February 2008 Edition

shop talk

Change the way you turn: M03 vs M04

By Steve Rose

Spindle direction on lathes is often referred to as M03, clockwise (CW) and M04 counter clockwise (CCW). Of course, this depends on the location from which you are viewing the spindle. Standing at the wrong end of the machine could allow you to inaccurately label the direction. A simpler, more accurate method is to think in terms of forward and reverse. When standing in front of the machine, this refers to whether the part is turning toward you or away from you. M03 can be called forward rotation and M04 can be called reverse rotation.

Most machines today are tooled for operating exclusively in the M03 spindle direction. Let's look as why it may be more useful to machine parts using the M04 direction.

Selecting the M04 command allows you to utilize left hand turret tooling. Left-hand tooling is an optimum method for two reasons.

1. In left-hand turret tooling, the insert faces the operator. Not only is it easier for the operator to watch the progress of the cutting process, but exchanging the insert becomes much quicker.

2. The other plus of using M04 relates to the machine's cutting forces. When machining in the M04 direction, the cutting forces are pushed into the machine bed, a force called compression. With the M03 direction, the cutting forces are being pulled away from the machine bed. This type of force is called tension. A machine's structural design is stronger in compression than in tension. In compression, the machine forces are directed into the structure of the machine and down toward the ground. If there is loss of control of the cutting forces, the energy will be directed into the machine and ground instead of into the tooling.

I have witnessed some machine crashes that illustrate this channeling of forces depending on spindle direction.

Crash #1: M03 direction: CNC Lathe with a 15" chuck and a 40hp spindle drive.

On this occasion, the operator had not bored soft jaws deep enough to withstand the cutting forces exerted by the part program. The part pulled out of the jaws and became trapped between the turret face and the chuck jaws. The resulting forces lifted the complete turret casting against the way keeper plates. The turret casting cracked under the 40hp forces. The repair bill was approximately $35,000 and the machine was out of service for nine weeks.

Crash #2: M04 direction: CNC lathe with a 10" chuck and a 25hp spindle drive.

This machine, equipped with a Fanuc control, set the machine datum point by using the G54 command. The operator simply forgot to set the correct workshift value. To compound this mistake, the first part ran in full rapid traverse mode of 800ipm. The machine spindle was running at 1550rpm in M04 spindle direction. The machine registered that the front of the chuck was the work zero datum point. The turret crashed into the chuck jaws knocking the jaws completely from the machine. No injuries occurred but this was a severe collision.

Results of this collision? The dowel pins in the turret broke and needed to be replaced. The main spindle cartridge needed realignment as it was knocked from true centerline. These damages, repaired for approximately $1,200, caused the machine to be out of service for five days.

There are many variables in these two examples, but I feel the simple choice of operating in M04 saved Crash #2 from being a very expensive and possibly more dangerous accident.

What are the problems when using M04 spindle direction? The programmer must use caution in selecting M03 for drilling and reversing the spindle to M04 for turning and boring. This may place extra load on the spindle drive equipment due to a greater frequency of spindle reversals.

Otherwise M04 is recommended to be used, in conjunction with left hand tooling, whenever possible. Keeping cutting forces into the bed of the machine tool – now there's a thought!

Steve Rose is a professional trainer and president of RTSI, Solon, OH. Rosaleen Rose offers Internet website development. They can be reached by phone at 440.542.3066; e-mail srose@rosetraining.com;
or on the web at www.rosetraining.com.

Copyright Rose Training Systems Inc., 2008

What do you think?
Will the information in this article increase efficiency or save time, money, or effort? Let us know by e-mail from our website at www.ToolingandProduction.com or e-mail the editor at dseeds@nelsonpub.com.