[Docop]

Hi

So i need to monitor the feed rate, the pressure and the thrust done by a drill bit for when drilling a composite part. I have got an high quality strain-gage for the pressure, but i'm stuck with the torque reading.. Here's the detail :
The base of the drill will have a metal plate on it and the strain-gage on top of it. A second plate, smaller will be put over the cell and finally the composite part to be drilled. And all those part, as well as the strain gage will be clamp tight using C-Clamp to the base of the drill.
So the gage, supported by the clamping force acting as a constant pressure, will then be set to zero on the meter.

But what i also need is the thrust of the drill bit pressing and acting against the part to be cut. In many articles, they use a dynamometer to mesure the torque induce by the drilling, but this equipment is very very expensive.

So if someone have any hints about how could i monitor the thrust, it will be very great and helpfull.

Thanks in advance

[jsheerin]

Maybe you mean something different than what I'm used to by 'strain gage', but the ones I've used would not work the way you're describing. You would need to mount it to a surface oriented parallel to the direction of thrust. Perhaps you're talking about a load cell instead?

For cheaply monitoring the torque on the spindle, how about measuring the electrical power going into the motor? It wouldn't account for a variety of losses in the motor and drive train, but it would be simple. You could measure the idle current and then the current while drilling. Or what about applying a strain gage to the shaft of the drill to measure torsion of the shaft. You could lead the wires out via some kind of ring and spring loaded contact setup.

[wildwestpat]

Hi

Let the part rest on a small table which is supported by precision thrust race with location bearing fixed to the table of the machine and concentric with the drill and trammed to be at right angles to the drill aaxis. A lever is then arranged to stop the small support table rotating. Measure the force between the lever and its fixed stop and this is a measure of the torque applied by the drill to the work. Use another strain guage to make the measurement multiplying the resultant force by the distance from the strain gauge to the centre line of the drill bit. However this is a total torque and includes the friction due to chip clearing. If this is for dynamic control then calibrate the motor input current and monitor this with a current sensing transformer along with the line voltage at the motor.

Hope this helps - Regards Pat