere in Ohio.

I've seen many examples where machining texts will tell you to grind once you hit this level of precision. The Monarch can hold accuracy which can help you to avoid grinding. This is especially useful where the Monarch usually ends up ... in laboratories and not in high volume production.

In high volume production you will usually find centerless grinding used or some other suitable high volume finishing method.


08-21-2004, 08:47 PM
I was just at a GSA auction Wendsday,they have a near perfect 10EE sitting in line for the next sale(me sharpening my bidder number)I want it bad.

Yes they are that accurate,and nothing,I mean nothing threads that good.

08-21-2004, 09:01 PM
Believe the claims, especially if they are talking about a new machine. If I could figure out how to get a picture of the accuracy page from the Monarch catalog posted here I would, but you are going to have to settle for a picture of my EE.
An EE in good working order is unlike any other lathe I have used. They are, for their size, incredibly powerful, they are extremely quiet, an perhaps the most user friendly lathe I have ever used. I can bring the spindle to a dead stop in less than 3 seconds from 3900 RPM, and be back up to speed just about as fast, faster would require an adjustment on the VFD. At 3900 RPM the machine does not vibrate, it will pass the full wine glass test so to speak.
The major problem with the EE, is the DC drive system that Monarch installed. These systems are now old, in need of repair , for the most part,and the parts are hard to find. I worked with the drive in my EE, which had been compromised, for quite awhile, finally I gave up scrapped the DC system and put a VFD with Sensorless Vector Control in its place. If you have read any of the posts on PM concerning the EE, fully 95% of them concern the drive.

08-21-2004, 09:16 PM
On a non-Monarch, some people may find it necessary to emtpy the wine glass before cranking it up to 3900 rpm http://bbs.homeshopmachinist.net//wink.gif

Does the 10EE variable speed directly drive the spindle or does it go thru belts or chains?


08-21-2004, 09:40 PM
The motor is in the base on the rear side of the machine, there are 2 V belts that directly drive the spindle. Belt whip is controlled by idlers on the front and back sides of the belts. The motor is mounted on a plate which in turn is mounted on isolation pads in a three point suspension. The feeds are driven, like the old style lathes, by a flat belt to the gear box. The only gearing connected to the spindle is for threading. It is a relatively complicated system that is incredibly smooth. You can get a pretty good idea by going to the Monarch selection on the this web site;
www.lathes.co.uk (http://www.lathes.co.uk)
There are some views of the older round dial machine, but the basic layout hasn't changed much at all.

J Tiers
08-21-2004, 10:15 PM
The EE drive is actually quite simple. It is just like an SCR drive, complete with IR compensation, but done with tubes.

The reason it is considered so difficult is probably due to the use of control tubes in the so-called "WiaD" (works in a drawer) drive, and the fact that everything interacts. The latter means you can chase changing problems forever, if you are not systematic.

I think it is relatively elegant. But at $700 per thyratron tube, it can be "un-cheap" to replace parts.

No reason a properly rated SCR DC drive cannot do the same job. But it must run at the over-line-voltage output of the power transformer.

I'd like to have one of them, even one with evident wear, but it is overkill for my needs, and I have no way to get it into my shop.

08-21-2004, 10:24 PM
JT: If I had a machine that quiet at top speed, at the first sign of a drive problem I'd come up with an electronic drive and then rig it up for constant angular velocity driven by cross slide position (with some sanity checks).

Forrest Addy
08-21-2004, 11:18 PM
I'm always get nervous when people start talking about EE spindle drives. People look at that huge DC motor read the label plate where is says 3 HP and they go "Hmm. Swap that out with something modern and a lot more efficient. Problem is the DC motor developed full HP from about 600 RPM to 2500 RPM via an electric motor trick called field weakening. Thus you had more or less constant HP where torque is inversely proportanate to motor RPM.

As Jerry says, after 30 or 40 years of trouble free operation the DC drive can go on the fritz. Where do you find parts for Ward Leonard M/G sets or the successor thyratorn drives? There are no EE electrical spares affordable even to the US Gummint.

Many have tried to swap in a plain vanilla 3 HP DC PM motor and an SCR drive only to fail. The spindle works fine at full RPM but as you turn the RPM down for larger diameters the motor's torque stays constant; it doesn't increase as the big ol' honkin' DC motor did. 3 HP at 600 RPM is different than 3 HP at 1800. 55C frame PM motors can't go there.

The best conversion route these days is a 10 HP AC motor and a sensorless flux vector drive set to run at constant HP with the constant torque knee at about 500 RPM. It's almost a no-brainer when you think about it.

If the drive is setup to run in constant HP mode the line breaker never knows there's more than a 3 HP motor hooked to it.

People having a need for a EE and wish to run it at wide rangeing RPMs should try for the version with the "backgear" (actually a two speed transmission) on the motor. Gives extra oopmh at lower RPMS.

[This message has been edited by Forrest Addy (edited 08-22-2004).]

J Tiers
08-22-2004, 12:19 AM
From what it sounds like on the monarch forum in the "other " site, the contactors are more of a problem than the drive electronics.

The insulation on the old wiring is a problem also. Shorts in a wire bundle, or intermittently to chassis can cause odd faults.

And don't let's forget repairs by "bubba" or his brother-in-law.

At least the tube drive is theoretically replaceable with solid-state plug-in parts. Some contactors were somewhat special then, and haven't been made like that for years.

Once you gut it, you are committed to living with what you get from your replacement. I bet in most cases, it is still cheaper to fix than replace, if you have some electrical smarts.

Of course, if you wanted to use it for production, you didn't buy a clunker anyway, so that old argument about scrap or fix don't fly too high.

08-22-2004, 03:04 AM
Well they certainly sound like good quality lathes with that level of accuracy. I wonder if any were imported here to Australia but no one would have been able to afford them anyway. The electrics sound a bit complicated but with modern day electronics you would be able to sort something out.

Anyway back to my Taiwanese model. I can nearly hold 0.02mm with it. http://bbs.homeshopmachinist.net//smile.gif