Need Help!- Spindle speed problem

[brent80111]

New guy here with some questions about speed control.

I am helping a friend get his R2/Boss8 mill working in exchange for some time on it. The problem is that the spindle only turns at 500 RPM regardless of the position of the hi/lo lever or the speed selected from the console (or from G code). No error messages are ever displayed and the rest of the machine works flawlessly. He was told by a tech some time ago that the tubular shaped proximity switch located within the Hi/Lo selector mechanism (top RH side of the head) was defective. A $500 replacement part from Bridgeport was deemed too expensive, and the mill has just been sitting.

I have a couple of questions -
1. Does anyone know what kind of detector it is? A simple magnetic switch, or an inductive type detector? There are 3 wires leading from the detector itself into the control panel which leads me to think it's some kind of electronic device rather than a simple magnetic switch. I'm sure I can find an alternate source for a replacement, but there are several different types to choose from. (ie http://www.balluff.com/Balluff/us/Pr...w/?menuLevel=1 )

2. Does anyone know what the detector is sensing, or how it functions? After removing the sensor from the linkage, and then selecting Hi/Lo, it's hard to tell what it is sensing as there is very little physical movement of parts other than the shaft that rotates about 180 and makes the gear change in the head. I can't see anything that appears to be magnetic so it must be sensing the proximity of something that I haven't yet seen.

3. Is anyone familiar with the circuit? I'm looking for troubleshooting techniques that can isolate the problem to the sensor.

One last point. The mill runs at 500 regardless of whether the sensor is physically installed in the shifter, or removed. I have not tried disconnecting the wires inside the control panel.

All answers, suggestions, ideas are most appreciated.

[jmelson]

How do you know the spindle speed? Are you reading it with a tach, estimating it by sound, or reading it off the CNC control?

There is a direct-drive clutch between the varispeed driven pulley (coaxial to the spindle) and the bull gear which houses the female spline that actually drives the spindle splines. The teeth of this clutch are activated by a slight vertical movement of the driven pulley. Usually a cam with helical slots raises the pulley by a pair of pins. The reduction gear is engaged by a pinion in the rear of the head that moves vertically to engage with the bull gear. This is operated by a crank mechanism at the rear of the head that works a shifter fork to move the pinion. On 2J (manual) heads these are connected by a rod linkage. I don't know if they have 2 separate air cylinders for this or just a double-acting cylinder with no neutral position.

I'm not sure why they need a sensor in this at all, and don't know why it won't shift without the sensor. I thought it would just throw the air cylinder with the motor stopped, and the clutch/gear would engage as soon as the motor starts.

I'd check the air cylinder, control valve and drive relay for it.

The varispeed change is done by an air motor that spins the varispeed crank mechanism. You should be able to activate this, but it needs the motor running to allow changes of the varispeed pulley. Maybe this is the problem, there is a rotation sensor that needs to detect spindle rotation, and it isn't. Most likely this would be a magnetic pickup or gear tooth sensor.

Jon